From 7ed29ac2fd3f1769f56b9482197eccf823bc5c81 Mon Sep 17 00:00:00 2001
From: Max Inden <mail@max-inden.de>
Date: Thu, 12 Dec 2024 21:27:27 +0100
Subject: [PATCH] fix(udp): retry send on first EINVAL

---
 quinn-udp/src/unix.rs | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/quinn-udp/src/unix.rs b/quinn-udp/src/unix.rs
index 55bd21059..d5c779ed3 100644
--- a/quinn-udp/src/unix.rs
+++ b/quinn-udp/src/unix.rs
@@ -332,8 +332,20 @@ fn send(
 
                     if e.raw_os_error() == Some(libc::EINVAL) {
                         // Some arguments to `sendmsg` are not supported.
-                        // Switch to fallback mode.
-                        state.set_sendmsg_einval();
+                        if !state.sendmsg_einval() {
+                            // Switch to fallback mode.
+                            state.set_sendmsg_einval();
+                            prepare_msg(
+                                transmit,
+                                &dst_addr,
+                                &mut msg_hdr,
+                                &mut iovec,
+                                &mut cmsgs,
+                                encode_src_ip,
+                                state.sendmsg_einval(),
+                            );
+                            continue;
+                        }
                     }
 
                     // - EMSGSIZE is expected for MTU probes. Future work might be able to avoid