terminal.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package term
     6  
     7  import (
     8  	"bytes"
     9  	"io"
    10  	"runtime"
    11  	"strconv"
    12  	"sync"
    13  	"unicode/utf8"
    14  )
    15  
    16  // EscapeCodes contains escape sequences that can be written to the terminal in
    17  // order to achieve different styles of text.
    18  type EscapeCodes struct {
    19  	// Foreground colors
    20  	Black, Red, Green, Yellow, Blue, Magenta, Cyan, White []byte
    21  
    22  	// Reset all attributes
    23  	Reset []byte
    24  }
    25  
    26  var vt100EscapeCodes = EscapeCodes{
    27  	Black:   []byte{keyEscape, '[', '3', '0', 'm'},
    28  	Red:     []byte{keyEscape, '[', '3', '1', 'm'},
    29  	Green:   []byte{keyEscape, '[', '3', '2', 'm'},
    30  	Yellow:  []byte{keyEscape, '[', '3', '3', 'm'},
    31  	Blue:    []byte{keyEscape, '[', '3', '4', 'm'},
    32  	Magenta: []byte{keyEscape, '[', '3', '5', 'm'},
    33  	Cyan:    []byte{keyEscape, '[', '3', '6', 'm'},
    34  	White:   []byte{keyEscape, '[', '3', '7', 'm'},
    35  
    36  	Reset: []byte{keyEscape, '[', '0', 'm'},
    37  }
    38  
    39  // Terminal contains the state for running a VT100 terminal that is capable of
    40  // reading lines of input.
    41  type Terminal struct {
    42  	// AutoCompleteCallback, if non-null, is called for each keypress with
    43  	// the full input line and the current position of the cursor (in
    44  	// bytes, as an index into |line|). If it returns ok=false, the key
    45  	// press is processed normally. Otherwise it returns a replacement line
    46  	// and the new cursor position.
    47  	AutoCompleteCallback func(line string, pos int, key rune) (newLine string, newPos int, ok bool)
    48  
    49  	// Escape contains a pointer to the escape codes for this terminal.
    50  	// It's always a valid pointer, although the escape codes themselves
    51  	// may be empty if the terminal doesn't support them.
    52  	Escape *EscapeCodes
    53  
    54  	// lock protects the terminal and the state in this object from
    55  	// concurrent processing of a key press and a Write() call.
    56  	lock sync.Mutex
    57  
    58  	c      io.ReadWriter
    59  	prompt []rune
    60  
    61  	// line is the current line being entered.
    62  	line []rune
    63  	// pos is the logical position of the cursor in line
    64  	pos int
    65  	// echo is true if local echo is enabled
    66  	echo bool
    67  	// pasteActive is true iff there is a bracketed paste operation in
    68  	// progress.
    69  	pasteActive bool
    70  
    71  	// cursorX contains the current X value of the cursor where the left
    72  	// edge is 0. cursorY contains the row number where the first row of
    73  	// the current line is 0.
    74  	cursorX, cursorY int
    75  	// maxLine is the greatest value of cursorY so far.
    76  	maxLine int
    77  
    78  	termWidth, termHeight int
    79  
    80  	// outBuf contains the terminal data to be sent.
    81  	outBuf []byte
    82  	// remainder contains the remainder of any partial key sequences after
    83  	// a read. It aliases into inBuf.
    84  	remainder []byte
    85  	inBuf     [256]byte
    86  
    87  	// history contains previously entered commands so that they can be
    88  	// accessed with the up and down keys.
    89  	history stRingBuffer
    90  	// historyIndex stores the currently accessed history entry, where zero
    91  	// means the immediately previous entry.
    92  	historyIndex int
    93  	// When navigating up and down the history it's possible to return to
    94  	// the incomplete, initial line. That value is stored in
    95  	// historyPending.
    96  	historyPending string
    97  }
    98  
    99  // NewTerminal runs a VT100 terminal on the given ReadWriter. If the ReadWriter is
   100  // a local terminal, that terminal must first have been put into raw mode.
   101  // prompt is a string that is written at the start of each input line (i.e.
   102  // "> ").
   103  func NewTerminal(c io.ReadWriter, prompt string) *Terminal {
   104  	return &Terminal{
   105  		Escape:       &vt100EscapeCodes,
   106  		c:            c,
   107  		prompt:       []rune(prompt),
   108  		termWidth:    80,
   109  		termHeight:   24,
   110  		echo:         true,
   111  		historyIndex: -1,
   112  	}
   113  }
   114  
   115  const (
   116  	keyCtrlC     = 3
   117  	keyCtrlD     = 4
   118  	keyCtrlU     = 21
   119  	keyEnter     = '\r'
   120  	keyEscape    = 27
   121  	keyBackspace = 127
   122  	keyUnknown   = 0xd800 /* UTF-16 surrogate area */ + iota
   123  	keyUp
   124  	keyDown
   125  	keyLeft
   126  	keyRight
   127  	keyAltLeft
   128  	keyAltRight
   129  	keyHome
   130  	keyEnd
   131  	keyDeleteWord
   132  	keyDeleteLine
   133  	keyClearScreen
   134  	keyPasteStart
   135  	keyPasteEnd
   136  )
   137  
   138  var (
   139  	crlf       = []byte{'\r', '\n'}
   140  	pasteStart = []byte{keyEscape, '[', '2', '0', '0', '~'}
   141  	pasteEnd   = []byte{keyEscape, '[', '2', '0', '1', '~'}
   142  )
   143  
   144  // bytesToKey tries to parse a key sequence from b. If successful, it returns
   145  // the key and the remainder of the input. Otherwise it returns utf8.RuneError.
   146  func bytesToKey(b []byte, pasteActive bool) (rune, []byte) {
   147  	if len(b) == 0 {
   148  		return utf8.RuneError, nil
   149  	}
   150  
   151  	if !pasteActive {
   152  		switch b[0] {
   153  		case 1: // ^A
   154  			return keyHome, b[1:]
   155  		case 2: // ^B
   156  			return keyLeft, b[1:]
   157  		case 5: // ^E
   158  			return keyEnd, b[1:]
   159  		case 6: // ^F
   160  			return keyRight, b[1:]
   161  		case 8: // ^H
   162  			return keyBackspace, b[1:]
   163  		case 11: // ^K
   164  			return keyDeleteLine, b[1:]
   165  		case 12: // ^L
   166  			return keyClearScreen, b[1:]
   167  		case 23: // ^W
   168  			return keyDeleteWord, b[1:]
   169  		case 14: // ^N
   170  			return keyDown, b[1:]
   171  		case 16: // ^P
   172  			return keyUp, b[1:]
   173  		}
   174  	}
   175  
   176  	if b[0] != keyEscape {
   177  		if !utf8.FullRune(b) {
   178  			return utf8.RuneError, b
   179  		}
   180  		r, l := utf8.DecodeRune(b)
   181  		return r, b[l:]
   182  	}
   183  
   184  	if !pasteActive && len(b) >= 3 && b[0] == keyEscape && b[1] == '[' {
   185  		switch b[2] {
   186  		case 'A':
   187  			return keyUp, b[3:]
   188  		case 'B':
   189  			return keyDown, b[3:]
   190  		case 'C':
   191  			return keyRight, b[3:]
   192  		case 'D':
   193  			return keyLeft, b[3:]
   194  		case 'H':
   195  			return keyHome, b[3:]
   196  		case 'F':
   197  			return keyEnd, b[3:]
   198  		}
   199  	}
   200  
   201  	if !pasteActive && len(b) >= 6 && b[0] == keyEscape && b[1] == '[' && b[2] == '1' && b[3] == ';' && b[4] == '3' {
   202  		switch b[5] {
   203  		case 'C':
   204  			return keyAltRight, b[6:]
   205  		case 'D':
   206  			return keyAltLeft, b[6:]
   207  		}
   208  	}
   209  
   210  	if !pasteActive && len(b) >= 6 && bytes.Equal(b[:6], pasteStart) {
   211  		return keyPasteStart, b[6:]
   212  	}
   213  
   214  	if pasteActive && len(b) >= 6 && bytes.Equal(b[:6], pasteEnd) {
   215  		return keyPasteEnd, b[6:]
   216  	}
   217  
   218  	// If we get here then we have a key that we don't recognise, or a
   219  	// partial sequence. It's not clear how one should find the end of a
   220  	// sequence without knowing them all, but it seems that [a-zA-Z~] only
   221  	// appears at the end of a sequence.
   222  	for i, c := range b[0:] {
   223  		if c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c == '~' {
   224  			return keyUnknown, b[i+1:]
   225  		}
   226  	}
   227  
   228  	return utf8.RuneError, b
   229  }
   230  
   231  // queue appends data to the end of t.outBuf
   232  func (t *Terminal) queue(data []rune) {
   233  	t.outBuf = append(t.outBuf, []byte(string(data))...)
   234  }
   235  
   236  var eraseUnderCursor = []rune{' ', keyEscape, '[', 'D'}
   237  var space = []rune{' '}
   238  
   239  func isPrintable(key rune) bool {
   240  	isInSurrogateArea := key >= 0xd800 && key <= 0xdbff
   241  	return key >= 32 && !isInSurrogateArea
   242  }
   243  
   244  // moveCursorToPos appends data to t.outBuf which will move the cursor to the
   245  // given, logical position in the text.
   246  func (t *Terminal) moveCursorToPos(pos int) {
   247  	if !t.echo {
   248  		return
   249  	}
   250  
   251  	x := visualLength(t.prompt) + pos
   252  	y := x / t.termWidth
   253  	x = x % t.termWidth
   254  
   255  	up := 0
   256  	if y < t.cursorY {
   257  		up = t.cursorY - y
   258  	}
   259  
   260  	down := 0
   261  	if y > t.cursorY {
   262  		down = y - t.cursorY
   263  	}
   264  
   265  	left := 0
   266  	if x < t.cursorX {
   267  		left = t.cursorX - x
   268  	}
   269  
   270  	right := 0
   271  	if x > t.cursorX {
   272  		right = x - t.cursorX
   273  	}
   274  
   275  	t.cursorX = x
   276  	t.cursorY = y
   277  	t.move(up, down, left, right)
   278  }
   279  
   280  func (t *Terminal) move(up, down, left, right int) {
   281  	m := []rune{}
   282  
   283  	// 1 unit up can be expressed as ^[[A or ^[A
   284  	// 5 units up can be expressed as ^[[5A
   285  
   286  	if up == 1 {
   287  		m = append(m, keyEscape, '[', 'A')
   288  	} else if up > 1 {
   289  		m = append(m, keyEscape, '[')
   290  		m = append(m, []rune(strconv.Itoa(up))...)
   291  		m = append(m, 'A')
   292  	}
   293  
   294  	if down == 1 {
   295  		m = append(m, keyEscape, '[', 'B')
   296  	} else if down > 1 {
   297  		m = append(m, keyEscape, '[')
   298  		m = append(m, []rune(strconv.Itoa(down))...)
   299  		m = append(m, 'B')
   300  	}
   301  
   302  	if right == 1 {
   303  		m = append(m, keyEscape, '[', 'C')
   304  	} else if right > 1 {
   305  		m = append(m, keyEscape, '[')
   306  		m = append(m, []rune(strconv.Itoa(right))...)
   307  		m = append(m, 'C')
   308  	}
   309  
   310  	if left == 1 {
   311  		m = append(m, keyEscape, '[', 'D')
   312  	} else if left > 1 {
   313  		m = append(m, keyEscape, '[')
   314  		m = append(m, []rune(strconv.Itoa(left))...)
   315  		m = append(m, 'D')
   316  	}
   317  
   318  	t.queue(m)
   319  }
   320  
   321  func (t *Terminal) clearLineToRight() {
   322  	op := []rune{keyEscape, '[', 'K'}
   323  	t.queue(op)
   324  }
   325  
   326  const maxLineLength = 4096
   327  
   328  func (t *Terminal) setLine(newLine []rune, newPos int) {
   329  	if t.echo {
   330  		t.moveCursorToPos(0)
   331  		t.writeLine(newLine)
   332  		for i := len(newLine); i < len(t.line); i++ {
   333  			t.writeLine(space)
   334  		}
   335  		t.moveCursorToPos(newPos)
   336  	}
   337  	t.line = newLine
   338  	t.pos = newPos
   339  }
   340  
   341  func (t *Terminal) advanceCursor(places int) {
   342  	t.cursorX += places
   343  	t.cursorY += t.cursorX / t.termWidth
   344  	if t.cursorY > t.maxLine {
   345  		t.maxLine = t.cursorY
   346  	}
   347  	t.cursorX = t.cursorX % t.termWidth
   348  
   349  	if places > 0 && t.cursorX == 0 {
   350  		// Normally terminals will advance the current position
   351  		// when writing a character. But that doesn't happen
   352  		// for the last character in a line. However, when
   353  		// writing a character (except a new line) that causes
   354  		// a line wrap, the position will be advanced two
   355  		// places.
   356  		//
   357  		// So, if we are stopping at the end of a line, we
   358  		// need to write a newline so that our cursor can be
   359  		// advanced to the next line.
   360  		t.outBuf = append(t.outBuf, '\r', '\n')
   361  	}
   362  }
   363  
   364  func (t *Terminal) eraseNPreviousChars(n int) {
   365  	if n == 0 {
   366  		return
   367  	}
   368  
   369  	if t.pos < n {
   370  		n = t.pos
   371  	}
   372  	t.pos -= n
   373  	t.moveCursorToPos(t.pos)
   374  
   375  	copy(t.line[t.pos:], t.line[n+t.pos:])
   376  	t.line = t.line[:len(t.line)-n]
   377  	if t.echo {
   378  		t.writeLine(t.line[t.pos:])
   379  		for i := 0; i < n; i++ {
   380  			t.queue(space)
   381  		}
   382  		t.advanceCursor(n)
   383  		t.moveCursorToPos(t.pos)
   384  	}
   385  }
   386  
   387  // countToLeftWord returns then number of characters from the cursor to the
   388  // start of the previous word.
   389  func (t *Terminal) countToLeftWord() int {
   390  	if t.pos == 0 {
   391  		return 0
   392  	}
   393  
   394  	pos := t.pos - 1
   395  	for pos > 0 {
   396  		if t.line[pos] != ' ' {
   397  			break
   398  		}
   399  		pos--
   400  	}
   401  	for pos > 0 {
   402  		if t.line[pos] == ' ' {
   403  			pos++
   404  			break
   405  		}
   406  		pos--
   407  	}
   408  
   409  	return t.pos - pos
   410  }
   411  
   412  // countToRightWord returns then number of characters from the cursor to the
   413  // start of the next word.
   414  func (t *Terminal) countToRightWord() int {
   415  	pos := t.pos
   416  	for pos < len(t.line) {
   417  		if t.line[pos] == ' ' {
   418  			break
   419  		}
   420  		pos++
   421  	}
   422  	for pos < len(t.line) {
   423  		if t.line[pos] != ' ' {
   424  			break
   425  		}
   426  		pos++
   427  	}
   428  	return pos - t.pos
   429  }
   430  
   431  // visualLength returns the number of visible glyphs in s.
   432  func visualLength(runes []rune) int {
   433  	inEscapeSeq := false
   434  	length := 0
   435  
   436  	for _, r := range runes {
   437  		switch {
   438  		case inEscapeSeq:
   439  			if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') {
   440  				inEscapeSeq = false
   441  			}
   442  		case r == '\x1b':
   443  			inEscapeSeq = true
   444  		default:
   445  			length++
   446  		}
   447  	}
   448  
   449  	return length
   450  }
   451  
   452  // handleKey processes the given key and, optionally, returns a line of text
   453  // that the user has entered.
   454  func (t *Terminal) handleKey(key rune) (line string, ok bool) {
   455  	if t.pasteActive && key != keyEnter {
   456  		t.addKeyToLine(key)
   457  		return
   458  	}
   459  
   460  	switch key {
   461  	case keyBackspace:
   462  		if t.pos == 0 {
   463  			return
   464  		}
   465  		t.eraseNPreviousChars(1)
   466  	case keyAltLeft:
   467  		// move left by a word.
   468  		t.pos -= t.countToLeftWord()
   469  		t.moveCursorToPos(t.pos)
   470  	case keyAltRight:
   471  		// move right by a word.
   472  		t.pos += t.countToRightWord()
   473  		t.moveCursorToPos(t.pos)
   474  	case keyLeft:
   475  		if t.pos == 0 {
   476  			return
   477  		}
   478  		t.pos--
   479  		t.moveCursorToPos(t.pos)
   480  	case keyRight:
   481  		if t.pos == len(t.line) {
   482  			return
   483  		}
   484  		t.pos++
   485  		t.moveCursorToPos(t.pos)
   486  	case keyHome:
   487  		if t.pos == 0 {
   488  			return
   489  		}
   490  		t.pos = 0
   491  		t.moveCursorToPos(t.pos)
   492  	case keyEnd:
   493  		if t.pos == len(t.line) {
   494  			return
   495  		}
   496  		t.pos = len(t.line)
   497  		t.moveCursorToPos(t.pos)
   498  	case keyUp:
   499  		entry, ok := t.history.NthPreviousEntry(t.historyIndex + 1)
   500  		if !ok {
   501  			return "", false
   502  		}
   503  		if t.historyIndex == -1 {
   504  			t.historyPending = string(t.line)
   505  		}
   506  		t.historyIndex++
   507  		runes := []rune(entry)
   508  		t.setLine(runes, len(runes))
   509  	case keyDown:
   510  		switch t.historyIndex {
   511  		case -1:
   512  			return
   513  		case 0:
   514  			runes := []rune(t.historyPending)
   515  			t.setLine(runes, len(runes))
   516  			t.historyIndex--
   517  		default:
   518  			entry, ok := t.history.NthPreviousEntry(t.historyIndex - 1)
   519  			if ok {
   520  				t.historyIndex--
   521  				runes := []rune(entry)
   522  				t.setLine(runes, len(runes))
   523  			}
   524  		}
   525  	case keyEnter:
   526  		t.moveCursorToPos(len(t.line))
   527  		t.queue([]rune("\r\n"))
   528  		line = string(t.line)
   529  		ok = true
   530  		t.line = t.line[:0]
   531  		t.pos = 0
   532  		t.cursorX = 0
   533  		t.cursorY = 0
   534  		t.maxLine = 0
   535  	case keyDeleteWord:
   536  		// Delete zero or more spaces and then one or more characters.
   537  		t.eraseNPreviousChars(t.countToLeftWord())
   538  	case keyDeleteLine:
   539  		// Delete everything from the current cursor position to the
   540  		// end of line.
   541  		for i := t.pos; i < len(t.line); i++ {
   542  			t.queue(space)
   543  			t.advanceCursor(1)
   544  		}
   545  		t.line = t.line[:t.pos]
   546  		t.moveCursorToPos(t.pos)
   547  	case keyCtrlD:
   548  		// Erase the character under the current position.
   549  		// The EOF case when the line is empty is handled in
   550  		// readLine().
   551  		if t.pos < len(t.line) {
   552  			t.pos++
   553  			t.eraseNPreviousChars(1)
   554  		}
   555  	case keyCtrlU:
   556  		t.eraseNPreviousChars(t.pos)
   557  	case keyClearScreen:
   558  		// Erases the screen and moves the cursor to the home position.
   559  		t.queue([]rune("\x1b[2J\x1b[H"))
   560  		t.queue(t.prompt)
   561  		t.cursorX, t.cursorY = 0, 0
   562  		t.advanceCursor(visualLength(t.prompt))
   563  		t.setLine(t.line, t.pos)
   564  	default:
   565  		if t.AutoCompleteCallback != nil {
   566  			prefix := string(t.line[:t.pos])
   567  			suffix := string(t.line[t.pos:])
   568  
   569  			t.lock.Unlock()
   570  			newLine, newPos, completeOk := t.AutoCompleteCallback(prefix+suffix, len(prefix), key)
   571  			t.lock.Lock()
   572  
   573  			if completeOk {
   574  				t.setLine([]rune(newLine), utf8.RuneCount([]byte(newLine)[:newPos]))
   575  				return
   576  			}
   577  		}
   578  		if !isPrintable(key) {
   579  			return
   580  		}
   581  		if len(t.line) == maxLineLength {
   582  			return
   583  		}
   584  		t.addKeyToLine(key)
   585  	}
   586  	return
   587  }
   588  
   589  // addKeyToLine inserts the given key at the current position in the current
   590  // line.
   591  func (t *Terminal) addKeyToLine(key rune) {
   592  	if len(t.line) == cap(t.line) {
   593  		newLine := make([]rune, len(t.line), 2*(1+len(t.line)))
   594  		copy(newLine, t.line)
   595  		t.line = newLine
   596  	}
   597  	t.line = t.line[:len(t.line)+1]
   598  	copy(t.line[t.pos+1:], t.line[t.pos:])
   599  	t.line[t.pos] = key
   600  	if t.echo {
   601  		t.writeLine(t.line[t.pos:])
   602  	}
   603  	t.pos++
   604  	t.moveCursorToPos(t.pos)
   605  }
   606  
   607  func (t *Terminal) writeLine(line []rune) {
   608  	for len(line) != 0 {
   609  		remainingOnLine := t.termWidth - t.cursorX
   610  		todo := len(line)
   611  		if todo > remainingOnLine {
   612  			todo = remainingOnLine
   613  		}
   614  		t.queue(line[:todo])
   615  		t.advanceCursor(visualLength(line[:todo]))
   616  		line = line[todo:]
   617  	}
   618  }
   619  
   620  // writeWithCRLF writes buf to w but replaces all occurrences of \n with \r\n.
   621  func writeWithCRLF(w io.Writer, buf []byte) (n int, err error) {
   622  	for len(buf) > 0 {
   623  		i := bytes.IndexByte(buf, '\n')
   624  		todo := len(buf)
   625  		if i >= 0 {
   626  			todo = i
   627  		}
   628  
   629  		var nn int
   630  		nn, err = w.Write(buf[:todo])
   631  		n += nn
   632  		if err != nil {
   633  			return n, err
   634  		}
   635  		buf = buf[todo:]
   636  
   637  		if i >= 0 {
   638  			if _, err = w.Write(crlf); err != nil {
   639  				return n, err
   640  			}
   641  			n++
   642  			buf = buf[1:]
   643  		}
   644  	}
   645  
   646  	return n, nil
   647  }
   648  
   649  func (t *Terminal) Write(buf []byte) (n int, err error) {
   650  	t.lock.Lock()
   651  	defer t.lock.Unlock()
   652  
   653  	if t.cursorX == 0 && t.cursorY == 0 {
   654  		// This is the easy case: there's nothing on the screen that we
   655  		// have to move out of the way.
   656  		return writeWithCRLF(t.c, buf)
   657  	}
   658  
   659  	// We have a prompt and possibly user input on the screen. We
   660  	// have to clear it first.
   661  	t.move(0 /* up */, 0 /* down */, t.cursorX /* left */, 0 /* right */)
   662  	t.cursorX = 0
   663  	t.clearLineToRight()
   664  
   665  	for t.cursorY > 0 {
   666  		t.move(1 /* up */, 0, 0, 0)
   667  		t.cursorY--
   668  		t.clearLineToRight()
   669  	}
   670  
   671  	if _, err = t.c.Write(t.outBuf); err != nil {
   672  		return
   673  	}
   674  	t.outBuf = t.outBuf[:0]
   675  
   676  	if n, err = writeWithCRLF(t.c, buf); err != nil {
   677  		return
   678  	}
   679  
   680  	t.writeLine(t.prompt)
   681  	if t.echo {
   682  		t.writeLine(t.line)
   683  	}
   684  
   685  	t.moveCursorToPos(t.pos)
   686  
   687  	if _, err = t.c.Write(t.outBuf); err != nil {
   688  		return
   689  	}
   690  	t.outBuf = t.outBuf[:0]
   691  	return
   692  }
   693  
   694  // ReadPassword temporarily changes the prompt and reads a password, without
   695  // echo, from the terminal.
   696  func (t *Terminal) ReadPassword(prompt string) (line string, err error) {
   697  	t.lock.Lock()
   698  	defer t.lock.Unlock()
   699  
   700  	oldPrompt := t.prompt
   701  	t.prompt = []rune(prompt)
   702  	t.echo = false
   703  
   704  	line, err = t.readLine()
   705  
   706  	t.prompt = oldPrompt
   707  	t.echo = true
   708  
   709  	return
   710  }
   711  
   712  // ReadLine returns a line of input from the terminal.
   713  func (t *Terminal) ReadLine() (line string, err error) {
   714  	t.lock.Lock()
   715  	defer t.lock.Unlock()
   716  
   717  	return t.readLine()
   718  }
   719  
   720  func (t *Terminal) readLine() (line string, err error) {
   721  	// t.lock must be held at this point
   722  
   723  	if t.cursorX == 0 && t.cursorY == 0 {
   724  		t.writeLine(t.prompt)
   725  		t.c.Write(t.outBuf)
   726  		t.outBuf = t.outBuf[:0]
   727  	}
   728  
   729  	lineIsPasted := t.pasteActive
   730  
   731  	for {
   732  		rest := t.remainder
   733  		lineOk := false
   734  		for !lineOk {
   735  			var key rune
   736  			key, rest = bytesToKey(rest, t.pasteActive)
   737  			if key == utf8.RuneError {
   738  				break
   739  			}
   740  			if !t.pasteActive {
   741  				if key == keyCtrlD {
   742  					if len(t.line) == 0 {
   743  						return "", io.EOF
   744  					}
   745  				}
   746  				if key == keyCtrlC {
   747  					return "", io.EOF
   748  				}
   749  				if key == keyPasteStart {
   750  					t.pasteActive = true
   751  					if len(t.line) == 0 {
   752  						lineIsPasted = true
   753  					}
   754  					continue
   755  				}
   756  			} else if key == keyPasteEnd {
   757  				t.pasteActive = false
   758  				continue
   759  			}
   760  			if !t.pasteActive {
   761  				lineIsPasted = false
   762  			}
   763  			line, lineOk = t.handleKey(key)
   764  		}
   765  		if len(rest) > 0 {
   766  			n := copy(t.inBuf[:], rest)
   767  			t.remainder = t.inBuf[:n]
   768  		} else {
   769  			t.remainder = nil
   770  		}
   771  		t.c.Write(t.outBuf)
   772  		t.outBuf = t.outBuf[:0]
   773  		if lineOk {
   774  			if t.echo {
   775  				t.historyIndex = -1
   776  				t.history.Add(line)
   777  			}
   778  			if lineIsPasted {
   779  				err = ErrPasteIndicator
   780  			}
   781  			return
   782  		}
   783  
   784  		// t.remainder is a slice at the beginning of t.inBuf
   785  		// containing a partial key sequence
   786  		readBuf := t.inBuf[len(t.remainder):]
   787  		var n int
   788  
   789  		t.lock.Unlock()
   790  		n, err = t.c.Read(readBuf)
   791  		t.lock.Lock()
   792  
   793  		if err != nil {
   794  			return
   795  		}
   796  
   797  		t.remainder = t.inBuf[:n+len(t.remainder)]
   798  	}
   799  }
   800  
   801  // SetPrompt sets the prompt to be used when reading subsequent lines.
   802  func (t *Terminal) SetPrompt(prompt string) {
   803  	t.lock.Lock()
   804  	defer t.lock.Unlock()
   805  
   806  	t.prompt = []rune(prompt)
   807  }
   808  
   809  func (t *Terminal) clearAndRepaintLinePlusNPrevious(numPrevLines int) {
   810  	// Move cursor to column zero at the start of the line.
   811  	t.move(t.cursorY, 0, t.cursorX, 0)
   812  	t.cursorX, t.cursorY = 0, 0
   813  	t.clearLineToRight()
   814  	for t.cursorY < numPrevLines {
   815  		// Move down a line
   816  		t.move(0, 1, 0, 0)
   817  		t.cursorY++
   818  		t.clearLineToRight()
   819  	}
   820  	// Move back to beginning.
   821  	t.move(t.cursorY, 0, 0, 0)
   822  	t.cursorX, t.cursorY = 0, 0
   823  
   824  	t.queue(t.prompt)
   825  	t.advanceCursor(visualLength(t.prompt))
   826  	t.writeLine(t.line)
   827  	t.moveCursorToPos(t.pos)
   828  }
   829  
   830  func (t *Terminal) SetSize(width, height int) error {
   831  	t.lock.Lock()
   832  	defer t.lock.Unlock()
   833  
   834  	if width == 0 {
   835  		width = 1
   836  	}
   837  
   838  	oldWidth := t.termWidth
   839  	t.termWidth, t.termHeight = width, height
   840  
   841  	switch {
   842  	case width == oldWidth:
   843  		// If the width didn't change then nothing else needs to be
   844  		// done.
   845  		return nil
   846  	case len(t.line) == 0 && t.cursorX == 0 && t.cursorY == 0:
   847  		// If there is nothing on current line and no prompt printed,
   848  		// just do nothing
   849  		return nil
   850  	case width < oldWidth:
   851  		// Some terminals (e.g. xterm) will truncate lines that were
   852  		// too long when shinking. Others, (e.g. gnome-terminal) will
   853  		// attempt to wrap them. For the former, repainting t.maxLine
   854  		// works great, but that behaviour goes badly wrong in the case
   855  		// of the latter because they have doubled every full line.
   856  
   857  		// We assume that we are working on a terminal that wraps lines
   858  		// and adjust the cursor position based on every previous line
   859  		// wrapping and turning into two. This causes the prompt on
   860  		// xterms to move upwards, which isn't great, but it avoids a
   861  		// huge mess with gnome-terminal.
   862  		if t.cursorX >= t.termWidth {
   863  			t.cursorX = t.termWidth - 1
   864  		}
   865  		t.cursorY *= 2
   866  		t.clearAndRepaintLinePlusNPrevious(t.maxLine * 2)
   867  	case width > oldWidth:
   868  		// If the terminal expands then our position calculations will
   869  		// be wrong in the future because we think the cursor is
   870  		// |t.pos| chars into the string, but there will be a gap at
   871  		// the end of any wrapped line.
   872  		//
   873  		// But the position will actually be correct until we move, so
   874  		// we can move back to the beginning and repaint everything.
   875  		t.clearAndRepaintLinePlusNPrevious(t.maxLine)
   876  	}
   877  
   878  	_, err := t.c.Write(t.outBuf)
   879  	t.outBuf = t.outBuf[:0]
   880  	return err
   881  }
   882  
   883  type pasteIndicatorError struct{}
   884  
   885  func (pasteIndicatorError) Error() string {
   886  	return "terminal: ErrPasteIndicator not correctly handled"
   887  }
   888  
   889  // ErrPasteIndicator may be returned from ReadLine as the error, in addition
   890  // to valid line data. It indicates that bracketed paste mode is enabled and
   891  // that the returned line consists only of pasted data. Programs may wish to
   892  // interpret pasted data more literally than typed data.
   893  var ErrPasteIndicator = pasteIndicatorError{}
   894  
   895  // SetBracketedPasteMode requests that the terminal bracket paste operations
   896  // with markers. Not all terminals support this but, if it is supported, then
   897  // enabling this mode will stop any autocomplete callback from running due to
   898  // pastes. Additionally, any lines that are completely pasted will be returned
   899  // from ReadLine with the error set to ErrPasteIndicator.
   900  func (t *Terminal) SetBracketedPasteMode(on bool) {
   901  	if on {
   902  		io.WriteString(t.c, "\x1b[?2004h")
   903  	} else {
   904  		io.WriteString(t.c, "\x1b[?2004l")
   905  	}
   906  }
   907  
   908  // stRingBuffer is a ring buffer of strings.
   909  type stRingBuffer struct {
   910  	// entries contains max elements.
   911  	entries []string
   912  	max     int
   913  	// head contains the index of the element most recently added to the ring.
   914  	head int
   915  	// size contains the number of elements in the ring.
   916  	size int
   917  }
   918  
   919  func (s *stRingBuffer) Add(a string) {
   920  	if s.entries == nil {
   921  		const defaultNumEntries = 100
   922  		s.entries = make([]string, defaultNumEntries)
   923  		s.max = defaultNumEntries
   924  	}
   925  
   926  	s.head = (s.head + 1) % s.max
   927  	s.entries[s.head] = a
   928  	if s.size < s.max {
   929  		s.size++
   930  	}
   931  }
   932  
   933  // NthPreviousEntry returns the value passed to the nth previous call to Add.
   934  // If n is zero then the immediately prior value is returned, if one, then the
   935  // next most recent, and so on. If such an element doesn't exist then ok is
   936  // false.
   937  func (s *stRingBuffer) NthPreviousEntry(n int) (value string, ok bool) {
   938  	if n >= s.size {
   939  		return "", false
   940  	}
   941  	index := s.head - n
   942  	if index < 0 {
   943  		index += s.max
   944  	}
   945  	return s.entries[index], true
   946  }
   947  
   948  // readPasswordLine reads from reader until it finds \n or io.EOF.
   949  // The slice returned does not include the \n.
   950  // readPasswordLine also ignores any \r it finds.
   951  // Windows uses \r as end of line. So, on Windows, readPasswordLine
   952  // reads until it finds \r and ignores any \n it finds during processing.
   953  func readPasswordLine(reader io.Reader) ([]byte, error) {
   954  	var buf [1]byte
   955  	var ret []byte
   956  
   957  	for {
   958  		n, err := reader.Read(buf[:])
   959  		if n > 0 {
   960  			switch buf[0] {
   961  			case '\b':
   962  				if len(ret) > 0 {
   963  					ret = ret[:len(ret)-1]
   964  				}
   965  			case '\n':
   966  				if runtime.GOOS != "windows" {
   967  					return ret, nil
   968  				}
   969  				// otherwise ignore \n
   970  			case '\r':
   971  				if runtime.GOOS == "windows" {
   972  					return ret, nil
   973  				}
   974  				// otherwise ignore \r
   975  			default:
   976  				ret = append(ret, buf[0])
   977  			}
   978  			continue
   979  		}
   980  		if err != nil {
   981  			if err == io.EOF && len(ret) > 0 {
   982  				return ret, nil
   983  			}
   984  			return ret, err
   985  		}
   986  	}
   987  }
   988
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