fix: increase UDP read buffer length to max datagram size

Co-authored-by: Tom Moulard <tom.moulard@traefik.io>

pkg/udp/proxy_test.go

@@ -1,7 +1,9 @@
 package udp
 
 import (
+	"crypto/rand"
 	"net"
+	"runtime"
 	"testing"
 	"time"
 
@@ -9,13 +11,14 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestUDPProxy(t *testing.T) {
+func TestProxy_ServeUDP(t *testing.T) {
 	backendAddr := ":8081"
-	go newServer(t, ":8081", HandlerFunc(func(conn *Conn) {
+	go newServer(t, backendAddr, HandlerFunc(func(conn *Conn) {
 		for {
 			b := make([]byte, 1024*1024)
 			n, err := conn.Read(b)
 			require.NoError(t, err)
+
 			_, err = conn.Write(b[:n])
 			require.NoError(t, err)
 		}
@@ -28,6 +31,7 @@ func TestUDPProxy(t *testing.T) {
 	go newServer(t, proxyAddr, proxy)
 
 	time.Sleep(time.Second)
+
 	udpConn, err := net.Dial("udp", proxyAddr)
 	require.NoError(t, err)
 
@@ -37,9 +41,58 @@ func TestUDPProxy(t *testing.T) {
 	b := make([]byte, 1024*1024)
 	n, err := udpConn.Read(b)
 	require.NoError(t, err)
+
 	assert.Equal(t, "DATAWRITE", string(b[:n]))
 }
 
+func TestProxy_ServeUDP_MaxDataSize(t *testing.T) {
+	if runtime.GOOS == "darwin" {
+		// sudo sysctl -w net.inet.udp.maxdgram=65507
+		t.Skip("Skip test on darwin as the maximum dgram size is set to 9216 bytes by default")
+	}
+
+	// Theoretical maximum size of data in a UDP datagram.
+	// 65535 − 8 (UDP header) − 20 (IP header).
+	dataSize := 65507
+
+	backendAddr := ":8083"
+	go newServer(t, backendAddr, HandlerFunc(func(conn *Conn) {
+		buffer := make([]byte, dataSize)
+
+		n, err := conn.Read(buffer)
+		require.NoError(t, err)
+
+		_, err = conn.Write(buffer[:n])
+		require.NoError(t, err)
+	}))
+
+	proxy, err := NewProxy(backendAddr)
+	require.NoError(t, err)
+
+	proxyAddr := ":8082"
+	go newServer(t, proxyAddr, proxy)
+
+	time.Sleep(time.Second)
+
+	udpConn, err := net.Dial("udp", proxyAddr)
+	require.NoError(t, err)
+
+	want := make([]byte, dataSize)
+
+	_, err = rand.Read(want)
+	require.NoError(t, err)
+
+	_, err = udpConn.Write(want)
+	require.NoError(t, err)
+
+	got := make([]byte, dataSize)
+
+	_, err = udpConn.Read(got)
+	require.NoError(t, err)
+
+	assert.Equal(t, want, got)
+}
+
 func newServer(t *testing.T, addr string, handler Handler) {
 	t.Helper()
 
@@ -52,6 +105,7 @@ func newServer(t *testing.T, addr string, handler Handler) {
 	for {
 		conn, err := listener.Accept()
 		require.NoError(t, err)
+
 		go handler.ServeUDP(conn)
 	}
 }