ssh/session_test.go - crypto.git - Git at Google

 // Copyright 2011 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 ssh

 // Session tests.

 import (
 	"bytes"
 	crypto_rand "crypto/rand"
 	"errors"
 	"io"
 	"math/rand"
 	"net"
 	"testing"

 	"golang.org/x/crypto/ssh/terminal"
 )

 type serverType func(Channel, <-chan *Request, *testing.T)

 // dial constructs a new test server and returns a *ClientConn.
 func dial(handler serverType, t *testing.T) *Client {
 	c1, c2, err := netPipe()
 	if err != nil {
 		t.Fatalf("netPipe: %v", err)
 	}

 	go func() {
 		defer c1.Close()
 		conf := ServerConfig{
 			NoClientAuth: true,
 		}
 		conf.AddHostKey(testSigners["rsa"])

 		conn, chans, reqs, err := NewServerConn(c1, &conf)
 		if err != nil {
 			t.Errorf("Unable to handshake: %v", err)
 			return
 		}
 		go DiscardRequests(reqs)

 		for newCh := range chans {
 			if newCh.ChannelType() != "session" {
 				newCh.Reject(UnknownChannelType, "unknown channel type")
 				continue
 			}

 			ch, inReqs, err := newCh.Accept()
 			if err != nil {
 				t.Errorf("Accept: %v", err)
 				continue
 			}
 			go func() {
 				handler(ch, inReqs, t)
 			}()
 		}
 		if err := conn.Wait(); err != io.EOF {
 			t.Logf("server exit reason: %v", err)
 		}
 	}()

 	config := &ClientConfig{
 		User:            "testuser",
 		HostKeyCallback: InsecureIgnoreHostKey(),
 	}

 	conn, chans, reqs, err := NewClientConn(c2, "", config)
 	if err != nil {
 		t.Fatalf("unable to dial remote side: %v", err)
 	}

 	return NewClient(conn, chans, reqs)
 }

 // Test a simple string is returned to session.Stdout.
 func TestSessionShell(t *testing.T) {
 	conn := dial(shellHandler, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatalf("Unable to request new session: %v", err)
 	}
 	defer session.Close()
 	stdout := new(bytes.Buffer)
 	session.Stdout = stdout
 	if err := session.Shell(); err != nil {
 		t.Fatalf("Unable to execute command: %s", err)
 	}
 	if err := session.Wait(); err != nil {
 		t.Fatalf("Remote command did not exit cleanly: %v", err)
 	}
 	actual := stdout.String()
 	if actual != "golang" {
 		t.Fatalf("Remote shell did not return expected string: expected=golang, actual=%s", actual)
 	}
 }

 // TODO(dfc) add support for Std{in,err}Pipe when the Server supports it.

 // Test a simple string is returned via StdoutPipe.
 func TestSessionStdoutPipe(t *testing.T) {
 	conn := dial(shellHandler, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatalf("Unable to request new session: %v", err)
 	}
 	defer session.Close()
 	stdout, err := session.StdoutPipe()
 	if err != nil {
 		t.Fatalf("Unable to request StdoutPipe(): %v", err)
 	}
 	var buf bytes.Buffer
 	if err := session.Shell(); err != nil {
 		t.Fatalf("Unable to execute command: %v", err)
 	}
 	done := make(chan bool, 1)
 	go func() {
 		if _, err := io.Copy(&buf, stdout); err != nil {
 			t.Errorf("Copy of stdout failed: %v", err)
 		}
 		done <- true
 	}()
 	if err := session.Wait(); err != nil {
 		t.Fatalf("Remote command did not exit cleanly: %v", err)
 	}
 	<-done
 	actual := buf.String()
 	if actual != "golang" {
 		t.Fatalf("Remote shell did not return expected string: expected=golang, actual=%s", actual)
 	}
 }

 // Test that a simple string is returned via the Output helper,
 // and that stderr is discarded.
 func TestSessionOutput(t *testing.T) {
 	conn := dial(fixedOutputHandler, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatalf("Unable to request new session: %v", err)
 	}
 	defer session.Close()

 	buf, err := session.Output("") // cmd is ignored by fixedOutputHandler
 	if err != nil {
 		t.Error("Remote command did not exit cleanly:", err)
 	}
 	w := "this-is-stdout."
 	g := string(buf)
 	if g != w {
 		t.Error("Remote command did not return expected string:")
 		t.Logf("want %q", w)
 		t.Logf("got  %q", g)
 	}
 }

 // Test that both stdout and stderr are returned
 // via the CombinedOutput helper.
 func TestSessionCombinedOutput(t *testing.T) {
 	conn := dial(fixedOutputHandler, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatalf("Unable to request new session: %v", err)
 	}
 	defer session.Close()

 	buf, err := session.CombinedOutput("") // cmd is ignored by fixedOutputHandler
 	if err != nil {
 		t.Error("Remote command did not exit cleanly:", err)
 	}
 	const stdout = "this-is-stdout."
 	const stderr = "this-is-stderr."
 	g := string(buf)
 	if g != stdout+stderr && g != stderr+stdout {
 		t.Error("Remote command did not return expected string:")
 		t.Logf("want %q, or %q", stdout+stderr, stderr+stdout)
 		t.Logf("got  %q", g)
 	}
 }

 // Test non-0 exit status is returned correctly.
 func TestExitStatusNonZero(t *testing.T) {
 	conn := dial(exitStatusNonZeroHandler, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatalf("Unable to request new session: %v", err)
 	}
 	defer session.Close()
 	if err := session.Shell(); err != nil {
 		t.Fatalf("Unable to execute command: %v", err)
 	}
 	err = session.Wait()
 	if err == nil {
 		t.Fatalf("expected command to fail but it didn't")
 	}
 	e, ok := err.(*ExitError)
 	if !ok {
 		t.Fatalf("expected *ExitError but got %T", err)
 	}
 	if e.ExitStatus() != 15 {
 		t.Fatalf("expected command to exit with 15 but got %v", e.ExitStatus())
 	}
 }

 // Test 0 exit status is returned correctly.
 func TestExitStatusZero(t *testing.T) {
 	conn := dial(exitStatusZeroHandler, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatalf("Unable to request new session: %v", err)
 	}
 	defer session.Close()

 	if err := session.Shell(); err != nil {
 		t.Fatalf("Unable to execute command: %v", err)
 	}
 	err = session.Wait()
 	if err != nil {
 		t.Fatalf("expected nil but got %v", err)
 	}
 }

 // Test exit signal and status are both returned correctly.
 func TestExitSignalAndStatus(t *testing.T) {
 	conn := dial(exitSignalAndStatusHandler, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatalf("Unable to request new session: %v", err)
 	}
 	defer session.Close()
 	if err := session.Shell(); err != nil {
 		t.Fatalf("Unable to execute command: %v", err)
 	}
 	err = session.Wait()
 	if err == nil {
 		t.Fatalf("expected command to fail but it didn't")
 	}
 	e, ok := err.(*ExitError)
 	if !ok {
 		t.Fatalf("expected *ExitError but got %T", err)
 	}
 	if e.Signal() != "TERM" || e.ExitStatus() != 15 {
 		t.Fatalf("expected command to exit with signal TERM and status 15 but got signal %s and status %v", e.Signal(), e.ExitStatus())
 	}
 }

 // Test exit signal and status are both returned correctly.
 func TestKnownExitSignalOnly(t *testing.T) {
 	conn := dial(exitSignalHandler, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatalf("Unable to request new session: %v", err)
 	}
 	defer session.Close()
 	if err := session.Shell(); err != nil {
 		t.Fatalf("Unable to execute command: %v", err)
 	}
 	err = session.Wait()
 	if err == nil {
 		t.Fatalf("expected command to fail but it didn't")
 	}
 	e, ok := err.(*ExitError)
 	if !ok {
 		t.Fatalf("expected *ExitError but got %T", err)
 	}
 	if e.Signal() != "TERM" || e.ExitStatus() != 143 {
 		t.Fatalf("expected command to exit with signal TERM and status 143 but got signal %s and status %v", e.Signal(), e.ExitStatus())
 	}
 }

 // Test exit signal and status are both returned correctly.
 func TestUnknownExitSignal(t *testing.T) {
 	conn := dial(exitSignalUnknownHandler, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatalf("Unable to request new session: %v", err)
 	}
 	defer session.Close()
 	if err := session.Shell(); err != nil {
 		t.Fatalf("Unable to execute command: %v", err)
 	}
 	err = session.Wait()
 	if err == nil {
 		t.Fatalf("expected command to fail but it didn't")
 	}
 	e, ok := err.(*ExitError)
 	if !ok {
 		t.Fatalf("expected *ExitError but got %T", err)
 	}
 	if e.Signal() != "SYS" || e.ExitStatus() != 128 {
 		t.Fatalf("expected command to exit with signal SYS and status 128 but got signal %s and status %v", e.Signal(), e.ExitStatus())
 	}
 }

 func TestExitWithoutStatusOrSignal(t *testing.T) {
 	conn := dial(exitWithoutSignalOrStatus, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatalf("Unable to request new session: %v", err)
 	}
 	defer session.Close()
 	if err := session.Shell(); err != nil {
 		t.Fatalf("Unable to execute command: %v", err)
 	}
 	err = session.Wait()
 	if err == nil {
 		t.Fatalf("expected command to fail but it didn't")
 	}
 	if _, ok := err.(*ExitMissingError); !ok {
 		t.Fatalf("got %T want *ExitMissingError", err)
 	}
 }

 // windowTestBytes is the number of bytes that we'll send to the SSH server.
 const windowTestBytes = 16000 * 200

 // TestServerWindow writes random data to the server. The server is expected to echo
 // the same data back, which is compared against the original.
 func TestServerWindow(t *testing.T) {
 	origBuf := bytes.NewBuffer(make([]byte, 0, windowTestBytes))
 	io.CopyN(origBuf, crypto_rand.Reader, windowTestBytes)
 	origBytes := origBuf.Bytes()

 	conn := dial(echoHandler, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer session.Close()
 	result := make(chan []byte)

 	go func() {
 		defer close(result)
 		echoedBuf := bytes.NewBuffer(make([]byte, 0, windowTestBytes))
 		serverStdout, err := session.StdoutPipe()
 		if err != nil {
 			t.Errorf("StdoutPipe failed: %v", err)
 			return
 		}
 		n, err := copyNRandomly("stdout", echoedBuf, serverStdout, windowTestBytes)
 		if err != nil && err != io.EOF {
 			t.Errorf("Read only %d bytes from server, expected %d: %v", n, windowTestBytes, err)
 		}
 		result <- echoedBuf.Bytes()
 	}()

 	serverStdin, err := session.StdinPipe()
 	if err != nil {
 		t.Fatalf("StdinPipe failed: %v", err)
 	}
 	written, err := copyNRandomly("stdin", serverStdin, origBuf, windowTestBytes)
 	if err != nil {
 		t.Errorf("failed to copy origBuf to serverStdin: %v", err)
 	} else if written != windowTestBytes {
 		t.Errorf("Wrote only %d of %d bytes to server", written, windowTestBytes)
 	}

 	echoedBytes := <-result

 	if !bytes.Equal(origBytes, echoedBytes) {
 		t.Fatalf("Echoed buffer differed from original, orig %d, echoed %d", len(origBytes), len(echoedBytes))
 	}
 }

 // Verify the client can handle a keepalive packet from the server.
 func TestClientHandlesKeepalives(t *testing.T) {
 	conn := dial(channelKeepaliveSender, t)
 	defer conn.Close()
 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer session.Close()
 	if err := session.Shell(); err != nil {
 		t.Fatalf("Unable to execute command: %v", err)
 	}
 	err = session.Wait()
 	if err != nil {
 		t.Fatalf("expected nil but got: %v", err)
 	}
 }

 type exitStatusMsg struct {
 	Status uint32
 }

 type exitSignalMsg struct {
 	Signal     string
 	CoreDumped bool
 	Errmsg     string
 	Lang       string
 }

 func handleTerminalRequests(in <-chan *Request) {
 	for req := range in {
 		ok := false
 		switch req.Type {
 		case "shell":
 			ok = true
 			if len(req.Payload) > 0 {
 				// We don't accept any commands, only the default shell.
 				ok = false
 			}
 		case "env":
 			ok = true
 		}
 		req.Reply(ok, nil)
 	}
 }

 func newServerShell(ch Channel, in <-chan *Request, prompt string) *terminal.Terminal {
 	term := terminal.NewTerminal(ch, prompt)
 	go handleTerminalRequests(in)
 	return term
 }

 func exitStatusZeroHandler(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	// this string is returned to stdout
 	shell := newServerShell(ch, in, "> ")
 	readLine(shell, t)
 	sendStatus(0, ch, t)
 }

 func exitStatusNonZeroHandler(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	shell := newServerShell(ch, in, "> ")
 	readLine(shell, t)
 	sendStatus(15, ch, t)
 }

 func exitSignalAndStatusHandler(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	shell := newServerShell(ch, in, "> ")
 	readLine(shell, t)
 	sendStatus(15, ch, t)
 	sendSignal("TERM", ch, t)
 }

 func exitSignalHandler(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	shell := newServerShell(ch, in, "> ")
 	readLine(shell, t)
 	sendSignal("TERM", ch, t)
 }

 func exitSignalUnknownHandler(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	shell := newServerShell(ch, in, "> ")
 	readLine(shell, t)
 	sendSignal("SYS", ch, t)
 }

 func exitWithoutSignalOrStatus(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	shell := newServerShell(ch, in, "> ")
 	readLine(shell, t)
 }

 func shellHandler(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	// this string is returned to stdout
 	shell := newServerShell(ch, in, "golang")
 	readLine(shell, t)
 	sendStatus(0, ch, t)
 }

 // Ignores the command, writes fixed strings to stderr and stdout.
 // Strings are "this-is-stdout." and "this-is-stderr.".
 func fixedOutputHandler(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	_, err := ch.Read(nil)

 	req, ok := <-in
 	if !ok {
 		t.Fatalf("error: expected channel request, got: %#v", err)
 		return
 	}

 	// ignore request, always send some text
 	req.Reply(true, nil)

 	_, err = io.WriteString(ch, "this-is-stdout.")
 	if err != nil {
 		t.Fatalf("error writing on server: %v", err)
 	}
 	_, err = io.WriteString(ch.Stderr(), "this-is-stderr.")
 	if err != nil {
 		t.Fatalf("error writing on server: %v", err)
 	}
 	sendStatus(0, ch, t)
 }

 func readLine(shell *terminal.Terminal, t *testing.T) {
 	if _, err := shell.ReadLine(); err != nil && err != io.EOF {
 		t.Errorf("unable to read line: %v", err)
 	}
 }

 func sendStatus(status uint32, ch Channel, t *testing.T) {
 	msg := exitStatusMsg{
 		Status: status,
 	}
 	if _, err := ch.SendRequest("exit-status", false, Marshal(&msg)); err != nil {
 		t.Errorf("unable to send status: %v", err)
 	}
 }

 func sendSignal(signal string, ch Channel, t *testing.T) {
 	sig := exitSignalMsg{
 		Signal:     signal,
 		CoreDumped: false,
 		Errmsg:     "Process terminated",
 		Lang:       "en-GB-oed",
 	}
 	if _, err := ch.SendRequest("exit-signal", false, Marshal(&sig)); err != nil {
 		t.Errorf("unable to send signal: %v", err)
 	}
 }

 func discardHandler(ch Channel, t *testing.T) {
 	defer ch.Close()
 	io.Copy(io.Discard, ch)
 }

 func echoHandler(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	if n, err := copyNRandomly("echohandler", ch, ch, windowTestBytes); err != nil {
 		t.Errorf("short write, wrote %d, expected %d: %v ", n, windowTestBytes, err)
 	}
 }

 // copyNRandomly copies n bytes from src to dst. It uses a variable, and random,
 // buffer size to exercise more code paths.
 func copyNRandomly(title string, dst io.Writer, src io.Reader, n int) (int, error) {
 	var (
 		buf       = make([]byte, 32*1024)
 		written   int
 		remaining = n
 	)
 	for remaining > 0 {
 		l := rand.Intn(1 << 15)
 		if remaining < l {
 			l = remaining
 		}
 		nr, er := src.Read(buf[:l])
 		nw, ew := dst.Write(buf[:nr])
 		remaining -= nw
 		written += nw
 		if ew != nil {
 			return written, ew
 		}
 		if nr != nw {
 			return written, io.ErrShortWrite
 		}
 		if er != nil && er != io.EOF {
 			return written, er
 		}
 	}
 	return written, nil
 }

 func channelKeepaliveSender(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	shell := newServerShell(ch, in, "> ")
 	readLine(shell, t)
 	if _, err := ch.SendRequest("keepalive@openssh.com", true, nil); err != nil {
 		t.Errorf("unable to send channel keepalive request: %v", err)
 	}
 	sendStatus(0, ch, t)
 }

 func TestClientWriteEOF(t *testing.T) {
 	conn := dial(simpleEchoHandler, t)
 	defer conn.Close()

 	session, err := conn.NewSession()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer session.Close()
 	stdin, err := session.StdinPipe()
 	if err != nil {
 		t.Fatalf("StdinPipe failed: %v", err)
 	}
 	stdout, err := session.StdoutPipe()
 	if err != nil {
 		t.Fatalf("StdoutPipe failed: %v", err)
 	}

 	data := []byte(`0000`)
 	_, err = stdin.Write(data)
 	if err != nil {
 		t.Fatalf("Write failed: %v", err)
 	}
 	stdin.Close()

 	res, err := io.ReadAll(stdout)
 	if err != nil {
 		t.Fatalf("Read failed: %v", err)
 	}

 	if !bytes.Equal(data, res) {
 		t.Fatalf("Read differed from write, wrote: %v, read: %v", data, res)
 	}
 }

 func simpleEchoHandler(ch Channel, in <-chan *Request, t *testing.T) {
 	defer ch.Close()
 	data, err := io.ReadAll(ch)
 	if err != nil {
 		t.Errorf("handler read error: %v", err)
 	}
 	_, err = ch.Write(data)
 	if err != nil {
 		t.Errorf("handler write error: %v", err)
 	}
 }

 func TestSessionID(t *testing.T) {
 	c1, c2, err := netPipe()
 	if err != nil {
 		t.Fatalf("netPipe: %v", err)
 	}
 	defer c1.Close()
 	defer c2.Close()

 	serverID := make(chan []byte, 1)
 	clientID := make(chan []byte, 1)

 	serverConf := &ServerConfig{
 		NoClientAuth: true,
 	}
 	serverConf.AddHostKey(testSigners["ecdsa"])
 	clientConf := &ClientConfig{
 		HostKeyCallback: InsecureIgnoreHostKey(),
 		User:            "user",
 	}

 	srvErrCh := make(chan error, 1)
 	go func() {
 		conn, chans, reqs, err := NewServerConn(c1, serverConf)
 		srvErrCh <- err
 		if err != nil {
 			return
 		}
 		serverID <- conn.SessionID()
 		go DiscardRequests(reqs)
 		for ch := range chans {
 			ch.Reject(Prohibited, "")
 		}
 	}()

 	cliErrCh := make(chan error, 1)
 	go func() {
 		conn, chans, reqs, err := NewClientConn(c2, "", clientConf)
 		cliErrCh <- err
 		if err != nil {
 			return
 		}
 		clientID <- conn.SessionID()
 		go DiscardRequests(reqs)
 		for ch := range chans {
 			ch.Reject(Prohibited, "")
 		}
 	}()

 	if err := <-srvErrCh; err != nil {
 		t.Fatalf("server handshake: %v", err)
 	}

 	if err := <-cliErrCh; err != nil {
 		t.Fatalf("client handshake: %v", err)
 	}

 	s := <-serverID
 	c := <-clientID
 	if bytes.Compare(s, c) != 0 {
 		t.Errorf("server session ID (%x) != client session ID (%x)", s, c)
 	} else if len(s) == 0 {
 		t.Errorf("client and server SessionID were empty.")
 	}
 }

 type noReadConn struct {
 	readSeen bool
 	net.Conn
 }

 func (c *noReadConn) Close() error {
 	return nil
 }

 func (c *noReadConn) Read(b []byte) (int, error) {
 	c.readSeen = true
 	return 0, errors.New("noReadConn error")
 }

 func TestInvalidServerConfiguration(t *testing.T) {
 	c1, c2, err := netPipe()
 	if err != nil {
 		t.Fatalf("netPipe: %v", err)
 	}
 	defer c1.Close()
 	defer c2.Close()

 	serveConn := noReadConn{Conn: c1}
 	serverConf := &ServerConfig{}

 	NewServerConn(&serveConn, serverConf)
 	if serveConn.readSeen {
 		t.Fatalf("NewServerConn attempted to Read() from Conn while configuration is missing host key")
 	}

 	serverConf.AddHostKey(testSigners["ecdsa"])

 	NewServerConn(&serveConn, serverConf)
 	if serveConn.readSeen {
 		t.Fatalf("NewServerConn attempted to Read() from Conn while configuration is missing authentication method")
 	}
 }

 func TestHostKeyAlgorithms(t *testing.T) {
 	serverConf := &ServerConfig{
 		NoClientAuth: true,
 	}
 	serverConf.AddHostKey(testSigners["rsa"])
 	serverConf.AddHostKey(testSigners["ecdsa"])

 	connect := func(clientConf *ClientConfig, want string) {
 		var alg string
 		clientConf.HostKeyCallback = func(h string, a net.Addr, key PublicKey) error {
 			alg = key.Type()
 			return nil
 		}
 		c1, c2, err := netPipe()
 		if err != nil {
 			t.Fatalf("netPipe: %v", err)
 		}
 		defer c1.Close()
 		defer c2.Close()

 		go NewServerConn(c1, serverConf)
 		_, _, _, err = NewClientConn(c2, "", clientConf)
 		if err != nil {
 			t.Fatalf("NewClientConn: %v", err)
 		}
 		if alg != want {
 			t.Errorf("selected key algorithm %s, want %s", alg, want)
 		}
 	}

 	// By default, we get the preferred algorithm, which is ECDSA 256.

 	clientConf := &ClientConfig{
 		HostKeyCallback: InsecureIgnoreHostKey(),
 	}
 	connect(clientConf, KeyAlgoECDSA256)

 	// Client asks for RSA explicitly.
 	clientConf.HostKeyAlgorithms = []string{KeyAlgoRSA}
 	connect(clientConf, KeyAlgoRSA)

 	// Client asks for RSA-SHA2-512 explicitly.
 	clientConf.HostKeyAlgorithms = []string{KeyAlgoRSASHA512}
 	// We get back an "ssh-rsa" key but the verification happened
 	// with an RSA-SHA2-512 signature.
 	connect(clientConf, KeyAlgoRSA)

 	c1, c2, err := netPipe()
 	if err != nil {
 		t.Fatalf("netPipe: %v", err)
 	}
 	defer c1.Close()
 	defer c2.Close()

 	go NewServerConn(c1, serverConf)
 	clientConf.HostKeyAlgorithms = []string{"nonexistent-hostkey-algo"}
 	_, _, _, err = NewClientConn(c2, "", clientConf)
 	if err == nil {
 		t.Fatal("succeeded connecting with unknown hostkey algorithm")
 	}
 }

 func TestServerClientAuthCallback(t *testing.T) {
 	c1, c2, err := netPipe()
 	if err != nil {
 		t.Fatalf("netPipe: %v", err)
 	}
 	defer c1.Close()
 	defer c2.Close()

 	userCh := make(chan string, 1)

 	serverConf := &ServerConfig{
 		NoClientAuth: true,
 		NoClientAuthCallback: func(conn ConnMetadata) (*Permissions, error) {
 			userCh <- conn.User()
 			return nil, nil
 		},
 	}
 	const someUsername = "some-username"

 	serverConf.AddHostKey(testSigners["ecdsa"])
 	clientConf := &ClientConfig{
 		HostKeyCallback: InsecureIgnoreHostKey(),
 		User:            someUsername,
 	}

 	go func() {
 		_, chans, reqs, err := NewServerConn(c1, serverConf)
 		if err != nil {
 			t.Errorf("server handshake: %v", err)
 			userCh <- "error"
 			return
 		}
 		go DiscardRequests(reqs)
 		for ch := range chans {
 			ch.Reject(Prohibited, "")
 		}
 	}()

 	conn, _, _, err := NewClientConn(c2, "", clientConf)
 	if err != nil {
 		t.Fatalf("client handshake: %v", err)
 		return
 	}
 	conn.Close()

 	got := <-userCh
 	if got != someUsername {
 		t.Errorf("username = %q; want %q", got, someUsername)
 	}
 }
	// Copyright 2011 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 ssh

	// Session tests.

	import (
	"bytes"
	crypto_rand "crypto/rand"
	"errors"
	"io"
	"math/rand"
	"net"
	"testing"

	"golang.org/x/crypto/ssh/terminal"
	)

	type serverType func(Channel, <-chan Request, testing.T)

	// dial constructs a new test server and returns a *ClientConn.
	func dial(handler serverType, t testing.T) Client {
	c1, c2, err := netPipe()
	if err != nil {
	t.Fatalf("netPipe: %v", err)
	}

	go func() {
	defer c1.Close()
	conf := ServerConfig{
	NoClientAuth: true,
	}
	conf.AddHostKey(testSigners["rsa"])

	conn, chans, reqs, err := NewServerConn(c1, &conf)
	if err != nil {
	t.Errorf("Unable to handshake: %v", err)
	return
	}
	go DiscardRequests(reqs)

	for newCh := range chans {
	if newCh.ChannelType() != "session" {
	newCh.Reject(UnknownChannelType, "unknown channel type")
	continue
	}

	ch, inReqs, err := newCh.Accept()
	if err != nil {
	t.Errorf("Accept: %v", err)
	continue
	}
	go func() {
	handler(ch, inReqs, t)
	}()
	}
	if err := conn.Wait(); err != io.EOF {
	t.Logf("server exit reason: %v", err)
	}
	}()

	config := &ClientConfig{
	User: "testuser",
	HostKeyCallback: InsecureIgnoreHostKey(),
	}

	conn, chans, reqs, err := NewClientConn(c2, "", config)
	if err != nil {
	t.Fatalf("unable to dial remote side: %v", err)
	}

	return NewClient(conn, chans, reqs)
	}

	// Test a simple string is returned to session.Stdout.
	func TestSessionShell(t *testing.T) {
	conn := dial(shellHandler, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatalf("Unable to request new session: %v", err)
	}
	defer session.Close()
	stdout := new(bytes.Buffer)
	session.Stdout = stdout
	if err := session.Shell(); err != nil {
	t.Fatalf("Unable to execute command: %s", err)
	}
	if err := session.Wait(); err != nil {
	t.Fatalf("Remote command did not exit cleanly: %v", err)
	}
	actual := stdout.String()
	if actual != "golang" {
	t.Fatalf("Remote shell did not return expected string: expected=golang, actual=%s", actual)
	}
	}

	// TODO(dfc) add support for Std{in,err}Pipe when the Server supports it.

	// Test a simple string is returned via StdoutPipe.
	func TestSessionStdoutPipe(t *testing.T) {
	conn := dial(shellHandler, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatalf("Unable to request new session: %v", err)
	}
	defer session.Close()
	stdout, err := session.StdoutPipe()
	if err != nil {
	t.Fatalf("Unable to request StdoutPipe(): %v", err)
	}
	var buf bytes.Buffer
	if err := session.Shell(); err != nil {
	t.Fatalf("Unable to execute command: %v", err)
	}
	done := make(chan bool, 1)
	go func() {
	if _, err := io.Copy(&buf, stdout); err != nil {
	t.Errorf("Copy of stdout failed: %v", err)
	}
	done <- true
	}()
	if err := session.Wait(); err != nil {
	t.Fatalf("Remote command did not exit cleanly: %v", err)
	}
	<-done
	actual := buf.String()
	if actual != "golang" {
	t.Fatalf("Remote shell did not return expected string: expected=golang, actual=%s", actual)
	}
	}

	// Test that a simple string is returned via the Output helper,
	// and that stderr is discarded.
	func TestSessionOutput(t *testing.T) {
	conn := dial(fixedOutputHandler, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatalf("Unable to request new session: %v", err)
	}
	defer session.Close()

	buf, err := session.Output("") // cmd is ignored by fixedOutputHandler
	if err != nil {
	t.Error("Remote command did not exit cleanly:", err)
	}
	w := "this-is-stdout."
	g := string(buf)
	if g != w {
	t.Error("Remote command did not return expected string:")
	t.Logf("want %q", w)
	t.Logf("got %q", g)
	}
	}

	// Test that both stdout and stderr are returned
	// via the CombinedOutput helper.
	func TestSessionCombinedOutput(t *testing.T) {
	conn := dial(fixedOutputHandler, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatalf("Unable to request new session: %v", err)
	}
	defer session.Close()

	buf, err := session.CombinedOutput("") // cmd is ignored by fixedOutputHandler
	if err != nil {
	t.Error("Remote command did not exit cleanly:", err)
	}
	const stdout = "this-is-stdout."
	const stderr = "this-is-stderr."
	g := string(buf)
	if g != stdout+stderr && g != stderr+stdout {
	t.Error("Remote command did not return expected string:")
	t.Logf("want %q, or %q", stdout+stderr, stderr+stdout)
	t.Logf("got %q", g)
	}
	}

	// Test non-0 exit status is returned correctly.
	func TestExitStatusNonZero(t *testing.T) {
	conn := dial(exitStatusNonZeroHandler, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatalf("Unable to request new session: %v", err)
	}
	defer session.Close()
	if err := session.Shell(); err != nil {
	t.Fatalf("Unable to execute command: %v", err)
	}
	err = session.Wait()
	if err == nil {
	t.Fatalf("expected command to fail but it didn't")
	}
	e, ok := err.(*ExitError)
	if !ok {
	t.Fatalf("expected *ExitError but got %T", err)
	}
	if e.ExitStatus() != 15 {
	t.Fatalf("expected command to exit with 15 but got %v", e.ExitStatus())
	}
	}

	// Test 0 exit status is returned correctly.
	func TestExitStatusZero(t *testing.T) {
	conn := dial(exitStatusZeroHandler, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatalf("Unable to request new session: %v", err)
	}
	defer session.Close()

	if err := session.Shell(); err != nil {
	t.Fatalf("Unable to execute command: %v", err)
	}
	err = session.Wait()
	if err != nil {
	t.Fatalf("expected nil but got %v", err)
	}
	}

	// Test exit signal and status are both returned correctly.
	func TestExitSignalAndStatus(t *testing.T) {
	conn := dial(exitSignalAndStatusHandler, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatalf("Unable to request new session: %v", err)
	}
	defer session.Close()
	if err := session.Shell(); err != nil {
	t.Fatalf("Unable to execute command: %v", err)
	}
	err = session.Wait()
	if err == nil {
	t.Fatalf("expected command to fail but it didn't")
	}
	e, ok := err.(*ExitError)
	if !ok {
	t.Fatalf("expected *ExitError but got %T", err)
	}
	if e.Signal() != "TERM" \|\| e.ExitStatus() != 15 {
	t.Fatalf("expected command to exit with signal TERM and status 15 but got signal %s and status %v", e.Signal(), e.ExitStatus())
	}
	}

	// Test exit signal and status are both returned correctly.
	func TestKnownExitSignalOnly(t *testing.T) {
	conn := dial(exitSignalHandler, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatalf("Unable to request new session: %v", err)
	}
	defer session.Close()
	if err := session.Shell(); err != nil {
	t.Fatalf("Unable to execute command: %v", err)
	}
	err = session.Wait()
	if err == nil {
	t.Fatalf("expected command to fail but it didn't")
	}
	e, ok := err.(*ExitError)
	if !ok {
	t.Fatalf("expected *ExitError but got %T", err)
	}
	if e.Signal() != "TERM" \|\| e.ExitStatus() != 143 {
	t.Fatalf("expected command to exit with signal TERM and status 143 but got signal %s and status %v", e.Signal(), e.ExitStatus())
	}
	}

	// Test exit signal and status are both returned correctly.
	func TestUnknownExitSignal(t *testing.T) {
	conn := dial(exitSignalUnknownHandler, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatalf("Unable to request new session: %v", err)
	}
	defer session.Close()
	if err := session.Shell(); err != nil {
	t.Fatalf("Unable to execute command: %v", err)
	}
	err = session.Wait()
	if err == nil {
	t.Fatalf("expected command to fail but it didn't")
	}
	e, ok := err.(*ExitError)
	if !ok {
	t.Fatalf("expected *ExitError but got %T", err)
	}
	if e.Signal() != "SYS" \|\| e.ExitStatus() != 128 {
	t.Fatalf("expected command to exit with signal SYS and status 128 but got signal %s and status %v", e.Signal(), e.ExitStatus())
	}
	}

	func TestExitWithoutStatusOrSignal(t *testing.T) {
	conn := dial(exitWithoutSignalOrStatus, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatalf("Unable to request new session: %v", err)
	}
	defer session.Close()
	if err := session.Shell(); err != nil {
	t.Fatalf("Unable to execute command: %v", err)
	}
	err = session.Wait()
	if err == nil {
	t.Fatalf("expected command to fail but it didn't")
	}
	if _, ok := err.(*ExitMissingError); !ok {
	t.Fatalf("got %T want *ExitMissingError", err)
	}
	}

	// windowTestBytes is the number of bytes that we'll send to the SSH server.
	const windowTestBytes = 16000 * 200

	// TestServerWindow writes random data to the server. The server is expected to echo
	// the same data back, which is compared against the original.
	func TestServerWindow(t *testing.T) {
	origBuf := bytes.NewBuffer(make([]byte, 0, windowTestBytes))
	io.CopyN(origBuf, crypto_rand.Reader, windowTestBytes)
	origBytes := origBuf.Bytes()

	conn := dial(echoHandler, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatal(err)
	}
	defer session.Close()
	result := make(chan []byte)

	go func() {
	defer close(result)
	echoedBuf := bytes.NewBuffer(make([]byte, 0, windowTestBytes))
	serverStdout, err := session.StdoutPipe()
	if err != nil {
	t.Errorf("StdoutPipe failed: %v", err)
	return
	}
	n, err := copyNRandomly("stdout", echoedBuf, serverStdout, windowTestBytes)
	if err != nil && err != io.EOF {
	t.Errorf("Read only %d bytes from server, expected %d: %v", n, windowTestBytes, err)
	}
	result <- echoedBuf.Bytes()
	}()

	serverStdin, err := session.StdinPipe()
	if err != nil {
	t.Fatalf("StdinPipe failed: %v", err)
	}
	written, err := copyNRandomly("stdin", serverStdin, origBuf, windowTestBytes)
	if err != nil {
	t.Errorf("failed to copy origBuf to serverStdin: %v", err)
	} else if written != windowTestBytes {
	t.Errorf("Wrote only %d of %d bytes to server", written, windowTestBytes)
	}

	echoedBytes := <-result

	if !bytes.Equal(origBytes, echoedBytes) {
	t.Fatalf("Echoed buffer differed from original, orig %d, echoed %d", len(origBytes), len(echoedBytes))
	}
	}

	// Verify the client can handle a keepalive packet from the server.
	func TestClientHandlesKeepalives(t *testing.T) {
	conn := dial(channelKeepaliveSender, t)
	defer conn.Close()
	session, err := conn.NewSession()
	if err != nil {
	t.Fatal(err)
	}
	defer session.Close()
	if err := session.Shell(); err != nil {
	t.Fatalf("Unable to execute command: %v", err)
	}
	err = session.Wait()
	if err != nil {
	t.Fatalf("expected nil but got: %v", err)
	}
	}

	type exitStatusMsg struct {
	Status uint32
	}

	type exitSignalMsg struct {
	Signal string
	CoreDumped bool
	Errmsg string
	Lang string
	}

	func handleTerminalRequests(in <-chan *Request) {
	for req := range in {
	ok := false
	switch req.Type {
	case "shell":
	ok = true
	if len(req.Payload) > 0 {
	// We don't accept any commands, only the default shell.
	ok = false
	}
	case "env":
	ok = true
	}
	req.Reply(ok, nil)
	}
	}

	func newServerShell(ch Channel, in <-chan Request, prompt string) terminal.Terminal {
	term := terminal.NewTerminal(ch, prompt)
	go handleTerminalRequests(in)
	return term
	}

	func exitStatusZeroHandler(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	// this string is returned to stdout
	shell := newServerShell(ch, in, "> ")
	readLine(shell, t)
	sendStatus(0, ch, t)
	}

	func exitStatusNonZeroHandler(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	shell := newServerShell(ch, in, "> ")
	readLine(shell, t)
	sendStatus(15, ch, t)
	}

	func exitSignalAndStatusHandler(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	shell := newServerShell(ch, in, "> ")
	readLine(shell, t)
	sendStatus(15, ch, t)
	sendSignal("TERM", ch, t)
	}

	func exitSignalHandler(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	shell := newServerShell(ch, in, "> ")
	readLine(shell, t)
	sendSignal("TERM", ch, t)
	}

	func exitSignalUnknownHandler(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	shell := newServerShell(ch, in, "> ")
	readLine(shell, t)
	sendSignal("SYS", ch, t)
	}

	func exitWithoutSignalOrStatus(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	shell := newServerShell(ch, in, "> ")
	readLine(shell, t)
	}

	func shellHandler(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	// this string is returned to stdout
	shell := newServerShell(ch, in, "golang")
	readLine(shell, t)
	sendStatus(0, ch, t)
	}

	// Ignores the command, writes fixed strings to stderr and stdout.
	// Strings are "this-is-stdout." and "this-is-stderr.".
	func fixedOutputHandler(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	_, err := ch.Read(nil)

	req, ok := <-in
	if !ok {
	t.Fatalf("error: expected channel request, got: %#v", err)
	return
	}

	// ignore request, always send some text
	req.Reply(true, nil)

	_, err = io.WriteString(ch, "this-is-stdout.")
	if err != nil {
	t.Fatalf("error writing on server: %v", err)
	}
	_, err = io.WriteString(ch.Stderr(), "this-is-stderr.")
	if err != nil {
	t.Fatalf("error writing on server: %v", err)
	}
	sendStatus(0, ch, t)
	}

	func readLine(shell terminal.Terminal, t testing.T) {
	if _, err := shell.ReadLine(); err != nil && err != io.EOF {
	t.Errorf("unable to read line: %v", err)
	}
	}

	func sendStatus(status uint32, ch Channel, t *testing.T) {
	msg := exitStatusMsg{
	Status: status,
	}
	if _, err := ch.SendRequest("exit-status", false, Marshal(&msg)); err != nil {
	t.Errorf("unable to send status: %v", err)
	}
	}

	func sendSignal(signal string, ch Channel, t *testing.T) {
	sig := exitSignalMsg{
	Signal: signal,
	CoreDumped: false,
	Errmsg: "Process terminated",
	Lang: "en-GB-oed",
	}
	if _, err := ch.SendRequest("exit-signal", false, Marshal(&sig)); err != nil {
	t.Errorf("unable to send signal: %v", err)
	}
	}

	func discardHandler(ch Channel, t *testing.T) {
	defer ch.Close()
	io.Copy(io.Discard, ch)
	}

	func echoHandler(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	if n, err := copyNRandomly("echohandler", ch, ch, windowTestBytes); err != nil {
	t.Errorf("short write, wrote %d, expected %d: %v ", n, windowTestBytes, err)
	}
	}

	// copyNRandomly copies n bytes from src to dst. It uses a variable, and random,
	// buffer size to exercise more code paths.
	func copyNRandomly(title string, dst io.Writer, src io.Reader, n int) (int, error) {
	var (
	buf = make([]byte, 32*1024)
	written int
	remaining = n
	)
	for remaining > 0 {
	l := rand.Intn(1 << 15)
	if remaining < l {
	l = remaining
	}
	nr, er := src.Read(buf[:l])
	nw, ew := dst.Write(buf[:nr])
	remaining -= nw
	written += nw
	if ew != nil {
	return written, ew
	}
	if nr != nw {
	return written, io.ErrShortWrite
	}
	if er != nil && er != io.EOF {
	return written, er
	}
	}
	return written, nil
	}

	func channelKeepaliveSender(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	shell := newServerShell(ch, in, "> ")
	readLine(shell, t)
	if _, err := ch.SendRequest("keepalive@openssh.com", true, nil); err != nil {
	t.Errorf("unable to send channel keepalive request: %v", err)
	}
	sendStatus(0, ch, t)
	}

	func TestClientWriteEOF(t *testing.T) {
	conn := dial(simpleEchoHandler, t)
	defer conn.Close()

	session, err := conn.NewSession()
	if err != nil {
	t.Fatal(err)
	}
	defer session.Close()
	stdin, err := session.StdinPipe()
	if err != nil {
	t.Fatalf("StdinPipe failed: %v", err)
	}
	stdout, err := session.StdoutPipe()
	if err != nil {
	t.Fatalf("StdoutPipe failed: %v", err)
	}

	data := []byte(`0000`)
	_, err = stdin.Write(data)
	if err != nil {
	t.Fatalf("Write failed: %v", err)
	}
	stdin.Close()

	res, err := io.ReadAll(stdout)
	if err != nil {
	t.Fatalf("Read failed: %v", err)
	}

	if !bytes.Equal(data, res) {
	t.Fatalf("Read differed from write, wrote: %v, read: %v", data, res)
	}
	}

	func simpleEchoHandler(ch Channel, in <-chan Request, t testing.T) {
	defer ch.Close()
	data, err := io.ReadAll(ch)
	if err != nil {
	t.Errorf("handler read error: %v", err)
	}
	_, err = ch.Write(data)
	if err != nil {
	t.Errorf("handler write error: %v", err)
	}
	}

	func TestSessionID(t *testing.T) {
	c1, c2, err := netPipe()
	if err != nil {
	t.Fatalf("netPipe: %v", err)
	}
	defer c1.Close()
	defer c2.Close()

	serverID := make(chan []byte, 1)
	clientID := make(chan []byte, 1)

	serverConf := &ServerConfig{
	NoClientAuth: true,
	}
	serverConf.AddHostKey(testSigners["ecdsa"])
	clientConf := &ClientConfig{
	HostKeyCallback: InsecureIgnoreHostKey(),
	User: "user",
	}

	srvErrCh := make(chan error, 1)
	go func() {
	conn, chans, reqs, err := NewServerConn(c1, serverConf)
	srvErrCh <- err
	if err != nil {
	return
	}
	serverID <- conn.SessionID()
	go DiscardRequests(reqs)
	for ch := range chans {
	ch.Reject(Prohibited, "")
	}
	}()

	cliErrCh := make(chan error, 1)
	go func() {
	conn, chans, reqs, err := NewClientConn(c2, "", clientConf)
	cliErrCh <- err
	if err != nil {
	return
	}
	clientID <- conn.SessionID()
	go DiscardRequests(reqs)
	for ch := range chans {
	ch.Reject(Prohibited, "")
	}
	}()

	if err := <-srvErrCh; err != nil {
	t.Fatalf("server handshake: %v", err)
	}

	if err := <-cliErrCh; err != nil {
	t.Fatalf("client handshake: %v", err)
	}

	s := <-serverID
	c := <-clientID
	if bytes.Compare(s, c) != 0 {
	t.Errorf("server session ID (%x) != client session ID (%x)", s, c)
	} else if len(s) == 0 {
	t.Errorf("client and server SessionID were empty.")
	}
	}

	type noReadConn struct {
	readSeen bool
	net.Conn
	}

	func (c *noReadConn) Close() error {
	return nil
	}

	func (c *noReadConn) Read(b []byte) (int, error) {
	c.readSeen = true
	return 0, errors.New("noReadConn error")
	}

	func TestInvalidServerConfiguration(t *testing.T) {
	c1, c2, err := netPipe()
	if err != nil {
	t.Fatalf("netPipe: %v", err)
	}
	defer c1.Close()
	defer c2.Close()

	serveConn := noReadConn{Conn: c1}
	serverConf := &ServerConfig{}

	NewServerConn(&serveConn, serverConf)
	if serveConn.readSeen {
	t.Fatalf("NewServerConn attempted to Read() from Conn while configuration is missing host key")
	}

	serverConf.AddHostKey(testSigners["ecdsa"])

	NewServerConn(&serveConn, serverConf)
	if serveConn.readSeen {
	t.Fatalf("NewServerConn attempted to Read() from Conn while configuration is missing authentication method")
	}
	}

	func TestHostKeyAlgorithms(t *testing.T) {
	serverConf := &ServerConfig{
	NoClientAuth: true,
	}
	serverConf.AddHostKey(testSigners["rsa"])
	serverConf.AddHostKey(testSigners["ecdsa"])

	connect := func(clientConf *ClientConfig, want string) {
	var alg string
	clientConf.HostKeyCallback = func(h string, a net.Addr, key PublicKey) error {
	alg = key.Type()
	return nil
	}
	c1, c2, err := netPipe()
	if err != nil {
	t.Fatalf("netPipe: %v", err)
	}
	defer c1.Close()
	defer c2.Close()

	go NewServerConn(c1, serverConf)
	_, _, _, err = NewClientConn(c2, "", clientConf)
	if err != nil {
	t.Fatalf("NewClientConn: %v", err)
	}
	if alg != want {
	t.Errorf("selected key algorithm %s, want %s", alg, want)
	}
	}

	// By default, we get the preferred algorithm, which is ECDSA 256.

	clientConf := &ClientConfig{
	HostKeyCallback: InsecureIgnoreHostKey(),
	}
	connect(clientConf, KeyAlgoECDSA256)

	// Client asks for RSA explicitly.
	clientConf.HostKeyAlgorithms = []string{KeyAlgoRSA}
	connect(clientConf, KeyAlgoRSA)

	// Client asks for RSA-SHA2-512 explicitly.
	clientConf.HostKeyAlgorithms = []string{KeyAlgoRSASHA512}
	// We get back an "ssh-rsa" key but the verification happened
	// with an RSA-SHA2-512 signature.
	connect(clientConf, KeyAlgoRSA)

	c1, c2, err := netPipe()
	if err != nil {
	t.Fatalf("netPipe: %v", err)
	}
	defer c1.Close()
	defer c2.Close()

	go NewServerConn(c1, serverConf)
	clientConf.HostKeyAlgorithms = []string{"nonexistent-hostkey-algo"}
	_, _, _, err = NewClientConn(c2, "", clientConf)
	if err == nil {
	t.Fatal("succeeded connecting with unknown hostkey algorithm")
	}
	}

	func TestServerClientAuthCallback(t *testing.T) {
	c1, c2, err := netPipe()
	if err != nil {
	t.Fatalf("netPipe: %v", err)
	}
	defer c1.Close()
	defer c2.Close()

	userCh := make(chan string, 1)

	serverConf := &ServerConfig{
	NoClientAuth: true,
	NoClientAuthCallback: func(conn ConnMetadata) (*Permissions, error) {
	userCh <- conn.User()
	return nil, nil
	},
	}
	const someUsername = "some-username"

	serverConf.AddHostKey(testSigners["ecdsa"])
	clientConf := &ClientConfig{
	HostKeyCallback: InsecureIgnoreHostKey(),
	User: someUsername,
	}

	go func() {
	_, chans, reqs, err := NewServerConn(c1, serverConf)
	if err != nil {
	t.Errorf("server handshake: %v", err)
	userCh <- "error"
	return
	}
	go DiscardRequests(reqs)
	for ch := range chans {
	ch.Reject(Prohibited, "")
	}
	}()

	conn, _, _, err := NewClientConn(c2, "", clientConf)
	if err != nil {
	t.Fatalf("client handshake: %v", err)
	return
	}
	conn.Close()

	got := <-userCh
	if got != someUsername {
	t.Errorf("username = %q; want %q", got, someUsername)
	}
	}