ssh: implement protocol handling for pure SSH-based protocol

bk2204 · bk2204 · commit b4544ca5bb44 · 2021-07-20T18:39:12.000Z
With the pure SSH-based protocol, we have a couple different types of
messages that can be sent and received.  Let's implement generic helpers
for these types so we can use them later on when we implement the actual
protocol.
diff --git a/ssh/protocol.go b/ssh/protocol.go
@@ -0,0 +1,252 @@
+package ssh
+
+import (
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+	"sync"
+
+	"github.com/git-lfs/git-lfs/errors"
+	"github.com/git-lfs/git-lfs/subprocess"
+)
+
+type PktlineConnection struct {
+	mu  sync.Mutex
+	cmd *subprocess.Cmd
+	pl  Pktline
+}
+
+func (conn *PktlineConnection) Lock() {
+	conn.mu.Lock()
+}
+
+func (conn *PktlineConnection) Unlock() {
+	conn.mu.Unlock()
+}
+
+func (conn *PktlineConnection) Start() error {
+	conn.Lock()
+	defer conn.Unlock()
+	return conn.negotiateVersion()
+}
+
+func (conn *PktlineConnection) End() error {
+	conn.Lock()
+	defer conn.Unlock()
+	err := conn.SendMessage("quit", nil)
+	if err != nil {
+		return err
+	}
+	_, err = conn.ReadStatus()
+	conn.cmd.Wait()
+	return err
+}
+
+func (conn *PktlineConnection) negotiateVersion() error {
+	pkts, err := conn.pl.ReadPacketList()
+	if err != nil {
+		return errors.NewProtocolError("Unable to negotiate version with remote side (unable to read capabilities)", err)
+	}
+	ok := false
+	for _, line := range pkts {
+		if line == "version=1" {
+			ok = true
+		}
+	}
+	if !ok {
+		return errors.NewProtocolError("Unable to negotiate version with remote side (missing version=1)", nil)
+	}
+	err = conn.SendMessage("version 1", nil)
+	if err != nil {
+		return errors.NewProtocolError("Unable to negotiate version with remote side (unable to send version)", err)
+	}
+	status, args, _, err := conn.ReadStatusWithLines()
+	if err != nil {
+		return errors.NewProtocolError("Unable to negotiate version with remote side (unable to read status)", err)
+	}
+	if status != 200 {
+		text := "no error provided"
+		if len(args) > 0 {
+			text = fmt.Sprintf("server said: %q", args[0])
+		}
+		return errors.NewProtocolError(fmt.Sprintf("Unable to negotiate version with remote side (unexpected status %d; %s)", status, text), nil)
+	}
+	return nil
+}
+
+func (conn *PktlineConnection) SendMessage(command string, args []string) error {
+	err := conn.pl.WritePacketText(command)
+	if err != nil {
+		return err
+	}
+	for _, arg := range args {
+		err = conn.pl.WritePacketText(arg)
+		if err != nil {
+			return err
+		}
+	}
+	return conn.pl.WriteFlush()
+}
+
+func (conn *PktlineConnection) SendMessageWithLines(command string, args []string, lines []string) error {
+	err := conn.pl.WritePacketText(command)
+	if err != nil {
+		return err
+	}
+	for _, arg := range args {
+		err = conn.pl.WritePacketText(arg)
+		if err != nil {
+			return err
+		}
+	}
+	err = conn.pl.WriteDelim()
+	if err != nil {
+		return err
+	}
+	for _, line := range lines {
+		err = conn.pl.WritePacketText(line)
+		if err != nil {
+			return err
+		}
+	}
+	return conn.pl.WriteFlush()
+}
+
+func (conn *PktlineConnection) SendMessageWithData(command string, args []string, data io.Reader) error {
+	err := conn.pl.WritePacketText(command)
+	if err != nil {
+		return err
+	}
+	for _, arg := range args {
+		err = conn.pl.WritePacketText(arg)
+		if err != nil {
+			return err
+		}
+	}
+	err = conn.pl.WriteDelim()
+	if err != nil {
+		return err
+	}
+	buf := make([]byte, 32768)
+	for {
+		n, err := data.Read(buf)
+		if n > 0 {
+			err := conn.pl.WritePacket(buf[0:n])
+			if err != nil {
+				return err
+			}
+		}
+		if err != nil {
+			break
+		}
+	}
+	return conn.pl.WriteFlush()
+}
+
+func (conn *PktlineConnection) ReadStatus() (int, error) {
+	status := 0
+	seenStatus := false
+	for {
+		s, pktLen, err := conn.pl.ReadPacketTextWithLength()
+		if err != nil {
+			return 0, errors.NewProtocolError("error reading packet", err)
+		}
+		switch {
+		case pktLen == 0:
+			if !seenStatus {
+				return 0, errors.NewProtocolError("no status seen", nil)
+			}
+			return status, nil
+		case !seenStatus:
+			ok := false
+			if strings.HasPrefix(s, "status ") {
+				status, err = strconv.Atoi(s[7:])
+				ok = err == nil
+			}
+			if !ok {
+				return 0, errors.NewProtocolError(fmt.Sprintf("expected status line, got %q", s), err)
+			}
+			seenStatus = true
+		default:
+			return 0, errors.NewProtocolError(fmt.Sprintf("unexpected data, got %q", s), err)
+		}
+	}
+}
+
+// ReadStatusWithData reads a status, arguments, and any binary data.  Note that
+// the reader must be fully exhausted before invoking any other read methods.
+func (conn *PktlineConnection) ReadStatusWithData() (int, []string, io.Reader, error) {
+	args := make([]string, 0, 100)
+	status := 0
+	seenStatus := false
+	for {
+		s, pktLen, err := conn.pl.ReadPacketTextWithLength()
+		if err != nil {
+			return 0, nil, nil, errors.NewProtocolError("error reading packet", err)
+		}
+		if pktLen == 0 {
+			if !seenStatus {
+				return 0, nil, nil, errors.NewProtocolError("no status seen", nil)
+			}
+			return 0, nil, nil, errors.NewProtocolError("unexpected flush packet", nil)
+		} else if !seenStatus {
+			ok := false
+			if strings.HasPrefix(s, "status ") {
+				status, err = strconv.Atoi(s[7:])
+				ok = err == nil
+			}
+			if !ok {
+				return 0, nil, nil, errors.NewProtocolError(fmt.Sprintf("expected status line, got %q", s), err)
+			}
+			seenStatus = true
+		} else if pktLen == 1 {
+			break
+		} else {
+			args = append(args, s)
+		}
+	}
+
+	return status, args, pktlineReader(conn.pl), nil
+}
+
+// ReadStatusWithLines reads a status, arguments, and a set of text lines.
+func (conn *PktlineConnection) ReadStatusWithLines() (int, []string, []string, error) {
+	args := make([]string, 0, 100)
+	lines := make([]string, 0, 100)
+	status := 0
+	seenDelim := false
+	seenStatus := false
+	for {
+		s, pktLen, err := conn.pl.ReadPacketTextWithLength()
+		if err != nil {
+			return 0, nil, nil, errors.NewProtocolError("error reading packet", err)
+		}
+		switch {
+		case pktLen == 0:
+			if !seenStatus {
+				return 0, nil, nil, errors.NewProtocolError("no status seen", nil)
+			}
+			return status, args, lines, nil
+		case seenDelim:
+			lines = append(lines, s)
+		case !seenStatus:
+			ok := false
+			if strings.HasPrefix(s, "status ") {
+				status, err = strconv.Atoi(s[7:])
+				ok = err == nil
+			}
+			if !ok {
+				return 0, nil, nil, errors.NewProtocolError(fmt.Sprintf("expected status line, got %q", s), err)
+			}
+			seenStatus = true
+		case pktLen == 1:
+			if seenDelim {
+				return 0, nil, nil, errors.NewProtocolError("unexpected delimiter packet", nil)
+			}
+			seenDelim = true
+		default:
+			args = append(args, s)
+		}
+	}
+}
