Modernize for current Go toolchains

The library already compiled and passed tests, but tooling and
dependencies were stale. This brings everything up to current standards
without changing public behavior.

Library (go 1.23.0):
- cmux_test.go: fix 8 `go vet` failures by sending writer-goroutine
  errors to the existing errCh (now buffered) instead of t.Fatal;
  ioutil.ReadAll -> io.ReadAll
- matchers.go: io/ioutil -> io (io.Discard); gofmt -s doc comment
- go.mod: go 1.11 -> 1.23.0; golang.org/x/net -> v0.42.0 (newest
  release that still permits a 1.23 directive)

Example submodule:
- golang.org/x/net/context -> stdlib context
- grpc v1.27.0 -> v1.80, modern protobuf; helloworld now comes from
  the separate google.golang.org/grpc/examples module (requires go 1.25,
  isolated to this demo-only module)

CI:
- remove ancient .travis.yml (Go 1.6-1.8)
- add .github/workflows/ci.yml: gofmt/vet/build/test -race for the
  library (Go 1.23 + 1.24 matrix) and the example

Temporary() methods and TLS version defaults are intentionally
unchanged: net.Error still requires Temporary(), and the TLS defaults
are public-API behavior.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -0,0 +1,50 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  library:
+    name: library (go ${{ matrix.go }})
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go: ["1.23", "1.24"]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: ${{ matrix.go }}
+      - name: gofmt
+        run: test -z "$(gofmt -s -l .)" || (gofmt -s -l . && exit 1)
+      - name: vet
+        run: go vet ./...
+      - name: build
+        run: go build ./...
+      - name: test
+        run: go test -race ./...
+
+  example:
+    name: example
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: example
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.25"
+      - name: gofmt
+        run: test -z "$(gofmt -s -l .)" || (gofmt -s -l . && exit 1)
+      - name: vet
+        run: go vet ./...
+      - name: build
+        run: go build ./...
+      - name: test
+        run: go test -race ./...

.travis.yml

@@ -1,29 +0,0 @@
-language: go
-
-go:
-  - 1.6
-  - 1.7
-  - 1.8
-  - tip
-
-matrix:
-  allow_failures:
-    - go: tip
-
-gobuild_args: -race
-
-before_install:
-  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then go get -u github.com/kisielk/errcheck; fi
-  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then go get -u github.com/golang/lint/golint; fi
-
-before_script:
-  - '! gofmt -s -l . | read'
-  - echo $TRAVIS_GO_VERSION
-  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then golint ./...; fi
-  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then errcheck ./...; fi
-  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then go tool vet .; fi
-  - if [[ $TRAVIS_GO_VERSION == 1.6* ]]; then go tool vet --shadow .; fi
-
-script:
-  - go test -bench . -v ./...
-  - go test -race -bench . -v ./...

README.md

@@ -25,7 +25,7 @@ trpcL := m.Match(cmux.Any()) // Any means anything that is not yet matched.
 
 // Create your protocol servers.
 grpcS := grpc.NewServer()
-grpchello.RegisterGreeterServer(grpcs, &server{})
+grpchello.RegisterGreeterServer(grpcS, &server{})
 
 httpS := &http.Server{
 	Handler: &helloHTTP1Handler{},

cmux.go

@@ -15,6 +15,7 @@
 package cmux
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -61,6 +62,9 @@ func (e errListenerClosed) Timeout() bool   { return false }
 // listener is closed.
 var ErrListenerClosed = errListenerClosed("mux: listener closed")
 
+// ErrServerClosed is returned from muxListener.Accept when mux server is closed.
+var ErrServerClosed = errors.New("mux: server closed")
+
 // for readability of readTimeout
 var noTimeout time.Duration
 
@@ -93,6 +97,8 @@ type CMux interface {
 	// Serve starts multiplexing the listener. Serve blocks and perhaps
 	// should be invoked concurrently within a go routine.
 	Serve() error
+	// Closes cmux server and stops accepting any connections on listener
+	Close()
 	// HandleError registers an error handler that handles listener errors.
 	HandleError(ErrorHandler)
 	// sets a timeout for the read of matchers
@@ -108,16 +114,18 @@ type cMux struct {
 	root        net.Listener
 	bufLen      int
 	errh        ErrorHandler
-	donec       chan struct{}
 	sls         []matchersListener
 	readTimeout time.Duration
+	donec       chan struct{}
+	mu          sync.Mutex
 }
 
 func matchersToMatchWriters(matchers []Matcher) []MatchWriter {
 	mws := make([]MatchWriter, 0, len(matchers))
 	for _, m := range matchers {
+		cm := m
 		mws = append(mws, func(w io.Writer, r io.Reader) bool {
-			return m(r)
+			return cm(r)
 		})
 	}
 	return mws
@@ -132,6 +140,7 @@ func (m *cMux) MatchWithWriters(matchers ...MatchWriter) net.Listener {
 	ml := muxListener{
 		Listener: m.root,
 		connc:    make(chan net.Conn, m.bufLen),
+		donec:    make(chan struct{}),
 	}
 	m.sls = append(m.sls, matchersListener{ss: matchers, l: ml})
 	return ml
@@ -145,7 +154,7 @@ func (m *cMux) Serve() error {
 	var wg sync.WaitGroup
 
 	defer func() {
-		close(m.donec)
+		m.closeDoneChans()
 		wg.Wait()
 
 		for _, sl := range m.sls {
@@ -203,6 +212,30 @@ func (m *cMux) serve(c net.Conn, donec <-chan struct{}, wg *sync.WaitGroup) {
 	}
 }
 
+func (m *cMux) Close() {
+	m.closeDoneChans()
+}
+
+func (m *cMux) closeDoneChans() {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	select {
+	case <-m.donec:
+		// Already closed. Don't close again
+	default:
+		close(m.donec)
+	}
+	for _, sl := range m.sls {
+		select {
+		case <-sl.l.donec:
+			// Already closed. Don't close again
+		default:
+			close(sl.l.donec)
+		}
+	}
+}
+
 func (m *cMux) HandleError(h ErrorHandler) {
 	m.errh = h
 }
@@ -222,14 +255,19 @@ func (m *cMux) handleErr(err error) bool {
 type muxListener struct {
 	net.Listener
 	connc chan net.Conn
+	donec chan struct{}
 }
 
 func (l muxListener) Accept() (net.Conn, error) {
-	c, ok := <-l.connc
+	select {
-	if !ok {
+	case c, ok := <-l.connc:
-		return nil, ErrListenerClosed
+		if !ok {
+			return nil, ErrListenerClosed
+		}
+		return c, nil
+	case <-l.donec:
+		return nil, ErrServerClosed
 	}
-	return c, nil
 }
 
 // MuxConn wraps a net.Conn and provides transparent sniffing of connection data.

cmux_test.go

@@ -22,7 +22,6 @@ import (
 	"fmt"
 	"go/build"
 	"io"
-	"io/ioutil"
 	"log"
 	"net"
 	"net/http"
@@ -128,7 +127,7 @@ func runTestHTTPServer(errCh chan<- error, l net.Listener) {
 			mu.Unlock()
 		},
 	}
-	if err := s.Serve(l); err != ErrListenerClosed {
+	if err := s.Serve(l); err != ErrListenerClosed && err != ErrServerClosed {
 		errCh <- err
 	}
 }
@@ -194,7 +193,7 @@ func runTestHTTPClient(t *testing.T, proto string, addr net.Addr) {
 		}
 	}()
 
-	b, err := ioutil.ReadAll(r.Body)
+	b, err := io.ReadAll(r.Body)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -218,7 +217,7 @@ func runTestRPCServer(errCh chan<- error, l net.Listener) {
 	for {
 		c, err := l.Accept()
 		if err != nil {
-			if err != ErrListenerClosed {
+			if err != ErrListenerClosed && err != ErrServerClosed {
 				errCh <- err
 			}
 			return
@@ -321,7 +320,7 @@ func TestTimeout(t *testing.T) {
 
 func TestRead(t *testing.T) {
 	defer leakCheck(t)()
-	errCh := make(chan error)
+	errCh := make(chan error, 1)
 	defer func() {
 		select {
 		case err := <-errCh:
@@ -335,10 +334,11 @@ func TestRead(t *testing.T) {
 	writer, reader := net.Pipe()
 	go func() {
 		if _, err := io.WriteString(writer, strings.Repeat(payload, mult)); err != nil {
-			t.Fatal(err)
+			errCh <- err
+			return
 		}
 		if err := writer.Close(); err != nil {
-			t.Fatal(err)
+			errCh <- err
 		}
 	}()
 
@@ -379,7 +379,7 @@ func TestRead(t *testing.T) {
 
 func TestAny(t *testing.T) {
 	defer leakCheck(t)()
-	errCh := make(chan error)
+	errCh := make(chan error, 1)
 	defer func() {
 		select {
 		case err := <-errCh:
@@ -403,7 +403,7 @@ func TestTLS(t *testing.T) {
 	generateTLSCert(t)
 	defer cleanupTLSCert(t)
 	defer leakCheck(t)()
-	errCh := make(chan error)
+	errCh := make(chan error, 1)
 	defer func() {
 		select {
 		case err := <-errCh:
@@ -428,7 +428,7 @@ func TestTLS(t *testing.T) {
 
 func TestHTTP2(t *testing.T) {
 	defer leakCheck(t)()
-	errCh := make(chan error)
+	errCh := make(chan error, 1)
 	defer func() {
 		select {
 		case err := <-errCh:
@@ -439,10 +439,11 @@ func TestHTTP2(t *testing.T) {
 	writer, reader := net.Pipe()
 	go func() {
 		if _, err := io.WriteString(writer, http2.ClientPreface); err != nil {
-			t.Fatal(err)
+			errCh <- err
+			return
 		}
 		if err := writer.Close(); err != nil {
-			t.Fatal(err)
+			errCh <- err
 		}
 	}()
 
@@ -493,7 +494,7 @@ func testHTTP2MatchHeaderField(
 	notMatchValue string,
 ) {
 	defer leakCheck(t)()
-	errCh := make(chan error)
+	errCh := make(chan error, 1)
 	defer func() {
 		select {
 		case err := <-errCh:
@@ -505,12 +506,14 @@ func testHTTP2MatchHeaderField(
 	writer, reader := net.Pipe()
 	go func() {
 		if _, err := io.WriteString(writer, http2.ClientPreface); err != nil {
-			t.Fatal(err)
+			errCh <- err
+			return
 		}
 		var buf bytes.Buffer
 		enc := hpack.NewEncoder(&buf)
 		if err := enc.WriteField(hpack.HeaderField{Name: name, Value: headerValue}); err != nil {
-			t.Fatal(err)
+			errCh <- err
+			return
 		}
 		framer := http2.NewFramer(writer, nil)
 		err := framer.WriteHeaders(http2.HeadersFrameParam{
@@ -520,10 +523,11 @@ func testHTTP2MatchHeaderField(
 			EndHeaders:    true,
 		})
 		if err != nil {
-			t.Fatal(err)
+			errCh <- err
+			return
 		}
 		if err := writer.Close(); err != nil {
-			t.Fatal(err)
+			errCh <- err
 		}
 	}()
 
@@ -558,7 +562,7 @@ func testHTTP2MatchHeaderField(
 
 func TestHTTPGoRPC(t *testing.T) {
 	defer leakCheck(t)()
-	errCh := make(chan error)
+	errCh := make(chan error, 1)
 	defer func() {
 		select {
 		case err := <-errCh:
@@ -583,7 +587,7 @@ func TestHTTPGoRPC(t *testing.T) {
 
 func TestErrorHandler(t *testing.T) {
 	defer leakCheck(t)()
-	errCh := make(chan error)
+	errCh := make(chan error, 1)
 	defer func() {
 		select {
 		case err := <-errCh:
@@ -622,9 +626,38 @@ func TestErrorHandler(t *testing.T) {
 	}
 }
 
-func TestClose(t *testing.T) {
+func TestMultipleMatchers(t *testing.T) {
 	defer leakCheck(t)()
-	errCh := make(chan error)
+	errCh := make(chan error, 1)
+	defer func() {
+		select {
+		case err := <-errCh:
+			t.Fatal(err)
+		default:
+		}
+	}()
+	l, cleanup := testListener(t)
+	defer cleanup()
+
+	matcher := func(r io.Reader) bool {
+		return true
+	}
+	unmatcher := func(r io.Reader) bool {
+		return false
+	}
+
+	muxl := New(l)
+	lis := muxl.Match(unmatcher, matcher, unmatcher)
+
+	go runTestHTTPServer(errCh, lis)
+	go safeServe(errCh, muxl)
+
+	runTestHTTP1Client(t, l.Addr())
+}
+
+func TestListenerClose(t *testing.T) {
+	defer leakCheck(t)()
+	errCh := make(chan error, 1)
 	defer func() {
 		select {
 		case err := <-errCh:
@@ -656,7 +689,7 @@ func TestClose(t *testing.T) {
 
 	// Second connection either goes through or it is closed.
 	if _, err := anyl.Accept(); err != nil {
-		if err != ErrListenerClosed {
+		if err != ErrListenerClosed && err != ErrServerClosed {
 			t.Fatal(err)
 		}
 		// The error is either io.ErrClosedPipe or net.OpError wrapping
@@ -667,6 +700,31 @@ func TestClose(t *testing.T) {
 	}
 }
 
+func TestClose(t *testing.T) {
+	defer leakCheck(t)()
+	errCh := make(chan error, 1)
+	defer func() {
+		select {
+		case err := <-errCh:
+			t.Fatal(err)
+		default:
+		}
+	}()
+	l, cleanup := testListener(t)
+	defer cleanup()
+
+	muxl := New(l)
+	anyl := muxl.Match(Any())
+
+	go safeServe(errCh, muxl)
+
+	muxl.Close()
+
+	if _, err := anyl.Accept(); err != ErrServerClosed {
+		t.Fatal(err)
+	}
+}
+
 // Cribbed from google.golang.org/grpc/test/end2end_test.go.
 
 // interestingGoroutines returns all goroutines we care about for the purpose

example/example_test.go

@@ -15,6 +15,7 @@
 package cmux_test
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"log"
@@ -25,10 +26,10 @@ import (
 
 	"google.golang.org/grpc"
 
-	"golang.org/x/net/context"
 	"golang.org/x/net/websocket"
 
 	"github.com/soheilhy/cmux"
+	"google.golang.org/grpc/examples/helloworld/helloworld"
 	grpchello "google.golang.org/grpc/examples/helloworld/helloworld"
 )
 
@@ -86,7 +87,9 @@ func serveRPC(l net.Listener) {
 	}
 }
 
-type grpcServer struct{}
+type grpcServer struct {
+	helloworld.UnimplementedGreeterServer
+}
 
 func (s *grpcServer) SayHello(ctx context.Context, in *grpchello.HelloRequest) (
 	*grpchello.HelloReply, error) {

example/go.mod

@@ -0,0 +1,19 @@
+module github.com/soheilhy/cmux/example
+
+go 1.25.0
+
+require (
+	github.com/soheilhy/cmux v0.0.0-00010101000000-000000000000
+	golang.org/x/net v0.53.0
+	google.golang.org/grpc v1.80.0
+	google.golang.org/grpc/examples v0.0.0-20260605180800-0f3086db7a75
+)
+
+require (
+	golang.org/x/sys v0.43.0 // indirect
+	golang.org/x/text v0.36.0 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20260414002931-afd174a4e478 // indirect
+	google.golang.org/protobuf v1.36.11 // indirect
+)
+
+replace github.com/soheilhy/cmux => ../

example/go.sum

@@ -0,0 +1,40 @@
+github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/go-logr/logr v1.4.3 h1:CjnDlHq8ikf6E492q6eKboGOC0T8CDaOvkHCIg8idEI=
+github.com/go-logr/logr v1.4.3/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
+github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
+github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
+github.com/golang/protobuf v1.5.4 h1:i7eJL8qZTpSEXOPTxNKhASYpMn+8e5Q6AdndVa1dWek=
+github.com/golang/protobuf v1.5.4/go.mod h1:lnTiLA8Wa4RWRcIUkrtSVa5nRhsEGBg48fD6rSs7xps=
+github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
+github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
+github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
+github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+go.opentelemetry.io/auto/sdk v1.2.1 h1:jXsnJ4Lmnqd11kwkBV2LgLoFMZKizbCi5fNZ/ipaZ64=
+go.opentelemetry.io/auto/sdk v1.2.1/go.mod h1:KRTj+aOaElaLi+wW1kO/DZRXwkF4C5xPbEe3ZiIhN7Y=
+go.opentelemetry.io/otel v1.43.0 h1:mYIM03dnh5zfN7HautFE4ieIig9amkNANT+xcVxAj9I=
+go.opentelemetry.io/otel v1.43.0/go.mod h1:JuG+u74mvjvcm8vj8pI5XiHy1zDeoCS2LB1spIq7Ay0=
+go.opentelemetry.io/otel/metric v1.43.0 h1:d7638QeInOnuwOONPp4JAOGfbCEpYb+K6DVWvdxGzgM=
+go.opentelemetry.io/otel/metric v1.43.0/go.mod h1:RDnPtIxvqlgO8GRW18W6Z/4P462ldprJtfxHxyKd2PY=
+go.opentelemetry.io/otel/sdk v1.43.0 h1:pi5mE86i5rTeLXqoF/hhiBtUNcrAGHLKQdhg4h4V9Dg=
+go.opentelemetry.io/otel/sdk v1.43.0/go.mod h1:P+IkVU3iWukmiit/Yf9AWvpyRDlUeBaRg6Y+C58QHzg=
+go.opentelemetry.io/otel/sdk/metric v1.43.0 h1:S88dyqXjJkuBNLeMcVPRFXpRw2fuwdvfCGLEo89fDkw=
+go.opentelemetry.io/otel/sdk/metric v1.43.0/go.mod h1:C/RJtwSEJ5hzTiUz5pXF1kILHStzb9zFlIEe85bhj6A=
+go.opentelemetry.io/otel/trace v1.43.0 h1:BkNrHpup+4k4w+ZZ86CZoHHEkohws8AY+WTX09nk+3A=
+go.opentelemetry.io/otel/trace v1.43.0/go.mod h1:/QJhyVBUUswCphDVxq+8mld+AvhXZLhe+8WVFxiFff0=
+golang.org/x/net v0.53.0 h1:d+qAbo5L0orcWAr0a9JweQpjXF19LMXJE8Ey7hwOdUA=
+golang.org/x/net v0.53.0/go.mod h1:JvMuJH7rrdiCfbeHoo3fCQU24Lf5JJwT9W3sJFulfgs=
+golang.org/x/sys v0.43.0 h1:Rlag2XtaFTxp19wS8MXlJwTvoh8ArU6ezoyFsMyCTNI=
+golang.org/x/sys v0.43.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/text v0.36.0 h1:JfKh3XmcRPqZPKevfXVpI1wXPTqbkE5f7JA92a55Yxg=
+golang.org/x/text v0.36.0/go.mod h1:NIdBknypM8iqVmPiuco0Dh6P5Jcdk8lJL0CUebqK164=
+gonum.org/v1/gonum v0.17.0 h1:VbpOemQlsSMrYmn7T2OUvQ4dqxQXU+ouZFQsZOx50z4=
+gonum.org/v1/gonum v0.17.0/go.mod h1:El3tOrEuMpv2UdMrbNlKEh9vd86bmQ6vqIcDwxEOc1E=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20260414002931-afd174a4e478 h1:RmoJA1ujG+/lRGNfUnOMfhCy5EipVMyvUE+KNbPbTlw=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20260414002931-afd174a4e478/go.mod h1:4Hqkh8ycfw05ld/3BWL7rJOSfebL2Q+DVDeRgYgxUU8=
+google.golang.org/grpc v1.80.0 h1:Xr6m2WmWZLETvUNvIUmeD5OAagMw3FiKmMlTdViWsHM=
+google.golang.org/grpc v1.80.0/go.mod h1:ho/dLnxwi3EDJA4Zghp7k2Ec1+c2jqup0bFkw07bwF4=
+google.golang.org/grpc/examples v0.0.0-20260605180800-0f3086db7a75 h1:AEIy9rWQCaqGLD5thytE2ox41wjT4vOe43/yh2enp+A=
+google.golang.org/grpc/examples v0.0.0-20260605180800-0f3086db7a75/go.mod h1:Cj6Qdy58KTzw400M0aa1PA3rNLrhQgPFdqXxShtOXmM=
+google.golang.org/protobuf v1.36.11 h1:fV6ZwhNocDyBLK0dj+fg8ektcVegBBuEolpbTQyBNVE=
+google.golang.org/protobuf v1.36.11/go.mod h1:HTf+CrKn2C3g5S8VImy6tdcUvCska2kB7j23XfzDpco=

go.mod

@@ -0,0 +1,7 @@
+module github.com/soheilhy/cmux
+
+go 1.23.0
+
+require golang.org/x/net v0.42.0
+
+require golang.org/x/text v0.27.0 // indirect

go.sum

@@ -0,0 +1,4 @@
+golang.org/x/net v0.42.0 h1:jzkYrhi3YQWD6MLBJcsklgQsoAcw89EcZbJw8Z614hs=
+golang.org/x/net v0.42.0/go.mod h1:FF1RA5d3u7nAYA4z2TkclSCKh68eSXtiFwcWQpPXdt8=
+golang.org/x/text v0.27.0 h1:4fGWRpyh641NLlecmyl4LOe6yDdfaYNrGb2zdfo4JV4=
+golang.org/x/text v0.27.0/go.mod h1:1D28KMCvyooCX9hBiosv5Tz/+YLxj0j7XhWjpSUF7CU=

matchers.go

@@ -18,7 +18,6 @@ import (
 	"bufio"
 	"crypto/tls"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"strings"
 
@@ -67,7 +66,8 @@ func HTTP1Fast(extMethods ...string) Matcher {
 //
 // By default, any TLS handshake packet is matched. An optional whitelist
 // of versions can be passed in to restrict the matcher, for example:
-//  TLS(tls.VersionTLS11, tls.VersionTLS12)
+//
+//	TLS(tls.VersionTLS11, tls.VersionTLS12)
 func TLS(versions ...int) Matcher {
 	if len(versions) == 0 {
 		versions = []int{
@@ -148,7 +148,7 @@ func HTTP1HeaderFieldPrefix(name, valuePrefix string) Matcher {
 // headers frame.
 func HTTP2HeaderField(name, value string) Matcher {
 	return func(r io.Reader) bool {
-		return matchHTTP2Field(ioutil.Discard, r, name, func(gotValue string) bool {
+		return matchHTTP2Field(io.Discard, r, name, func(gotValue string) bool {
 			return gotValue == value
 		})
 	}
@@ -159,7 +159,7 @@ func HTTP2HeaderField(name, value string) Matcher {
 // valuePrefix, this will match.
 func HTTP2HeaderFieldPrefix(name, valuePrefix string) Matcher {
 	return func(r io.Reader) bool {
-		return matchHTTP2Field(ioutil.Discard, r, name, func(gotValue string) bool {
+		return matchHTTP2Field(io.Discard, r, name, func(gotValue string) bool {
 			return strings.HasPrefix(gotValue, valuePrefix)
 		})
 	}
@@ -240,6 +240,11 @@ func matchHTTP2Field(w io.Writer, r io.Reader, name string, matches func(string)
 
 		switch f := f.(type) {
 		case *http2.SettingsFrame:
+			// Sender acknoweldged the SETTINGS frame. No need to write
+			// SETTINGS again.
+			if f.IsAck() {
+				break
+			}
 			if err := framer.WriteSettings(); err != nil {
 				return false
 			}