From 2bcfe5bc4b4d09716e7c7b708adbe5736fa87560 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Thu, 20 Jul 2023 20:31:57 -0700
Subject: [PATCH] check for WSAEMSGSIZE errors when receiving UDP packets on
 Windows (#3982)

* check for WSAEMSGSIZE errors when receiving UDP packets on Windows

* check EMSGSIZE error on macOS
---
 send_queue.go          | 2 +-
 sys_conn_df.go         | 7 ++++++-
 sys_conn_df_darwin.go  | 4 +++-
 sys_conn_df_linux.go   | 4 +++-
 sys_conn_df_windows.go | 7 ++++++-
 transport.go           | 4 ++++
 6 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/send_queue.go b/send_queue.go
index ab7a45ca..a9f7ca1a 100644
--- a/send_queue.go
+++ b/send_queue.go
@@ -82,7 +82,7 @@ func (h *sendQueue) Run() error {
 				// 1. Checking for "datagram too large" message from the kernel, as such,
 				// 2. Path MTU discovery,and
 				// 3. Eventual detection of loss PingFrame.
-				if !isMsgSizeErr(err) {
+				if !isSendMsgSizeErr(err) {
 					return err
 				}
 			}
diff --git a/sys_conn_df.go b/sys_conn_df.go
index b90a13da..0db61509 100644
--- a/sys_conn_df.go
+++ b/sys_conn_df.go
@@ -11,7 +11,12 @@ func setDF(syscall.RawConn) (bool, error) {
 	return false, nil
 }
 
-func isMsgSizeErr(err error) bool {
+func isSendMsgSizeErr(err error) bool {
+	// to be implemented for more specific platforms
+	return false
+}
+
+func isRecvMsgSizeErr(err error) bool {
 	// to be implemented for more specific platforms
 	return false
 }
diff --git a/sys_conn_df_darwin.go b/sys_conn_df_darwin.go
index e3a9b77f..b51cd8f1 100644
--- a/sys_conn_df_darwin.go
+++ b/sys_conn_df_darwin.go
@@ -47,10 +47,12 @@ func setDF(rawConn syscall.RawConn) (bool, error) {
 	return true, nil
 }
 
-func isMsgSizeErr(err error) bool {
+func isSendMsgSizeErr(err error) bool {
 	return errors.Is(err, unix.EMSGSIZE)
 }
 
+func isRecvMsgSizeErr(error) bool { return false }
+
 func isAtLeastMacOS11() (bool, error) {
 	uname := &unix.Utsname{}
 	err := unix.Uname(uname)
diff --git a/sys_conn_df_linux.go b/sys_conn_df_linux.go
index abd64dd9..199f6347 100644
--- a/sys_conn_df_linux.go
+++ b/sys_conn_df_linux.go
@@ -57,11 +57,13 @@ func maybeSetGSO(rawConn syscall.RawConn) bool {
 	return true
 }
 
-func isMsgSizeErr(err error) bool {
+func isSendMsgSizeErr(err error) bool {
 	// https://man7.org/linux/man-pages/man7/udp.7.html
 	return errors.Is(err, unix.EMSGSIZE)
 }
 
+func isRecvMsgSizeErr(err error) bool { return false }
+
 func appendUDPSegmentSizeMsg(b []byte, size uint16) []byte {
 	startLen := len(b)
 	const dataLen = 2 // payload is a uint16
diff --git a/sys_conn_df_windows.go b/sys_conn_df_windows.go
index a7f1351a..e27635ec 100644
--- a/sys_conn_df_windows.go
+++ b/sys_conn_df_windows.go
@@ -43,7 +43,12 @@ func setDF(rawConn syscall.RawConn) (bool, error) {
 	return true, nil
 }
 
-func isMsgSizeErr(err error) bool {
+func isSendMsgSizeErr(err error) bool {
+	// https://docs.microsoft.com/en-us/windows/win32/winsock/windows-sockets-error-codes-2
+	return errors.Is(err, windows.WSAEMSGSIZE)
+}
+
+func isRecvMsgSizeErr(err error) bool {
 	// https://docs.microsoft.com/en-us/windows/win32/winsock/windows-sockets-error-codes-2
 	return errors.Is(err, windows.WSAEMSGSIZE)
 }
diff --git a/transport.go b/transport.go
index 3c985965..290b647f 100644
--- a/transport.go
+++ b/transport.go
@@ -330,6 +330,10 @@ func (t *Transport) listen(conn rawConn) {
 			continue
 		}
 		if err != nil {
+			// Windows returns an error when receiving a UDP datagram that doesn't fit into the provided buffer.
+			if isRecvMsgSizeErr(err) {
+				continue
+			}
 			t.close(err)
 			return
 		}