th5/handshake_client_test.go

// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package tls

import (
	"bytes"
	"crypto/ecdsa"
	"crypto/rsa"
	"crypto/x509"
	"encoding/base64"
	"encoding/binary"
	"encoding/pem"
	"errors"
	"fmt"
	"io"
	"net"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"testing"
	"time"
)

// Note: see comment in handshake_test.go for details of how the reference
// tests work.

// blockingSource is an io.Reader that blocks a Read call until it's closed.
type blockingSource chan bool

func (b blockingSource) Read([]byte) (n int, err error) {
	<-b
	return 0, io.EOF
}

// clientTest represents a test of the TLS client handshake against a reference
// implementation.
type clientTest struct {
	// name is a freeform string identifying the test and the file in which
	// the expected results will be stored.
	name string
	// command, if not empty, contains a series of arguments for the
	// command to run for the reference server.
	command []string
	// config, if not nil, contains a custom Config to use for this test.
	config *Config
	// cert, if not empty, contains a DER-encoded certificate for the
	// reference server.
	cert []byte
	// key, if not nil, contains either a *rsa.PrivateKey or
	// *ecdsa.PrivateKey which is the private key for the reference server.
	key interface{}
	// extensions, if not nil, contains a list of extension data to be returned
	// from the ServerHello. The data should be in standard TLS format with
	// a 2-byte uint16 type, 2-byte data length, followed by the extension data.
	extensions [][]byte
	// validate, if not nil, is a function that will be called with the
	// ConnectionState of the resulting connection. It returns a non-nil
	// error if the ConnectionState is unacceptable.
	validate func(ConnectionState) error
}

var defaultServerCommand = []string{"openssl", "s_server"}

// connFromCommand starts the reference server process, connects to it and
// returns a recordingConn for the connection. The stdin return value is a
// blockingSource for the stdin of the child process. It must be closed before
// Waiting for child.
func (test *clientTest) connFromCommand() (conn *recordingConn, child *exec.Cmd, stdin blockingSource, err error) {
	cert := testRSACertificate
	if len(test.cert) > 0 {
		cert = test.cert
	}
	certPath := tempFile(string(cert))
	defer os.Remove(certPath)

	var key interface{} = testRSAPrivateKey
	if test.key != nil {
		key = test.key
	}
	var pemType string
	var derBytes []byte
	switch key := key.(type) {
	case *rsa.PrivateKey:
		pemType = "RSA"
		derBytes = x509.MarshalPKCS1PrivateKey(key)
	case *ecdsa.PrivateKey:
		pemType = "EC"
		var err error
		derBytes, err = x509.MarshalECPrivateKey(key)
		if err != nil {
			panic(err)
		}
	default:
		panic("unknown key type")
	}

	var pemOut bytes.Buffer
	pem.Encode(&pemOut, &pem.Block{Type: pemType + " PRIVATE KEY", Bytes: derBytes})

	keyPath := tempFile(string(pemOut.Bytes()))
	defer os.Remove(keyPath)

	var command []string
	if len(test.command) > 0 {
		command = append(command, test.command...)
	} else {
		command = append(command, defaultServerCommand...)
	}
	command = append(command, "-cert", certPath, "-certform", "DER", "-key", keyPath)
	// serverPort contains the port that OpenSSL will listen on. OpenSSL
	// can't take "0" as an argument here so we have to pick a number and
	// hope that it's not in use on the machine. Since this only occurs
	// when -update is given and thus when there's a human watching the
	// test, this isn't too bad.
	const serverPort = 24323
	command = append(command, "-accept", strconv.Itoa(serverPort))

	if len(test.extensions) > 0 {
		var serverInfo bytes.Buffer
		for _, ext := range test.extensions {
			pem.Encode(&serverInfo, &pem.Block{
				Type:  fmt.Sprintf("SERVERINFO FOR EXTENSION %d", binary.BigEndian.Uint16(ext)),
				Bytes: ext,
			})
		}
		serverInfoPath := tempFile(serverInfo.String())
		defer os.Remove(serverInfoPath)
		command = append(command, "-serverinfo", serverInfoPath)
	}

	cmd := exec.Command(command[0], command[1:]...)
	stdin = blockingSource(make(chan bool))
	cmd.Stdin = stdin
	var out bytes.Buffer
	cmd.Stdout = &out
	cmd.Stderr = &out
	if err := cmd.Start(); err != nil {
		return nil, nil, nil, err
	}

	// OpenSSL does print an "ACCEPT" banner, but it does so *before*
	// opening the listening socket, so we can't use that to wait until it
	// has started listening. Thus we are forced to poll until we get a
	// connection.
	var tcpConn net.Conn
	for i := uint(0); i < 5; i++ {
		tcpConn, err = net.DialTCP("tcp", nil, &net.TCPAddr{
			IP:   net.IPv4(127, 0, 0, 1),
			Port: serverPort,
		})
		if err == nil {
			break
		}
		time.Sleep((1 << i) * 5 * time.Millisecond)
	}
	if err != nil {
		close(stdin)
		out.WriteTo(os.Stdout)
		cmd.Process.Kill()
		return nil, nil, nil, cmd.Wait()
	}

	record := &recordingConn{
		Conn: tcpConn,
	}

	return record, cmd, stdin, nil
}

func (test *clientTest) dataPath() string {
	return filepath.Join("testdata", "Client-"+test.name)
}

func (test *clientTest) loadData() (flows [][]byte, err error) {
	in, err := os.Open(test.dataPath())
	if err != nil {
		return nil, err
	}
	defer in.Close()
	return parseTestData(in)
}

func (test *clientTest) run(t *testing.T, write bool) {
	var clientConn, serverConn net.Conn
	var recordingConn *recordingConn
	var childProcess *exec.Cmd
	var stdin blockingSource

	if write {
		var err error
		recordingConn, childProcess, stdin, err = test.connFromCommand()
		if err != nil {
			t.Fatalf("Failed to start subcommand: %s", err)
		}
		clientConn = recordingConn
	} else {
		clientConn, serverConn = net.Pipe()
	}

	config := test.config
	if config == nil {
		config = testConfig
	}
	client := Client(clientConn, config)

	doneChan := make(chan bool)
	go func() {
		if _, err := client.Write([]byte("hello\n")); err != nil {
			t.Errorf("Client.Write failed: %s", err)
		}
		if test.validate != nil {
			if err := test.validate(client.ConnectionState()); err != nil {
				t.Errorf("validate callback returned error: %s", err)
			}
		}
		client.Close()
		clientConn.Close()
		doneChan <- true
	}()

	if !write {
		flows, err := test.loadData()
		if err != nil {
			t.Fatalf("%s: failed to load data from %s: %v", test.name, test.dataPath(), err)
		}
		for i, b := range flows {
			if i%2 == 1 {
				serverConn.Write(b)
				continue
			}
			bb := make([]byte, len(b))
			_, err := io.ReadFull(serverConn, bb)
			if err != nil {
				t.Fatalf("%s #%d: %s", test.name, i, err)
			}
			if !bytes.Equal(b, bb) {
				t.Fatalf("%s #%d: mismatch on read: got:%x want:%x", test.name, i, bb, b)
			}
		}
		serverConn.Close()
	}

	<-doneChan

	if write {
		path := test.dataPath()
		out, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
		if err != nil {
			t.Fatalf("Failed to create output file: %s", err)
		}
		defer out.Close()
		recordingConn.Close()
		close(stdin)
		childProcess.Process.Kill()
		childProcess.Wait()
		if len(recordingConn.flows) < 3 {
			childProcess.Stdout.(*bytes.Buffer).WriteTo(os.Stdout)
			t.Fatalf("Client connection didn't work")
		}
		recordingConn.WriteTo(out)
		fmt.Printf("Wrote %s\n", path)
	}
}

func runClientTestForVersion(t *testing.T, template *clientTest, prefix, option string) {
	test := *template
	test.name = prefix + test.name
	if len(test.command) == 0 {
		test.command = defaultClientCommand
	}
	test.command = append([]string(nil), test.command...)
	test.command = append(test.command, option)
	test.run(t, *update)
}

func runClientTestTLS10(t *testing.T, template *clientTest) {
	runClientTestForVersion(t, template, "TLSv10-", "-tls1")
}

func runClientTestTLS11(t *testing.T, template *clientTest) {
	runClientTestForVersion(t, template, "TLSv11-", "-tls1_1")
}

func runClientTestTLS12(t *testing.T, template *clientTest) {
	runClientTestForVersion(t, template, "TLSv12-", "-tls1_2")
}

func TestHandshakeClientRSARC4(t *testing.T) {
	test := &clientTest{
		name:    "RSA-RC4",
		command: []string{"openssl", "s_server", "-cipher", "RC4-SHA"},
	}
	runClientTestTLS10(t, test)
	runClientTestTLS11(t, test)
	runClientTestTLS12(t, test)
}

func TestHandshakeClientRSAAES128GCM(t *testing.T) {
	test := &clientTest{
		name:    "AES128-GCM-SHA256",
		command: []string{"openssl", "s_server", "-cipher", "AES128-GCM-SHA256"},
	}
	runClientTestTLS12(t, test)
}

func TestHandshakeClientRSAAES256GCM(t *testing.T) {
	test := &clientTest{
		name:    "AES256-GCM-SHA384",
		command: []string{"openssl", "s_server", "-cipher", "AES256-GCM-SHA384"},
	}
	runClientTestTLS12(t, test)
}

func TestHandshakeClientECDHERSAAES(t *testing.T) {
	test := &clientTest{
		name:    "ECDHE-RSA-AES",
		command: []string{"openssl", "s_server", "-cipher", "ECDHE-RSA-AES128-SHA"},
	}
	runClientTestTLS10(t, test)
	runClientTestTLS11(t, test)
	runClientTestTLS12(t, test)
}

func TestHandshakeClientECDHEECDSAAES(t *testing.T) {
	test := &clientTest{
		name:    "ECDHE-ECDSA-AES",
		command: []string{"openssl", "s_server", "-cipher", "ECDHE-ECDSA-AES128-SHA"},
		cert:    testECDSACertificate,
		key:     testECDSAPrivateKey,
	}
	runClientTestTLS10(t, test)
	runClientTestTLS11(t, test)
	runClientTestTLS12(t, test)
}

func TestHandshakeClientECDHEECDSAAESGCM(t *testing.T) {
	test := &clientTest{
		name:    "ECDHE-ECDSA-AES-GCM",
		command: []string{"openssl", "s_server", "-cipher", "ECDHE-ECDSA-AES128-GCM-SHA256"},
		cert:    testECDSACertificate,
		key:     testECDSAPrivateKey,
	}
	runClientTestTLS12(t, test)
}

func TestHandshakeClientAES256GCMSHA384(t *testing.T) {
	test := &clientTest{
		name:    "ECDHE-ECDSA-AES256-GCM-SHA384",
		command: []string{"openssl", "s_server", "-cipher", "ECDHE-ECDSA-AES256-GCM-SHA384"},
		cert:    testECDSACertificate,
		key:     testECDSAPrivateKey,
	}
	runClientTestTLS12(t, test)
}

func TestHandshakeClientCertRSA(t *testing.T) {
	config := *testConfig
	cert, _ := X509KeyPair([]byte(clientCertificatePEM), []byte(clientKeyPEM))
	config.Certificates = []Certificate{cert}

	test := &clientTest{
		name:    "ClientCert-RSA-RSA",
		command: []string{"openssl", "s_server", "-cipher", "RC4-SHA", "-verify", "1"},
		config:  &config,
	}

	runClientTestTLS10(t, test)
	runClientTestTLS12(t, test)

	test = &clientTest{
		name:    "ClientCert-RSA-ECDSA",
		command: []string{"openssl", "s_server", "-cipher", "ECDHE-ECDSA-AES128-SHA", "-verify", "1"},
		config:  &config,
		cert:    testECDSACertificate,
		key:     testECDSAPrivateKey,
	}

	runClientTestTLS10(t, test)
	runClientTestTLS12(t, test)

	test = &clientTest{
		name:    "ClientCert-RSA-AES256-GCM-SHA384",
		command: []string{"openssl", "s_server", "-cipher", "ECDHE-RSA-AES256-GCM-SHA384", "-verify", "1"},
		config:  &config,
		cert:    testRSACertificate,
		key:     testRSAPrivateKey,
	}

	runClientTestTLS12(t, test)
}

func TestHandshakeClientCertECDSA(t *testing.T) {
	config := *testConfig
	cert, _ := X509KeyPair([]byte(clientECDSACertificatePEM), []byte(clientECDSAKeyPEM))
	config.Certificates = []Certificate{cert}

	test := &clientTest{
		name:    "ClientCert-ECDSA-RSA",
		command: []string{"openssl", "s_server", "-cipher", "RC4-SHA", "-verify", "1"},
		config:  &config,
	}

	runClientTestTLS10(t, test)
	runClientTestTLS12(t, test)

	test = &clientTest{
		name:    "ClientCert-ECDSA-ECDSA",
		command: []string{"openssl", "s_server", "-cipher", "ECDHE-ECDSA-AES128-SHA", "-verify", "1"},
		config:  &config,
		cert:    testECDSACertificate,
		key:     testECDSAPrivateKey,
	}

	runClientTestTLS10(t, test)
	runClientTestTLS12(t, test)
}

func TestClientResumption(t *testing.T) {
	serverConfig := &Config{
		CipherSuites: []uint16{TLS_RSA_WITH_RC4_128_SHA, TLS_ECDHE_RSA_WITH_RC4_128_SHA},
		Certificates: testConfig.Certificates,
	}

	issuer, err := x509.ParseCertificate(testRSACertificateIssuer)
	if err != nil {
		panic(err)
	}

	rootCAs := x509.NewCertPool()
	rootCAs.AddCert(issuer)

	clientConfig := &Config{
		CipherSuites:       []uint16{TLS_RSA_WITH_RC4_128_SHA},
		ClientSessionCache: NewLRUClientSessionCache(32),
		RootCAs:            rootCAs,
		ServerName:         "example.golang",
	}

	testResumeState := func(test string, didResume bool) {
		_, hs, err := testHandshake(clientConfig, serverConfig)
		if err != nil {
			t.Fatalf("%s: handshake failed: %s", test, err)
		}
		if hs.DidResume != didResume {
			t.Fatalf("%s resumed: %v, expected: %v", test, hs.DidResume, didResume)
		}
		if didResume && (hs.PeerCertificates == nil || hs.VerifiedChains == nil) {
			t.Fatalf("expected non-nil certificates after resumption. Got peerCertificates: %#v, verifiedCertificates: %#v", hs.PeerCertificates, hs.VerifiedChains)
		}
	}

	getTicket := func() []byte {
		return clientConfig.ClientSessionCache.(*lruSessionCache).q.Front().Value.(*lruSessionCacheEntry).state.sessionTicket
	}
	randomKey := func() [32]byte {
		var k [32]byte
		if _, err := io.ReadFull(serverConfig.rand(), k[:]); err != nil {
			t.Fatalf("Failed to read new SessionTicketKey: %s", err)
		}
		return k
	}

	testResumeState("Handshake", false)
	ticket := getTicket()
	testResumeState("Resume", true)
	if !bytes.Equal(ticket, getTicket()) {
		t.Fatal("first ticket doesn't match ticket after resumption")
	}

	key2 := randomKey()
	serverConfig.SetSessionTicketKeys([][32]byte{key2})

	testResumeState("InvalidSessionTicketKey", false)
	testResumeState("ResumeAfterInvalidSessionTicketKey", true)

	serverConfig.SetSessionTicketKeys([][32]byte{randomKey(), key2})
	ticket = getTicket()
	testResumeState("KeyChange", true)
	if bytes.Equal(ticket, getTicket()) {
		t.Fatal("new ticket wasn't included while resuming")
	}
	testResumeState("KeyChangeFinish", true)

	clientConfig.CipherSuites = []uint16{TLS_ECDHE_RSA_WITH_RC4_128_SHA}
	testResumeState("DifferentCipherSuite", false)
	testResumeState("DifferentCipherSuiteRecovers", true)

	clientConfig.ClientSessionCache = nil
	testResumeState("WithoutSessionCache", false)
}

func TestLRUClientSessionCache(t *testing.T) {
	// Initialize cache of capacity 4.
	cache := NewLRUClientSessionCache(4)
	cs := make([]ClientSessionState, 6)
	keys := []string{"0", "1", "2", "3", "4", "5", "6"}

	// Add 4 entries to the cache and look them up.
	for i := 0; i < 4; i++ {
		cache.Put(keys[i], &cs[i])
	}
	for i := 0; i < 4; i++ {
		if s, ok := cache.Get(keys[i]); !ok || s != &cs[i] {
			t.Fatalf("session cache failed lookup for added key: %s", keys[i])
		}
	}

	// Add 2 more entries to the cache. First 2 should be evicted.
	for i := 4; i < 6; i++ {
		cache.Put(keys[i], &cs[i])
	}
	for i := 0; i < 2; i++ {
		if s, ok := cache.Get(keys[i]); ok || s != nil {
			t.Fatalf("session cache should have evicted key: %s", keys[i])
		}
	}

	// Touch entry 2. LRU should evict 3 next.
	cache.Get(keys[2])
	cache.Put(keys[0], &cs[0])
	if s, ok := cache.Get(keys[3]); ok || s != nil {
		t.Fatalf("session cache should have evicted key 3")
	}

	// Update entry 0 in place.
	cache.Put(keys[0], &cs[3])
	if s, ok := cache.Get(keys[0]); !ok || s != &cs[3] {
		t.Fatalf("session cache failed update for key 0")
	}

	// Adding a nil entry is valid.
	cache.Put(keys[0], nil)
	if s, ok := cache.Get(keys[0]); !ok || s != nil {
		t.Fatalf("failed to add nil entry to cache")
	}
}

func TestHandshakeClientALPNMatch(t *testing.T) {
	config := *testConfig
	config.NextProtos = []string{"proto2", "proto1"}

	test := &clientTest{
		name: "ALPN",
		// Note that this needs OpenSSL 1.0.2 because that is the first
		// version that supports the -alpn flag.
		command: []string{"openssl", "s_server", "-alpn", "proto1,proto2"},
		config:  &config,
		validate: func(state ConnectionState) error {
			// The server's preferences should override the client.
			if state.NegotiatedProtocol != "proto1" {
				return fmt.Errorf("Got protocol %q, wanted proto1", state.NegotiatedProtocol)
			}
			return nil
		},
	}
	runClientTestTLS12(t, test)
}

func TestHandshakeClientALPNNoMatch(t *testing.T) {
	config := *testConfig
	config.NextProtos = []string{"proto3"}

	test := &clientTest{
		name: "ALPN-NoMatch",
		// Note that this needs OpenSSL 1.0.2 because that is the first
		// version that supports the -alpn flag.
		command: []string{"openssl", "s_server", "-alpn", "proto1,proto2"},
		config:  &config,
		validate: func(state ConnectionState) error {
			// There's no overlap so OpenSSL will not select a protocol.
			if state.NegotiatedProtocol != "" {
				return fmt.Errorf("Got protocol %q, wanted ''", state.NegotiatedProtocol)
			}
			return nil
		},
	}
	runClientTestTLS12(t, test)
}

// sctsBase64 contains data from `openssl s_client -serverinfo 18 -connect ritter.vg:443`
const sctsBase64 = "ABIBaQFnAHUApLkJkLQYWBSHuxOizGdwCjw1mAT5G9+443fNDsgN3BAAAAFHl5nuFgAABAMARjBEAiAcS4JdlW5nW9sElUv2zvQyPoZ6ejKrGGB03gjaBZFMLwIgc1Qbbn+hsH0RvObzhS+XZhr3iuQQJY8S9G85D9KeGPAAdgBo9pj4H2SCvjqM7rkoHUz8cVFdZ5PURNEKZ6y7T0/7xAAAAUeX4bVwAAAEAwBHMEUCIDIhFDgG2HIuADBkGuLobU5a4dlCHoJLliWJ1SYT05z6AiEAjxIoZFFPRNWMGGIjskOTMwXzQ1Wh2e7NxXE1kd1J0QsAdgDuS723dc5guuFCaR+r4Z5mow9+X7By2IMAxHuJeqj9ywAAAUhcZIqHAAAEAwBHMEUCICmJ1rBT09LpkbzxtUC+Hi7nXLR0J+2PmwLp+sJMuqK+AiEAr0NkUnEVKVhAkccIFpYDqHOlZaBsuEhWWrYpg2RtKp0="

func TestHandshakClientSCTs(t *testing.T) {
	config := *testConfig

	scts, err := base64.StdEncoding.DecodeString(sctsBase64)
	if err != nil {
		t.Fatal(err)
	}

	test := &clientTest{
		name: "SCT",
		// Note that this needs OpenSSL 1.0.2 because that is the first
		// version that supports the -serverinfo flag.
		command:    []string{"openssl", "s_server"},
		config:     &config,
		extensions: [][]byte{scts},
		validate: func(state ConnectionState) error {
			expectedSCTs := [][]byte{
				scts[8:125],
				scts[127:245],
				scts[247:],
			}
			if n := len(state.SignedCertificateTimestamps); n != len(expectedSCTs) {
				return fmt.Errorf("Got %d scts, wanted %d", n, len(expectedSCTs))
			}
			for i, expected := range expectedSCTs {
				if sct := state.SignedCertificateTimestamps[i]; !bytes.Equal(sct, expected) {
					return fmt.Errorf("SCT #%d contained %x, expected %x", i, sct, expected)
				}
			}
			return nil
		},
	}
	runClientTestTLS12(t, test)
}

var hostnameInSNITests = []struct {
	in, out string
}{
	// Opaque string
	{"", ""},
	{"localhost", "localhost"},
	{"foo, bar, baz and qux", "foo, bar, baz and qux"},

	// DNS hostname
	{"golang.org", "golang.org"},
	{"golang.org.", "golang.org"},

	// Literal IPv4 address
	{"1.2.3.4", ""},

	// Literal IPv6 address
	{"::1", ""},
	{"::1%lo0", ""}, // with zone identifier
	{"[::1]", ""},   // as per RFC 5952 we allow the [] style as IPv6 literal
	{"[::1%lo0]", ""},
}

func TestHostnameInSNI(t *testing.T) {
	for _, tt := range hostnameInSNITests {
		c, s := net.Pipe()

		go func(host string) {
			Client(c, &Config{ServerName: host, InsecureSkipVerify: true}).Handshake()
		}(tt.in)

		var header [5]byte
		if _, err := io.ReadFull(s, header[:]); err != nil {
			t.Fatal(err)
		}
		recordLen := int(header[3])<<8 | int(header[4])

		record := make([]byte, recordLen)
		if _, err := io.ReadFull(s, record[:]); err != nil {
			t.Fatal(err)
		}

		c.Close()
		s.Close()

		var m clientHelloMsg
		if !m.unmarshal(record) {
			t.Errorf("unmarshaling ClientHello for %q failed", tt.in)
			continue
		}
		if tt.in != tt.out && m.serverName == tt.in {
			t.Errorf("prohibited %q found in ClientHello: %x", tt.in, record)
		}
		if m.serverName != tt.out {
			t.Errorf("expected %q not found in ClientHello: %x", tt.out, record)
		}
	}
}

func TestServerSelectingUnconfiguredCipherSuite(t *testing.T) {
	// This checks that the server can't select a cipher suite that the
	// client didn't offer. See #13174.

	c, s := net.Pipe()
	errChan := make(chan error, 1)

	go func() {
		client := Client(c, &Config{
			ServerName:   "foo",
			CipherSuites: []uint16{TLS_RSA_WITH_AES_128_GCM_SHA256},
		})
		errChan <- client.Handshake()
	}()

	var header [5]byte
	if _, err := io.ReadFull(s, header[:]); err != nil {
		t.Fatal(err)
	}
	recordLen := int(header[3])<<8 | int(header[4])

	record := make([]byte, recordLen)
	if _, err := io.ReadFull(s, record); err != nil {
		t.Fatal(err)
	}

	// Create a ServerHello that selects a different cipher suite than the
	// sole one that the client offered.
	serverHello := &serverHelloMsg{
		vers:        VersionTLS12,
		random:      make([]byte, 32),
		cipherSuite: TLS_RSA_WITH_AES_256_GCM_SHA384,
	}
	serverHelloBytes := serverHello.marshal()

	s.Write([]byte{
		byte(recordTypeHandshake),
		byte(VersionTLS12 >> 8),
		byte(VersionTLS12 & 0xff),
		byte(len(serverHelloBytes) >> 8),
		byte(len(serverHelloBytes)),
	})
	s.Write(serverHelloBytes)
	s.Close()

	if err := <-errChan; !strings.Contains(err.Error(), "unconfigured cipher") {
		t.Fatalf("Expected error about unconfigured cipher suite but got %q", err)
	}
}

// brokenConn wraps a net.Conn and causes all Writes after a certain number to
// fail with brokenConnErr.
type brokenConn struct {
	net.Conn

	// breakAfter is the number of successful writes that will be allowed
	// before all subsequent writes fail.
	breakAfter int

	// numWrites is the number of writes that have been done.
	numWrites int
}

// brokenConnErr is the error that brokenConn returns once exhausted.
var brokenConnErr = errors.New("too many writes to brokenConn")

func (b *brokenConn) Write(data []byte) (int, error) {
	if b.numWrites >= b.breakAfter {
		return 0, brokenConnErr
	}

	b.numWrites++
	return b.Conn.Write(data)
}

func TestFailedWrite(t *testing.T) {
	// Test that a write error during the handshake is returned.
	for _, breakAfter := range []int{0, 1, 2, 3} {
		c, s := net.Pipe()
		done := make(chan bool)

		go func() {
			Server(s, testConfig).Handshake()
			s.Close()
			done <- true
		}()

		brokenC := &brokenConn{Conn: c, breakAfter: breakAfter}
		err := Client(brokenC, testConfig).Handshake()
		if err != brokenConnErr {
			t.Errorf("#%d: expected error from brokenConn but got %q", breakAfter, err)
		}
		brokenC.Close()

		<-done
	}
}