src/pkg/exp/ssh/server_shell.go - go - 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

 import "io"

 // ServerShell contains the state for running a VT100 terminal that is capable
 // of reading lines of input.
 type ServerShell struct {
 	c      Channel
 	prompt string

 	// line is the current line being entered.
 	line []byte
 	// pos is the logical position of the cursor in line
 	pos int

 	// cursorX contains the current X value of the cursor where the left
 	// edge is 0. cursorY contains the row number where the first row of
 	// the current line is 0.
 	cursorX, cursorY int
 	// maxLine is the greatest value of cursorY so far.
 	maxLine int

 	termWidth, termHeight int

 	// outBuf contains the terminal data to be sent.
 	outBuf []byte
 	// remainder contains the remainder of any partial key sequences after
 	// a read. It aliases into inBuf.
 	remainder []byte
 	inBuf     [256]byte
 }

 // NewServerShell runs a VT100 terminal on the given channel. prompt is a
 // string that is written at the start of each input line. For example: "> ".
 func NewServerShell(c Channel, prompt string) *ServerShell {
 	return &ServerShell{
 		c:          c,
 		prompt:     prompt,
 		termWidth:  80,
 		termHeight: 24,
 	}
 }

 const (
 	keyCtrlD     = 4
 	keyEnter     = '\r'
 	keyEscape    = 27
 	keyBackspace = 127
 	keyUnknown   = 256 + iota
 	keyUp
 	keyDown
 	keyLeft
 	keyRight
 	keyAltLeft
 	keyAltRight
 )

 // bytesToKey tries to parse a key sequence from b. If successful, it returns
 // the key and the remainder of the input. Otherwise it returns -1.
 func bytesToKey(b []byte) (int, []byte) {
 	if len(b) == 0 {
 		return -1, nil
 	}

 	if b[0] != keyEscape {
 		return int(b[0]), b[1:]
 	}

 	if len(b) >= 3 && b[0] == keyEscape && b[1] == '[' {
 		switch b[2] {
 		case 'A':
 			return keyUp, b[3:]
 		case 'B':
 			return keyDown, b[3:]
 		case 'C':
 			return keyRight, b[3:]
 		case 'D':
 			return keyLeft, b[3:]
 		}
 	}

 	if len(b) >= 6 && b[0] == keyEscape && b[1] == '[' && b[2] == '1' && b[3] == ';' && b[4] == '3' {
 		switch b[5] {
 		case 'C':
 			return keyAltRight, b[6:]
 		case 'D':
 			return keyAltLeft, b[6:]
 		}
 	}

 	// If we get here then we have a key that we don't recognise, or a
 	// partial sequence. It's not clear how one should find the end of a
 	// sequence without knowing them all, but it seems that [a-zA-Z] only
 	// appears at the end of a sequence.
 	for i, c := range b[0:] {
 		if c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' {
 			return keyUnknown, b[i+1:]
 		}
 	}

 	return -1, b
 }

 // queue appends data to the end of ss.outBuf
 func (ss *ServerShell) queue(data []byte) {
 	if len(ss.outBuf)+len(data) > cap(ss.outBuf) {
 		newOutBuf := make([]byte, len(ss.outBuf), 2*(len(ss.outBuf)+len(data)))
 		copy(newOutBuf, ss.outBuf)
 		ss.outBuf = newOutBuf
 	}

 	oldLen := len(ss.outBuf)
 	ss.outBuf = ss.outBuf[:len(ss.outBuf)+len(data)]
 	copy(ss.outBuf[oldLen:], data)
 }

 var eraseUnderCursor = []byte{' ', keyEscape, '[', 'D'}

 func isPrintable(key int) bool {
 	return key >= 32 && key < 127
 }

 // moveCursorToPos appends data to ss.outBuf which will move the cursor to the
 // given, logical position in the text.
 func (ss *ServerShell) moveCursorToPos(pos int) {
 	x := len(ss.prompt) + pos
 	y := x / ss.termWidth
 	x = x % ss.termWidth

 	up := 0
 	if y < ss.cursorY {
 		up = ss.cursorY - y
 	}

 	down := 0
 	if y > ss.cursorY {
 		down = y - ss.cursorY
 	}

 	left := 0
 	if x < ss.cursorX {
 		left = ss.cursorX - x
 	}

 	right := 0
 	if x > ss.cursorX {
 		right = x - ss.cursorX
 	}

 	movement := make([]byte, 3*(up+down+left+right))
 	m := movement
 	for i := 0; i < up; i++ {
 		m[0] = keyEscape
 		m[1] = '['
 		m[2] = 'A'
 		m = m[3:]
 	}
 	for i := 0; i < down; i++ {
 		m[0] = keyEscape
 		m[1] = '['
 		m[2] = 'B'
 		m = m[3:]
 	}
 	for i := 0; i < left; i++ {
 		m[0] = keyEscape
 		m[1] = '['
 		m[2] = 'D'
 		m = m[3:]
 	}
 	for i := 0; i < right; i++ {
 		m[0] = keyEscape
 		m[1] = '['
 		m[2] = 'C'
 		m = m[3:]
 	}

 	ss.cursorX = x
 	ss.cursorY = y
 	ss.queue(movement)
 }

 const maxLineLength = 4096

 // handleKey processes the given key and, optionally, returns a line of text
 // that the user has entered.
 func (ss *ServerShell) handleKey(key int) (line string, ok bool) {
 	switch key {
 	case keyBackspace:
 		if ss.pos == 0 {
 			return
 		}
 		ss.pos--

 		copy(ss.line[ss.pos:], ss.line[1+ss.pos:])
 		ss.line = ss.line[:len(ss.line)-1]
 		ss.writeLine(ss.line[ss.pos:])
 		ss.moveCursorToPos(ss.pos)
 		ss.queue(eraseUnderCursor)
 	case keyAltLeft:
 		// move left by a word.
 		if ss.pos == 0 {
 			return
 		}
 		ss.pos--
 		for ss.pos > 0 {
 			if ss.line[ss.pos] != ' ' {
 				break
 			}
 			ss.pos--
 		}
 		for ss.pos > 0 {
 			if ss.line[ss.pos] == ' ' {
 				ss.pos++
 				break
 			}
 			ss.pos--
 		}
 		ss.moveCursorToPos(ss.pos)
 	case keyAltRight:
 		// move right by a word.
 		for ss.pos < len(ss.line) {
 			if ss.line[ss.pos] == ' ' {
 				break
 			}
 			ss.pos++
 		}
 		for ss.pos < len(ss.line) {
 			if ss.line[ss.pos] != ' ' {
 				break
 			}
 			ss.pos++
 		}
 		ss.moveCursorToPos(ss.pos)
 	case keyLeft:
 		if ss.pos == 0 {
 			return
 		}
 		ss.pos--
 		ss.moveCursorToPos(ss.pos)
 	case keyRight:
 		if ss.pos == len(ss.line) {
 			return
 		}
 		ss.pos++
 		ss.moveCursorToPos(ss.pos)
 	case keyEnter:
 		ss.moveCursorToPos(len(ss.line))
 		ss.queue([]byte("\r\n"))
 		line = string(ss.line)
 		ok = true
 		ss.line = ss.line[:0]
 		ss.pos = 0
 		ss.cursorX = 0
 		ss.cursorY = 0
 		ss.maxLine = 0
 	default:
 		if !isPrintable(key) {
 			return
 		}
 		if len(ss.line) == maxLineLength {
 			return
 		}
 		if len(ss.line) == cap(ss.line) {
 			newLine := make([]byte, len(ss.line), 2*(1+len(ss.line)))
 			copy(newLine, ss.line)
 			ss.line = newLine
 		}
 		ss.line = ss.line[:len(ss.line)+1]
 		copy(ss.line[ss.pos+1:], ss.line[ss.pos:])
 		ss.line[ss.pos] = byte(key)
 		ss.writeLine(ss.line[ss.pos:])
 		ss.pos++
 		ss.moveCursorToPos(ss.pos)
 	}
 	return
 }

 func (ss *ServerShell) writeLine(line []byte) {
 	for len(line) != 0 {
 		if ss.cursorX == ss.termWidth {
 			ss.queue([]byte("\r\n"))
 			ss.cursorX = 0
 			ss.cursorY++
 			if ss.cursorY > ss.maxLine {
 				ss.maxLine = ss.cursorY
 			}
 		}

 		remainingOnLine := ss.termWidth - ss.cursorX
 		todo := len(line)
 		if todo > remainingOnLine {
 			todo = remainingOnLine
 		}
 		ss.queue(line[:todo])
 		ss.cursorX += todo
 		line = line[todo:]
 	}
 }

 // parsePtyRequest parses the payload of the pty-req message and extracts the
 // dimensions of the terminal. See RFC 4254, section 6.2.
 func parsePtyRequest(s []byte) (width, height int, ok bool) {
 	_, s, ok = parseString(s)
 	if !ok {
 		return
 	}
 	width32, s, ok := parseUint32(s)
 	if !ok {
 		return
 	}
 	height32, _, ok := parseUint32(s)
 	width = int(width32)
 	height = int(height32)
 	if width < 1 {
 		ok = false
 	}
 	if height < 1 {
 		ok = false
 	}
 	return
 }

 func (ss *ServerShell) Write(buf []byte) (n int, err error) {
 	return ss.c.Write(buf)
 }

 // ReadLine returns a line of input from the terminal.
 func (ss *ServerShell) ReadLine() (line string, err error) {
 	ss.writeLine([]byte(ss.prompt))
 	ss.c.Write(ss.outBuf)
 	ss.outBuf = ss.outBuf[:0]

 	for {
 		// ss.remainder is a slice at the beginning of ss.inBuf
 		// containing a partial key sequence
 		readBuf := ss.inBuf[len(ss.remainder):]
 		var n int
 		n, err = ss.c.Read(readBuf)
 		if err == nil {
 			ss.remainder = ss.inBuf[:n+len(ss.remainder)]
 			rest := ss.remainder
 			lineOk := false
 			for !lineOk {
 				var key int
 				key, rest = bytesToKey(rest)
 				if key < 0 {
 					break
 				}
 				if key == keyCtrlD {
 					return "", io.EOF
 				}
 				line, lineOk = ss.handleKey(key)
 			}
 			if len(rest) > 0 {
 				n := copy(ss.inBuf[:], rest)
 				ss.remainder = ss.inBuf[:n]
 			} else {
 				ss.remainder = nil
 			}
 			ss.c.Write(ss.outBuf)
 			ss.outBuf = ss.outBuf[:0]
 			if lineOk {
 				return
 			}
 			continue
 		}

 		if req, ok := err.(ChannelRequest); ok {
 			ok := false
 			switch req.Request {
 			case "pty-req":
 				ss.termWidth, ss.termHeight, ok = parsePtyRequest(req.Payload)
 				if !ok {
 					ss.termWidth = 80
 					ss.termHeight = 24
 				}
 			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
 			}
 			if req.WantReply {
 				ss.c.AckRequest(ok)
 			}
 		} else {
 			return "", err
 		}
 	}
 	panic("unreachable")
 }
	// 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

	import "io"

	// ServerShell contains the state for running a VT100 terminal that is capable
	// of reading lines of input.
	type ServerShell struct {
	c Channel
	prompt string

	// line is the current line being entered.
	line []byte
	// pos is the logical position of the cursor in line
	pos int

	// cursorX contains the current X value of the cursor where the left
	// edge is 0. cursorY contains the row number where the first row of
	// the current line is 0.
	cursorX, cursorY int
	// maxLine is the greatest value of cursorY so far.
	maxLine int

	termWidth, termHeight int

	// outBuf contains the terminal data to be sent.
	outBuf []byte
	// remainder contains the remainder of any partial key sequences after
	// a read. It aliases into inBuf.
	remainder []byte
	inBuf [256]byte
	}

	// NewServerShell runs a VT100 terminal on the given channel. prompt is a
	// string that is written at the start of each input line. For example: "> ".
	func NewServerShell(c Channel, prompt string) *ServerShell {
	return &ServerShell{
	c: c,
	prompt: prompt,
	termWidth: 80,
	termHeight: 24,
	}
	}

	const (
	keyCtrlD = 4
	keyEnter = '\r'
	keyEscape = 27
	keyBackspace = 127
	keyUnknown = 256 + iota
	keyUp
	keyDown
	keyLeft
	keyRight
	keyAltLeft
	keyAltRight
	)

	// bytesToKey tries to parse a key sequence from b. If successful, it returns
	// the key and the remainder of the input. Otherwise it returns -1.
	func bytesToKey(b []byte) (int, []byte) {
	if len(b) == 0 {
	return -1, nil
	}

	if b[0] != keyEscape {
	return int(b[0]), b[1:]
	}

	if len(b) >= 3 && b[0] == keyEscape && b[1] == '[' {
	switch b[2] {
	case 'A':
	return keyUp, b[3:]
	case 'B':
	return keyDown, b[3:]
	case 'C':
	return keyRight, b[3:]
	case 'D':
	return keyLeft, b[3:]
	}
	}

	if len(b) >= 6 && b[0] == keyEscape && b[1] == '[' && b[2] == '1' && b[3] == ';' && b[4] == '3' {
	switch b[5] {
	case 'C':
	return keyAltRight, b[6:]
	case 'D':
	return keyAltLeft, b[6:]
	}
	}

	// If we get here then we have a key that we don't recognise, or a
	// partial sequence. It's not clear how one should find the end of a
	// sequence without knowing them all, but it seems that [a-zA-Z] only
	// appears at the end of a sequence.
	for i, c := range b[0:] {
	if c >= 'a' && c <= 'z' \|\| c >= 'A' && c <= 'Z' {
	return keyUnknown, b[i+1:]
	}
	}

	return -1, b
	}

	// queue appends data to the end of ss.outBuf
	func (ss *ServerShell) queue(data []byte) {
	if len(ss.outBuf)+len(data) > cap(ss.outBuf) {
	newOutBuf := make([]byte, len(ss.outBuf), 2*(len(ss.outBuf)+len(data)))
	copy(newOutBuf, ss.outBuf)
	ss.outBuf = newOutBuf
	}

	oldLen := len(ss.outBuf)
	ss.outBuf = ss.outBuf[:len(ss.outBuf)+len(data)]
	copy(ss.outBuf[oldLen:], data)
	}

	var eraseUnderCursor = []byte{' ', keyEscape, '[', 'D'}

	func isPrintable(key int) bool {
	return key >= 32 && key < 127
	}

	// moveCursorToPos appends data to ss.outBuf which will move the cursor to the
	// given, logical position in the text.
	func (ss *ServerShell) moveCursorToPos(pos int) {
	x := len(ss.prompt) + pos
	y := x / ss.termWidth
	x = x % ss.termWidth

	up := 0
	if y < ss.cursorY {
	up = ss.cursorY - y
	}

	down := 0
	if y > ss.cursorY {
	down = y - ss.cursorY
	}

	left := 0
	if x < ss.cursorX {
	left = ss.cursorX - x
	}

	right := 0
	if x > ss.cursorX {
	right = x - ss.cursorX
	}

	movement := make([]byte, 3*(up+down+left+right))
	m := movement
	for i := 0; i < up; i++ {
	m[0] = keyEscape
	m[1] = '['
	m[2] = 'A'
	m = m[3:]
	}
	for i := 0; i < down; i++ {
	m[0] = keyEscape
	m[1] = '['
	m[2] = 'B'
	m = m[3:]
	}
	for i := 0; i < left; i++ {
	m[0] = keyEscape
	m[1] = '['
	m[2] = 'D'
	m = m[3:]
	}
	for i := 0; i < right; i++ {
	m[0] = keyEscape
	m[1] = '['
	m[2] = 'C'
	m = m[3:]
	}

	ss.cursorX = x
	ss.cursorY = y
	ss.queue(movement)
	}

	const maxLineLength = 4096

	// handleKey processes the given key and, optionally, returns a line of text
	// that the user has entered.
	func (ss *ServerShell) handleKey(key int) (line string, ok bool) {
	switch key {
	case keyBackspace:
	if ss.pos == 0 {
	return
	}
	ss.pos--

	copy(ss.line[ss.pos:], ss.line[1+ss.pos:])
	ss.line = ss.line[:len(ss.line)-1]
	ss.writeLine(ss.line[ss.pos:])
	ss.moveCursorToPos(ss.pos)
	ss.queue(eraseUnderCursor)
	case keyAltLeft:
	// move left by a word.
	if ss.pos == 0 {
	return
	}
	ss.pos--
	for ss.pos > 0 {
	if ss.line[ss.pos] != ' ' {
	break
	}
	ss.pos--
	}
	for ss.pos > 0 {
	if ss.line[ss.pos] == ' ' {
	ss.pos++
	break
	}
	ss.pos--
	}
	ss.moveCursorToPos(ss.pos)
	case keyAltRight:
	// move right by a word.
	for ss.pos < len(ss.line) {
	if ss.line[ss.pos] == ' ' {
	break
	}
	ss.pos++
	}
	for ss.pos < len(ss.line) {
	if ss.line[ss.pos] != ' ' {
	break
	}
	ss.pos++
	}
	ss.moveCursorToPos(ss.pos)
	case keyLeft:
	if ss.pos == 0 {
	return
	}
	ss.pos--
	ss.moveCursorToPos(ss.pos)
	case keyRight:
	if ss.pos == len(ss.line) {
	return
	}
	ss.pos++
	ss.moveCursorToPos(ss.pos)
	case keyEnter:
	ss.moveCursorToPos(len(ss.line))
	ss.queue([]byte("\r\n"))
	line = string(ss.line)
	ok = true
	ss.line = ss.line[:0]
	ss.pos = 0
	ss.cursorX = 0
	ss.cursorY = 0
	ss.maxLine = 0
	default:
	if !isPrintable(key) {
	return
	}
	if len(ss.line) == maxLineLength {
	return
	}
	if len(ss.line) == cap(ss.line) {
	newLine := make([]byte, len(ss.line), 2*(1+len(ss.line)))
	copy(newLine, ss.line)
	ss.line = newLine
	}
	ss.line = ss.line[:len(ss.line)+1]
	copy(ss.line[ss.pos+1:], ss.line[ss.pos:])
	ss.line[ss.pos] = byte(key)
	ss.writeLine(ss.line[ss.pos:])
	ss.pos++
	ss.moveCursorToPos(ss.pos)
	}
	return
	}

	func (ss *ServerShell) writeLine(line []byte) {
	for len(line) != 0 {
	if ss.cursorX == ss.termWidth {
	ss.queue([]byte("\r\n"))
	ss.cursorX = 0
	ss.cursorY++
	if ss.cursorY > ss.maxLine {
	ss.maxLine = ss.cursorY
	}
	}

	remainingOnLine := ss.termWidth - ss.cursorX
	todo := len(line)
	if todo > remainingOnLine {
	todo = remainingOnLine
	}
	ss.queue(line[:todo])
	ss.cursorX += todo
	line = line[todo:]
	}
	}

	// parsePtyRequest parses the payload of the pty-req message and extracts the
	// dimensions of the terminal. See RFC 4254, section 6.2.
	func parsePtyRequest(s []byte) (width, height int, ok bool) {
	_, s, ok = parseString(s)
	if !ok {
	return
	}
	width32, s, ok := parseUint32(s)
	if !ok {
	return
	}
	height32, _, ok := parseUint32(s)
	width = int(width32)
	height = int(height32)
	if width < 1 {
	ok = false
	}
	if height < 1 {
	ok = false
	}
	return
	}

	func (ss *ServerShell) Write(buf []byte) (n int, err error) {
	return ss.c.Write(buf)
	}

	// ReadLine returns a line of input from the terminal.
	func (ss *ServerShell) ReadLine() (line string, err error) {
	ss.writeLine([]byte(ss.prompt))
	ss.c.Write(ss.outBuf)
	ss.outBuf = ss.outBuf[:0]

	for {
	// ss.remainder is a slice at the beginning of ss.inBuf
	// containing a partial key sequence
	readBuf := ss.inBuf[len(ss.remainder):]
	var n int
	n, err = ss.c.Read(readBuf)
	if err == nil {
	ss.remainder = ss.inBuf[:n+len(ss.remainder)]
	rest := ss.remainder
	lineOk := false
	for !lineOk {
	var key int
	key, rest = bytesToKey(rest)
	if key < 0 {
	break
	}
	if key == keyCtrlD {
	return "", io.EOF
	}
	line, lineOk = ss.handleKey(key)
	}
	if len(rest) > 0 {
	n := copy(ss.inBuf[:], rest)
	ss.remainder = ss.inBuf[:n]
	} else {
	ss.remainder = nil
	}
	ss.c.Write(ss.outBuf)
	ss.outBuf = ss.outBuf[:0]
	if lineOk {
	return
	}
	continue
	}

	if req, ok := err.(ChannelRequest); ok {
	ok := false
	switch req.Request {
	case "pty-req":
	ss.termWidth, ss.termHeight, ok = parsePtyRequest(req.Payload)
	if !ok {
	ss.termWidth = 80
	ss.termHeight = 24
	}
	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
	}
	if req.WantReply {
	ss.c.AckRequest(ok)
	}
	} else {
	return "", err
	}
	}
	panic("unreachable")
	}