fix(network): deadlock in lwIP UDP handler's Close function

network/lwip2transport/udp_test.go

@@ -0,0 +1,86 @@
+// Copyright 2023 Jigsaw Operations LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package lwip2transport
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"net/netip"
+	"testing"
+
+	"github.com/Jigsaw-Code/outline-internal-sdk/network"
+	"github.com/stretchr/testify/require"
+)
+
+// Make sure we can successfully Close the request sender and response receiver only once
+func TestUDPResponseWriterClose(t *testing.T) {
+	proxy := &noopSingleSessionPacketProxy{}
+	h := newUDPHandler(proxy)
+
+	// Create one and only one session in the proxy
+	localAddr := net.UDPAddrFromAddrPort(netip.MustParseAddrPort("127.0.0.1:60127"))
+	destAddr := net.UDPAddrFromAddrPort(netip.MustParseAddrPort("1.2.3.4:4321"))
+	err := h.ReceiveTo(&noopLwIPUDPConn{localAddr}, []byte{}, destAddr)
+	require.NoError(t, err)
+
+	// Close this single session (i.e. the request sender), it will close proxy.respWriter
+	// udpHandler must make sure only one `Close()` is called, and there should be no deadlocks
+	err = proxy.Close()
+	require.NoError(t, err)
+}
+
+/********** Test Utilities **********/
+
+type noopSingleSessionPacketProxy struct {
+	respWriter network.PacketResponseReceiver
+}
+
+func (p *noopSingleSessionPacketProxy) NewSession(respWriter network.PacketResponseReceiver) (network.PacketRequestSender, error) {
+	if p.respWriter != nil {
+		return nil, errors.New("don't support multiple sessions in this proxy")
+	}
+	p.respWriter = respWriter
+	return p, nil
+}
+
+func (p *noopSingleSessionPacketProxy) Close() error {
+	fmt.Println("Closing !!!!!")
+	return p.respWriter.Close()
+}
+
+func (p *noopSingleSessionPacketProxy) WriteTo([]byte, net.Addr) (int, error) {
+	return 0, nil
+}
+
+type noopLwIPUDPConn struct {
+	localAddr *net.UDPAddr
+}
+
+func (*noopLwIPUDPConn) Close() error {
+	return nil
+}
+
+func (conn *noopLwIPUDPConn) LocalAddr() *net.UDPAddr {
+	return conn.localAddr
+}
+
+func (*noopLwIPUDPConn) ReceiveTo(data []byte, addr *net.UDPAddr) error {
+	return nil
+}
+
+func (*noopLwIPUDPConn) WriteFrom(data []byte, addr *net.UDPAddr) (int, error) {
+	return 0, nil
+}