transport: create Client interface (#132)

* plumbing: move plumbing/client package to plumbing/transport.

* transport: create Client interface.

* A Client can instantiate any client transport service.
* InstallProtocol installs a Client for a given protocol,
  instead of just a UploadPackService.
* A Client can open a session for fetch-pack or send-pack
  for a specific Endpoint.
* Adapt ssh and http clients to the new client interface.

* updated doc

7 files changed, 748 insertions, 0 deletions

diff --git a/plumbing/transport/ssh/auth_method.go b/plumbing/transport/ssh/auth_method.go
new file mode 100644
index 0000000..9c3d6f3
--- /dev/null
+++ b/plumbing/transport/ssh/auth_method.go
@@ -0,0 +1,157 @@
+package ssh
+
+import (
+	"fmt"
+	"net"
+	"os"
+
+	"golang.org/x/crypto/ssh"
+	"golang.org/x/crypto/ssh/agent"
+)
+
+// AuthMethod is the interface all auth methods for the ssh client
+// must implement. The clientConfig method returns the ssh client
+// configuration needed to establish an ssh connection.
+type AuthMethod interface {
+	clientConfig() *ssh.ClientConfig
+}
+
+// The names of the AuthMethod implementations. To be returned by the
+// Name() method. Most git servers only allow PublicKeysName and
+// PublicKeysCallbackName.
+const (
+	KeyboardInteractiveName = "ssh-keyboard-interactive"
+	PasswordName            = "ssh-password"
+	PasswordCallbackName    = "ssh-password-callback"
+	PublicKeysName          = "ssh-public-keys"
+	PublicKeysCallbackName  = "ssh-public-key-callback"
+)
+
+// KeyboardInteractive implements AuthMethod by using a
+// prompt/response sequence controlled by the server.
+type KeyboardInteractive struct {
+	User      string
+	Challenge ssh.KeyboardInteractiveChallenge
+}
+
+func (a *KeyboardInteractive) Name() string {
+	return KeyboardInteractiveName
+}
+
+func (a *KeyboardInteractive) String() string {
+	return fmt.Sprintf("user: %s, name: %s", a.User, a.Name())
+}
+
+func (a *KeyboardInteractive) clientConfig() *ssh.ClientConfig {
+	return &ssh.ClientConfig{
+		User: a.User,
+		Auth: []ssh.AuthMethod{ssh.KeyboardInteractiveChallenge(a.Challenge)},
+	}
+}
+
+// Password implements AuthMethod by using the given password.
+type Password struct {
+	User string
+	Pass string
+}
+
+func (a *Password) Name() string {
+	return PasswordName
+}
+
+func (a *Password) String() string {
+	return fmt.Sprintf("user: %s, name: %s", a.User, a.Name())
+}
+
+func (a *Password) clientConfig() *ssh.ClientConfig {
+	return &ssh.ClientConfig{
+		User: a.User,
+		Auth: []ssh.AuthMethod{ssh.Password(a.Pass)},
+	}
+}
+
+// PasswordCallback implements AuthMethod by using a callback
+// to fetch the password.
+type PasswordCallback struct {
+	User     string
+	Callback func() (pass string, err error)
+}
+
+func (a *PasswordCallback) Name() string {
+	return PasswordCallbackName
+}
+
+func (a *PasswordCallback) String() string {
+	return fmt.Sprintf("user: %s, name: %s", a.User, a.Name())
+}
+
+func (a *PasswordCallback) clientConfig() *ssh.ClientConfig {
+	return &ssh.ClientConfig{
+		User: a.User,
+		Auth: []ssh.AuthMethod{ssh.PasswordCallback(a.Callback)},
+	}
+}
+
+// PublicKeys implements AuthMethod by using the given
+// key pairs.
+type PublicKeys struct {
+	User   string
+	Signer ssh.Signer
+}
+
+func (a *PublicKeys) Name() string {
+	return PublicKeysName
+}
+
+func (a *PublicKeys) String() string {
+	return fmt.Sprintf("user: %s, name: %s", a.User, a.Name())
+}
+
+func (a *PublicKeys) clientConfig() *ssh.ClientConfig {
+	return &ssh.ClientConfig{
+		User: a.User,
+		Auth: []ssh.AuthMethod{ssh.PublicKeys(a.Signer)},
+	}
+}
+
+// PublicKeysCallback implements AuthMethod by asking a
+// ssh.agent.Agent to act as a signer.
+type PublicKeysCallback struct {
+	User     string
+	Callback func() (signers []ssh.Signer, err error)
+}
+
+func (a *PublicKeysCallback) Name() string {
+	return PublicKeysCallbackName
+}
+
+func (a *PublicKeysCallback) String() string {
+	return fmt.Sprintf("user: %s, name: %s", a.User, a.Name())
+}
+
+func (a *PublicKeysCallback) clientConfig() *ssh.ClientConfig {
+	return &ssh.ClientConfig{
+		User: a.User,
+		Auth: []ssh.AuthMethod{ssh.PublicKeysCallback(a.Callback)},
+	}
+}
+
+const DefaultSSHUsername = "git"
+
+// Opens a pipe with the ssh agent and uses the pipe
+// as the implementer of the public key callback function.
+func NewSSHAgentAuth(user string) (*PublicKeysCallback, error) {
+	if user == "" {
+		user = DefaultSSHUsername
+	}
+
+	pipe, err := net.Dial("unix", os.Getenv("SSH_AUTH_SOCK"))
+	if err != nil {
+		return nil, err
+	}
+
+	return &PublicKeysCallback{
+		User:     user,
+		Callback: agent.NewClient(pipe).Signers,
+	}, nil
+}
diff --git a/plumbing/transport/ssh/auth_method_test.go b/plumbing/transport/ssh/auth_method_test.go
new file mode 100644
index 0000000..f9e7dec
--- /dev/null
+++ b/plumbing/transport/ssh/auth_method_test.go
@@ -0,0 +1,91 @@
+package ssh
+
+import (
+	"fmt"
+
+	. "gopkg.in/check.v1"
+)
+
+type SuiteCommon struct{}
+
+var _ = Suite(&SuiteCommon{})
+
+func (s *SuiteCommon) TestKeyboardInteractiveName(c *C) {
+	a := &KeyboardInteractive{
+		User:      "test",
+		Challenge: nil,
+	}
+	c.Assert(a.Name(), Equals, KeyboardInteractiveName)
+}
+
+func (s *SuiteCommon) TestKeyboardInteractiveString(c *C) {
+	a := &KeyboardInteractive{
+		User:      "test",
+		Challenge: nil,
+	}
+	c.Assert(a.String(), Equals, fmt.Sprintf("user: test, name: %s", KeyboardInteractiveName))
+}
+
+func (s *SuiteCommon) TestPasswordName(c *C) {
+	a := &Password{
+		User: "test",
+		Pass: "",
+	}
+	c.Assert(a.Name(), Equals, PasswordName)
+}
+
+func (s *SuiteCommon) TestPasswordString(c *C) {
+	a := &Password{
+		User: "test",
+		Pass: "",
+	}
+	c.Assert(a.String(), Equals, fmt.Sprintf("user: test, name: %s", PasswordName))
+}
+
+func (s *SuiteCommon) TestPasswordCallbackName(c *C) {
+	a := &PasswordCallback{
+		User:     "test",
+		Callback: nil,
+	}
+	c.Assert(a.Name(), Equals, PasswordCallbackName)
+}
+
+func (s *SuiteCommon) TestPasswordCallbackString(c *C) {
+	a := &PasswordCallback{
+		User:     "test",
+		Callback: nil,
+	}
+	c.Assert(a.String(), Equals, fmt.Sprintf("user: test, name: %s", PasswordCallbackName))
+}
+
+func (s *SuiteCommon) TestPublicKeysName(c *C) {
+	a := &PublicKeys{
+		User:   "test",
+		Signer: nil,
+	}
+	c.Assert(a.Name(), Equals, PublicKeysName)
+}
+
+func (s *SuiteCommon) TestPublicKeysString(c *C) {
+	a := &PublicKeys{
+		User:   "test",
+		Signer: nil,
+	}
+	c.Assert(a.String(), Equals, fmt.Sprintf("user: test, name: %s", PublicKeysName))
+}
+
+func (s *SuiteCommon) TestPublicKeysCallbackName(c *C) {
+	a := &PublicKeysCallback{
+		User:     "test",
+		Callback: nil,
+	}
+	c.Assert(a.Name(), Equals, PublicKeysCallbackName)
+}
+
+func (s *SuiteCommon) TestPublicKeysCallbackString(c *C) {
+	a := &PublicKeysCallback{
+		User:     "test",
+		Callback: nil,
+	}
+	c.Assert(a.String(), Equals, fmt.Sprintf("user: test, name: %s", PublicKeysCallbackName))
+}
diff --git a/plumbing/transport/ssh/common.go b/plumbing/transport/ssh/common.go
new file mode 100644
index 0000000..6f0f3d4
--- /dev/null
+++ b/plumbing/transport/ssh/common.go
@@ -0,0 +1,151 @@
+package ssh
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+
+	"gopkg.in/src-d/go-git.v4/plumbing/transport"
+
+	"golang.org/x/crypto/ssh"
+)
+
+// New errors introduced by this package.
+var (
+	ErrAdvertistedReferencesAlreadyCalled = errors.New("cannot call AdvertisedReference twice")
+	ErrAlreadyConnected                   = errors.New("ssh session already created")
+	ErrAuthRequired                       = errors.New("cannot connect: auth required")
+	ErrNotConnected                       = errors.New("not connected")
+	ErrUploadPackAnswerFormat             = errors.New("git-upload-pack bad answer format")
+	ErrUnsupportedVCS                     = errors.New("only git is supported")
+	ErrUnsupportedRepo                    = errors.New("only github.com is supported")
+)
+
+type Client struct{}
+
+var DefaultClient = NewClient()
+
+func NewClient() transport.Client {
+	return &Client{}
+}
+
+func (c *Client) NewFetchPackSession(ep transport.Endpoint) (
+	transport.FetchPackSession, error) {
+
+	return newFetchPackSession(ep)
+}
+
+func (c *Client) NewSendPackSession(ep transport.Endpoint) (
+	transport.SendPackSession, error) {
+
+	return newSendPackSession(ep)
+}
+
+type session struct {
+	connected   bool
+	endpoint    transport.Endpoint
+	client      *ssh.Client
+	session     *ssh.Session
+	stdin       io.WriteCloser
+	stdout      io.Reader
+	sessionDone chan error
+	auth        AuthMethod
+}
+
+func (s *session) SetAuth(auth transport.AuthMethod) error {
+	a, ok := auth.(AuthMethod)
+	if !ok {
+		return transport.ErrInvalidAuthMethod
+	}
+
+	s.auth = a
+	return nil
+}
+
+// Close closes the SSH session.
+func (s *session) Close() error {
+	if !s.connected {
+		return nil
+	}
+
+	s.connected = false
+	return s.client.Close()
+}
+
+// ensureConnected connects to the SSH server, unless a AuthMethod was set with
+// SetAuth method, by default uses an auth method based on PublicKeysCallback,
+// it connects to a SSH agent, using the address stored in the SSH_AUTH_SOCK
+// environment var.
+func (s *session) connect() error {
+	if s.connected {
+		return ErrAlreadyConnected
+	}
+
+	if err := s.setAuthFromEndpoint(); err != nil {
+		return err
+	}
+
+	var err error
+	s.client, err = ssh.Dial("tcp", s.getHostWithPort(), s.auth.clientConfig())
+	if err != nil {
+		return err
+	}
+
+	if err := s.openSSHSession(); err != nil {
+		_ = s.client.Close()
+		return err
+	}
+
+	s.connected = true
+	return nil
+}
+
+func (s *session) getHostWithPort() string {
+	host := s.endpoint.Host
+	if strings.Index(s.endpoint.Host, ":") == -1 {
+		host += ":22"
+	}
+
+	return host
+}
+
+func (s *session) setAuthFromEndpoint() error {
+	var u string
+	if info := s.endpoint.User; info != nil {
+		u = info.Username()
+	}
+
+	var err error
+	s.auth, err = NewSSHAgentAuth(u)
+	return err
+}
+
+func (s *session) openSSHSession() error {
+	var err error
+	s.session, err = s.client.NewSession()
+	if err != nil {
+		return fmt.Errorf("cannot open SSH session: %s", err)
+	}
+
+	s.stdin, err = s.session.StdinPipe()
+	if err != nil {
+		return fmt.Errorf("cannot pipe remote stdin: %s", err)
+	}
+
+	s.stdout, err = s.session.StdoutPipe()
+	if err != nil {
+		return fmt.Errorf("cannot pipe remote stdout: %s", err)
+	}
+
+	return nil
+}
+
+func (s *session) runCommand(cmd string) chan error {
+	done := make(chan error)
+	go func() {
+		done <- s.session.Run(cmd)
+	}()
+
+	return done
+}
diff --git a/plumbing/transport/ssh/common_test.go b/plumbing/transport/ssh/common_test.go
new file mode 100644
index 0000000..ac4d03e
--- /dev/null
+++ b/plumbing/transport/ssh/common_test.go
@@ -0,0 +1,17 @@
+package ssh
+
+import (
+	"testing"
+
+	. "gopkg.in/check.v1"
+)
+
+func Test(t *testing.T) { TestingT(t) }
+
+type ClientSuite struct{}
+
+var _ = Suite(&ClientSuite{})
+
+func (s *ClientSuite) TestNewClient(c *C) {
+	c.Assert(DefaultClient, DeepEquals, NewClient())
+}
diff --git a/plumbing/transport/ssh/fetch_pack.go b/plumbing/transport/ssh/fetch_pack.go
new file mode 100644
index 0000000..bda4edf
--- /dev/null
+++ b/plumbing/transport/ssh/fetch_pack.go
@@ -0,0 +1,202 @@
+// Package ssh implements a ssh client for go-git.
+package ssh
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+
+	"gopkg.in/src-d/go-git.v4/plumbing/format/packp/pktline"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/packp/ulreq"
+	"gopkg.in/src-d/go-git.v4/plumbing/transport"
+
+	"golang.org/x/crypto/ssh"
+)
+
+type fetchPackSession struct {
+	*session
+	cmdRun     bool
+	advRefsRun bool
+	done       chan error
+}
+
+func newFetchPackSession(ep transport.Endpoint) (*fetchPackSession, error) {
+	s := &fetchPackSession{
+		session: &session{
+			endpoint: ep,
+		},
+	}
+	if err := s.connect(); err != nil {
+		return nil, err
+	}
+
+	return s, nil
+}
+
+func (s *fetchPackSession) AdvertisedReferences() (*transport.UploadPackInfo, error) {
+	if s.advRefsRun {
+		return nil, ErrAdvertistedReferencesAlreadyCalled
+	}
+
+	if err := s.ensureRunCommand(); err != nil {
+		return nil, err
+	}
+
+	defer func() { s.advRefsRun = true }()
+
+	i := transport.NewUploadPackInfo()
+	return i, i.Decode(s.stdout)
+}
+
+// FetchPack returns a packfile for a given upload request.
+// Closing the returned reader will close the SSH session.
+func (s *fetchPackSession) FetchPack(req *transport.UploadPackRequest) (
+	io.ReadCloser, error) {
+
+	if !s.advRefsRun {
+		if _, err := s.AdvertisedReferences(); err != nil {
+			return nil, err
+		}
+	}
+
+	if err := fetchPack(s.stdin, s.stdout, req); err != nil {
+		return nil, err
+	}
+
+	return &fetchSession{
+		Reader:  s.stdout,
+		session: s.session.session,
+		done:    s.done,
+	}, nil
+}
+
+func (s *fetchPackSession) ensureRunCommand() error {
+	if s.cmdRun {
+		return nil
+	}
+
+	s.cmdRun = true
+	s.done = s.runCommand(s.getCommand())
+	return nil
+}
+
+type fetchSession struct {
+	io.Reader
+	session *ssh.Session
+	done    <-chan error
+}
+
+// Close closes the session and collects the output state of the remote
+// SSH command.
+//
+// If both the remote command and the closing of the session completes
+// susccessfully it returns nil.
+//
+// If the remote command completes unsuccessfully or is interrupted by a
+// signal, it returns the corresponding *ExitError.
+//
+// Otherwise, if clossing the SSH session fails it returns the close
+// error.  Closing the session when the other has already close it is
+// not cosidered an error.
+func (f *fetchSession) Close() (err error) {
+	if err := <-f.done; err != nil {
+		return err
+	}
+
+	if err := f.session.Close(); err != nil && err != io.EOF {
+		return err
+	}
+
+	return nil
+}
+
+func (s *fetchPackSession) getCommand() string {
+	directory := s.endpoint.Path
+	directory = directory[1:]
+
+	return fmt.Sprintf("git-upload-pack '%s'", directory)
+}
+
+var (
+	nak = []byte("NAK")
+	eol = []byte("\n")
+)
+
+// FetchPack implements the git-fetch-pack protocol.
+//
+// TODO support multi_ack mode
+// TODO support multi_ack_detailed mode
+// TODO support acks for common objects
+// TODO build a proper state machine for all these processing options
+func fetchPack(w io.WriteCloser, r io.Reader,
+	req *transport.UploadPackRequest) error {
+
+	if err := sendUlReq(w, req); err != nil {
+		return fmt.Errorf("sending upload-req message: %s", err)
+	}
+
+	if err := sendHaves(w, req); err != nil {
+		return fmt.Errorf("sending haves message: %s", err)
+	}
+
+	if err := sendDone(w); err != nil {
+		return fmt.Errorf("sending done message: %s", err)
+	}
+
+	if err := w.Close(); err != nil {
+		return fmt.Errorf("closing input: %s", err)
+	}
+
+	if err := readNAK(r); err != nil {
+		return fmt.Errorf("reading NAK: %s", err)
+	}
+
+	return nil
+}
+
+func sendUlReq(w io.Writer, req *transport.UploadPackRequest) error {
+	ur := ulreq.New()
+	ur.Wants = req.Wants
+	ur.Depth = ulreq.DepthCommits(req.Depth)
+	e := ulreq.NewEncoder(w)
+
+	return e.Encode(ur)
+}
+
+func sendHaves(w io.Writer, req *transport.UploadPackRequest) error {
+	e := pktline.NewEncoder(w)
+	for _, have := range req.Haves {
+		if err := e.Encodef("have %s\n", have); err != nil {
+			return fmt.Errorf("sending haves for %q: %s", have, err)
+		}
+	}
+
+	if len(req.Haves) != 0 {
+		if err := e.Flush(); err != nil {
+			return fmt.Errorf("sending flush-pkt after haves: %s", err)
+		}
+	}
+
+	return nil
+}
+
+func sendDone(w io.Writer) error {
+	e := pktline.NewEncoder(w)
+
+	return e.Encodef("done\n")
+}
+
+func readNAK(r io.Reader) error {
+	s := pktline.NewScanner(r)
+	if !s.Scan() {
+		return s.Err()
+	}
+
+	b := s.Bytes()
+	b = bytes.TrimSuffix(b, eol)
+	if !bytes.Equal(b, nak) {
+		return fmt.Errorf("expecting NAK, found %q instead", string(b))
+	}
+
+	return nil
+}
diff --git a/plumbing/transport/ssh/fetch_pack_test.go b/plumbing/transport/ssh/fetch_pack_test.go
new file mode 100644
index 0000000..3d62e57
--- /dev/null
+++ b/plumbing/transport/ssh/fetch_pack_test.go
@@ -0,0 +1,100 @@
+package ssh
+
+import (
+	"io/ioutil"
+	"os"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/transport"
+
+	. "gopkg.in/check.v1"
+)
+
+type FetchPackSuite struct {
+	Endpoint transport.Endpoint
+}
+
+var _ = Suite(&FetchPackSuite{})
+
+func (s *FetchPackSuite) SetUpSuite(c *C) {
+	var err error
+	s.Endpoint, err = transport.NewEndpoint("git@github.com:git-fixtures/basic.git")
+	c.Assert(err, IsNil)
+
+	if os.Getenv("SSH_AUTH_SOCK") == "" {
+		c.Skip("SSH_AUTH_SOCK is not set")
+	}
+}
+
+func (s *FetchPackSuite) TestDefaultBranch(c *C) {
+	r, err := DefaultClient.NewFetchPackSession(s.Endpoint)
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(r.Close(), IsNil) }()
+
+	info, err := r.AdvertisedReferences()
+	c.Assert(err, IsNil)
+	c.Assert(info.Capabilities.SymbolicReference("HEAD"), Equals, "refs/heads/master")
+}
+
+func (s *FetchPackSuite) TestCapabilities(c *C) {
+	r, err := DefaultClient.NewFetchPackSession(s.Endpoint)
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(r.Close(), IsNil) }()
+
+	info, err := r.AdvertisedReferences()
+	c.Assert(err, IsNil)
+	c.Assert(info.Capabilities.Get("agent").Values, HasLen, 1)
+}
+
+func (s *FetchPackSuite) TestFullFetchPack(c *C) {
+	r, err := DefaultClient.NewFetchPackSession(s.Endpoint)
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(r.Close(), IsNil) }()
+
+	_, err = r.AdvertisedReferences()
+	c.Assert(err, IsNil)
+
+	req := &transport.UploadPackRequest{}
+	req.Want(plumbing.NewHash("6ecf0ef2c2dffb796033e5a02219af86ec6584e5"))
+	req.Want(plumbing.NewHash("e8d3ffab552895c19b9fcf7aa264d277cde33881"))
+	reader, err := r.FetchPack(req)
+	c.Assert(err, IsNil)
+
+	defer func() { c.Assert(reader.Close(), IsNil) }()
+
+	b, err := ioutil.ReadAll(reader)
+	c.Assert(err, IsNil)
+	c.Check(len(b), Equals, 85585)
+}
+
+func (s *FetchPackSuite) TestFetchPack(c *C) {
+	r, err := DefaultClient.NewFetchPackSession(s.Endpoint)
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(r.Close(), IsNil) }()
+
+	req := &transport.UploadPackRequest{}
+	req.Want(plumbing.NewHash("6ecf0ef2c2dffb796033e5a02219af86ec6584e5"))
+	req.Want(plumbing.NewHash("e8d3ffab552895c19b9fcf7aa264d277cde33881"))
+	reader, err := r.FetchPack(req)
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(reader.Close(), IsNil) }()
+
+	b, err := ioutil.ReadAll(reader)
+	c.Assert(err, IsNil)
+	c.Check(len(b), Equals, 85585)
+}
+
+func (s *FetchPackSuite) TestFetchError(c *C) {
+	r, err := DefaultClient.NewFetchPackSession(s.Endpoint)
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(r.Close(), IsNil) }()
+
+	req := &transport.UploadPackRequest{}
+	req.Want(plumbing.NewHash("1111111111111111111111111111111111111111"))
+
+	reader, err := r.FetchPack(req)
+	c.Assert(err, IsNil)
+
+	err = reader.Close()
+	c.Assert(err, Not(IsNil))
+}
diff --git a/plumbing/transport/ssh/send_pack.go b/plumbing/transport/ssh/send_pack.go
new file mode 100644
index 0000000..afe7510
--- /dev/null
+++ b/plumbing/transport/ssh/send_pack.go
@@ -0,0 +1,30 @@
+package ssh
+
+import (
+	"errors"
+	"io"
+
+	"gopkg.in/src-d/go-git.v4/plumbing/transport"
+)
+
+var errSendPackNotSupported = errors.New("send-pack not supported yet")
+
+type sendPackSession struct {
+	*session
+}
+
+func newSendPackSession(ep transport.Endpoint) (transport.SendPackSession,
+	error) {
+
+	return &sendPackSession{&session{}}, nil
+}
+
+func (s *sendPackSession) AdvertisedReferences() (*transport.UploadPackInfo,
+	error) {
+
+	return nil, errSendPackNotSupported
+}
+
+func (s *sendPackSession) SendPack() (io.WriteCloser, error) {
+	return nil, errSendPackNotSupported
+}