From 91dd91fa99aeee6bc439f4c70c4424e4b824ad03 Mon Sep 17 00:00:00 2001
From: Benjamin Saunders <ben.e.saunders@gmail.com>
Date: Tue, 28 Dec 2021 21:25:56 -0800
Subject: [PATCH] Tolerate wide IP_TOS cmsgs

---
 quinn-udp/src/unix.rs | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/quinn-udp/src/unix.rs b/quinn-udp/src/unix.rs
index fd057497e..cf5c06a96 100644
--- a/quinn-udp/src/unix.rs
+++ b/quinn-udp/src/unix.rs
@@ -488,7 +488,16 @@ fn decode_recv(
         match (cmsg.cmsg_level, cmsg.cmsg_type) {
             // FreeBSD uses IP_RECVTOS here, and we can be liberal because cmsgs are opt-in.
             (libc::IPPROTO_IP, libc::IP_TOS) | (libc::IPPROTO_IP, libc::IP_RECVTOS) => unsafe {
-                ecn_bits = cmsg::decode::<u8>(cmsg);
+                // Linux reportedly returns 4-byte values here instead of the expected, documented
+                // 1-byte, e.g. in kernel 4.4.0-19041-Microsoft or on Github Actions. Future work:
+                // find out why, report upstream?
+                if cmsg.cmsg_len as usize
+                    == libc::CMSG_LEN(mem::size_of::<libc::c_int>() as _) as usize
+                {
+                    ecn_bits = cmsg::decode::<libc::c_int>(cmsg) as u8;
+                } else {
+                    ecn_bits = cmsg::decode::<u8>(cmsg);
+                }
             },
             (libc::IPPROTO_IPV6, libc::IPV6_TCLASS) => unsafe {
                 // Temporary hack around broken macos ABI. Remove once upstream fixes it.