fix(client): reject runtime-invalid negotiated dscp

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

@@ -52,3 +52,19 @@ fn strict_negotiation_rejects_negative_returned_length() {
         Err(ClientError::NegotiationRejected { reason }) if reason == "length must be non-negative"
     ));
 }
+
+#[test]
+fn loose_negotiation_rejects_runtime_invalid_returned_dscp() {
+    let config = ClientConfig::default();
+    let requested = params_from_config(&config).unwrap();
+
+    for dscp in [-1, 64] {
+        let mut returned = requested.clone();
+        returned.dscp = dscp;
+        assert!(matches!(
+            validate_negotiated_params(&requested, &returned, NegotiationPolicy::Loose),
+            Err(ClientError::NegotiationRejected { reason })
+                if reason == "dscp must be in range 0..=63"
+        ));
+    }
+}

crates/irtt-client/src/session.rs

@@ -3,7 +3,7 @@ use std::time::Instant;
 use irtt_proto::{Params, PROTOCOL_VERSION};
 
 use crate::{
-    config::NegotiationPolicy,
+    config::{NegotiationPolicy, MAX_DSCP_CODEPOINT},
     error::ClientError,
     probe::{CompletedSet, PendingMap, TimedOutMap},
 };
@@ -63,6 +63,7 @@ pub(crate) fn validate_negotiated_params(
             reason: "interval must be positive".to_owned(),
         });
     }
+    validate_dscp_restriction(returned.dscp)?;
 
     if policy == NegotiationPolicy::Strict && returned != requested {
         return Err(ClientError::NegotiationRejected {
@@ -94,6 +95,16 @@ fn validate_duration_restriction(requested: i64, returned: i64) -> Result<(), Cl
     Ok(())
 }
 
+fn validate_dscp_restriction(returned: i64) -> Result<(), ClientError> {
+    if !(0..=i64::from(MAX_DSCP_CODEPOINT)).contains(&returned) {
+        return Err(ClientError::NegotiationRejected {
+            reason: format!("dscp must be in range 0..={MAX_DSCP_CODEPOINT}"),
+        });
+    }
+
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;