refactor(client): make configuration reusable across endpoints

2026-10-04 17:30:18 +07:00
1 parent c436bfb686
commit 20960e1b8d
@@ -1,41 +1,45 @@
 use std::time::Duration;

-use irtt_client::{Authentication, ClientConfig, HmacKey, NegotiationPolicy, SocketConfig};
+use irtt_client::{
+    Authentication, ClientConfig, HmacKey, NegotiationPolicy, OpenPolicy, SessionRequest,
+    SocketConfig,
+};

 use super::args::CommonClientArgs;

-pub const DEFAULT_RECV_TIMEOUT: Duration = Duration::from_millis(20);
-
 impl CommonClientArgs {
    /// Build the shared client configuration template for a managed run.
    ///
-    /// The template carries no server address: the managed driver replaces it
-    /// per target from that target's configuration, so deriving one here from
-    /// an arbitrary target would be dead data.
+    /// The config is endpoint-independent; managed targets own their addresses.
    pub fn to_client_config(&self, duration: Duration) -> ClientConfig {
        ClientConfig {
-            duration: (!duration.is_zero()).then_some(duration),
-            interval: self.interval,
-            length: self.length,
-            received_stats: self.stats.into(),
-            stamp_at: self.tstamp.into(),
-            clock: self.clock.into(),
-            dscp: self.dscp,
+            open: OpenPolicy {
+                negotiation: if self.loose {
+                    NegotiationPolicy::Loose
+                } else {
+                    NegotiationPolicy::Strict
+                },
+                ..Default::default()
+            },
+            request: SessionRequest {
+                duration: (!duration.is_zero()).then_some(duration),
+                interval: self.interval,
+                length: self.length,
+                received_stats: self.stats.into(),
+                stamp_at: self.tstamp.into(),
+                clock: self.clock.into(),
+                dscp: self.dscp,
+                server_fill: self.server_fill.clone(),
+                ..Default::default()
+            },
            auth: self
                .hmac
                .as_ref()
                .map_or(Authentication::Unauthenticated, |key| {
                    Authentication::Hmac(HmacKey::new(key.as_bytes()))
                }),
-            server_fill: self.server_fill.clone(),
-            negotiation_policy: if self.loose {
-                NegotiationPolicy::Loose
-            } else {
-                NegotiationPolicy::Strict
-            },
-            socket_config: SocketConfig {
+            socket: SocketConfig {
                ttl: self.ttl,
-                recv_timeout: Some(DEFAULT_RECV_TIMEOUT),
                ..SocketConfig::default()
            },
            ..ClientConfig::default()
@@ -8,7 +8,7 @@ pub use args::{
    parse_dscp, parse_duration, parse_length, parse_server_fill, parse_test_duration, parse_ttl,
    ClockArg, CommonClientArgs, ReceivedStatsArg, TimestampArg,
 };
-pub use config::{expected_probe_count, DEFAULT_RECV_TIMEOUT};
+pub use config::expected_probe_count;
 pub use prepare::{
    prepare_managed_run, ManagedRunSetup, TargetSelection, MANAGED_EVENT_CAPACITY,
    STDIN_MAX_DESIRED_TARGETS, STDIN_MAX_LIVE_TARGET_GENERATIONS, STDIN_OUTCOME_HISTORY_LIMIT,
@@ -34,6 +34,38 @@ dependency at all.

 See `examples/` in the repository for runnable examples of each tier.

+## Reusable configuration
+
+`ClientConfig` contains no endpoint. The low-level APIs take it separately:
+`Client::connect(endpoint, config)` and
+`AsyncClient::connect(endpoint, config).await`, accepting `String` or `&str`
+endpoints. An omitted port defaults to 2112.
+
+Configuration is grouped by ownership:
+
+- `address_family`: `AddressFamily::{Any, Ipv4, Ipv6}`, defaulting to `Any`.
+  It filters remote resolution; `Ipv6` also sets `IPV6_V6ONLY`.
+- `socket`: `SocketConfig` for local bind, device/routing options, and TTL.
+- `request`: `SessionRequest` for duration, interval, length, received stats,
+  timestamps, clock, DSCP, server fill, and run mode.
+- `open`: `OpenPolicy` for attempt `timeouts` and `negotiation` policy.
+- `auth`, `probe_timeout`, and `max_pending_probes`: authentication and local
+  probe tracking policy.
+
+Clone one config to connect to multiple endpoints. Managed targets retain their
+own ID, endpoint, and authentication inheritance/override; shared
+`ManagedClientConfig.client` is reusable without endpoint mutation.
+
+Blocking receive policy belongs to `Client`:
+`client.set_recv_timeout(Some(duration))?` sets it before or after opening,
+and `client.set_recv_timeout(None)?` restores the default indefinite wait.
+Open attempts use only `open.timeouts`, restoring the adapter setting afterward.
+Async and managed clients have no blocking receive-timeout setting.
+
+This breaks the former flat config, endpoint-in-config, socket family flags,
+and `SocketConfig.recv_timeout` APIs. Use the grouped fields and adapter method
+directly; defaults and protocol/runtime behavior are preserved.
+
 ## Authentication

 `ClientConfig.auth` is concrete: `Authentication::Unauthenticated` or
@@ -12,32 +12,33 @@
 //! ```
 //!
 //! Without a reachable server this exits quickly with an open-timeout error
-//! instead of hanging, because the example shortens `open_timeouts` for a
+//! instead of hanging, because the example shortens `open.timeouts` for a
 //! fast demonstration; a real caller would normally keep the default retry
 //! schedule.

 use std::time::{Duration, Instant};

-use irtt_client::{Client, ClientConfig, ClientEvent, OpenOutcome};
+use irtt_client::{Client, ClientConfig, ClientEvent, OpenOutcome, OpenPolicy, SessionRequest};

 const RUN_DURATION: Duration = Duration::from_secs(2);

 fn main() {
    let config = ClientConfig {
-        server_addr: "127.0.0.1:2112".to_owned(),
-        duration: Some(RUN_DURATION),
-        interval: Duration::from_millis(200),
-        // A single short attempt keeps this example fast when no server is
-        // reachable; production callers should generally keep the default.
-        open_timeouts: vec![Duration::from_millis(300)],
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(100)),
+        open: OpenPolicy {
+            // A single short attempt keeps this example fast when no server is
+            // reachable; production callers should generally keep the default.
+            timeouts: vec![Duration::from_millis(300)],
+            ..Default::default()
+        },
+        request: SessionRequest {
+            duration: Some(RUN_DURATION),
+            interval: Duration::from_millis(200),
            ..Default::default()
        },
        ..Default::default()
    };

-    let mut client = match Client::connect(config) {
+    let mut client = match Client::connect("127.0.0.1:2112", config) {
        Ok(client) => client,
        Err(err) => {
            eprintln!("failed to prepare client socket: {err}");
@@ -45,6 +46,11 @@ fn main() {
        }
    };

+    if let Err(err) = client.set_recv_timeout(Some(Duration::from_millis(100))) {
+        eprintln!("failed to configure receive timeout: {err}");
+        return;
+    }
+
    let negotiated = match client.open() {
        Ok(OpenOutcome::Started {
            event, negotiated, ..
@@ -22,14 +22,20 @@ use irtt_client::managed::{
    BlockingManagedClient, ManagedClientConfig, ManagedCompletionPolicy, ManagedEvent,
    ManagedTargetConfig,
 };
-use irtt_client::ClientConfig;
+use irtt_client::{ClientConfig, OpenPolicy, SessionRequest};

 fn main() {
    let config = ManagedClientConfig {
        client: ClientConfig {
-            duration: None,
-            interval: Duration::from_millis(200),
-            open_timeouts: vec![Duration::from_millis(300)],
+            open: OpenPolicy {
+                timeouts: vec![Duration::from_millis(300)],
+                ..Default::default()
+            },
+            request: SessionRequest {
+                duration: None,
+                interval: Duration::from_millis(200),
+                ..Default::default()
+            },
            ..Default::default()
        },
        completion: ManagedCompletionPolicy::ExplicitStop,
@@ -13,12 +13,14 @@
 //! ```
 //!
 //! Without a reachable server this exits quickly with an open-timeout error
-//! instead of hanging, because the example shortens `open_timeouts` for a
+//! instead of hanging, because the example shortens `open.timeouts` for a
 //! fast demonstration.

 use std::time::{Duration, Instant};

-use irtt_client::{AsyncClient, ClientConfig, ClientEvent, OpenOutcome};
+use irtt_client::{
+    AsyncClient, ClientConfig, ClientEvent, OpenOutcome, OpenPolicy, SessionRequest,
+};

 /// Upper bound on how long the receive wait can go without also calling
 /// `poll_timeouts()`. `AsyncClient` does not expose the earliest pending
@@ -41,16 +43,21 @@ fn main() {

 async fn run() {
    let config = ClientConfig {
-        server_addr: "127.0.0.1:2112".to_owned(),
-        duration: Some(Duration::from_secs(2)),
-        interval: Duration::from_millis(200),
-        // A single short attempt keeps this example fast when no server is
-        // reachable; production callers should generally keep the default.
-        open_timeouts: vec![Duration::from_millis(300)],
+        open: OpenPolicy {
+            // A single short attempt keeps this example fast when no server is
+            // reachable; production callers should generally keep the default.
+            timeouts: vec![Duration::from_millis(300)],
+            ..Default::default()
+        },
+        request: SessionRequest {
+            duration: Some(Duration::from_secs(2)),
+            interval: Duration::from_millis(200),
+            ..Default::default()
+        },
        ..Default::default()
    };

-    let mut client = match AsyncClient::connect(config).await {
+    let mut client = match AsyncClient::connect("127.0.0.1:2112", config).await {
        Ok(client) => client,
        Err(err) => {
            eprintln!("failed to prepare client socket: {err}");
@@ -19,7 +19,7 @@ use crate::{
        recv_buffer_size, OpenDatagramDisposition, PreparedOpenAcceptance, PreparedOpenRequest,
        PreparedProbe, SessionMachine, TimeoutBatch, MAX_OPEN_PACKET_SIZE,
    },
-    socket::{connect_tokio_udp_socket, resolve_remote_tokio, validate_open_timeouts},
+    socket::{connect_tokio_udp_socket, resolve_remote_tokio},
    socket_options::{apply_traffic_class_to_tokio_socket, clear_dscp_on_tokio_socket},
    timing::ClientTimestamp,
 };
@@ -170,7 +170,7 @@ impl AsyncOpenState {
 /// use irtt_client::{AsyncClient, ClientConfig};
 ///
 /// # async fn run() -> Result<(), Box<dyn std::error::Error>> {
-/// let mut client = AsyncClient::connect(ClientConfig::default()).await?;
+/// let mut client = AsyncClient::connect("127.0.0.1:2112", ClientConfig::default()).await?;
 /// let outcome = client.open().await?;
 /// println!("opened: {outcome:?}");
 /// let sent = client.send_probe().await?;
@@ -199,19 +199,26 @@ pub struct AsyncClient {
 }

 impl AsyncClient {
-    /// Resolve the configured server and construct one connected Tokio UDP
+    /// Resolve the endpoint and construct one connected Tokio UDP
    /// socket.
    ///
    /// Polling this future without a current Tokio runtime returns
    /// [`ClientError::NoTokioRuntime`]. A runtime without enabled I/O or time
    /// drivers is outside this type's runtime contract.
-    pub async fn connect(config: ClientConfig) -> Result<Self, ClientError> {
+    ///
+    /// The endpoint accepts a name or address; an omitted port defaults to 2112.
+    /// IPv6 literals may be bracketed or unbracketed with the default port.
+    /// The reusable config contains no endpoint identity.
+    pub async fn connect(
+        endpoint: impl AsRef<str>,
+        config: ClientConfig,
+    ) -> Result<Self, ClientError> {
        tokio::runtime::Handle::try_current().map_err(|_| ClientError::NoTokioRuntime)?;
-        validate_open_timeouts(&config.open_timeouts)?;
-        let remote = resolve_remote_tokio(&config).await?;
+        config.open.validate()?;
+        let remote = resolve_remote_tokio(endpoint.as_ref(), config.address_family).await?;
        let machine = SessionMachine::new(config.clone(), remote)?;
        let prepared_open = machine.prepare_open_request()?;
-        let socket = connect_tokio_udp_socket(&config.socket_config, remote)?;
+        let socket = connect_tokio_udp_socket(&config.socket, remote, config.address_family)?;

        Ok(Self {
            socket,
@@ -307,7 +314,7 @@ impl AsyncClient {
                return self.poll_open_cleanup(state, cx);
            }

-            let attempt_count = self.machine.config().open_timeouts.len();
+            let attempt_count = self.machine.config().open.timeouts.len();
            if state.attempt >= attempt_count {
                return Poll::Ready(Err(ClientError::OpenTimeout));
            }
@@ -316,7 +323,7 @@ impl AsyncClient {
                return Poll::Ready(Err(ClientError::OpenTimeout));
            }
            if state.deadline.is_none() {
-                let timeout = self.machine.config().open_timeouts[state.attempt];
+                let timeout = self.machine.config().open.timeouts[state.attempt];
                if let Err(error) = state.start_attempt(timeout) {
                    return Poll::Ready(Err(error));
                }
@@ -13,7 +13,7 @@ use crate::{
        recv_buffer_size, OpenDatagramDisposition, PreparedOpenAcceptance, ProbeSent,
        SessionMachine, MAX_OPEN_PACKET_SIZE,
    },
-    socket::{connect_udp_socket, resolve_remote, validate_open_timeouts},
+    socket::{connect_udp_socket, resolve_remote},
    socket_options::{apply_traffic_class_to_socket, clear_dscp_on_socket},
    timing::ClientTimestamp,
 };
@@ -50,7 +50,7 @@ struct PreparedClientOpenFailure {
 /// use irtt_client::{Client, ClientConfig};
 ///
 /// # fn run() -> Result<(), Box<dyn std::error::Error>> {
-/// let mut client = Client::connect(ClientConfig::default())?;
+/// let mut client = Client::connect("127.0.0.1:2112", ClientConfig::default())?;
 /// let outcome = client.open()?;
 /// println!("opened: {outcome:?}");
 /// let sent = client.send_probe()?;
@@ -70,6 +70,7 @@ pub struct Client {
    socket: UdpSocket,
    remote: SocketAddr,
    recv_buffer: Vec<u8>,
+    recv_timeout: Option<Duration>,
    applied_traffic_class: Option<u8>,
    /// Whether the socket's `SO_TIMESTAMPING` flags carry `TX_SOFTWARE` +
    /// `OPT_ID` + `OPT_TSONLY`. Always `false` off Linux, without the
@@ -81,32 +82,53 @@ pub struct Client {
 }

 impl Client {
-    /// Resolve the configured server and create a connected UDP socket.
+    /// Resolve the endpoint and create a connected UDP socket.
    ///
    /// This validates local configuration and prepares the open request, but it
    /// does not contact the server. Call [`open`](Self::open) to perform the
    /// IRTT open exchange.
-    pub fn connect(config: ClientConfig) -> Result<Self, ClientError> {
-        validate_open_timeouts(&config.open_timeouts)?;
-        let remote = resolve_remote(&config)?;
+    ///
+    /// The endpoint accepts a name or address; an omitted port defaults to 2112.
+    /// IPv6 literals may be bracketed or unbracketed with the default port.
+    /// The reusable config contains no endpoint identity.
+    pub fn connect(endpoint: impl AsRef<str>, config: ClientConfig) -> Result<Self, ClientError> {
+        config.open.validate()?;
+        let remote = resolve_remote(endpoint.as_ref(), config.address_family)?;
        let runtime = SessionMachine::new(config.clone(), remote)?;
-        let socket = connect_udp_socket(&config.socket_config, remote)?;
+        let socket = connect_udp_socket(&config.socket, remote, config.address_family)?;

        Ok(Self {
            runtime,
            socket,
            remote,
            recv_buffer: vec![0_u8; recv_buffer_size(false, None)?],
+            recv_timeout: None,
            applied_traffic_class: None,
            tx_timestamping_enabled: false,
        })
    }

+    /// Set the blocking receive timeout used outside open attempts.
+    ///
+    /// `None` (the default) lets `recv_once()` block indefinitely. A nonzero
+    /// timeout bounds one logical receive, including retries after EINTR.
+    /// `recv_available()` retains its bounded drain behavior. Open attempts
+    /// use only [`OpenPolicy::timeouts`](crate::OpenPolicy::timeouts) and
+    /// restore this setting on success or failure.
+    ///
+    /// A zero duration is rejected by the socket; the previous setting is
+    /// retained when applying the new timeout fails.
+    pub fn set_recv_timeout(&mut self, timeout: Option<Duration>) -> Result<(), ClientError> {
+        self.socket.set_read_timeout(timeout)?;
+        self.recv_timeout = timeout;
+        Ok(())
+    }
+
    /// Perform the IRTT open exchange.
    ///
    /// On success, returns the negotiated open outcome and transitions the
    /// client into either an open probe session or completed no-test state.
-    /// Open attempts use [`ClientConfig::open_timeouts`]. Malformed or
+    /// Open attempts use [`OpenPolicy::timeouts`](crate::OpenPolicy::timeouts). Malformed or
    /// unrelated datagrams are ignored until the current attempt's absolute
    /// deadline, so one attempt may consume several datagrams without
    /// retransmitting. Silence or ignored traffic eventually produces
@@ -121,9 +143,7 @@ impl Client {
    pub fn open(&mut self) -> Result<OpenOutcome, ClientError> {
        let result = self.open_transaction();
        if result.is_err() {
-            let _ = self
-                .socket
-                .set_read_timeout(self.runtime.config().socket_config.recv_timeout);
+            let _ = self.socket.set_read_timeout(self.recv_timeout);
        }
        result
    }
@@ -225,8 +245,7 @@ impl Client {
    /// Requires an open session; lifecycle errors are returned before socket I/O.
    pub fn recv_once(&mut self) -> Result<Vec<ClientEvent>, ClientError> {
        self.runtime.ensure_open()?;
-        self.socket
-            .set_read_timeout(self.runtime.config().socket_config.recv_timeout)?;
+        self.socket.set_read_timeout(self.recv_timeout)?;
        self.recv_once_inner()
    }

@@ -267,7 +286,7 @@ impl Client {
    fn recv_datagram_retrying_interrupted(
        &mut self,
    ) -> Result<Option<ReceivedDatagram>, ClientError> {
-        let configured_timeout = self.runtime.config().socket_config.recv_timeout;
+        let configured_timeout = self.recv_timeout;
        let deadline = match configured_timeout {
            Some(timeout) => Some(
                Instant::now()
@@ -322,8 +341,7 @@ impl Client {
    /// Requires an open session; lifecycle errors are returned before socket I/O.
    pub fn recv_available(&mut self, budget: RecvBudget) -> Result<Vec<ClientEvent>, ClientError> {
        self.runtime.ensure_open()?;
-        self.socket
-            .set_read_timeout(self.runtime.config().socket_config.recv_timeout)?;
+        self.socket.set_read_timeout(self.recv_timeout)?;
        let mut all_events = Vec::new();
        for _ in 0..budget.max_packets {
            let events = self.recv_once_inner()?;
@@ -383,10 +401,10 @@ impl Client {
    fn open_transaction(&mut self) -> Result<OpenOutcome, ClientError> {
        let request = self.runtime.prepare_open_request()?;
        let mut buf = [0_u8; MAX_OPEN_PACKET_SIZE];
-        let attempt_count = self.runtime.config().open_timeouts.len();
+        let attempt_count = self.runtime.config().open.timeouts.len();

        for attempt in 0..attempt_count {
-            let timeout = self.runtime.config().open_timeouts[attempt];
+            let timeout = self.runtime.config().open.timeouts[attempt];
            let deadline = Instant::now()
                .checked_add(timeout)
                .ok_or(ClientError::DurationOverflow)?;
@@ -470,7 +488,7 @@ impl Client {
                recv_buffer_len: None,
                negotiated_traffic_class: None,
                previous_traffic_class: self.applied_traffic_class,
-                post_open_recv_timeout: self.runtime.config().socket_config.recv_timeout,
+                post_open_recv_timeout: self.recv_timeout,
            });
        };
        let recv_buffer_len = match recv_buffer_size(self.runtime.has_hmac(), Some(negotiated)) {
@@ -495,7 +513,7 @@ impl Client {
            recv_buffer_len: Some(recv_buffer_len),
            negotiated_traffic_class: Some(negotiated_traffic_class),
            previous_traffic_class: self.applied_traffic_class,
-            post_open_recv_timeout: self.runtime.config().socket_config.recv_timeout,
+            post_open_recv_timeout: self.recv_timeout,
        })
    }

@@ -1,12 +1,12 @@
 use std::{net::SocketAddr, time::Duration};

-use crate::Authentication;
+use crate::{Authentication, ClientError};

 /// Protocol compatibility bound for a requested `server_fill` value, in UTF-8
 /// bytes.
 ///
 /// This is the maximum encoded server-fill string accepted by this client and
-/// protocol decoder. [`ClientConfig::server_fill`] enforces the same bound
+/// protocol decoder. [`SessionRequest::server_fill`] enforces the same bound
 /// before opening a session.
 pub use irtt_proto::MAX_SERVER_FILL_BYTES;
 use irtt_proto::{Clock, ReceivedStats, StampAt};
@@ -28,7 +28,7 @@ pub const MAX_TTL: u32 = 255;
 /// Largest UDP payload length accepted by client configuration, in bytes.
 ///
 /// This is the maximum UDP payload size excluding IP and UDP headers. It caps
-/// [`ClientConfig::length`] before protocol packets are encoded or sent.
+/// [`SessionRequest::length`] before protocol packets are encoded or sent.
 pub const MAX_UDP_PAYLOAD_LENGTH: u32 = 65_507;
 pub(crate) const DEFAULT_DURATION: Duration = Duration::from_secs(3);
 pub(crate) const DEFAULT_INTERVAL: Duration = Duration::from_secs(1);
@@ -58,29 +58,82 @@ pub(crate) const DEFAULT_MAX_PENDING: usize = 4096;
 /// ```
 /// use std::time::Duration;
 ///
-/// use irtt_client::{ClientConfig, NegotiationPolicy};
+/// use irtt_client::{ClientConfig, NegotiationPolicy, OpenPolicy, SessionRequest};
 ///
 /// let config = ClientConfig {
-///     server_addr: "example.net:2112".into(),
-///     duration: Some(Duration::from_secs(10)),
-///     interval: Duration::from_millis(250),
-///     length: 1200,
-///     negotiation_policy: NegotiationPolicy::Loose,
+///     request: SessionRequest {
+///         duration: Some(Duration::from_secs(10)),
+///         interval: Duration::from_millis(250),
+///         length: 1200,
+///         ..SessionRequest::default()
+///     },
+///     open: OpenPolicy {
+///         negotiation: NegotiationPolicy::Loose,
+///         ..OpenPolicy::default()
+///     },
 ///     ..ClientConfig::default()
 /// };
 ///
-/// assert_eq!(config.duration, Some(Duration::from_secs(10)));
-/// assert_eq!(config.interval, Duration::from_millis(250));
-/// assert_eq!(config.length, 1200);
+/// assert_eq!(config.request.duration, Some(Duration::from_secs(10)));
+/// assert_eq!(config.request.interval, Duration::from_millis(250));
+/// assert_eq!(config.request.length, 1200);
 /// ```
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ClientConfig {
-    /// Remote server name or address.
+    /// Remote address families allowed during resolution and socket creation.
+    pub address_family: AddressFamily,
+    /// Local UDP socket properties.
+    pub socket: SocketConfig,
+    /// Protocol and session values requested from the server.
+    pub request: SessionRequest,
+    /// Open retry timeouts and negotiation policy.
+    pub open: OpenPolicy,
+    /// Concrete authentication for open, echo, and close packets.
    ///
-    /// If no port is present, the default IRTT port 2112 is used. IPv6
-    /// literals may be supplied either bracketed or unbracketed when the
-    /// default port should be used.
-    pub server_addr: String,
+    /// HMAC peers must use the same key. An empty HMAC key remains authenticated.
+    pub auth: Authentication,
+    /// Time after sending a probe before the client reports it as lost.
+    ///
+    /// This timeout is local client behavior; it is not negotiated with the
+    /// server. It must be greater than zero.
+    pub probe_timeout: Duration,
+    /// Maximum number of probes tracked as pending/timed-out/completed.
+    ///
+    /// This bounds memory used for reply classification and must be greater
+    /// than zero. A very small value can reject sends when replies are still
+    /// outstanding.
+    pub max_pending_probes: usize,
+}
+
+impl Default for ClientConfig {
+    fn default() -> Self {
+        Self {
+            address_family: AddressFamily::default(),
+            socket: SocketConfig::default(),
+            request: SessionRequest::default(),
+            open: OpenPolicy::default(),
+            auth: Authentication::Unauthenticated,
+            probe_timeout: DEFAULT_PROBE_TIMEOUT,
+            max_pending_probes: DEFAULT_MAX_PENDING,
+        }
+    }
+}
+
+/// Allowed remote address families. IPv6-only selection also sets IPV6_V6ONLY.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub enum AddressFamily {
+    /// Accept IPv4 and IPv6 addresses.
+    #[default]
+    Any,
+    /// Accept only IPv4 addresses.
+    Ipv4,
+    /// Accept only IPv6 addresses and use IPv6-only sockets.
+    Ipv6,
+}
+
+/// Requested IRTT protocol and session semantics, reusable across endpoints.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct SessionRequest {
    /// Requested run duration.
    ///
    /// `Some(duration)` requests a finite test and must be greater than zero.
@@ -120,46 +173,20 @@ pub struct ClientConfig {
    /// This is the six-bit DSCP value, not the full traffic-class byte, and
    /// must be less than or equal to [`MAX_DSCP_CODEPOINT`].
    pub dscp: u8,
-    /// Concrete authentication for open, echo, and close packets.
-    ///
-    /// HMAC peers must use the same key. An empty HMAC key remains authenticated.
-    pub auth: Authentication,
    /// Optional server payload fill request.
    ///
    /// `None` leaves server fill behavior unspecified. `Some(value)` requests
    /// a non-empty server fill mode/value and must not exceed
    /// [`MAX_SERVER_FILL_BYTES`] bytes when UTF-8 encoded.
    pub server_fill: Option<String>,
-    /// Per-attempt receive timeouts used while opening the session.
-    ///
-    /// The client sends an open request for each entry until a valid open reply
-    /// is received. The list must not be empty, and each timeout must be at
-    /// least 200 ms.
-    pub open_timeouts: Vec<Duration>,
    /// Whether opening the session should start a probe test or perform a
    /// negotiation-only no-test exchange.
    pub run_mode: RunMode,
-    /// Policy for server changes to negotiable protocol parameters.
-    pub negotiation_policy: NegotiationPolicy,
-    /// Local UDP socket configuration.
-    pub socket_config: SocketConfig,
-    /// Time after sending a probe before the client reports it as lost.
-    ///
-    /// This timeout is local client behavior; it is not negotiated with the
-    /// server. It must be greater than zero.
-    pub probe_timeout: Duration,
-    /// Maximum number of probes tracked as pending/timed-out/completed.
-    ///
-    /// This bounds memory used for reply classification and must be greater
-    /// than zero. A very small value can reject sends when replies are still
-    /// outstanding.
-    pub max_pending_probes: usize,
 }

-impl Default for ClientConfig {
+impl Default for SessionRequest {
    fn default() -> Self {
        Self {
-            server_addr: format!("127.0.0.1:{DEFAULT_PORT}"),
            duration: Some(DEFAULT_DURATION),
            interval: DEFAULT_INTERVAL,
            length: 0,
@@ -167,23 +194,55 @@ impl Default for ClientConfig {
            stamp_at: StampAt::Both,
            clock: Clock::Both,
            dscp: 0,
-            auth: Authentication::Unauthenticated,
            server_fill: None,
-            open_timeouts: DEFAULT_OPEN_TIMEOUTS.to_vec(),
            run_mode: RunMode::Normal,
-            negotiation_policy: NegotiationPolicy::Strict,
-            socket_config: SocketConfig::default(),
-            probe_timeout: DEFAULT_PROBE_TIMEOUT,
-            max_pending_probes: DEFAULT_MAX_PENDING,
+        }
+    }
+}
+
+/// Opening behavior shared by blocking, async, and managed clients.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct OpenPolicy {
+    /// Per-attempt receive timeouts used while opening the session.
+    ///
+    /// The client sends an open request for each entry until a valid open reply
+    /// is received. The list must not be empty, and each timeout must be at
+    /// least 200 ms.
+    pub timeouts: Vec<Duration>,
+    /// Policy for server changes to negotiable protocol parameters.
+    pub negotiation: NegotiationPolicy,
+}
+
+impl OpenPolicy {
+    pub(crate) fn validate(&self) -> Result<(), ClientError> {
+        if self.timeouts.is_empty() {
+            return Err(ClientError::NoOpenTimeouts);
+        }
+        for timeout in &self.timeouts {
+            if *timeout < MIN_OPEN_TIMEOUT {
+                return Err(ClientError::OpenTimeoutTooSmall {
+                    timeout: *timeout,
+                    minimum: MIN_OPEN_TIMEOUT,
+                });
+            }
+        }
+        Ok(())
+    }
+}
+
+impl Default for OpenPolicy {
+    fn default() -> Self {
+        Self {
+            timeouts: DEFAULT_OPEN_TIMEOUTS.to_vec(),
+            negotiation: NegotiationPolicy::Strict,
        }
    }
 }

 /// Local UDP socket options used by [`ClientConfig`].
 ///
-/// These settings affect how the client binds, resolves, and receives from the
-/// socket. They do not change the IRTT protocol parameters negotiated with the
-/// server.
+/// These settings affect how the client binds and sends from the socket. They
+/// do not change the IRTT protocol parameters negotiated with the server.
 ///
 /// # Example
 ///
@@ -192,20 +251,20 @@ impl Default for ClientConfig {
 /// ```
 /// use std::net::{Ipv4Addr, SocketAddr};
 ///
-/// use irtt_client::{ClientConfig, SocketConfig};
+/// use irtt_client::{AddressFamily, ClientConfig, SocketConfig};
 ///
 /// let config = ClientConfig {
-///     socket_config: SocketConfig {
+///     address_family: AddressFamily::Ipv4,
+///     socket: SocketConfig {
 ///         bind_addr: Some(SocketAddr::from((Ipv4Addr::UNSPECIFIED, 0))),
 ///         ttl: Some(32),
-///         ipv4_only: true,
 ///         ..SocketConfig::default()
 ///     },
 ///     ..ClientConfig::default()
 /// };
 ///
-/// assert_eq!(config.socket_config.ttl, Some(32));
-/// assert!(config.socket_config.ipv4_only);
+/// assert_eq!(config.socket.ttl, Some(32));
+/// assert_eq!(config.address_family, AddressFamily::Ipv4);
 /// ```
 #[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub struct SocketConfig {
@@ -229,17 +288,6 @@ pub struct SocketConfig {
    /// platform socket option range; [`MAX_TTL`] is the public configuration
    /// bound used by this crate.
    pub ttl: Option<u32>,
-    /// Restrict name resolution to IPv4 addresses.
-    pub ipv4_only: bool,
-    /// Restrict name resolution to IPv6 addresses and set IPV6_V6ONLY for IPv6
-    /// sockets.
-    pub ipv6_only: bool,
-    /// Socket read timeout used after the session is open.
-    ///
-    /// `None` leaves reads blocking for APIs that perform a single receive.
-    /// Managed sessions may replace `None` or long timeouts with a short
-    /// timeout so cooperative cancellation can be observed promptly.
-    pub recv_timeout: Option<Duration>,
 }

 /// How strictly to handle server-side negotiation restrictions.
@@ -53,8 +53,9 @@ pub use async_client::AsyncClient;
 pub use auth::{Authentication, HmacKey};
 pub use client::Client;
 pub use config::{
-    ClientConfig, NegotiationPolicy, RecvBudget, RunMode, SocketConfig, MAX_DSCP_CODEPOINT,
-    MAX_SERVER_FILL_BYTES, MAX_TTL, MAX_UDP_PAYLOAD_LENGTH,
+    AddressFamily, ClientConfig, NegotiationPolicy, OpenPolicy, RecvBudget, RunMode,
+    SessionRequest, SocketConfig, MAX_DSCP_CODEPOINT, MAX_SERVER_FILL_BYTES, MAX_TTL,
+    MAX_UDP_PAYLOAD_LENGTH,
 };
 pub use error::ClientError;
 pub use event::{
@@ -85,6 +85,8 @@ pub enum ManagedCompletionPolicy {
 /// Shared configuration for one managed task.
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct ManagedClientConfig {
+    /// Reusable session/socket configuration shared across target generations.
+    /// Each target supplies its endpoint and resolves its authentication policy.
    pub client: ClientConfig,
    pub pacing: ManagedPacing,
    pub completion: ManagedCompletionPolicy,
@@ -20,7 +20,6 @@ use tokio::{
 use crate::{
    async_client::{AsyncClient, AsyncOpenState},
    session::machine::SessionMachine,
-    socket::validate_open_timeouts,
    socket_options::validate_ttl,
    ClientConfig, ClientError, ClientEvent, OpenOutcome,
 };
@@ -62,7 +61,10 @@ const MAX_BROADCAST_CHANNEL_CAPACITY: usize = usize::MAX >> 1;
 /// # async fn run() -> Result<(), Box<dyn std::error::Error>> {
 /// let config = ManagedClientConfig {
 ///     client: ClientConfig {
-///         duration: Some(std::time::Duration::from_secs(10)),
+///         request: irtt_client::SessionRequest {
+///             duration: Some(std::time::Duration::from_secs(10)),
+///             ..irtt_client::SessionRequest::default()
+///         },
 ///         ..ClientConfig::default()
 ///     },
 ///     ..ManagedClientConfig::default()
@@ -944,7 +946,6 @@ impl ManagedClientTask {
                return Err(ManagedCommandApplyError::DuplicateTargetId { id: target.id });
            }
            let mut client_config = self.config.client.clone();
-            client_config.server_addr.clone_from(&target.server_addr);
            client_config.auth = target.auth.resolve(&self.config.client.auth);
            validate_target_config(&client_config).map_err(|source| {
                ManagedCommandApplyError::InvalidTarget {
@@ -1060,7 +1061,8 @@ impl ManagedClientTask {
    }

    fn start_connecting(&mut self, index: usize, config: ClientConfig) {
-        let future = Box::pin(AsyncClient::connect(config));
+        let endpoint = Arc::clone(&self.targets[index].server_addr);
+        let future = Box::pin(async move { AsyncClient::connect(endpoint, config).await });
        self.install_target_state(index, TargetState::Connecting { future });
    }

@@ -2248,7 +2250,6 @@ fn build_task(
            .checked_add(1)
            .ok_or(ManagedConfigError::GenerationExhausted)?;
        let mut client_config = config.client.clone();
-        client_config.server_addr.clone_from(&target.server_addr);
        client_config.auth = target.auth.resolve(&config.client.auth);
        validate_target_config(&client_config).map_err(|source| {
            ManagedConfigError::InvalidTarget {
@@ -2361,14 +2362,9 @@ fn build_task(
 }

 fn validate_target_config(config: &ClientConfig) -> Result<(), ClientError> {
-    validate_open_timeouts(&config.open_timeouts)?;
+    config.open.validate()?;
    SessionMachine::validate_config(config)?;
-    if config.socket_config.ipv4_only && config.socket_config.ipv6_only {
-        return Err(ClientError::InvalidConfig {
-            reason: "ipv4_only and ipv6_only cannot both be true".to_owned(),
-        });
-    }
-    if let Some(ttl) = config.socket_config.ttl {
+    if let Some(ttl) = config.socket.ttl {
        validate_ttl(ttl)?;
    }
    Ok(())
@@ -2429,12 +2425,9 @@ mod tests {
                    vec![ManagedTargetConfig::new("target", "127.0.0.1:9")],
                )
                .unwrap();
-                let client = AsyncClient::connect(ClientConfig {
-                    server_addr: "127.0.0.1:9".into(),
-                    ..ClientConfig::default()
-                })
-                .await
-                .unwrap();
+                let client = AsyncClient::connect("127.0.0.1:9", ClientConfig::default())
+                    .await
+                    .unwrap();
                task.state = DriverState::Running;
                task.install_target_state(0, TargetState::Active { client });
                task.send_gate = Some(end + Duration::from_secs(1));
@@ -7,7 +7,8 @@ use irtt_proto::{

 use crate::{
    config::{
-        ClientConfig, RunMode, MAX_DSCP_CODEPOINT, MAX_SERVER_FILL_BYTES, MAX_UDP_PAYLOAD_LENGTH,
+        ClientConfig, RunMode, SessionRequest, MAX_DSCP_CODEPOINT, MAX_SERVER_FILL_BYTES,
+        MAX_UDP_PAYLOAD_LENGTH,
    },
    error::ClientError,
    event::{
@@ -172,7 +173,7 @@ impl SessionMachine {
        remote: std::net::SocketAddr,
    ) -> Result<Self, ClientError> {
        Self::validate_config(&config)?;
-        let requested = params_from_config(&config)?;
+        let requested = params_from_request(&config.request)?;

        Ok(Self {
            config,
@@ -193,7 +194,7 @@ impl SessionMachine {
                reason: "probe_timeout must be greater than zero".to_owned(),
            });
        }
-        params_from_config(config).map(|_| ())
+        params_from_request(&config.request).map(|_| ())
    }

    pub(crate) fn config(&self) -> &ClientConfig {
@@ -209,7 +210,7 @@ impl SessionMachine {
        let bytes = encode_request(
            RequestToEncode::Open {
                params: &self.requested,
-                no_test: self.config.run_mode == RunMode::NoTest,
+                no_test: self.config.request.run_mode == RunMode::NoTest,
            },
            self.config.auth.hmac_key(),
        )?;
@@ -269,7 +270,7 @@ impl SessionMachine {
            ));
        }

-        match self.config.run_mode {
+        match self.config.request.run_mode {
            RunMode::Normal if reply_is_close => Err(OpenAcceptanceFailure::new(
                ClientError::ServerRejected,
                cleanup_close,
@@ -602,14 +603,11 @@ impl SessionMachine {
        cleanup_close: Option<Box<[u8]>>,
    ) -> Result<PreparedOpenAcceptance, OpenAcceptanceFailure> {
        let token = reply.token;
-        let negotiated = match negotiate_params(
-            &self.requested,
-            reply.params,
-            self.config.negotiation_policy,
-        ) {
-            Ok(negotiated) => negotiated,
-            Err(primary) => return Err(OpenAcceptanceFailure::new(primary, cleanup_close)),
-        };
+        let negotiated =
+            match negotiate_params(&self.requested, reply.params, self.config.open.negotiation) {
+                Ok(negotiated) => negotiated,
+                Err(primary) => return Err(OpenAcceptanceFailure::new(primary, cleanup_close)),
+            };
        let local_close_packet =
            cleanup_close.expect("normal non-zero-token replies prepare a cleanup close");
        let next_state = MachineState::Open(Box::new(ActiveSession {
@@ -649,12 +647,9 @@ impl SessionMachine {
        reply: OpenReply,
        now: ClientTimestamp,
    ) -> Result<PreparedOpenAcceptance, OpenAcceptanceFailure> {
-        let negotiated = negotiate_params(
-            &self.requested,
-            reply.params,
-            self.config.negotiation_policy,
-        )
-        .map_err(OpenAcceptanceFailure::without_cleanup)?;
+        let negotiated =
+            negotiate_params(&self.requested, reply.params, self.config.open.negotiation)
+                .map_err(OpenAcceptanceFailure::without_cleanup)?;
        let event = ClientEvent::NoTestCompleted {
            remote: self.remote,
            negotiated: negotiated.clone(),
@@ -888,21 +883,24 @@ pub(crate) fn recv_buffer_size(
    })
 }

-pub(crate) fn params_from_config(config: &ClientConfig) -> Result<Params, ClientError> {
-    validate_protocol_config(config)?;
+pub(crate) fn params_from_request(request: &SessionRequest) -> Result<Params, ClientError> {
+    validate_request(request)?;
    Ok(Params {
        protocol_version: PROTOCOL_VERSION,
-        duration_ns: match config.duration {
+        duration_ns: match request.duration {
            Some(duration) => config_duration_to_ns("duration", duration)?,
            None => 0,
        },
-        interval_ns: config_duration_to_ns("interval", config.interval)?,
-        length: i64::from(config.length),
-        received_stats: config.received_stats,
-        stamp_at: config.stamp_at,
-        clock: config.clock,
-        dscp: i64::from(dscp_codepoint_to_traffic_class(config.dscp)?),
-        server_fill: config.server_fill.clone().map(|value| ServerFill { value }),
+        interval_ns: config_duration_to_ns("interval", request.interval)?,
+        length: i64::from(request.length),
+        received_stats: request.received_stats,
+        stamp_at: request.stamp_at,
+        clock: request.clock,
+        dscp: i64::from(dscp_codepoint_to_traffic_class(request.dscp)?),
+        server_fill: request
+            .server_fill
+            .clone()
+            .map(|value| ServerFill { value }),
    })
 }

@@ -1083,34 +1081,34 @@ fn build_received_stats(reply: &EchoReply) -> Option<ReceivedStatsSample> {
    })
 }

-fn validate_protocol_config(config: &ClientConfig) -> Result<(), ClientError> {
-    if config.duration == Some(Duration::ZERO) {
+fn validate_request(request: &SessionRequest) -> Result<(), ClientError> {
+    if request.duration == Some(Duration::ZERO) {
        return Err(ClientError::InvalidConfig {
            reason: "duration must be greater than zero; use None for continuous mode".to_owned(),
        });
    }
-    if config.interval == Duration::ZERO {
+    if request.interval == Duration::ZERO {
        return Err(ClientError::InvalidConfig {
            reason: "interval must be greater than zero".to_owned(),
        });
    }
-    if config.clock == Clock::Unspecified {
+    if request.clock == Clock::Unspecified {
        return Err(ClientError::InvalidConfig {
            reason: "clock must be wall, monotonic, or both".to_owned(),
        });
    }
-    if config.dscp > MAX_DSCP_CODEPOINT {
+    if request.dscp > MAX_DSCP_CODEPOINT {
        return Err(ClientError::InvalidConfig {
            reason: format!("dscp must be <= {MAX_DSCP_CODEPOINT}"),
        });
    }
-    if config.length > MAX_UDP_PAYLOAD_LENGTH {
+    if request.length > MAX_UDP_PAYLOAD_LENGTH {
        return Err(ClientError::InvalidConfig {
            reason: format!("packet length must be <= {MAX_UDP_PAYLOAD_LENGTH}"),
        });
    }

-    if let Some(fill) = &config.server_fill {
+    if let Some(fill) = &request.server_fill {
        let len = fill.len();
        if len == 0 {
            return Err(ClientError::InvalidConfig {
@@ -1191,9 +1189,12 @@ mod tests {
    fn opened() -> SessionMachine {
        let mut machine = SessionMachine::new(
            ClientConfig {
+                request: crate::SessionRequest {
+                    clock: Clock::Wall,
+                    stamp_at: irtt_proto::StampAt::Receive,
+                    ..Default::default()
+                },
                max_pending_probes: 2,
-                clock: Clock::Wall,
-                stamp_at: irtt_proto::StampAt::Receive,
                ..ClientConfig::default()
            },
            "127.0.0.1:2112".parse().unwrap(),
@@ -13,7 +13,7 @@ use crate::{config::NegotiationPolicy, error::ClientError};
 /// `params.dscp` is the raw IP TOS / Traffic Class byte, not a DSCP
 /// codepoint: for a configured codepoint of 46 (EF), an unrestricted
 /// negotiation leaves `params.dscp == 184`. [`NegotiationRestriction::DscpChanged`]
-/// reports codepoints instead, for consistency with [`crate::ClientConfig::dscp`].
+/// reports codepoints instead, for consistency with [`crate::SessionRequest::dscp`].
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct NegotiatedParams {
    /// Server-returned protocol parameters used for the session.
@@ -61,7 +61,7 @@ pub enum NegotiationRestriction {
    /// Returned DSCP codepoint differs from the request.
    ///
    /// These values are DSCP codepoints (`0..=63`) for human-facing
-    /// consistency with [`crate::ClientConfig::dscp`], not the raw wire
+    /// consistency with [`crate::SessionRequest::dscp`], not the raw wire
    /// `Params::dscp` byte carried by [`NegotiatedParams::params`].
    DscpChanged { requested: i64, negotiated: i64 },
    /// Returned server payload fill behavior differs from the request.
@@ -1,12 +1,9 @@
-use std::{
-    net::{SocketAddr, ToSocketAddrs, UdpSocket},
-    time::Duration,
-};
+use std::net::{SocketAddr, ToSocketAddrs, UdpSocket};

 use socket2::{Domain, Protocol, Socket, Type};

 use crate::{
-    config::{ClientConfig, SocketConfig, DEFAULT_PORT, MIN_OPEN_TIMEOUT},
+    config::{AddressFamily, SocketConfig, DEFAULT_PORT},
    error::ClientError,
    receive::configure_receive_metadata,
    socket_options::apply_ttl_to_socket,
@@ -20,36 +17,27 @@ use crate::{
 ))]
 use crate::socket_options::apply_routing_options;

-pub(crate) fn validate_open_timeouts(timeouts: &[Duration]) -> Result<(), ClientError> {
-    if timeouts.is_empty() {
-        return Err(ClientError::NoOpenTimeouts);
-    }
-    for timeout in timeouts {
-        if *timeout < MIN_OPEN_TIMEOUT {
-            return Err(ClientError::OpenTimeoutTooSmall {
-                timeout: *timeout,
-                minimum: MIN_OPEN_TIMEOUT,
-            });
-        }
-    }
-    Ok(())
-}
-
-pub(crate) fn resolve_remote(config: &ClientConfig) -> Result<SocketAddr, ClientError> {
-    let addr = normalize_server_addr(&config.server_addr);
+pub(crate) fn resolve_remote(
+    endpoint: &str,
+    family: AddressFamily,
+) -> Result<SocketAddr, ClientError> {
+    let addr = normalize_server_addr(endpoint);
    let mut addrs = addr
        .to_socket_addrs()
        .map_err(|_| ClientError::Resolve { addr: addr.clone() })?;
    addrs
-        .find(|addr| address_family_allowed(config, *addr))
+        .find(|addr| address_family_allowed(family, *addr))
        .ok_or(ClientError::Resolve { addr })
 }

 #[cfg(feature = "tokio")]
-pub(crate) async fn resolve_remote_tokio(config: &ClientConfig) -> Result<SocketAddr, ClientError> {
-    let addr = normalize_server_addr(&config.server_addr);
+pub(crate) async fn resolve_remote_tokio(
+    endpoint: &str,
+    family: AddressFamily,
+) -> Result<SocketAddr, ClientError> {
+    let addr = normalize_server_addr(endpoint);
    if let Ok(remote) = addr.parse::<SocketAddr>() {
-        return address_family_allowed(config, remote)
+        return address_family_allowed(family, remote)
            .then_some(remote)
            .ok_or(ClientError::Resolve { addr });
    }
@@ -58,13 +46,16 @@ pub(crate) async fn resolve_remote_tokio(config: &ClientConfig) -> Result<Socket
        .await
        .map_err(|_| ClientError::Resolve { addr: addr.clone() })?;
    addrs
-        .find(|remote| address_family_allowed(config, *remote))
+        .find(|remote| address_family_allowed(family, *remote))
        .ok_or_else(|| ClientError::Resolve { addr: addr.clone() })
 }

-fn address_family_allowed(config: &ClientConfig, remote: SocketAddr) -> bool {
-    (!config.socket_config.ipv4_only || remote.is_ipv4())
-        && (!config.socket_config.ipv6_only || remote.is_ipv6())
+fn address_family_allowed(family: AddressFamily, remote: SocketAddr) -> bool {
+    match family {
+        AddressFamily::Any => true,
+        AddressFamily::Ipv4 => remote.is_ipv4(),
+        AddressFamily::Ipv6 => remote.is_ipv6(),
+    }
 }

 pub(crate) fn normalize_server_addr(addr: &str) -> String {
@@ -92,17 +83,9 @@ pub(crate) fn normalize_server_addr(addr: &str) -> String {
 pub(crate) fn connect_udp_socket(
    config: &SocketConfig,
    remote: SocketAddr,
+    family: AddressFamily,
 ) -> Result<UdpSocket, ClientError> {
-    let socket = create_connected_udp_socket(config, remote)?;
-    socket.set_read_timeout(config.recv_timeout)?;
-    Ok(socket)
-}
-
-fn create_connected_udp_socket(
-    config: &SocketConfig,
-    remote: SocketAddr,
-) -> Result<UdpSocket, ClientError> {
-    let socket = create_prebind_udp_socket(config, remote)?;
+    let socket = create_prebind_udp_socket(remote, family)?;
    #[cfg(any(
        target_os = "android",
        target_os = "freebsd",
@@ -133,8 +116,8 @@ fn create_connected_udp_socket(
 }

 fn create_prebind_udp_socket(
-    config: &SocketConfig,
    remote: SocketAddr,
+    family: AddressFamily,
 ) -> Result<Socket, ClientError> {
    let domain = if remote.is_ipv4() {
        Domain::IPV4
@@ -143,7 +126,7 @@ fn create_prebind_udp_socket(
    };
    let socket = Socket::new(domain, Type::DGRAM, Some(Protocol::UDP))?;

-    if config.ipv6_only && remote.is_ipv6() {
+    if family == AddressFamily::Ipv6 && remote.is_ipv6() {
        socket.set_only_v6(true)?;
    }
    Ok(socket)
@@ -153,8 +136,9 @@ fn create_prebind_udp_socket(
 pub(crate) fn connect_tokio_udp_socket(
    config: &SocketConfig,
    remote: SocketAddr,
+    family: AddressFamily,
 ) -> Result<tokio::net::UdpSocket, ClientError> {
-    let socket = create_connected_udp_socket(config, remote)?;
+    let socket = connect_udp_socket(config, remote, family)?;
    socket.set_nonblocking(true)?;
    Ok(tokio::net::UdpSocket::from_std(socket)?)
 }
@@ -9,9 +9,12 @@ fn operations_fail_after_local_close_without_datagrams() {
        socket.send_to(&reply, peer).unwrap();
        let _ = recv_request(&socket, &tx);
    });
-    let mut config = default_test_config(server.addr);
-    config.socket_config.recv_timeout = Some(Duration::from_millis(50));
-    let mut client = Client::connect(config).unwrap();
+    let config = default_test_config();
+
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(50)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    client.close().unwrap();
    assert!(matches!(client.open(), Err(ClientError::AlreadyClosed)));
@@ -52,7 +55,7 @@ fn send_probe_fails_after_close() {
            }
        }
    });
-    let mut client = Client::connect(default_test_config(server.addr)).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();
    assert_open_started(client.open().unwrap());
    client.close().unwrap();
    assert!(matches!(
@@ -89,7 +92,7 @@ fn recv_available_stops_after_peer_close() {
            socket.send_to(&close, peer).unwrap();
        }
    });
-    let mut client = Client::connect(default_test_config(server.addr)).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();
    assert_open_started(client.open().unwrap());
    client.send_probe().unwrap();

@@ -137,14 +140,10 @@ fn close_flagged_duplicate_emits_duplicate_then_closes() {
            socket.send_to(&close, peer).unwrap();
        }
    });
-    let mut client = Client::connect(ClientConfig {
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
-    })
-    .unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    client.send_probe().unwrap();

@@ -194,15 +193,17 @@ fn close_flagged_retained_timeout_emits_late_then_closes() {
                .unwrap();
        }
    });
-    let mut client = Client::connect(ClientConfig {
-        probe_timeout: Duration::from_millis(50),
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
+    let mut client = Client::connect(
+        server.addr.to_string(),
+        ClientConfig {
+            probe_timeout: Duration::from_millis(50),
+            ..default_test_config()
        },
-        ..default_test_config(server.addr)
-    })
+    )
    .unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    let sent = client.send_probe().unwrap();
    let ClientEvent::EchoSent { sent_at, .. } = &sent[0] else {
@@ -289,15 +290,17 @@ fn close_flagged_evicted_sequence_emits_late_then_closes() {
                .unwrap();
        }
    });
-    let mut client = Client::connect(ClientConfig {
-        max_pending_probes: 1,
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
+    let mut client = Client::connect(
+        server.addr.to_string(),
+        ClientConfig {
+            max_pending_probes: 1,
+            ..default_test_config()
        },
-        ..default_test_config(server.addr)
-    })
+    )
    .unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());

    client.send_probe().unwrap();
@@ -354,14 +357,10 @@ fn close_flagged_untracked_sequence_emits_warning_then_closes() {
                .unwrap();
        }
    });
-    let mut client = Client::connect(ClientConfig {
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
-    })
-    .unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());

    assert!(matches!(
@@ -412,14 +411,10 @@ fn wrong_token_close_flag_does_not_close_session() {
            let _ = recv_request(&socket, &tx);
        }
    });
-    let mut client = Client::connect(ClientConfig {
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
-    })
-    .unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    client.send_probe().unwrap();

@@ -467,14 +462,11 @@ fn close_flagged_echo_reply_emits_reply_then_closes_without_sending_close() {
            while recv_request_timeout(&socket, &tx).is_some() {}
        }
    });
-    let config = ClientConfig {
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
-    };
-    let mut client = Client::connect(config).unwrap();
+    let config = default_test_config();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    client.send_probe().unwrap();

@@ -8,7 +8,10 @@ fn connect_rejects_invalid_configuration() {
        (
            "oversized UDP payload",
            ClientConfig {
-                length: MAX_UDP_PAYLOAD_LENGTH + 1,
+                request: SessionRequest {
+                    length: MAX_UDP_PAYLOAD_LENGTH + 1,
+                    ..Default::default()
+                },
                ..ClientConfig::default()
            },
            "packet length",
@@ -16,7 +19,10 @@ fn connect_rejects_invalid_configuration() {
        (
            "zero finite duration",
            ClientConfig {
-                duration: Some(Duration::ZERO),
+                request: SessionRequest {
+                    duration: Some(Duration::ZERO),
+                    ..Default::default()
+                },
                ..ClientConfig::default()
            },
            "duration must be greater than zero; use None for continuous mode",
@@ -24,7 +30,10 @@ fn connect_rejects_invalid_configuration() {
        (
            "zero interval",
            ClientConfig {
-                interval: Duration::ZERO,
+                request: SessionRequest {
+                    interval: Duration::ZERO,
+                    ..Default::default()
+                },
                ..ClientConfig::default()
            },
            "interval must be greater than zero",
@@ -32,7 +41,10 @@ fn connect_rejects_invalid_configuration() {
        (
            "duration nanosecond overflow",
            ClientConfig {
-                duration: Some(too_large),
+                request: SessionRequest {
+                    duration: Some(too_large),
+                    ..Default::default()
+                },
                ..ClientConfig::default()
            },
            "duration is too large to encode as nanoseconds",
@@ -40,7 +52,10 @@ fn connect_rejects_invalid_configuration() {
        (
            "interval nanosecond overflow",
            ClientConfig {
-                interval: too_large,
+                request: SessionRequest {
+                    interval: too_large,
+                    ..Default::default()
+                },
                ..ClientConfig::default()
            },
            "interval is too large to encode as nanoseconds",
@@ -48,7 +63,10 @@ fn connect_rejects_invalid_configuration() {
        (
            "invalid DSCP codepoint",
            ClientConfig {
-                dscp: 64,
+                request: SessionRequest {
+                    dscp: 64,
+                    ..Default::default()
+                },
                ..ClientConfig::default()
            },
            "dscp",
@@ -58,7 +76,10 @@ fn connect_rejects_invalid_configuration() {
            // client mode; a client that needs timestamps must name a clock.
            "unspecified clock",
            ClientConfig {
-                clock: Clock::Unspecified,
+                request: SessionRequest {
+                    clock: Clock::Unspecified,
+                    ..Default::default()
+                },
                ..ClientConfig::default()
            },
            "clock must be wall, monotonic, or both",
@@ -66,7 +87,10 @@ fn connect_rejects_invalid_configuration() {
        (
            "empty server fill",
            ClientConfig {
-                server_fill: Some("".to_owned()),
+                request: SessionRequest {
+                    server_fill: Some("".to_owned()),
+                    ..Default::default()
+                },
                ..ClientConfig::default()
            },
            "server_fill",
@@ -74,7 +98,10 @@ fn connect_rejects_invalid_configuration() {
        (
            "oversized server fill",
            ClientConfig {
-                server_fill: Some("0123456789abcdef0123456789abcdefx".to_owned()),
+                request: SessionRequest {
+                    server_fill: Some("0123456789abcdef0123456789abcdefx".to_owned()),
+                    ..Default::default()
+                },
                ..ClientConfig::default()
            },
            "server_fill",
@@ -84,7 +111,7 @@ fn connect_rejects_invalid_configuration() {
    for (name, config, expected_reason) in cases {
        assert!(
            matches!(
-                Client::connect(config),
+                Client::connect("127.0.0.1:2112", config),
                Err(ClientError::InvalidConfig { .. })
            ),
            "{name} should fail with InvalidConfig ({expected_reason})"
@@ -95,11 +122,14 @@ fn connect_rejects_invalid_configuration() {
 #[test]
 fn minimum_open_timeout_under_200ms_is_rejected() {
    let config = ClientConfig {
-        open_timeouts: vec![Duration::from_millis(199)],
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(199)],
+            ..Default::default()
+        },
        ..ClientConfig::default()
    };
    assert!(matches!(
-        Client::connect(config),
+        Client::connect("127.0.0.1:2112", config),
        Err(ClientError::OpenTimeoutTooSmall { .. })
    ));
 }
@@ -107,11 +137,14 @@ fn minimum_open_timeout_under_200ms_is_rejected() {
 #[test]
 fn empty_open_timeouts_is_rejected() {
    let config = ClientConfig {
-        open_timeouts: vec![],
+        open: OpenPolicy {
+            timeouts: vec![],
+            ..Default::default()
+        },
        ..ClientConfig::default()
    };
    assert!(matches!(
-        Client::connect(config),
+        Client::connect("127.0.0.1:2112", config),
        Err(ClientError::NoOpenTimeouts)
    ));
 }
@@ -4,7 +4,7 @@ use irtt_client::{Authentication, HmacKey};
 #[test]
 fn hmac_open_ignores_missing_hmac_before_valid_reply() {
    let key = b"secret".to_vec();
-    let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 1)));
+    let mut config = default_test_config();
    config.auth = Authentication::Hmac(HmacKey::new(key.clone()));
    let params = default_params();
    let server = start_fake_server(move |socket, tx| {
@@ -14,8 +14,7 @@ fn hmac_open_ignores_missing_hmac_before_valid_reply() {
        socket.send_to(&missing, peer).unwrap();
        socket.send_to(&valid, peer).unwrap();
    });
-    config.server_addr = server.addr.to_string();
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
    assert_open_started(client.open().unwrap());
    assert_eq!(server.rx.iter().take(1).count(), 1);
    assert!(server.rx.try_recv().is_err());
@@ -26,7 +25,7 @@ fn hmac_open_ignores_missing_hmac_before_valid_reply() {
 fn hmac_open_ignores_bad_hmac_before_valid_reply() {
    let key = b"secret".to_vec();
    let wrong_key = b"wrong".to_vec();
-    let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 1)));
+    let mut config = default_test_config();
    config.auth = Authentication::Hmac(HmacKey::new(key.clone()));
    let params = default_params();
    let server = start_fake_server(move |socket, tx| {
@@ -36,8 +35,7 @@ fn hmac_open_ignores_bad_hmac_before_valid_reply() {
        socket.send_to(&bad, peer).unwrap();
        socket.send_to(&valid, peer).unwrap();
    });
-    config.server_addr = server.addr.to_string();
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
    assert_open_started(client.open().unwrap());
    assert_eq!(server.rx.iter().take(1).count(), 1);
    assert!(server.rx.try_recv().is_err());
@@ -47,7 +45,7 @@ fn hmac_open_ignores_bad_hmac_before_valid_reply() {
 #[test]
 fn post_token_hmac_negotiation_failure_sends_authenticated_cleanup_close() {
    let key = b"secret".to_vec();
-    let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 1)));
+    let mut config = default_test_config();
    config.auth = Authentication::Hmac(HmacKey::new(key.clone()));
    let mut returned = default_params();
    returned.interval_ns += 1;
@@ -58,8 +56,7 @@ fn post_token_hmac_negotiation_failure_sends_authenticated_cleanup_close() {
        socket.send_to(&reply, peer).unwrap();
        let _ = recv_request(&socket, &tx);
    });
-    config.server_addr = server.addr.to_string();
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();

    assert!(matches!(
        client.open(),
@@ -2,8 +2,8 @@ use super::*;

 #[test]
 fn no_test_rejects_non_close_open_reply() {
-    let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 1)));
-    config.run_mode = RunMode::NoTest;
+    let mut config = default_test_config();
+    config.request.run_mode = RunMode::NoTest;
    let params = default_params();
    let server = start_fake_server(move |socket, tx| {
        let (_, peer) = recv_request(&socket, &tx);
@@ -15,8 +15,7 @@ fn no_test_rejects_non_close_open_reply() {
            .unwrap();
        let _ = recv_request(&socket, &tx);
    });
-    config.server_addr = server.addr.to_string();
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
    assert!(matches!(
        client.open(),
        Err(ClientError::UnexpectedNoTestReply)
@@ -32,12 +31,11 @@ fn no_test_rejects_non_close_open_reply() {

 #[test]
 fn no_test_rejects_non_zero_token_with_close_reply() {
-    let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 1)));
-    config.run_mode = RunMode::NoTest;
+    let mut config = default_test_config();
+    config.request.run_mode = RunMode::NoTest;
    let params = default_params();
    let server = no_test_server(params, TOKEN);
-    config.server_addr = server.addr.to_string();
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
    assert!(matches!(
        client.open(),
        Err(ClientError::NonZeroNoTestToken { token: TOKEN })
@@ -47,13 +45,12 @@ fn no_test_rejects_non_zero_token_with_close_reply() {

 #[test]
 fn no_test_strict_negotiation_rejects_changed_params() {
-    let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 1)));
-    config.run_mode = RunMode::NoTest;
+    let mut config = default_test_config();
+    config.request.run_mode = RunMode::NoTest;
    let mut params = default_params();
    params.dscp = 1;
    let server = no_test_server(params, 0);
-    config.server_addr = server.addr.to_string();
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
    assert!(matches!(
        client.open(),
        Err(ClientError::NegotiationRejected { .. })
@@ -63,15 +60,14 @@ fn no_test_strict_negotiation_rejects_changed_params() {

 #[test]
 fn no_test_loose_negotiation_accepts_restricted_params() {
-    let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 1)));
-    config.run_mode = RunMode::NoTest;
-    config.negotiation_policy = NegotiationPolicy::Loose;
+    let mut config = default_test_config();
+    config.request.run_mode = RunMode::NoTest;
+    config.open.negotiation = NegotiationPolicy::Loose;
    let requested = default_params();
    let mut params = requested.clone();
    params.duration_ns /= 2;
    let server = no_test_server(params.clone(), 0);
-    config.server_addr = server.addr.to_string();
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
    let negotiated = assert_no_test_completed(client.open().unwrap());
    assert_eq!(negotiated.params, params);
    assert_eq!(
@@ -86,12 +82,11 @@ fn no_test_loose_negotiation_accepts_restricted_params() {

 #[test]
 fn send_probe_fails_after_no_test_completed() {
-    let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 1)));
-    config.run_mode = RunMode::NoTest;
+    let mut config = default_test_config();
+    config.request.run_mode = RunMode::NoTest;
    let params = default_params();
    let server = no_test_server(params, 0);
-    config.server_addr = server.addr.to_string();
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
    assert_no_test_completed(client.open().unwrap());
    assert!(matches!(
        client.send_probe(),
@@ -102,13 +97,15 @@ fn send_probe_fails_after_no_test_completed() {

 #[test]
 fn operations_fail_after_no_test_completed_without_datagrams() {
-    let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 1)));
-    config.run_mode = RunMode::NoTest;
-    config.socket_config.recv_timeout = Some(Duration::from_millis(50));
+    let mut config = default_test_config();
+    config.request.run_mode = RunMode::NoTest;
+
    let params = default_params();
    let server = no_test_server(params, 0);
-    config.server_addr = server.addr.to_string();
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(50)))
+        .unwrap();
    assert_no_test_completed(client.open().unwrap());
    assert!(matches!(client.open(), Err(ClientError::AlreadyCompleted)));
    let results = [
@@ -3,10 +3,13 @@ use super::*;
 #[test]
 fn receive_before_open_returns_not_open_without_datagrams() {
    let peer = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
-    let mut config = default_test_config(peer.local_addr().unwrap());
+    let config = default_test_config();
    // Bound the old implementation's blocking receive without sending a packet.
-    config.socket_config.recv_timeout = Some(Duration::from_millis(50));
-    let mut client = Client::connect(config).unwrap();
+
+    let mut client = Client::connect(peer.local_addr().unwrap().to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(50)))
+        .unwrap();

    let results = [
        client.recv_once(),
@@ -35,10 +38,13 @@ fn loose_open_rejects_nonpositive_returned_intervals() {
        returned.interval_ns = interval_ns;
        let server = open_success_server(returned);
        let config = ClientConfig {
-            negotiation_policy: NegotiationPolicy::Loose,
-            ..default_test_config(server.addr)
+            open: OpenPolicy {
+                negotiation: NegotiationPolicy::Loose,
+                ..default_test_config().open
+            },
+            ..default_test_config()
        };
-        let mut client = Client::connect(config).unwrap();
+        let mut client = Client::connect(server.addr.to_string(), config).unwrap();
        assert!(
            matches!(client.open(), Err(ClientError::NegotiationRejected { .. })),
            "returned interval {interval_ns} must be rejected"
@@ -51,7 +57,7 @@ fn loose_open_rejects_nonpositive_returned_intervals() {
 fn open_fails_when_already_open() {
    let params = default_params();
    let server = open_success_server(params);
-    let mut client = Client::connect(default_test_config(server.addr)).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();
    assert_open_started(client.open().unwrap());
    assert!(matches!(client.open(), Err(ClientError::AlreadyOpen)));
    server.join();
@@ -68,10 +74,13 @@ fn open_retries_after_first_timeout() {
        socket.send_to(&reply, peer).unwrap();
    });
    let config = ClientConfig {
-        open_timeouts: vec![Duration::from_millis(200), Duration::from_millis(500)],
-        ..default_test_config(server.addr)
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(200), Duration::from_millis(500)],
+            ..default_test_config().open
+        },
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
    let outcome = client.open().unwrap();
    assert_open_started(outcome);
    assert_eq!(server.rx.iter().take(2).count(), 2);
@@ -80,12 +89,12 @@ fn open_retries_after_first_timeout() {

 #[test]
 fn protocol_version_mismatch_fails() {
-    let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 1)));
-    config.negotiation_policy = NegotiationPolicy::Loose;
+    let mut config = default_test_config();
+    config.open.negotiation = NegotiationPolicy::Loose;
    let mut params = default_params();
    params.protocol_version = 2;
    let server = open_success_server(params);
-    let mut client = Client::connect(default_test_config(server.addr)).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();
    assert!(matches!(
        client.open(),
        Err(ClientError::ProtocolVersionMismatch { received: 2, .. })
@@ -102,7 +111,7 @@ fn server_rejection_fails_in_normal_mode() {
        let reply = open_reply(FLAG_OPEN | FLAG_REPLY | flags::FLAG_CLOSE, 0, &params, None);
        socket.send_to(&reply, peer).unwrap();
    });
-    let mut client = Client::connect(default_test_config(server.addr)).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();
    assert!(matches!(client.open(), Err(ClientError::ServerRejected)));
    assert_eq!(server.rx.iter().take(1).count(), 1);
    server.join();
@@ -119,10 +128,13 @@ fn ignored_datagrams_do_not_restart_the_attempt_deadline() {
        let _ = recv_request(&socket, &tx);
    });
    let config = ClientConfig {
-        open_timeouts: vec![Duration::from_millis(250), Duration::from_millis(250)],
-        ..default_test_config(server.addr)
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(250), Duration::from_millis(250)],
+            ..default_test_config().open
+        },
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
    let started = Instant::now();

    assert!(matches!(client.open(), Err(ClientError::OpenTimeout)));
@@ -139,10 +151,13 @@ fn ignored_datagrams_do_not_restart_the_attempt_deadline() {
 fn opening_deadline_overflow_occurs_before_send() {
    let server = timeout_server(Duration::from_millis(250));
    let config = ClientConfig {
-        open_timeouts: vec![Duration::MAX],
-        ..default_test_config(server.addr)
+        open: OpenPolicy {
+            timeouts: vec![Duration::MAX],
+            ..default_test_config().open
+        },
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();

    assert!(matches!(client.open(), Err(ClientError::DurationOverflow)));
    assert!(server.rx.try_recv().is_err());
@@ -163,7 +178,7 @@ fn post_token_negotiation_failure_sends_cleanup_close() {
            .unwrap();
        let _ = recv_request(&socket, &tx);
    });
-    let mut client = Client::connect(default_test_config(server.addr)).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();

    assert!(matches!(
        client.open(),
@@ -182,14 +197,16 @@ fn post_token_negotiation_failure_sends_cleanup_close() {
 fn open_timeout_after_all_timeouts() {
    let server = timeout_server(Duration::from_millis(700));
    let config = ClientConfig {
-        open_timeouts: vec![Duration::from_millis(200), Duration::from_millis(200)],
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(50)),
-            ..Default::default()
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(200), Duration::from_millis(200)],
+            ..default_test_config().open
        },
-        ..default_test_config(server.addr)
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(50)))
+        .unwrap();
    assert!(matches!(client.open(), Err(ClientError::OpenTimeout)));
    assert_eq!(server.rx.iter().take(2).count(), 2);
    server.join();
@@ -221,7 +238,7 @@ fn multiple_untrusted_datagrams_before_valid_reply_use_one_attempt() {
            socket.send_to(&packet, peer).unwrap();
        }
    });
-    let mut client = Client::connect(default_test_config(server.addr)).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();

    assert_open_started(client.open().unwrap());
    assert_eq!(server.rx.iter().take(1).count(), 1);
@@ -241,14 +258,16 @@ fn only_ignored_open_datagrams_eventually_time_out() {
        thread::sleep(Duration::from_millis(300));
    });
    let config = ClientConfig {
-        open_timeouts: vec![Duration::from_millis(200), Duration::from_millis(200)],
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(50)),
-            ..Default::default()
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(200), Duration::from_millis(200)],
+            ..default_test_config().open
        },
-        ..default_test_config(server.addr)
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(50)))
+        .unwrap();

    assert!(matches!(client.open(), Err(ClientError::OpenTimeout)));
    assert_eq!(server.rx.iter().take(2).count(), 2);
@@ -268,7 +287,7 @@ fn trusted_zero_token_normal_reply_is_terminal() {
        reply[HMAC_OFFSET..HMAC_OFFSET + 8].copy_from_slice(&0_u64.to_le_bytes());
        socket.send_to(&reply, peer).unwrap();
    });
-    let mut client = Client::connect(default_test_config(server.addr)).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), default_test_config()).unwrap();

    assert!(matches!(
        client.open(),
@@ -23,14 +23,16 @@ fn short_echo_reply_does_not_emit_echo_reply() {
        }
    });
    let config = ClientConfig {
-        length: 64,
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
+        request: SessionRequest {
+            length: 64,
+            ..default_test_config().request
        },
-        ..default_test_config(server.addr)
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    client.send_probe().unwrap();

@@ -69,14 +71,16 @@ fn overlong_datagram_detection_uses_extra_receive_byte() {
        }
    });
    let config = ClientConfig {
-        length: 4096,
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
+        request: SessionRequest {
+            length: 4096,
+            ..default_test_config().request
        },
-        ..default_test_config(server.addr)
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    client.send_probe().unwrap();

@@ -112,14 +116,16 @@ fn exact_length_echo_reply_still_emits_echo_reply() {
        }
    });
    let config = ClientConfig {
-        length: 4096,
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
+        request: SessionRequest {
+            length: 4096,
+            ..default_test_config().request
        },
-        ..default_test_config(server.addr)
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    client.send_probe().unwrap();

@@ -22,14 +22,11 @@ fn duplicate_reply_emits_duplicate_event() {
            socket.send_to(&reply_packet, peer).unwrap();
        }
    });
-    let config = ClientConfig {
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
-    };
-    let mut client = Client::connect(config).unwrap();
+    let config = default_test_config();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    client.send_probe().unwrap();
    thread::sleep(Duration::from_millis(50));
@@ -76,14 +73,11 @@ fn out_of_order_reply_emits_late_event() {
        let reply0 = echo_reply_packet(TOKEN, seqs[0], &params, &ts, None);
        socket.send_to(&reply0, peer).unwrap();
    });
-    let config = ClientConfig {
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
-    };
-    let mut client = Client::connect(config).unwrap();
+    let config = default_test_config();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    client.send_probe().unwrap();
    client.send_probe().unwrap();
@@ -4,14 +4,11 @@ use super::*;
 fn recv_once_returns_empty_on_timeout() {
    let params = default_params();
    let server = open_success_server(params);
-    let config = ClientConfig {
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(50)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
-    };
-    let mut client = Client::connect(config).unwrap();
+    let config = default_test_config();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(50)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    let events = client.recv_once().unwrap();
    assert!(events.is_empty());
@@ -52,14 +49,11 @@ fn recv_once_decodes_only_received_bytes_after_longer_datagram() {
        );
        socket.send_to(&shorter, peer).unwrap();
    });
-    let config = ClientConfig {
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
-    };
-    let mut client = Client::connect(config).unwrap();
+    let config = default_test_config();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());

    client.send_probe().unwrap();
@@ -19,14 +19,11 @@ fn echo_reply_metadata_propagates_observed_dscp_with_ancillary() {
            echo_reply_packet(TOKEN, seq, &params, &TimestampFields::default(), None);
        socket.send_to(&reply_packet, peer).unwrap();
    });
-    let config = ClientConfig {
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
-    };
-    let mut client = Client::connect(config).unwrap();
+    let config = default_test_config();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());

    client.send_probe().unwrap();
@@ -20,9 +20,9 @@ fn probe_timeout_overflow_transmits_no_echo() {
    });
    let config = ClientConfig {
        probe_timeout: Duration::MAX,
-        ..default_test_config(server.addr)
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
    assert_open_started(client.open().unwrap());
    assert!(matches!(
        client.send_probe(),
@@ -46,13 +46,12 @@ fn poll_timeouts_emits_echo_loss() {
    let server = silent_open_server(params);
    let config = ClientConfig {
        probe_timeout: Duration::from_millis(100),
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(50)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(50)))
+        .unwrap();
    assert_open_started(client.open().unwrap());

    client.send_probe().unwrap();
@@ -97,13 +96,12 @@ fn late_reply_after_timeout_preserves_measurement_metadata() {
    });
    let config = ClientConfig {
        probe_timeout: Duration::from_millis(40),
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());

    client.send_probe().unwrap();
@@ -157,15 +155,17 @@ fn pending_full_does_not_send_packet() {
    };
    let server = silent_open_server(params);
    let config = ClientConfig {
-        duration: Some(Duration::from_secs(60)),
-        max_pending_probes: 2,
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(50)),
-            ..Default::default()
+        request: SessionRequest {
+            duration: Some(Duration::from_secs(60)),
+            ..SessionRequest::default()
        },
-        ..default_test_config(server.addr)
+        max_pending_probes: 2,
+        ..default_test_config()
    };
-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(50)))
+        .unwrap();
    assert_open_started(client.open().unwrap());

    client.send_probe().unwrap();
@@ -25,10 +25,12 @@ impl FakeServer {
    }
 }

-pub(super) fn default_test_config(addr: SocketAddr) -> ClientConfig {
+pub(super) fn default_test_config() -> ClientConfig {
    ClientConfig {
-        server_addr: addr.to_string(),
-        open_timeouts: vec![Duration::from_millis(200), Duration::from_millis(200)],
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(200), Duration::from_millis(200)],
+            ..Default::default()
+        },
        ..ClientConfig::default()
    }
 }
@@ -252,14 +254,11 @@ pub(super) fn assert_no_test_completed(outcome: OpenOutcome) -> NegotiatedParams

 pub(super) fn open_client_with_echo_server(params: &Params) -> (Client, FakeServer) {
    let server = echo_server(params.clone());
-    let config = ClientConfig {
-        socket_config: irtt_client::SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..Default::default()
-        },
-        ..default_test_config(server.addr)
-    };
-    let mut client = Client::connect(config).unwrap();
+    let config = default_test_config();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert_open_started(client.open().unwrap());
    (client, server)
 }
@@ -3,19 +3,19 @@ use super::*;
 #[test]
 fn connect_accepts_valid_ttl_config_values() {
    for ttl in [None, Some(1), Some(255)] {
-        let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 9)));
-        config.socket_config.ttl = ttl;
-        Client::connect(config).unwrap();
+        let mut config = default_test_config();
+        config.socket.ttl = ttl;
+        Client::connect(SocketAddr::from(([127, 0, 0, 1], 9)).to_string(), config).unwrap();
    }
 }

 #[test]
 fn connect_rejects_invalid_ttl_values() {
    for ttl in [0, 256] {
-        let mut config = default_test_config(SocketAddr::from(([127, 0, 0, 1], 9)));
-        config.socket_config.ttl = Some(ttl);
+        let mut config = default_test_config();
+        config.socket.ttl = Some(ttl);
        assert!(matches!(
-            Client::connect(config),
+            Client::connect(SocketAddr::from(([127, 0, 0, 1], 9)).to_string(), config),
            Err(ClientError::InvalidConfig { .. })
        ));
    }
@@ -9,7 +9,9 @@ use std::{
    time::{Duration, SystemTime, UNIX_EPOCH},
 };

-use irtt_client::{Client, ClientConfig, ClientEvent, NegotiationPolicy, SocketConfig};
+use irtt_client::{
+    Client, ClientConfig, ClientEvent, NegotiationPolicy, OpenPolicy, SessionRequest, SocketConfig,
+};
 use irtt_proto::{decode_request, Clock, DecodedRequestKind, ReceivedStats, StampAt};
 use irtt_server::{ServerConfig, ServerCore};
 use nix::sys::socket::{recvmsg, ControlMessageOwned, MsgFlags};
@@ -81,21 +83,24 @@ fn peer(dscp_allowed: bool, probes: usize) -> (SocketAddr, thread::JoinHandle<Ve
    (addr, task)
 }

-fn config(addr: SocketAddr) -> ClientConfig {
+fn config() -> ClientConfig {
    ClientConfig {
-        server_addr: addr.to_string(),
-        dscp: 46,
-        negotiation_policy: NegotiationPolicy::Loose,
-        duration: None,
-        interval: Duration::from_millis(10),
-        clock: Clock::Both,
-        stamp_at: StampAt::Both,
-        received_stats: ReceivedStats::Both,
-        length: 128,
-        open_timeouts: vec![Duration::from_secs(1)],
-        socket_config: SocketConfig {
+        open: OpenPolicy {
+            negotiation: NegotiationPolicy::Loose,
+            timeouts: vec![Duration::from_secs(1)],
+        },
+        request: SessionRequest {
+            dscp: 46,
+            duration: None,
+            interval: Duration::from_millis(10),
+            clock: Clock::Both,
+            stamp_at: StampAt::Both,
+            received_stats: ReceivedStats::Both,
+            length: 128,
+            ..Default::default()
+        },
+        socket: SocketConfig {
            ttl: Some(TEST_TTL),
-            recv_timeout: Some(Duration::from_secs(1)),
            ..SocketConfig::default()
        },
        ..ClientConfig::default()
@@ -149,7 +154,10 @@ fn blocking_probes_use_kernel_tx_timing_and_negotiated_packet_marking() {
    for allowed in [true, false] {
        const PROBES: usize = 3;
        let (addr, peer) = peer(allowed, PROBES);
-        let mut client = Client::connect(config(addr)).unwrap();
+        let mut client = Client::connect(addr.to_string(), config()).unwrap();
+        client
+            .set_recv_timeout(Some(Duration::from_secs(1)))
+            .unwrap();
        client.open().unwrap();
        assert_eq!(
            client.negotiated_params().unwrap().params.dscp,
@@ -189,7 +197,7 @@ fn async_probes_use_kernel_tx_timing_and_negotiated_packet_marking() {
        let (addr, peer) = peer(allowed, PROBES);
        runtime.block_on(async {
            tokio::time::timeout(Duration::from_secs(5), async {
-                let mut client = irtt_client::AsyncClient::connect(config(addr))
+                let mut client = irtt_client::AsyncClient::connect(addr.to_string(), config())
                    .await
                    .unwrap();
                client.open().await.unwrap();
@@ -245,7 +253,10 @@ fn a_closed_udp_peer_surfaces_a_socket_error() {
        close_rx.recv_timeout(Duration::from_secs(3)).unwrap();
        drop(socket);
    });
-    let mut client = Client::connect(config(addr)).unwrap();
+    let mut client = Client::connect(addr.to_string(), config()).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_secs(1)))
+        .unwrap();
    client.open().unwrap();
    close_tx.send(()).unwrap();
    task.join().unwrap();
@@ -1,6 +1,8 @@
 use std::time::Duration;

-use irtt_client::{AsyncClient, ClientConfig, ClientEvent, OpenOutcome, SocketConfig};
+use irtt_client::{
+    AsyncClient, ClientConfig, ClientEvent, OpenOutcome, OpenPolicy, SessionRequest,
+};
 use irtt_proto::{Clock, ReceivedStats, StampAt};
 use irtt_server::{Server, ServerConfig};
 use tokio::{sync::oneshot, time::timeout};
@@ -27,22 +29,26 @@ async fn exercise_client_server() {
    });

    let config = ClientConfig {
-        server_addr: server_addr.to_string(),
-        duration: Some(Duration::from_secs(1)),
-        interval: Duration::from_millis(100),
-        length: 64,
-        received_stats: ReceivedStats::Both,
-        stamp_at: StampAt::Both,
-        clock: Clock::Both,
-        open_timeouts: vec![Duration::from_millis(200)],
-        socket_config: SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..SocketConfig::default()
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(200)],
+            ..Default::default()
        },
+        request: SessionRequest {
+            duration: Some(Duration::from_secs(1)),
+            interval: Duration::from_millis(100),
+            length: 64,
+            received_stats: ReceivedStats::Both,
+            stamp_at: StampAt::Both,
+            clock: Clock::Both,
+            ..Default::default()
+        },
+
        probe_timeout: Duration::from_millis(200),
        ..ClientConfig::default()
    };
-    let mut client = AsyncClient::connect(config).await.unwrap();
+    let mut client = AsyncClient::connect(server_addr.to_string(), config)
+        .await
+        .unwrap();

    let opened = client.open().await.unwrap();
    match &opened {
@@ -1,4 +1,4 @@
-use irtt_client::{Authentication, HmacKey};
+use irtt_client::{Authentication, HmacKey, OpenPolicy, SessionRequest};
 use std::{
    future::Future,
    net::UdpSocket,
@@ -17,7 +17,7 @@ use tokio::runtime::{Builder, Runtime};
 mod support;

 use irtt_client::{AsyncClient, ClientConfig, ClientError, ClientEvent, OpenOutcome};
-use irtt_client::{Client, RunMode, SocketConfig};
+use irtt_client::{Client, RunMode};
 use irtt_server::ServerConfig;
 use std::{
    io,
@@ -49,26 +49,27 @@ fn runtime() -> Runtime {
        .unwrap()
 }

-fn config(addr: SocketAddr, key: Option<Vec<u8>>, dscp: u8) -> ClientConfig {
+fn config(key: Option<Vec<u8>>, dscp: u8) -> ClientConfig {
    ClientConfig {
-        server_addr: addr.to_string(),
-        received_stats: ReceivedStats::None,
-        stamp_at: StampAt::None,
-        dscp,
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(200)],
+            ..Default::default()
+        },
+        request: SessionRequest {
+            received_stats: ReceivedStats::None,
+            stamp_at: StampAt::None,
+            dscp,
+            ..Default::default()
+        },
        auth: key.map_or(Authentication::Unauthenticated, |key| {
            Authentication::Hmac(HmacKey::new(key))
        }),
-        open_timeouts: vec![Duration::from_millis(200)],
-        socket_config: SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..SocketConfig::default()
-        },
        ..ClientConfig::default()
    }
 }

 async fn opened_client(addr: SocketAddr, dscp: u8) -> AsyncClient {
-    let mut client = AsyncClient::connect(config(addr, None, dscp))
+    let mut client = AsyncClient::connect(addr.to_string(), config(None, dscp))
        .await
        .unwrap();
    client.open().await.unwrap();
@@ -251,7 +252,10 @@ fn poll_recv_once(client: &mut AsyncClient) -> Poll<Result<Vec<ClientEvent>, Cli

 #[test]
 fn connect_requires_current_runtime_when_polled() {
-    let mut future = Box::pin(AsyncClient::connect(ClientConfig::default()));
+    let mut future = Box::pin(AsyncClient::connect(
+        "127.0.0.1:2112",
+        ClientConfig::default(),
+    ));
    assert!(matches!(
        poll_once(Pin::as_mut(&mut future)),
        Poll::Ready(Err(ClientError::NoTokioRuntime))
@@ -262,7 +266,9 @@ fn connect_requires_current_runtime_when_polled() {
 fn recv_before_open_fails_on_first_poll_without_socket_readiness() {
    runtime().block_on(async {
        let remote = SocketAddr::from(([127, 0, 0, 1], 2112));
-        let mut client = AsyncClient::connect(config(remote, None, 0)).await.unwrap();
+        let mut client = AsyncClient::connect(remote.to_string(), config(None, 0))
+            .await
+            .unwrap();

        assert!(matches!(
            poll_recv_once(&mut client),
@@ -312,11 +318,13 @@ fn ignored_open_traffic_cannot_extend_the_absolute_attempt_deadline() {
        }
        panic!("second open request did not arrive after the first absolute deadline");
    });
-    let mut client_config = config(server.addr, None, 0);
-    client_config.open_timeouts = vec![Duration::from_millis(200), Duration::from_millis(200)];
+    let mut client_config = config(None, 0);
+    client_config.open.timeouts = vec![Duration::from_millis(200), Duration::from_millis(200)];

    runtime().block_on(async {
-        let mut client = AsyncClient::connect(client_config).await.unwrap();
+        let mut client = AsyncClient::connect(server.addr.to_string(), client_config)
+            .await
+            .unwrap();
        assert!(matches!(
            client.open().await.unwrap(),
            OpenOutcome::Started { .. }
@@ -339,11 +347,13 @@ fn authenticated_rejection_is_terminal_without_retry() {
            0,
        );
    });
-    let mut client_config = config(server.addr, None, 0);
-    client_config.open_timeouts = vec![Duration::from_millis(200), Duration::from_millis(200)];
+    let mut client_config = config(None, 0);
+    client_config.open.timeouts = vec![Duration::from_millis(200), Duration::from_millis(200)];

    runtime().block_on(async {
-        let mut client = AsyncClient::connect(client_config).await.unwrap();
+        let mut client = AsyncClient::connect(server.addr.to_string(), client_config)
+            .await
+            .unwrap();
        assert!(matches!(
            client.open().await,
            Err(ClientError::ServerRejected)
@@ -371,9 +381,11 @@ fn recv_after_local_close_and_no_test_fails_on_first_poll() {

    let no_test_server = start_no_test_server();
    runtime().block_on(async {
-        let mut client_config = config(no_test_server.addr, None, 0);
-        client_config.run_mode = RunMode::NoTest;
-        let mut client = AsyncClient::connect(client_config).await.unwrap();
+        let mut client_config = config(None, 0);
+        client_config.request.run_mode = RunMode::NoTest;
+        let mut client = AsyncClient::connect(no_test_server.addr.to_string(), client_config)
+            .await
+            .unwrap();
        client.open().await.unwrap();
        assert!(matches!(
            poll_recv_once(&mut client),
@@ -388,7 +400,7 @@ fn authenticated_async_lifecycle_negotiates_dscp() {
    let key = b"async-lifecycle-key".to_vec();
    let server = InTreeServer::start(ServerConfig::default().with_hmac_key(key.clone()));
    runtime().block_on(async {
-        let mut client = AsyncClient::connect(config(server.addr, Some(key), 46))
+        let mut client = AsyncClient::connect(server.addr.to_string(), config(Some(key), 46))
            .await
            .unwrap();
        let opened = client.open().await.unwrap();
@@ -403,7 +415,10 @@ fn authenticated_async_lifecycle_negotiates_dscp() {
 fn blocking_and_async_peer_close_are_semantically_equivalent() {
    let blocking_peer_close_server = start_peer_close_server();
    let mut blocking_peer_close =
-        Client::connect(config(blocking_peer_close_server.addr, None, 0)).unwrap();
+        Client::connect(blocking_peer_close_server.addr.to_string(), config(None, 0)).unwrap();
+    blocking_peer_close
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    blocking_peer_close.open().unwrap();
    blocking_peer_close.send_probe().unwrap();
    let blocking_peer_close_events = blocking_peer_close.recv_once().unwrap();
@@ -412,9 +427,10 @@ fn blocking_and_async_peer_close_are_semantically_equivalent() {

    let async_peer_close_server = start_peer_close_server();
    let async_peer_close_events = runtime().block_on(async {
-        let mut client = AsyncClient::connect(config(async_peer_close_server.addr, None, 0))
-            .await
-            .unwrap();
+        let mut client =
+            AsyncClient::connect(async_peer_close_server.addr.to_string(), config(None, 0))
+                .await
+                .unwrap();
        client.open().await.unwrap();
        client.send_probe().await.unwrap();
        let events = client.recv().await.unwrap();
@@ -525,7 +541,10 @@ fn blocking_and_async_roll_back_a_failed_open_and_accept_a_retry() {
    // One open attempt is ignored, so the first open times out and the second
    // must be able to open the same connected client.
    let blocking_server = start_silent_then_open_server(1);
-    let mut blocking = Client::connect(config(blocking_server.addr, None, 0)).unwrap();
+    let mut blocking = Client::connect(blocking_server.addr.to_string(), config(None, 0)).unwrap();
+    blocking
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    assert!(!blocking.has_pending_probes());
    let blocking_first = blocking.open().unwrap_err();
    assert!(!blocking.has_pending_probes());
@@ -539,7 +558,7 @@ fn blocking_and_async_roll_back_a_failed_open_and_accept_a_retry() {
    let async_server = start_silent_then_open_server(1);
    let (async_first, async_second, async_sent, async_reply, async_close) =
        runtime().block_on(async {
-            let mut client = AsyncClient::connect(config(async_server.addr, None, 0))
+            let mut client = AsyncClient::connect(async_server.addr.to_string(), config(None, 0))
                .await
                .unwrap();
            assert!(!client.has_pending_probes());
@@ -580,16 +599,16 @@ fn blocking_and_async_roll_back_a_failed_open_and_accept_a_retry() {
 #[test]
 fn blocking_and_async_complete_every_caller_paced_probe() {
    const PROBES: u32 = 3;
-    fn caller_config(addr: SocketAddr) -> ClientConfig {
-        ClientConfig {
-            duration: Some(Duration::from_millis(1)),
-            interval: Duration::from_secs(1),
-            ..config(addr, None, 0)
-        }
-    }
+    let mut caller_config = config(None, 0);
+    caller_config.request.duration = Some(Duration::from_millis(1));
+    caller_config.request.interval = Duration::from_secs(1);

    let blocking_server = InTreeServer::start(ServerConfig::default());
-    let mut blocking = Client::connect(caller_config(blocking_server.addr)).unwrap();
+    let mut blocking =
+        Client::connect(blocking_server.addr.to_string(), caller_config.clone()).unwrap();
+    blocking
+        .set_recv_timeout(Some(Duration::from_millis(200)))
+        .unwrap();
    let outcome = blocking.open().unwrap();
    assert_eq!(
        blocking.negotiated_params(),
@@ -613,7 +632,7 @@ fn blocking_and_async_complete_every_caller_paced_probe() {

    let async_server = InTreeServer::start(ServerConfig::default());
    let (async_sent, async_replies) = runtime().block_on(async {
-        let mut client = AsyncClient::connect(caller_config(async_server.addr))
+        let mut client = AsyncClient::connect(async_server.addr.to_string(), caller_config)
            .await
            .unwrap();
        let outcome = client.open().await.unwrap();
@@ -670,11 +689,13 @@ fn ignored_open_traffic_uses_one_request_and_deadline_per_attempt() {
            }
        }
    });
-    let mut client_config = config(server.addr, None, 0);
-    client_config.open_timeouts = vec![Duration::from_millis(200), Duration::from_millis(200)];
+    let mut client_config = config(None, 0);
+    client_config.open.timeouts = vec![Duration::from_millis(200), Duration::from_millis(200)];

    runtime().block_on(async {
-        let mut client = AsyncClient::connect(client_config).await.unwrap();
+        let mut client = AsyncClient::connect(server.addr.to_string(), client_config)
+            .await
+            .unwrap();
        assert!(matches!(client.open().await, Err(ClientError::OpenTimeout)));
    });
    assert_eq!(server.finish().len(), 2);
@@ -1,3 +1,4 @@
+use irtt_client::{OpenPolicy, SessionRequest};
 use std::{
    net::{SocketAddr, UdpSocket},
    sync::{Arc, Condvar, Mutex},
@@ -146,12 +147,18 @@ fn test_runtime() -> tokio::runtime::Runtime {
 fn config(completion: ManagedCompletionPolicy) -> ManagedClientConfig {
    ManagedClientConfig {
        client: ClientConfig {
-            duration: Some(Duration::from_millis(120)),
-            interval: Duration::from_millis(20),
+            open: OpenPolicy {
+                timeouts: vec![Duration::from_millis(200)],
+                ..Default::default()
+            },
+            request: SessionRequest {
+                duration: Some(Duration::from_millis(120)),
+                interval: Duration::from_millis(20),
+                received_stats: ReceivedStats::None,
+                stamp_at: StampAt::None,
+                ..Default::default()
+            },
            probe_timeout: Duration::from_millis(40),
-            open_timeouts: vec![Duration::from_millis(200)],
-            received_stats: ReceivedStats::None,
-            stamp_at: StampAt::None,
            ..ClientConfig::default()
        },
        pacing: ManagedPacing::Burst,
@@ -1,6 +1,9 @@
+use std::time::Duration;
 mod support;

-use irtt_client::{Client, ClientConfig, ClientError, NegotiationPolicy};
+use irtt_client::{
+    Client, ClientConfig, ClientError, NegotiationPolicy, OpenPolicy, SessionRequest,
+};
 use irtt_proto::{Params, TimestampFields};

 use support::{
@@ -52,11 +55,14 @@ fn server_fill_none_short_and_max_map_into_open_params() {
 fn server_fill_empty_and_oversized_values_are_rejected_at_config_boundary() {
    for fill in ["", "0123456789abcdef0123456789abcdefx"] {
        let config = ClientConfig {
-            server_fill: Some(fill.to_owned()),
+            request: SessionRequest {
+                server_fill: Some(fill.to_owned()),
+                ..Default::default()
+            },
            ..ClientConfig::default()
        };
        assert!(matches!(
-            Client::connect(config),
+            Client::connect("127.0.0.1:2112", config),
            Err(ClientError::InvalidConfig { .. })
        ));
    }
@@ -69,7 +75,10 @@ fn server_fill_negotiated_params_reflect_accepted_value() {
    let mut params = default_params();
    params.server_fill = server_fill("rand");
    let server = InTreeServer::start(irtt_server::ServerConfig::default());
-    let mut client = Client::connect(config_for_params(server.addr, &params)).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config_for_params(&params)).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(500)))
+        .unwrap();
    let outcome = client.open().unwrap();
    let negotiated = match outcome {
        irtt_client::OpenOutcome::Started { negotiated, .. } => negotiated,
@@ -99,7 +108,11 @@ fn server_fill_strict_rejects_removed_changed_or_unexpected_fill() {
        returned.server_fill = returned_fill.and_then(server_fill);

        let server = start_open_server(returned, None);
-        let mut client = Client::connect(config_for_params(server.addr, &requested)).unwrap();
+        let mut client =
+            Client::connect(server.addr.to_string(), config_for_params(&requested)).unwrap();
+        client
+            .set_recv_timeout(Some(Duration::from_millis(500)))
+            .unwrap();
        assert!(matches!(
            client.open(),
            Err(ClientError::NegotiationRejected { .. })
@@ -117,10 +130,13 @@ fn server_fill_loose_allows_server_to_remove_fill() {
    returned.server_fill = None;

    let requested_for_config = requested.clone();
-    let run = run_one_probe_with_config(returned, TimestampFields::default(), None, |addr| {
+    let run = run_one_probe_with_config(returned, TimestampFields::default(), None, || {
        ClientConfig {
-            negotiation_policy: NegotiationPolicy::Loose,
-            ..config_for_params(addr, &requested_for_config)
+            open: OpenPolicy {
+                negotiation: NegotiationPolicy::Loose,
+                ..config_for_params(&requested_for_config).open
+            },
+            ..config_for_params(&requested_for_config)
        }
    });

@@ -10,7 +10,8 @@
 use std::time::Duration;

 use irtt_client::{
-    AsyncClient, ClientConfig, NegotiationPolicy, NegotiationRestriction, OpenOutcome, SocketConfig,
+    AsyncClient, ClientConfig, NegotiationPolicy, NegotiationRestriction, OpenOutcome, OpenPolicy,
+    SessionRequest,
 };
 use irtt_proto::{
    decode_echo_reply, decode_open_reply, echo_header_len, encode_request, Clock, Params,
@@ -132,24 +133,26 @@ async fn exercise_fallback_negotiation() {
    // `ClientConfig` accepts any non-empty descriptor within the wire bound, so
    // an unknown one genuinely reaches the server.
    let config = |policy| ClientConfig {
-        server_addr: server_addr.to_string(),
-        duration: Some(Duration::from_secs(1)),
-        interval: Duration::from_millis(100),
-        length: 64,
-        server_fill: Some("bogus".to_owned()),
-        negotiation_policy: policy,
-        open_timeouts: vec![Duration::from_millis(200)],
-        socket_config: SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..SocketConfig::default()
+        open: OpenPolicy {
+            negotiation: policy,
+            timeouts: vec![Duration::from_millis(200)],
        },
+        request: SessionRequest {
+            duration: Some(Duration::from_secs(1)),
+            interval: Duration::from_millis(100),
+            length: 64,
+            server_fill: Some("bogus".to_owned()),
+            ..Default::default()
+        },
+
        probe_timeout: Duration::from_millis(200),
        ..ClientConfig::default()
    };

-    let mut strict = AsyncClient::connect(config(NegotiationPolicy::Strict))
-        .await
-        .unwrap();
+    let mut strict =
+        AsyncClient::connect(server_addr.to_string(), config(NegotiationPolicy::Strict))
+            .await
+            .unwrap();
    let rejected = strict
        .open()
        .await
@@ -159,7 +162,7 @@ async fn exercise_fallback_negotiation() {
        "the restriction names the fill: {rejected}"
    );

-    let mut loose = AsyncClient::connect(config(NegotiationPolicy::Loose))
+    let mut loose = AsyncClient::connect(server_addr.to_string(), config(NegotiationPolicy::Loose))
        .await
        .unwrap();
    match loose.open().await.unwrap() {
@@ -3,9 +3,7 @@ mod support;

 use std::time::Duration;

-use irtt_client::{
-    Client, ClientConfig, ClientError, ClientEvent, OpenOutcome, SocketConfig, WarningKind,
-};
+use irtt_client::{Client, ClientConfig, ClientError, ClientEvent, OpenOutcome, WarningKind};
 use irtt_proto::TimestampFields;

 use support::{
@@ -27,9 +25,9 @@ fn hmac_open_success_negotiates_without_warnings() {
        params.clone(),
        TimestampFields::default(),
        Some(key),
-        |addr| ClientConfig {
+        || ClientConfig {
            auth: Authentication::Hmac(HmacKey::new(config_key)),
-            ..config_for_params(addr, &config_params)
+            ..config_for_params(&config_params)
        },
    );

@@ -51,10 +49,10 @@ fn hmac_echo_success_verifies_request_and_accepts_reply() {
    let config_params = params.clone();
    let config_key = key.clone();

-    let run = run_one_probe_with_config(params.clone(), standard_timestamps(), Some(key), |addr| {
+    let run = run_one_probe_with_config(params.clone(), standard_timestamps(), Some(key), || {
        ClientConfig {
            auth: Authentication::Hmac(HmacKey::new(config_key)),
-            ..config_for_params(addr, &config_params)
+            ..config_for_params(&config_params)
        }
    });

@@ -94,10 +92,13 @@ fn hmac_close_success_sends_authenticated_close_and_closes_session() {
    let key = b"compat-secret".to_vec();
    let params = default_params();
    let server = start_hmac_close_server(params.clone(), key.clone());
-    let mut config = config_for_params(server.addr, &params);
+    let mut config = config_for_params(&params);
    config.auth = Authentication::Hmac(HmacKey::new(key));

-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(500)))
+        .unwrap();
    let outcome = client.open().unwrap();
    assert_started(outcome, &params);

@@ -134,13 +135,16 @@ fn hmac_required_server_rejects_missing_or_wrong_client_key() {
    ] {
        let server_key = b"compat-secret".to_vec();
        let server = start_hmac_required_open_drop_server(server_key, Duration::from_millis(250));
-        let mut config = config_for_params(server.addr, &default_params());
-        config.open_timeouts = vec![Duration::from_millis(200)];
+        let mut config = config_for_params(&default_params());
+        config.open.timeouts = vec![Duration::from_millis(200)];
        config.auth = hmac_key.map_or(Authentication::Unauthenticated, |key| {
            Authentication::Hmac(HmacKey::new(key))
        });

-        let mut client = Client::connect(config).unwrap();
+        let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+        client
+            .set_recv_timeout(Some(Duration::from_millis(500)))
+            .unwrap();
        assert!(matches!(client.open(), Err(ClientError::OpenTimeout)));

        let observations = server.observations(1);
@@ -160,14 +164,13 @@ fn bad_hmac_echo_reply_is_rejected_without_echo_reply_event() {
    let key = b"compat-secret".to_vec();
    let params = default_params();
    let server = start_bad_hmac_echo_reply_server(params.clone(), key.clone());
-    let mut config = config_for_params(server.addr, &params);
+    let mut config = config_for_params(&params);
    config.auth = Authentication::Hmac(HmacKey::new(key));
-    config.socket_config = SocketConfig {
-        recv_timeout: Some(Duration::from_millis(500)),
-        ..Default::default()
-    };

-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(500)))
+        .unwrap();
    let outcome = client.open().unwrap();
    assert_started(outcome, &params);

@@ -207,10 +210,13 @@ fn hmac_open_reply_with_bad_hmac_is_ignored_until_timeout() {
    let wrong_key = b"wrong-secret".to_vec();
    let params = default_params();
    let server = support::start_bad_hmac_open_reply_server(params.clone(), key.clone(), wrong_key);
-    let mut config = config_for_params(server.addr, &params);
+    let mut config = config_for_params(&params);
    config.auth = Authentication::Hmac(HmacKey::new(key));

-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(500)))
+        .unwrap();
    assert!(matches!(client.open(), Err(ClientError::OpenTimeout)));
    server.join();
 }
@@ -223,10 +229,13 @@ fn non_hmac_client_open_does_not_set_hmac_flag() {
        irtt_proto::Clock::Both,
    );
    let server = support::start_open_server(params.clone(), None);
-    let mut config = config_for_params(server.addr, &params);
+    let mut config = config_for_params(&params);
    config.auth = Authentication::Unauthenticated;

-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(500)))
+        .unwrap();
    let outcome = client.open().unwrap();
    assert_started(outcome, &params);

@@ -280,10 +289,13 @@ fn backend_hmac_correct_key_succeeds() {
    let key = b"compat-secret".to_vec();
    let params = default_params();
    let peer = BackendPeer::start_open_echo(Some(key.clone()));
-    let mut config = config_for_params(peer.addr(), &params);
+    let mut config = config_for_params(&params);
    config.auth = Authentication::Hmac(HmacKey::new(key));

-    let mut client = Client::connect(config).unwrap();
+    let mut client = Client::connect(peer.addr().to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(500)))
+        .unwrap();
    let outcome = client.open().unwrap();
    assert!(matches!(outcome, OpenOutcome::Started { .. }));

@@ -302,13 +314,16 @@ fn backend_hmac_required_rejects_missing_or_wrong_client_key() {
    for hmac_key in [None, Some(b"wrong-secret".to_vec())] {
        let server_key = b"compat-secret".to_vec();
        let peer = BackendPeer::start_hmac_required(server_key);
-        let mut config = config_for_params(peer.addr(), &default_params());
-        config.open_timeouts = vec![Duration::from_millis(200)];
+        let mut config = config_for_params(&default_params());
+        config.open.timeouts = vec![Duration::from_millis(200)];
        config.auth = hmac_key.map_or(Authentication::Unauthenticated, |key| {
            Authentication::Hmac(HmacKey::new(key))
        });

-        let mut client = Client::connect(config).unwrap();
+        let mut client = Client::connect(peer.addr().to_string(), config).unwrap();
+        client
+            .set_recv_timeout(Some(Duration::from_millis(500)))
+            .unwrap();
        assert!(matches!(client.open(), Err(ClientError::OpenTimeout)));
    }
 }
@@ -1,6 +1,6 @@
 mod support;

-use irtt_client::{Client, ClientConfig, ClientEvent, NegotiationPolicy};
+use irtt_client::{Client, ClientEvent, NegotiationPolicy};
 use irtt_proto::{echo_header_len, Params, TimestampFields};

 use support::{config_for_params, default_params, run_one_probe, BackendPeer, ServerObservation};
@@ -84,12 +84,13 @@ fn echo_reply_bytes_consistent_with_echo_packet_len_for_various_lengths() {
 fn backend_large_packet_smoke() {
    let params = params_with_length(1472);
    let peer = BackendPeer::start_open_echo(None);
-    let mut client = Client::connect(ClientConfig {
-        negotiation_policy: NegotiationPolicy::Loose,
-        length: 1472,
-        ..config_for_params(peer.addr(), &params)
-    })
-    .unwrap();
+    let mut config = config_for_params(&params);
+    config.open.negotiation = NegotiationPolicy::Loose;
+    config.request.length = 1472;
+    let mut client = Client::connect(peer.addr().to_string(), config).unwrap();
+    client
+        .set_recv_timeout(Some(std::time::Duration::from_millis(500)))
+        .unwrap();

    let outcome = client.open().unwrap();
    assert!(matches!(outcome, irtt_client::OpenOutcome::Started { .. }));
@@ -2,7 +2,7 @@ mod support;

 use std::{collections::HashMap, time::Duration};

-use irtt_client::{managed::*, ClientConfig, ClientEvent};
+use irtt_client::{managed::*, ClientConfig, ClientEvent, OpenPolicy, SessionRequest};
 use irtt_server::ServerConfig;
 use support::InTreeServer;
 use tokio::time::timeout;
@@ -18,10 +18,16 @@ async fn both_pacing_modes_serve_every_target_on_its_negotiated_grid() {
            for _ in 0..3 {
                let config = ManagedClientConfig {
                    client: ClientConfig {
-                        duration: Some(Duration::from_millis(600)),
-                        interval: Duration::from_millis(100),
+                        open: OpenPolicy {
+                            timeouts: vec![Duration::from_millis(200)],
+                            ..Default::default()
+                        },
+                        request: SessionRequest {
+                            duration: Some(Duration::from_millis(600)),
+                            interval: Duration::from_millis(100),
+                            ..Default::default()
+                        },
                        probe_timeout: Duration::from_millis(100),
-                        open_timeouts: vec![Duration::from_millis(200)],
                        ..ClientConfig::default()
                    },
                    pacing,
@@ -111,10 +117,16 @@ async fn target_updates_preserve_identical_sessions_and_retire_removed_generatio
        let server = InTreeServer::start(ServerConfig::default());
        let config = ManagedClientConfig {
            client: ClientConfig {
-                duration: None,
-                interval: Duration::from_millis(20),
+                open: OpenPolicy {
+                    timeouts: vec![Duration::from_millis(200)],
+                    ..Default::default()
+                },
+                request: SessionRequest {
+                    duration: None,
+                    interval: Duration::from_millis(20),
+                    ..Default::default()
+                },
                probe_timeout: Duration::from_millis(100),
-                open_timeouts: vec![Duration::from_millis(200)],
                ..ClientConfig::default()
            },
            completion: ManagedCompletionPolicy::ExplicitStop,
@@ -1,4 +1,4 @@
-use irtt_client::{Authentication, HmacKey};
+use irtt_client::{Authentication, HmacKey, OpenPolicy, SessionRequest};
 use std::{
    future::Future,
    net::{SocketAddr, UdpSocket},
@@ -176,12 +176,18 @@ fn runtime() -> Runtime {
 fn config(pacing: ManagedPacing) -> ManagedClientConfig {
    ManagedClientConfig {
        client: ClientConfig {
-            duration: Some(Duration::from_millis(130)),
-            interval: Duration::from_millis(60),
+            open: OpenPolicy {
+                timeouts: vec![Duration::from_millis(200)],
+                ..Default::default()
+            },
+            request: SessionRequest {
+                duration: Some(Duration::from_millis(130)),
+                interval: Duration::from_millis(60),
+                received_stats: ReceivedStats::None,
+                stamp_at: StampAt::None,
+                ..Default::default()
+            },
            probe_timeout: Duration::from_millis(35),
-            open_timeouts: vec![Duration::from_millis(200)],
-            received_stats: ReceivedStats::None,
-            stamp_at: StampAt::None,
            ..ClientConfig::default()
        },
        pacing,
@@ -340,7 +346,7 @@ fn finite_immediate_replies_use_retained_drain_deadline() {
 fn no_test_target_completion() {
    let server = start_server(ServerBehavior::NoTest, None);
    let mut config = config(ManagedPacing::Staggered);
-    config.client.run_mode = RunMode::NoTest;
+    config.client.request.run_mode = RunMode::NoTest;
    let (task, _) = ManagedClient::task(config, vec![target("no-test", server.addr)]).unwrap();
    let outcome = runtime().block_on(task);
    let records = server.finish();
@@ -411,8 +417,8 @@ fn pending_limit_failure_drains_reply_and_closes_session() {
        Some(key.clone()),
    );
    let mut managed = config(ManagedPacing::Staggered);
-    managed.client.duration = Some(Duration::from_millis(250));
-    managed.client.interval = Duration::from_millis(20);
+    managed.client.request.duration = Some(Duration::from_millis(250));
+    managed.client.request.interval = Duration::from_millis(20);
    managed.client.probe_timeout = Duration::from_secs(2);
    managed.client.max_pending_probes = 1;
    managed.final_drain = Duration::from_millis(50);
@@ -10,7 +10,8 @@
 use std::time::Duration;

 use irtt_client::{
-    AsyncClient, ClientConfig, NegotiationPolicy, NegotiationRestriction, OpenOutcome, SocketConfig,
+    AsyncClient, ClientConfig, NegotiationPolicy, NegotiationRestriction, OpenOutcome, OpenPolicy,
+    SessionRequest,
 };
 use irtt_proto::{Clock, ReceivedStats, StampAt};
 use irtt_server::{Server, ServerConfig, TimestampAllowance};
@@ -84,13 +85,19 @@ async fn exercise_dscp_restriction() {
    // The client's configuration is a DSCP codepoint; 46 (EF) is raw byte 184 on
    // the wire, and this test does not change either convention.
    let with_dscp = |policy| ClientConfig {
-        dscp: 46,
-        ..test_config(server_addr, policy)
+        request: SessionRequest {
+            dscp: 46,
+            ..test_config(policy).request
+        },
+        ..test_config(policy)
    };

-    let mut strict = AsyncClient::connect(with_dscp(NegotiationPolicy::Strict))
-        .await
-        .unwrap();
+    let mut strict = AsyncClient::connect(
+        server_addr.to_string(),
+        with_dscp(NegotiationPolicy::Strict),
+    )
+    .await
+    .unwrap();
    let rejected = strict
        .open()
        .await
@@ -100,9 +107,10 @@ async fn exercise_dscp_restriction() {
        "the restriction names DSCP: {rejected}"
    );

-    let mut loose = AsyncClient::connect(with_dscp(NegotiationPolicy::Loose))
-        .await
-        .unwrap();
+    let mut loose =
+        AsyncClient::connect(server_addr.to_string(), with_dscp(NegotiationPolicy::Loose))
+            .await
+            .unwrap();
    let negotiated = match loose.open().await.unwrap() {
        OpenOutcome::Started { negotiated, .. } => negotiated,
        OpenOutcome::NoTestCompleted { .. } => panic!("normal client unexpectedly ran no-test"),
@@ -138,10 +146,16 @@ async fn a_default_server_restricts_nothing_an_ordinary_client_asks_for() {
 async fn exercise_default_policy() {
    let (server_addr, shutdown_tx, server_task) = serve(ServerConfig::default()).await;

-    let mut client = AsyncClient::connect(ClientConfig {
-        dscp: 46,
-        ..test_config(server_addr, NegotiationPolicy::Strict)
-    })
+    let mut client = AsyncClient::connect(
+        server_addr.to_string(),
+        ClientConfig {
+            request: SessionRequest {
+                dscp: 46,
+                ..test_config(NegotiationPolicy::Strict).request
+            },
+            ..test_config(NegotiationPolicy::Strict)
+        },
+    )
    .await
    .unwrap();
    let negotiated = match client.open().await.unwrap() {
@@ -186,28 +200,29 @@ async fn serve(
 }

 /// A short deterministic client requesting both timestamps from both clocks.
-fn test_config(server_addr: std::net::SocketAddr, policy: NegotiationPolicy) -> ClientConfig {
+fn test_config(policy: NegotiationPolicy) -> ClientConfig {
    ClientConfig {
-        server_addr: server_addr.to_string(),
-        duration: Some(Duration::from_secs(1)),
-        interval: Duration::from_millis(100),
-        length: 64,
-        received_stats: ReceivedStats::Both,
-        stamp_at: StampAt::Both,
-        clock: Clock::Both,
-        negotiation_policy: policy,
-        open_timeouts: vec![Duration::from_millis(200)],
-        socket_config: SocketConfig {
-            recv_timeout: Some(Duration::from_millis(200)),
-            ..SocketConfig::default()
+        open: OpenPolicy {
+            negotiation: policy,
+            timeouts: vec![Duration::from_millis(200)],
        },
+        request: SessionRequest {
+            duration: Some(Duration::from_secs(1)),
+            interval: Duration::from_millis(100),
+            length: 64,
+            received_stats: ReceivedStats::Both,
+            stamp_at: StampAt::Both,
+            clock: Clock::Both,
+            ..Default::default()
+        },
+
        probe_timeout: Duration::from_millis(200),
        ..ClientConfig::default()
    }
 }

 async fn client(server_addr: std::net::SocketAddr, policy: NegotiationPolicy) -> AsyncClient {
-    AsyncClient::connect(test_config(server_addr, policy))
+    AsyncClient::connect(server_addr.to_string(), test_config(policy))
        .await
        .unwrap()
 }
@@ -1,4 +1,4 @@
-use irtt_client::{Authentication, HmacKey};
+use irtt_client::{Authentication, HmacKey, OpenPolicy};
 mod support;
 mod protocol_options {
    pub mod backend_smoke;
@@ -147,10 +147,10 @@ fn hmac_rich_mode_uses_negotiated_echo_layout_and_decodes_reply() {
    let params = params_for_modes(ReceivedStats::Both, StampAt::Both, Clock::Both);
    let config_params = params.clone();
    let config_key = key.clone();
-    let run = run_one_probe_with_config(params.clone(), standard_timestamps(), Some(key), |addr| {
+    let run = run_one_probe_with_config(params.clone(), standard_timestamps(), Some(key), || {
        ClientConfig {
            auth: Authentication::Hmac(HmacKey::new(config_key)),
-            ..config_for_params(addr, &config_params)
+            ..config_for_params(&config_params)
        }
    });
    assert_negotiated_echo_use(&run, &params, true);
@@ -171,9 +171,11 @@ fn strict_open_rejects_changed_compatibility_params_from_server() {

    for returned in changed_compatibility_params(&requested) {
        let server = start_open_server(returned, None);
-        let mut config = config_for_params(server.addr, &requested);
-        config.server_addr = server.addr.to_string();
-        let mut client = Client::connect(config).unwrap();
+        let config = config_for_params(&requested);
+        let mut client = Client::connect(server.addr.to_string(), config).unwrap();
+        client
+            .set_recv_timeout(Some(Duration::from_millis(500)))
+            .unwrap();
        assert!(matches!(
            client.open(),
            Err(ClientError::NegotiationRejected { .. })
@@ -199,10 +201,13 @@ fn loose_open_uses_returned_params_for_echo_layout_and_reply_parsing() {
    returned.server_fill = None;

    let requested_for_config = requested.clone();
-    let run = run_one_probe_with_config(returned.clone(), standard_timestamps(), None, |addr| {
+    let run = run_one_probe_with_config(returned.clone(), standard_timestamps(), None, || {
        ClientConfig {
-            negotiation_policy: irtt_client::NegotiationPolicy::Loose,
-            ..config_for_params(addr, &requested_for_config)
+            open: OpenPolicy {
+                negotiation: irtt_client::NegotiationPolicy::Loose,
+                ..config_for_params(&requested_for_config).open
+            },
+            ..config_for_params(&requested_for_config)
        }
    });

@@ -1,5 +1,6 @@
 use irtt_client::{Client, ClientEvent};
 use irtt_proto::{Clock, ReceivedStats, StampAt};
+use std::time::Duration;

 use crate::support::{config_for_params, default_params, params_for_modes, BackendPeer};

@@ -7,7 +8,10 @@ use crate::support::{config_for_params, default_params, params_for_modes, Backen
 fn backend_basic_open_echo_close() {
    let params = default_params();
    let peer = BackendPeer::start_open_echo(None);
-    let mut client = Client::connect(config_for_params(peer.addr(), &params)).unwrap();
+    let mut client = Client::connect(peer.addr().to_string(), config_for_params(&params)).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(500)))
+        .unwrap();

    let outcome = client.open().unwrap();
    assert!(matches!(outcome, irtt_client::OpenOutcome::Started { .. }));
@@ -32,7 +36,11 @@ fn backend_received_stats_smoke() {
    ] {
        let params = params_for_modes(mode, StampAt::None, Clock::Both);
        let peer = BackendPeer::start_open_echo(None);
-        let mut client = Client::connect(config_for_params(peer.addr(), &params)).unwrap();
+        let mut client =
+            Client::connect(peer.addr().to_string(), config_for_params(&params)).unwrap();
+        client
+            .set_recv_timeout(Some(Duration::from_millis(500)))
+            .unwrap();

        client.open().unwrap();
        client.send_probe().unwrap();
@@ -55,7 +63,11 @@ fn backend_timestamp_smoke() {
    ] {
        let params = params_for_modes(ReceivedStats::None, mode, Clock::Both);
        let peer = BackendPeer::start_open_echo(None);
-        let mut client = Client::connect(config_for_params(peer.addr(), &params)).unwrap();
+        let mut client =
+            Client::connect(peer.addr().to_string(), config_for_params(&params)).unwrap();
+        client
+            .set_recv_timeout(Some(Duration::from_millis(500)))
+            .unwrap();

        client.open().unwrap();
        client.send_probe().unwrap();
@@ -102,7 +114,11 @@ fn backend_clock_smoke() {
    for clock in [Clock::Wall, Clock::Monotonic, Clock::Both] {
        let params = params_for_modes(ReceivedStats::None, StampAt::Both, clock);
        let peer = BackendPeer::start_open_echo(None);
-        let mut client = Client::connect(config_for_params(peer.addr(), &params)).unwrap();
+        let mut client =
+            Client::connect(peer.addr().to_string(), config_for_params(&params)).unwrap();
+        client
+            .set_recv_timeout(Some(Duration::from_millis(500)))
+            .unwrap();

        client.open().unwrap();
        client.send_probe().unwrap();
@@ -12,7 +12,9 @@ use std::{
    time::{Duration, Instant, SystemTime},
 };

-use irtt_client::{Client, ClientConfig, ClientEvent, NegotiatedParams, OpenOutcome, SocketConfig};
+use irtt_client::{
+    Client, ClientConfig, ClientEvent, NegotiatedParams, OpenOutcome, OpenPolicy, SessionRequest,
+};
 use irtt_proto::{
    compute_hmac_in_place, decode_request, echo_packet_len, encode_echo_reply, encode_open_reply,
    flags, verify_packet_hmac, Clock, DecodedRequest, DecodedRequestKind, EchoReply, OpenReply,
@@ -166,12 +168,12 @@ pub fn params_for_modes(received_stats: ReceivedStats, stamp_at: StampAt, clock:
 /// Builds a [`ClientConfig`] whose negotiated `Params` will match `params`.
 ///
 /// `params.dscp` is the raw IP TOS / Traffic Class byte, while
-/// [`ClientConfig::dscp`] is the six-bit codepoint that produces it; shift
+/// [`SessionRequest::dscp`] is the six-bit codepoint that produces it; shift
 /// right by two to recover the codepoint the resulting config must request.
 /// Panics if `params.dscp` has any ECN bits set, since those cannot be
 /// recovered from a codepoint and this helper's contract would silently stop
 /// holding otherwise.
-pub fn config_for_params(addr: SocketAddr, params: &Params) -> ClientConfig {
+pub fn config_for_params(params: &Params) -> ClientConfig {
    let traffic_class =
        u8::try_from(params.dscp).expect("test DSCP must fit the raw traffic-class byte");
    assert_eq!(
@@ -180,26 +182,27 @@ pub fn config_for_params(addr: SocketAddr, params: &Params) -> ClientConfig {
        "test Params::dscp must be representable by ClientConfig's DSCP codepoint"
    );
    ClientConfig {
-        server_addr: addr.to_string(),
-        duration: if params.duration_ns == 0 {
-            None
-        } else {
-            Some(Duration::from_nanos(
-                u64::try_from(params.duration_ns).expect("test duration must be non-negative"),
-            ))
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(200)],
+            ..Default::default()
        },
-        interval: Duration::from_nanos(
-            u64::try_from(params.interval_ns).expect("test interval must be non-negative"),
-        ),
-        length: u32::try_from(params.length).unwrap(),
-        received_stats: params.received_stats,
-        stamp_at: params.stamp_at,
-        clock: params.clock,
-        dscp: traffic_class >> 2,
-        server_fill: params.server_fill.as_ref().map(|fill| fill.value.clone()),
-        open_timeouts: vec![Duration::from_millis(200)],
-        socket_config: SocketConfig {
-            recv_timeout: Some(Duration::from_millis(500)),
+        request: SessionRequest {
+            duration: if params.duration_ns == 0 {
+                None
+            } else {
+                Some(Duration::from_nanos(
+                    u64::try_from(params.duration_ns).expect("test duration must be non-negative"),
+                ))
+            },
+            interval: Duration::from_nanos(
+                u64::try_from(params.interval_ns).expect("test interval must be non-negative"),
+            ),
+            length: u32::try_from(params.length).unwrap(),
+            received_stats: params.received_stats,
+            stamp_at: params.stamp_at,
+            clock: params.clock,
+            dscp: traffic_class >> 2,
+            server_fill: params.server_fill.as_ref().map(|fill| fill.value.clone()),
            ..Default::default()
        },
        ..ClientConfig::default()
@@ -219,8 +222,8 @@ pub fn standard_timestamps() -> TimestampFields {

 pub fn run_one_probe(params: Params, timestamps: TimestampFields) -> OneProbeRun {
    let config_params = params.clone();
-    run_one_probe_with_config(params, timestamps, None, |addr| {
-        config_for_params(addr, &config_params)
+    run_one_probe_with_config(params, timestamps, None, || {
+        config_for_params(&config_params)
    })
 }

@@ -231,10 +234,13 @@ pub fn run_one_probe_with_config<F>(
    build_config: F,
 ) -> OneProbeRun
 where
-    F: FnOnce(SocketAddr) -> ClientConfig,
+    F: FnOnce() -> ClientConfig,
 {
    let server = start_one_probe_server(server_params, timestamps, hmac_key);
-    let mut client = Client::connect(build_config(server.addr)).unwrap();
+    let mut client = Client::connect(server.addr.to_string(), build_config()).unwrap();
+    client
+        .set_recv_timeout(Some(Duration::from_millis(500)))
+        .unwrap();
    let negotiated = assert_started(client.open().unwrap());

    let sent_events = client.send_probe().unwrap();
@@ -14,7 +14,9 @@

 use std::{io, net::SocketAddr, time::Duration};

-use irtt_client::{AsyncClient, ClientConfig, ClientEvent, OpenOutcome, PacketMeta, SocketConfig};
+use irtt_client::{
+    AsyncClient, ClientConfig, ClientEvent, OpenOutcome, OpenPolicy, PacketMeta, SessionRequest,
+};
 use irtt_proto::{Clock, ReceivedStats, StampAt};
 use irtt_server::{Server, ServerConfig, ServerRuntimeError};
 use tokio::{sync::oneshot, task::JoinHandle, time::timeout};
@@ -193,23 +195,27 @@ impl OpenSession {
 /// A client with an open session requesting `dscp` as a codepoint.
 async fn opened_session(server_addr: SocketAddr, dscp: u8) -> OpenSession {
    let config = ClientConfig {
-        server_addr: server_addr.to_string(),
-        duration: Some(Duration::from_secs(30)),
-        interval: Duration::from_millis(10),
-        length: 64,
-        dscp,
-        received_stats: ReceivedStats::Both,
-        stamp_at: StampAt::Both,
-        clock: Clock::Both,
-        open_timeouts: vec![Duration::from_millis(500)],
-        socket_config: SocketConfig {
-            recv_timeout: Some(Duration::from_millis(500)),
-            ..SocketConfig::default()
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(500)],
+            ..Default::default()
        },
+        request: SessionRequest {
+            duration: Some(Duration::from_secs(30)),
+            interval: Duration::from_millis(10),
+            length: 64,
+            dscp,
+            received_stats: ReceivedStats::Both,
+            stamp_at: StampAt::Both,
+            clock: Clock::Both,
+            ..Default::default()
+        },
+
        probe_timeout: Duration::from_millis(500),
        ..ClientConfig::default()
    };
-    let mut client = AsyncClient::connect(config).await.unwrap();
+    let mut client = AsyncClient::connect(server_addr.to_string(), config)
+        .await
+        .unwrap();
    match client.open().await.unwrap() {
        OpenOutcome::Started { negotiated, .. } => assert_eq!(
            negotiated.params.dscp,
@@ -18,7 +18,9 @@ use std::{
    time::Duration,
 };

-use irtt_client::{AsyncClient, ClientConfig, ClientEvent, OpenOutcome, PacketMeta, SocketConfig};
+use irtt_client::{
+    AsyncClient, ClientConfig, ClientEvent, OpenOutcome, OpenPolicy, PacketMeta, SessionRequest,
+};
 use irtt_proto::{Clock, ReceivedStats, StampAt};
 use irtt_server::{Server, ServerConfig, ServerRuntimeError};
 use tokio::{sync::oneshot, task::JoinHandle, time::timeout};
@@ -193,23 +195,27 @@ fn unthrottled() -> ServerConfig {

 async fn connected_client(server_addr: SocketAddr) -> AsyncClient {
    let config = ClientConfig {
-        server_addr: server_addr.to_string(),
-        duration: Some(Duration::from_secs(30)),
-        interval: Duration::from_millis(10),
-        length: 64,
-        dscp: EF_DSCP,
-        received_stats: ReceivedStats::Both,
-        stamp_at: StampAt::Both,
-        clock: Clock::Both,
-        open_timeouts: vec![Duration::from_millis(500)],
-        socket_config: SocketConfig {
-            recv_timeout: Some(Duration::from_millis(500)),
-            ..SocketConfig::default()
+        open: OpenPolicy {
+            timeouts: vec![Duration::from_millis(500)],
+            ..Default::default()
        },
+        request: SessionRequest {
+            duration: Some(Duration::from_secs(30)),
+            interval: Duration::from_millis(10),
+            length: 64,
+            dscp: EF_DSCP,
+            received_stats: ReceivedStats::Both,
+            stamp_at: StampAt::Both,
+            clock: Clock::Both,
+            ..Default::default()
+        },
+
        probe_timeout: Duration::from_millis(500),
        ..ClientConfig::default()
    };
-    AsyncClient::connect(config).await.unwrap()
+    AsyncClient::connect(server_addr.to_string(), config)
+        .await
+        .unwrap()
 }

 async fn assert_started(client: &mut AsyncClient, server_addr: SocketAddr) {