quic: enable qlog output in tests

Set QLOG=/some/dir to enable qlog logging in tests.

Change-Id: Id4006c66fd555ad0ca47914d0af9f9ab46467c9c
Reviewed-on: https://go-review.googlesource.com/c/net/+/550796
Reviewed-by: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

internal/quic/conn_test.go

@@ -13,15 +13,21 @@ import (
 	"errors"
 	"flag"
 	"fmt"
+	"log/slog"
 	"math"
 	"net/netip"
 	"reflect"
 	"strings"
 	"testing"
 	"time"
+
+	"golang.org/x/net/internal/quic/qlog"
 )
 
-var testVV = flag.Bool("vv", false, "even more verbose test output")
+var (
+	testVV  = flag.Bool("vv", false, "even more verbose test output")
+	qlogdir = flag.String("qlog", "", "write qlog logs to directory")
+)
 
 func TestConnTestConn(t *testing.T) {
 	tc := newTestConn(t, serverSide)
@@ -199,6 +205,10 @@ func newTestConn(t *testing.T, side connSide, opts ...any) *testConn {
 	config := &Config{
 		TLSConfig:         newTestTLSConfig(side),
 		StatelessResetKey: testStatelessResetKey,
+		QLogLogger: slog.New(qlog.NewJSONHandler(qlog.HandlerOptions{
+			Level: QLogLevelFrame,
+			Dir:   *qlogdir,
+		})),
 	}
 	var cids newServerConnIDs
 	if side == serverSide {

internal/quic/endpoint_test.go

@@ -11,10 +11,13 @@ import (
 	"context"
 	"crypto/tls"
 	"io"
+	"log/slog"
 	"net"
 	"net/netip"
 	"testing"
 	"time"
+
+	"golang.org/x/net/internal/quic/qlog"
 )
 
 func TestConnect(t *testing.T) {
@@ -83,6 +86,12 @@ func newLocalEndpoint(t *testing.T, side connSide, conf *Config) *Endpoint {
 		conf = &newConf
 		conf.TLSConfig = newTestTLSConfig(side)
 	}
+	if conf.QLogLogger == nil {
+		conf.QLogLogger = slog.New(qlog.NewJSONHandler(qlog.HandlerOptions{
+			Level: QLogLevelFrame,
+			Dir:   *qlogdir,
+		}))
+	}
 	e, err := Listen("udp", "127.0.0.1:0", conf)
 	if err != nil {
 		t.Fatal(err)