Log

neqo-transport/Cargo.toml

@@ -22,7 +22,7 @@ indexmap = { version = "2.2", default-features = false } # See https://github.co
 log = { workspace = true }
 neqo-common = { path = "../neqo-common" }
 neqo-crypto = { path = "../neqo-crypto" }
-mtu = { version = "0.1.3", default-features = false }
+mtu = { path = "../../mtu", default-features = false }
 qlog = { workspace = true }
 smallvec = { version = "1.11", default-features = false }
 static_assertions = { version = "1.1", default-features = false }

neqo-transport/src/path.rs

@@ -15,7 +15,9 @@ use std::{
     time::{Duration, Instant},
 };
 
-use neqo_common::{hex, qdebug, qinfo, qlog::NeqoQlog, qtrace, Datagram, Encoder, IpTos, IpTosEcn};
+use neqo_common::{
+    hex, qdebug, qinfo, qlog::NeqoQlog, qtrace, qwarn, Datagram, Encoder, IpTos, IpTosEcn,
+};
 use neqo_crypto::random;
 
 use crate::{
@@ -569,8 +571,19 @@ impl Path {
         qlog: NeqoQlog,
         now: Instant,
     ) -> Self {
-        let iface_mtu =
-            mtu::interface_and_mtu(&(local, remote)).map_or_else(|_| usize::MAX, |(_, m)| m);
+        // We're passing `None` into `mtu::interface_and_mtu` here, which force the lookup to only
+        // take the local address into account. Taking the remote address into account would require
+        // a call to `connect`, which Firefox blocklists for Rust dependencies.
+        let iface_mtu = match mtu::interface_and_mtu(&(local.ip(), remote)) {
+            Ok((name, mtu)) => {
+                qdebug!("Outbound interface {name} has MTU {mtu}");
+                mtu
+            }
+            Err(e) => {
+                qwarn!("Failed to determine outbound interface: {e}");
+                usize::MAX
+            }
+        };
         let mut sender = PacketSender::new(cc, pacing, Pmtud::new(remote.ip(), iface_mtu), now);
         sender.set_qlog(qlog.clone());
         Self {