add integration test

.vscode/settings.json

@@ -3,7 +3,7 @@
   // to develop this project.
   "files.eol": "\n",
   "editor.formatOnSave": true,
-  "go.buildTags": "linux",
+  "go.buildTags": "linux,integration",
   "go.toolsEnvVars": {
     "CGO_ENABLED": "0"
   },

internal/socks5/udp_router.go

@@ -209,7 +209,7 @@ func (r *udpRouter) clientAddrPortForAssociation(associationID uint64) (
 
 func (r *udpRouter) runAssociationHandler(ctx context.Context, association udpAssociation) {
 	config := &net.ListenConfig{}
-	socket, err := config.ListenPacket(ctx, "udp", "127.0.0.1:0")
+	socket, err := config.ListenPacket(ctx, "udp", ":0")
 	if err != nil {
 		r.logger.Warnf("creating per-association UDP socket: %s", err)
 		return

internal/socks5/udp_router_integration_test.go

@@ -0,0 +1,162 @@
+//go:build integration
+
+package socks5
+
+import (
+	"bytes"
+	"context"
+	"math/rand/v2"
+	"net"
+	"net/netip"
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/golang/mock/gomock"
+	"github.com/miekg/dns"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_udpRouter_ResolveGithubFromCloudflareDNS(t *testing.T) {
+	ctx := t.Context()
+	var cancel context.CancelFunc
+	deadline, hasDeadline := ctx.Deadline()
+	if hasDeadline {
+		const deadlineBuffer = 500 * time.Millisecond
+		deadline = deadline.Add(-deadlineBuffer)
+	} else {
+		const defaultTimeout = 10 * time.Second
+		deadline = time.Now().Add(defaultTimeout)
+	}
+	ctx, cancel = context.WithDeadline(ctx, deadline)
+
+	ctrl := gomock.NewController(t)
+	logger := NewMockLogger(ctrl)
+
+	router, err := newUDPRouter(ctx, "127.0.0.1:0", logger)
+	require.NoError(t, err)
+
+	routerRunErrCh := make(chan error)
+	go func() {
+		routerRunErrCh <- router.run(ctx)
+	}()
+
+	t.Cleanup(func() {
+		cancel()
+		err := router.close()
+		assert.NoError(t, err, "closing router")
+		runErr := <-routerRunErrCh
+		assert.NoError(t, runErr)
+	})
+
+	controlListener, err := (&net.ListenConfig{}).Listen(ctx, "tcp", "127.0.0.1:0")
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		err := controlListener.Close()
+		assert.NoError(t, err, "closing control listener")
+	})
+
+	acceptedConnCh := make(chan net.Conn)
+	go func() {
+		acceptedConn, acceptErr := controlListener.Accept()
+		assert.NoError(t, acceptErr, "accepting control connection")
+		if acceptErr != nil {
+			return
+		}
+		acceptedConnCh <- acceptedConn
+	}()
+
+	clientControlConn, err := (&net.Dialer{}).DialContext(ctx, "tcp", controlListener.Addr().String())
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		err = clientControlConn.Close()
+		assert.NoError(t, err, "closing client control connection")
+	})
+
+	serverControlConn := <-acceptedConnCh
+	t.Cleanup(func() {
+		err := serverControlConn.Close()
+		assert.NoError(t, err, "closing server control connection")
+	})
+
+	association, err := router.registerAssociation(serverControlConn)
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		router.unregisterAssociation(association)
+	})
+
+	associationCtx, associationCancel := context.WithCancel(ctx)
+	handlerDoneCh := make(chan struct{})
+	go func() {
+		router.runAssociationHandler(associationCtx, association)
+		close(handlerDoneCh)
+	}()
+	t.Cleanup(func() {
+		associationCancel()
+		<-handlerDoneCh
+	})
+
+	udpRouterAddress, err := net.ResolveUDPAddr("udp", router.localAddress().String())
+	require.NoError(t, err)
+
+	clientUDPConn, err := net.DialUDP("udp", nil, udpRouterAddress)
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		err := clientUDPConn.Close()
+		assert.NoError(t, err, "closing client UDP connection")
+	})
+
+	queryID := uint16(rand.Uint())
+	dnsRequest := &dns.Msg{
+		MsgHdr: dns.MsgHdr{
+			Id:               queryID,
+			RecursionDesired: true,
+		},
+		Question: []dns.Question{{
+			Name:   dns.Fqdn("github.com"),
+			Qtype:  dns.TypeA,
+			Qclass: dns.ClassINET,
+		}},
+	}
+	dnsQuery, err := dnsRequest.Pack()
+	require.NoError(t, err)
+
+	targetAddrPort := netip.MustParseAddrPort("1.1.1.1:53")
+	socksDatagramBuffer := bytes.NewBuffer(nil)
+	err = encodeUDPDatagramToBuffer(socksDatagramBuffer, targetAddrPort, dnsQuery)
+	require.NoError(t, err)
+	socksDatagram := socksDatagramBuffer.Bytes()
+
+	err = clientUDPConn.SetDeadline(deadline)
+	require.NoError(t, err)
+
+	_, err = clientUDPConn.Write(socksDatagram)
+	require.NoError(t, err)
+
+	responseBuffer := make([]byte, maxUDPPacketLength)
+	responseLength, err := clientUDPConn.Read(responseBuffer)
+	require.NoError(t, err)
+
+	responseDestination, responsePayload, err := decodeUDPDatagram(responseBuffer[:responseLength])
+	require.NoError(t, err)
+
+	responseHost, responsePortString, err := net.SplitHostPort(responseDestination)
+	require.NoError(t, err)
+	responsePort, err := strconv.ParseUint(responsePortString, 10, 16)
+	require.NoError(t, err)
+	assert.Equal(t, uint64(53), responsePort)
+	assert.NotEmpty(t, responseHost)
+
+	dnsResponse := new(dns.Msg)
+	err = dnsResponse.Unpack(responsePayload)
+	require.NoError(t, err)
+	assert.Equal(t, queryID, dnsResponse.Id)
+	assert.True(t, dnsResponse.Response)
+	assert.Equal(t, dns.RcodeSuccess, dnsResponse.Rcode)
+	require.NotEmpty(t, dnsResponse.Question)
+	assert.Equal(t, dns.Fqdn("github.com"), dnsResponse.Question[0].Name)
+	assert.Equal(t, uint16(dns.TypeA), dnsResponse.Question[0].Qtype)
+	assert.NotEmpty(t, dnsResponse.Answer)
+	require.NoError(t, err)
+}