fix(proto): reject packet lengths usize cannot represent

crates/irtt-client/src/async_client.rs

@@ -246,7 +246,7 @@ impl AsyncClient {
             machine,
             schedule: None,
             remote,
-            recv_buffer: vec![0_u8; recv_buffer_size(false, None)],
+            recv_buffer: vec![0_u8; recv_buffer_size(false, None)?],
             applied_traffic_class: None,
             prepared_open: Some(prepared_open),
             prepared_probe: None,
@@ -820,7 +820,12 @@ impl AsyncClient {
                 return Err(Box::new(PreparedAsyncOpenFailure { primary, machine }));
             }
         };
-        let recv_buffer_len = recv_buffer_size(self.machine.has_hmac(), Some(negotiated));
+        let recv_buffer_len = match recv_buffer_size(self.machine.has_hmac(), Some(negotiated)) {
+            Ok(size) => size,
+            Err(primary) => {
+                return Err(Box::new(PreparedAsyncOpenFailure { primary, machine }));
+            }
+        };
         let negotiated_traffic_class = match u8::try_from(negotiated.params.dscp) {
             Ok(traffic_class) => traffic_class,
             Err(_) => {

crates/irtt-client/src/client.rs

@@ -131,7 +131,7 @@ impl Client {
             schedule: None,
             socket,
             remote,
-            recv_buffer: vec![0_u8; recv_buffer_size(false, None)],
+            recv_buffer: vec![0_u8; recv_buffer_size(false, None)?],
             applied_traffic_class: None,
             #[cfg(test)]
             test_hooks: ClientTestHooks::default(),
@@ -530,7 +530,10 @@ impl Client {
             Ok(schedule) => schedule,
             Err(primary) => return Err(Box::new(PreparedClientOpenFailure { primary, machine })),
         };
-        let recv_buffer_len = recv_buffer_size(self.runtime.has_hmac(), Some(negotiated));
+        let recv_buffer_len = match recv_buffer_size(self.runtime.has_hmac(), Some(negotiated)) {
+            Ok(size) => size,
+            Err(primary) => return Err(Box::new(PreparedClientOpenFailure { primary, machine })),
+        };
         #[cfg(test)]
         let recv_buffer_len = self
             .test_hooks

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

@@ -1,8 +1,8 @@
 use super::*;
-pub(crate) use irtt_proto::echo_packet_len;
 use irtt_proto::{
-    encode_echo_reply, encode_open_reply, flags::FLAG_OPEN, flags::FLAG_REPLY,
-    layout::PacketLayout, Clock, EchoReply, OpenReply, ReceivedStats, StampAt,
+    echo_packet_len as checked_echo_packet_len, encode_echo_reply, encode_open_reply,
+    flags::FLAG_OPEN, flags::FLAG_REPLY, layout::PacketLayout, Clock, EchoReply, OpenReply,
+    ReceivedStats, StampAt,
 };
 use std::{
     net::UdpSocket,
@@ -72,6 +72,12 @@ pub(super) fn open_reply(
     .unwrap()
 }
 
+/// Test params always name a representable length, so the platform
+/// representability check cannot fire here.
+pub(crate) fn echo_packet_len(hmac: bool, params: &Params) -> usize {
+    checked_echo_packet_len(hmac, params).expect("test params must have a representable length")
+}
+
 pub(super) fn echo_reply_packet(
     token: u64,
     seq: u32,

crates/irtt-client/src/session/machine.rs

@@ -823,13 +823,23 @@ impl SessionMachine {
     }
 }
 
-pub(crate) fn recv_buffer_size(has_hmac: bool, negotiated: Option<&NegotiatedParams>) -> usize {
-    match negotiated {
-        Some(negotiated) => echo_packet_len(has_hmac, &negotiated.params)
+/// Sizes the receive buffer for the negotiated layout.
+///
+/// Fallible only because a negotiated length wider than `usize` cannot name a
+/// buffer at all. Negotiation already rejects a returned length that is
+/// negative or larger than this client requested, and the requested length is a
+/// `u32`, so the error is unreachable here in practice — it is propagated
+/// rather than asserted away so that no 64-bit assumption is baked in.
+pub(crate) fn recv_buffer_size(
+    has_hmac: bool,
+    negotiated: Option<&NegotiatedParams>,
+) -> Result<usize, ClientError> {
+    Ok(match negotiated {
+        Some(negotiated) => echo_packet_len(has_hmac, &negotiated.params)?
             .saturating_add(1)
             .max(MIN_RECV_BUFFER_SIZE),
         None => MIN_RECV_BUFFER_SIZE,
-    }
+    })
 }
 
 pub(crate) fn params_from_config(config: &ClientConfig) -> Result<Params, ClientError> {