fix(client): validate packet length configuration

crates/irtt-client/src/client.rs

@@ -11,7 +11,10 @@ use irtt_proto::{
 };
 
 use crate::{
-    config::{ClientConfig, RecvBudget, RunMode, MAX_DSCP_CODEPOINT, MAX_SERVER_FILL_BYTES},
+    config::{
+        ClientConfig, RecvBudget, RunMode, MAX_DSCP_CODEPOINT, MAX_SERVER_FILL_BYTES,
+        MAX_UDP_PAYLOAD_LENGTH,
+    },
     error::ClientError,
     event::{
         ClientEvent, OneWayDelaySample, OpenOutcome, ReceivedStatsSample, RttSample, ServerTiming,
@@ -782,6 +785,11 @@ fn validate_protocol_config(config: &ClientConfig) -> Result<(), ClientError> {
             reason: format!("dscp must be <= {MAX_DSCP_CODEPOINT}"),
         });
     }
+    if config.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 {
         let len = fill.len();

crates/irtt-client/src/client/tests/config.rs

@@ -50,6 +50,32 @@ fn params_from_config_maps_compatibility_fields() {
     assert_eq!(config.hmac_key.as_deref(), Some(b"secret".as_slice()));
 }
 
+#[test]
+fn params_from_config_accepts_udp_payload_length_boundary_values() {
+    for length in [0, 1, 1472, 4096, MAX_UDP_PAYLOAD_LENGTH] {
+        let config = ClientConfig {
+            length,
+            ..ClientConfig::default()
+        };
+        assert_eq!(
+            params_from_config(&config).unwrap().length,
+            i64::from(length)
+        );
+    }
+}
+
+#[test]
+fn params_from_config_rejects_oversized_udp_payload_length() {
+    let config = ClientConfig {
+        length: MAX_UDP_PAYLOAD_LENGTH + 1,
+        ..ClientConfig::default()
+    };
+    assert!(matches!(
+        params_from_config(&config),
+        Err(ClientError::InvalidConfig { reason }) if reason.contains("packet length")
+    ));
+}
+
 #[test]
 fn params_from_config_encodes_continuous_duration_as_zero() {
     let config = ClientConfig {

crates/irtt-client/src/config.rs

@@ -5,6 +5,7 @@ use irtt_proto::{Clock, ReceivedStats, StampAt};
 pub(crate) const DEFAULT_PORT: u16 = 2112;
 pub const MAX_DSCP_CODEPOINT: u8 = 63;
 pub const MAX_TTL: u32 = 255;
+pub const MAX_UDP_PAYLOAD_LENGTH: u32 = 65_507;
 pub const MAX_SERVER_FILL_BYTES: usize = 32;
 pub(crate) const DEFAULT_DURATION: Duration = Duration::from_secs(3);
 pub(crate) const DEFAULT_INTERVAL: Duration = Duration::from_secs(1);

crates/irtt-client/src/lib.rs

@@ -20,7 +20,7 @@ mod timing;
 pub use client::Client;
 pub use config::{
     ClientConfig, NegotiationPolicy, RecvBudget, RunMode, SocketConfig, MAX_DSCP_CODEPOINT,
-    MAX_SERVER_FILL_BYTES, MAX_TTL,
+    MAX_SERVER_FILL_BYTES, MAX_TTL, MAX_UDP_PAYLOAD_LENGTH,
 };
 pub use error::{ClientError, EventSubscriptionError};
 pub use event::{