syncthing/vendor/golang.org/x/crypto/ssh/terminal/terminal.go
Jakob Borg 916ec63af6 cmd/stdiscosrv: New discovery server (fixes #4618)
This is a new revision of the discovery server. Relevant changes and
non-changes:

- Protocol towards clients is unchanged.

- Recommended large scale design is still to be deployed nehind nginx (I
  tested, and it's still a lot faster at terminating TLS).

- Database backend is leveldb again, only. It scales enough, is easy to
  setup, and we don't need any backend to take care of.

- Server supports replication. This is a simple TCP channel - protect it
  with a firewall when deploying over the internet. (We deploy this within
  the same datacenter, and with firewall.) Any incoming client announces
  are sent over the replication channel(s) to other peer discosrvs.
  Incoming replication changes are applied to the database as if they came
  from clients, but without the TLS/certificate overhead.

- Metrics are exposed using the prometheus library, when enabled.

- The database values and replication protocol is protobuf, because JSON
  was quite CPU intensive when I tried that and benchmarked it.

- The "Retry-After" value for failed lookups gets slowly increased from
  a default of 120 seconds, by 5 seconds for each failed lookup,
  independently by each discosrv. This lowers the query load over time for
  clients that are never seen. The Retry-After maxes out at 3600 after a
  couple of weeks of this increase. The number of failed lookups is
  stored in the database, now and then (avoiding making each lookup a
  database put).

All in all this means clients can be pointed towards a cluster using
just multiple A / AAAA records to gain both load sharing and redundancy
(if one is down, clients will talk to the remaining ones).

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4648
2018-01-14 08:52:31 +00:00

952 lines
22 KiB
Go

// 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 terminal
import (
"bytes"
"io"
"sync"
"unicode/utf8"
)
// EscapeCodes contains escape sequences that can be written to the terminal in
// order to achieve different styles of text.
type EscapeCodes struct {
// Foreground colors
Black, Red, Green, Yellow, Blue, Magenta, Cyan, White []byte
// Reset all attributes
Reset []byte
}
var vt100EscapeCodes = EscapeCodes{
Black: []byte{keyEscape, '[', '3', '0', 'm'},
Red: []byte{keyEscape, '[', '3', '1', 'm'},
Green: []byte{keyEscape, '[', '3', '2', 'm'},
Yellow: []byte{keyEscape, '[', '3', '3', 'm'},
Blue: []byte{keyEscape, '[', '3', '4', 'm'},
Magenta: []byte{keyEscape, '[', '3', '5', 'm'},
Cyan: []byte{keyEscape, '[', '3', '6', 'm'},
White: []byte{keyEscape, '[', '3', '7', 'm'},
Reset: []byte{keyEscape, '[', '0', 'm'},
}
// Terminal contains the state for running a VT100 terminal that is capable of
// reading lines of input.
type Terminal struct {
// AutoCompleteCallback, if non-null, is called for each keypress with
// the full input line and the current position of the cursor (in
// bytes, as an index into |line|). If it returns ok=false, the key
// press is processed normally. Otherwise it returns a replacement line
// and the new cursor position.
AutoCompleteCallback func(line string, pos int, key rune) (newLine string, newPos int, ok bool)
// Escape contains a pointer to the escape codes for this terminal.
// It's always a valid pointer, although the escape codes themselves
// may be empty if the terminal doesn't support them.
Escape *EscapeCodes
// lock protects the terminal and the state in this object from
// concurrent processing of a key press and a Write() call.
lock sync.Mutex
c io.ReadWriter
prompt []rune
// line is the current line being entered.
line []rune
// pos is the logical position of the cursor in line
pos int
// echo is true if local echo is enabled
echo bool
// pasteActive is true iff there is a bracketed paste operation in
// progress.
pasteActive bool
// 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
// history contains previously entered commands so that they can be
// accessed with the up and down keys.
history stRingBuffer
// historyIndex stores the currently accessed history entry, where zero
// means the immediately previous entry.
historyIndex int
// When navigating up and down the history it's possible to return to
// the incomplete, initial line. That value is stored in
// historyPending.
historyPending string
}
// NewTerminal runs a VT100 terminal on the given ReadWriter. If the ReadWriter is
// a local terminal, that terminal must first have been put into raw mode.
// prompt is a string that is written at the start of each input line (i.e.
// "> ").
func NewTerminal(c io.ReadWriter, prompt string) *Terminal {
return &Terminal{
Escape: &vt100EscapeCodes,
c: c,
prompt: []rune(prompt),
termWidth: 80,
termHeight: 24,
echo: true,
historyIndex: -1,
}
}
const (
keyCtrlD = 4
keyCtrlU = 21
keyEnter = '\r'
keyEscape = 27
keyBackspace = 127
keyUnknown = 0xd800 /* UTF-16 surrogate area */ + iota
keyUp
keyDown
keyLeft
keyRight
keyAltLeft
keyAltRight
keyHome
keyEnd
keyDeleteWord
keyDeleteLine
keyClearScreen
keyPasteStart
keyPasteEnd
)
var (
crlf = []byte{'\r', '\n'}
pasteStart = []byte{keyEscape, '[', '2', '0', '0', '~'}
pasteEnd = []byte{keyEscape, '[', '2', '0', '1', '~'}
)
// bytesToKey tries to parse a key sequence from b. If successful, it returns
// the key and the remainder of the input. Otherwise it returns utf8.RuneError.
func bytesToKey(b []byte, pasteActive bool) (rune, []byte) {
if len(b) == 0 {
return utf8.RuneError, nil
}
if !pasteActive {
switch b[0] {
case 1: // ^A
return keyHome, b[1:]
case 5: // ^E
return keyEnd, b[1:]
case 8: // ^H
return keyBackspace, b[1:]
case 11: // ^K
return keyDeleteLine, b[1:]
case 12: // ^L
return keyClearScreen, b[1:]
case 23: // ^W
return keyDeleteWord, b[1:]
}
}
if b[0] != keyEscape {
if !utf8.FullRune(b) {
return utf8.RuneError, b
}
r, l := utf8.DecodeRune(b)
return r, b[l:]
}
if !pasteActive && 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:]
case 'H':
return keyHome, b[3:]
case 'F':
return keyEnd, b[3:]
}
}
if !pasteActive && 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 !pasteActive && len(b) >= 6 && bytes.Equal(b[:6], pasteStart) {
return keyPasteStart, b[6:]
}
if pasteActive && len(b) >= 6 && bytes.Equal(b[:6], pasteEnd) {
return keyPasteEnd, 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' || c == '~' {
return keyUnknown, b[i+1:]
}
}
return utf8.RuneError, b
}
// queue appends data to the end of t.outBuf
func (t *Terminal) queue(data []rune) {
t.outBuf = append(t.outBuf, []byte(string(data))...)
}
var eraseUnderCursor = []rune{' ', keyEscape, '[', 'D'}
var space = []rune{' '}
func isPrintable(key rune) bool {
isInSurrogateArea := key >= 0xd800 && key <= 0xdbff
return key >= 32 && !isInSurrogateArea
}
// moveCursorToPos appends data to t.outBuf which will move the cursor to the
// given, logical position in the text.
func (t *Terminal) moveCursorToPos(pos int) {
if !t.echo {
return
}
x := visualLength(t.prompt) + pos
y := x / t.termWidth
x = x % t.termWidth
up := 0
if y < t.cursorY {
up = t.cursorY - y
}
down := 0
if y > t.cursorY {
down = y - t.cursorY
}
left := 0
if x < t.cursorX {
left = t.cursorX - x
}
right := 0
if x > t.cursorX {
right = x - t.cursorX
}
t.cursorX = x
t.cursorY = y
t.move(up, down, left, right)
}
func (t *Terminal) move(up, down, left, right int) {
movement := make([]rune, 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:]
}
t.queue(movement)
}
func (t *Terminal) clearLineToRight() {
op := []rune{keyEscape, '[', 'K'}
t.queue(op)
}
const maxLineLength = 4096
func (t *Terminal) setLine(newLine []rune, newPos int) {
if t.echo {
t.moveCursorToPos(0)
t.writeLine(newLine)
for i := len(newLine); i < len(t.line); i++ {
t.writeLine(space)
}
t.moveCursorToPos(newPos)
}
t.line = newLine
t.pos = newPos
}
func (t *Terminal) advanceCursor(places int) {
t.cursorX += places
t.cursorY += t.cursorX / t.termWidth
if t.cursorY > t.maxLine {
t.maxLine = t.cursorY
}
t.cursorX = t.cursorX % t.termWidth
if places > 0 && t.cursorX == 0 {
// Normally terminals will advance the current position
// when writing a character. But that doesn't happen
// for the last character in a line. However, when
// writing a character (except a new line) that causes
// a line wrap, the position will be advanced two
// places.
//
// So, if we are stopping at the end of a line, we
// need to write a newline so that our cursor can be
// advanced to the next line.
t.outBuf = append(t.outBuf, '\r', '\n')
}
}
func (t *Terminal) eraseNPreviousChars(n int) {
if n == 0 {
return
}
if t.pos < n {
n = t.pos
}
t.pos -= n
t.moveCursorToPos(t.pos)
copy(t.line[t.pos:], t.line[n+t.pos:])
t.line = t.line[:len(t.line)-n]
if t.echo {
t.writeLine(t.line[t.pos:])
for i := 0; i < n; i++ {
t.queue(space)
}
t.advanceCursor(n)
t.moveCursorToPos(t.pos)
}
}
// countToLeftWord returns then number of characters from the cursor to the
// start of the previous word.
func (t *Terminal) countToLeftWord() int {
if t.pos == 0 {
return 0
}
pos := t.pos - 1
for pos > 0 {
if t.line[pos] != ' ' {
break
}
pos--
}
for pos > 0 {
if t.line[pos] == ' ' {
pos++
break
}
pos--
}
return t.pos - pos
}
// countToRightWord returns then number of characters from the cursor to the
// start of the next word.
func (t *Terminal) countToRightWord() int {
pos := t.pos
for pos < len(t.line) {
if t.line[pos] == ' ' {
break
}
pos++
}
for pos < len(t.line) {
if t.line[pos] != ' ' {
break
}
pos++
}
return pos - t.pos
}
// visualLength returns the number of visible glyphs in s.
func visualLength(runes []rune) int {
inEscapeSeq := false
length := 0
for _, r := range runes {
switch {
case inEscapeSeq:
if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') {
inEscapeSeq = false
}
case r == '\x1b':
inEscapeSeq = true
default:
length++
}
}
return length
}
// handleKey processes the given key and, optionally, returns a line of text
// that the user has entered.
func (t *Terminal) handleKey(key rune) (line string, ok bool) {
if t.pasteActive && key != keyEnter {
t.addKeyToLine(key)
return
}
switch key {
case keyBackspace:
if t.pos == 0 {
return
}
t.eraseNPreviousChars(1)
case keyAltLeft:
// move left by a word.
t.pos -= t.countToLeftWord()
t.moveCursorToPos(t.pos)
case keyAltRight:
// move right by a word.
t.pos += t.countToRightWord()
t.moveCursorToPos(t.pos)
case keyLeft:
if t.pos == 0 {
return
}
t.pos--
t.moveCursorToPos(t.pos)
case keyRight:
if t.pos == len(t.line) {
return
}
t.pos++
t.moveCursorToPos(t.pos)
case keyHome:
if t.pos == 0 {
return
}
t.pos = 0
t.moveCursorToPos(t.pos)
case keyEnd:
if t.pos == len(t.line) {
return
}
t.pos = len(t.line)
t.moveCursorToPos(t.pos)
case keyUp:
entry, ok := t.history.NthPreviousEntry(t.historyIndex + 1)
if !ok {
return "", false
}
if t.historyIndex == -1 {
t.historyPending = string(t.line)
}
t.historyIndex++
runes := []rune(entry)
t.setLine(runes, len(runes))
case keyDown:
switch t.historyIndex {
case -1:
return
case 0:
runes := []rune(t.historyPending)
t.setLine(runes, len(runes))
t.historyIndex--
default:
entry, ok := t.history.NthPreviousEntry(t.historyIndex - 1)
if ok {
t.historyIndex--
runes := []rune(entry)
t.setLine(runes, len(runes))
}
}
case keyEnter:
t.moveCursorToPos(len(t.line))
t.queue([]rune("\r\n"))
line = string(t.line)
ok = true
t.line = t.line[:0]
t.pos = 0
t.cursorX = 0
t.cursorY = 0
t.maxLine = 0
case keyDeleteWord:
// Delete zero or more spaces and then one or more characters.
t.eraseNPreviousChars(t.countToLeftWord())
case keyDeleteLine:
// Delete everything from the current cursor position to the
// end of line.
for i := t.pos; i < len(t.line); i++ {
t.queue(space)
t.advanceCursor(1)
}
t.line = t.line[:t.pos]
t.moveCursorToPos(t.pos)
case keyCtrlD:
// Erase the character under the current position.
// The EOF case when the line is empty is handled in
// readLine().
if t.pos < len(t.line) {
t.pos++
t.eraseNPreviousChars(1)
}
case keyCtrlU:
t.eraseNPreviousChars(t.pos)
case keyClearScreen:
// Erases the screen and moves the cursor to the home position.
t.queue([]rune("\x1b[2J\x1b[H"))
t.queue(t.prompt)
t.cursorX, t.cursorY = 0, 0
t.advanceCursor(visualLength(t.prompt))
t.setLine(t.line, t.pos)
default:
if t.AutoCompleteCallback != nil {
prefix := string(t.line[:t.pos])
suffix := string(t.line[t.pos:])
t.lock.Unlock()
newLine, newPos, completeOk := t.AutoCompleteCallback(prefix+suffix, len(prefix), key)
t.lock.Lock()
if completeOk {
t.setLine([]rune(newLine), utf8.RuneCount([]byte(newLine)[:newPos]))
return
}
}
if !isPrintable(key) {
return
}
if len(t.line) == maxLineLength {
return
}
t.addKeyToLine(key)
}
return
}
// addKeyToLine inserts the given key at the current position in the current
// line.
func (t *Terminal) addKeyToLine(key rune) {
if len(t.line) == cap(t.line) {
newLine := make([]rune, len(t.line), 2*(1+len(t.line)))
copy(newLine, t.line)
t.line = newLine
}
t.line = t.line[:len(t.line)+1]
copy(t.line[t.pos+1:], t.line[t.pos:])
t.line[t.pos] = key
if t.echo {
t.writeLine(t.line[t.pos:])
}
t.pos++
t.moveCursorToPos(t.pos)
}
func (t *Terminal) writeLine(line []rune) {
for len(line) != 0 {
remainingOnLine := t.termWidth - t.cursorX
todo := len(line)
if todo > remainingOnLine {
todo = remainingOnLine
}
t.queue(line[:todo])
t.advanceCursor(visualLength(line[:todo]))
line = line[todo:]
}
}
// writeWithCRLF writes buf to w but replaces all occurrences of \n with \r\n.
func writeWithCRLF(w io.Writer, buf []byte) (n int, err error) {
for len(buf) > 0 {
i := bytes.IndexByte(buf, '\n')
todo := len(buf)
if i >= 0 {
todo = i
}
var nn int
nn, err = w.Write(buf[:todo])
n += nn
if err != nil {
return n, err
}
buf = buf[todo:]
if i >= 0 {
if _, err = w.Write(crlf); err != nil {
return n, err
}
n++
buf = buf[1:]
}
}
return n, nil
}
func (t *Terminal) Write(buf []byte) (n int, err error) {
t.lock.Lock()
defer t.lock.Unlock()
if t.cursorX == 0 && t.cursorY == 0 {
// This is the easy case: there's nothing on the screen that we
// have to move out of the way.
return writeWithCRLF(t.c, buf)
}
// We have a prompt and possibly user input on the screen. We
// have to clear it first.
t.move(0 /* up */, 0 /* down */, t.cursorX /* left */, 0 /* right */)
t.cursorX = 0
t.clearLineToRight()
for t.cursorY > 0 {
t.move(1 /* up */, 0, 0, 0)
t.cursorY--
t.clearLineToRight()
}
if _, err = t.c.Write(t.outBuf); err != nil {
return
}
t.outBuf = t.outBuf[:0]
if n, err = writeWithCRLF(t.c, buf); err != nil {
return
}
t.writeLine(t.prompt)
if t.echo {
t.writeLine(t.line)
}
t.moveCursorToPos(t.pos)
if _, err = t.c.Write(t.outBuf); err != nil {
return
}
t.outBuf = t.outBuf[:0]
return
}
// ReadPassword temporarily changes the prompt and reads a password, without
// echo, from the terminal.
func (t *Terminal) ReadPassword(prompt string) (line string, err error) {
t.lock.Lock()
defer t.lock.Unlock()
oldPrompt := t.prompt
t.prompt = []rune(prompt)
t.echo = false
line, err = t.readLine()
t.prompt = oldPrompt
t.echo = true
return
}
// ReadLine returns a line of input from the terminal.
func (t *Terminal) ReadLine() (line string, err error) {
t.lock.Lock()
defer t.lock.Unlock()
return t.readLine()
}
func (t *Terminal) readLine() (line string, err error) {
// t.lock must be held at this point
if t.cursorX == 0 && t.cursorY == 0 {
t.writeLine(t.prompt)
t.c.Write(t.outBuf)
t.outBuf = t.outBuf[:0]
}
lineIsPasted := t.pasteActive
for {
rest := t.remainder
lineOk := false
for !lineOk {
var key rune
key, rest = bytesToKey(rest, t.pasteActive)
if key == utf8.RuneError {
break
}
if !t.pasteActive {
if key == keyCtrlD {
if len(t.line) == 0 {
return "", io.EOF
}
}
if key == keyPasteStart {
t.pasteActive = true
if len(t.line) == 0 {
lineIsPasted = true
}
continue
}
} else if key == keyPasteEnd {
t.pasteActive = false
continue
}
if !t.pasteActive {
lineIsPasted = false
}
line, lineOk = t.handleKey(key)
}
if len(rest) > 0 {
n := copy(t.inBuf[:], rest)
t.remainder = t.inBuf[:n]
} else {
t.remainder = nil
}
t.c.Write(t.outBuf)
t.outBuf = t.outBuf[:0]
if lineOk {
if t.echo {
t.historyIndex = -1
t.history.Add(line)
}
if lineIsPasted {
err = ErrPasteIndicator
}
return
}
// t.remainder is a slice at the beginning of t.inBuf
// containing a partial key sequence
readBuf := t.inBuf[len(t.remainder):]
var n int
t.lock.Unlock()
n, err = t.c.Read(readBuf)
t.lock.Lock()
if err != nil {
return
}
t.remainder = t.inBuf[:n+len(t.remainder)]
}
}
// SetPrompt sets the prompt to be used when reading subsequent lines.
func (t *Terminal) SetPrompt(prompt string) {
t.lock.Lock()
defer t.lock.Unlock()
t.prompt = []rune(prompt)
}
func (t *Terminal) clearAndRepaintLinePlusNPrevious(numPrevLines int) {
// Move cursor to column zero at the start of the line.
t.move(t.cursorY, 0, t.cursorX, 0)
t.cursorX, t.cursorY = 0, 0
t.clearLineToRight()
for t.cursorY < numPrevLines {
// Move down a line
t.move(0, 1, 0, 0)
t.cursorY++
t.clearLineToRight()
}
// Move back to beginning.
t.move(t.cursorY, 0, 0, 0)
t.cursorX, t.cursorY = 0, 0
t.queue(t.prompt)
t.advanceCursor(visualLength(t.prompt))
t.writeLine(t.line)
t.moveCursorToPos(t.pos)
}
func (t *Terminal) SetSize(width, height int) error {
t.lock.Lock()
defer t.lock.Unlock()
if width == 0 {
width = 1
}
oldWidth := t.termWidth
t.termWidth, t.termHeight = width, height
switch {
case width == oldWidth:
// If the width didn't change then nothing else needs to be
// done.
return nil
case len(t.line) == 0 && t.cursorX == 0 && t.cursorY == 0:
// If there is nothing on current line and no prompt printed,
// just do nothing
return nil
case width < oldWidth:
// Some terminals (e.g. xterm) will truncate lines that were
// too long when shinking. Others, (e.g. gnome-terminal) will
// attempt to wrap them. For the former, repainting t.maxLine
// works great, but that behaviour goes badly wrong in the case
// of the latter because they have doubled every full line.
// We assume that we are working on a terminal that wraps lines
// and adjust the cursor position based on every previous line
// wrapping and turning into two. This causes the prompt on
// xterms to move upwards, which isn't great, but it avoids a
// huge mess with gnome-terminal.
if t.cursorX >= t.termWidth {
t.cursorX = t.termWidth - 1
}
t.cursorY *= 2
t.clearAndRepaintLinePlusNPrevious(t.maxLine * 2)
case width > oldWidth:
// If the terminal expands then our position calculations will
// be wrong in the future because we think the cursor is
// |t.pos| chars into the string, but there will be a gap at
// the end of any wrapped line.
//
// But the position will actually be correct until we move, so
// we can move back to the beginning and repaint everything.
t.clearAndRepaintLinePlusNPrevious(t.maxLine)
}
_, err := t.c.Write(t.outBuf)
t.outBuf = t.outBuf[:0]
return err
}
type pasteIndicatorError struct{}
func (pasteIndicatorError) Error() string {
return "terminal: ErrPasteIndicator not correctly handled"
}
// ErrPasteIndicator may be returned from ReadLine as the error, in addition
// to valid line data. It indicates that bracketed paste mode is enabled and
// that the returned line consists only of pasted data. Programs may wish to
// interpret pasted data more literally than typed data.
var ErrPasteIndicator = pasteIndicatorError{}
// SetBracketedPasteMode requests that the terminal bracket paste operations
// with markers. Not all terminals support this but, if it is supported, then
// enabling this mode will stop any autocomplete callback from running due to
// pastes. Additionally, any lines that are completely pasted will be returned
// from ReadLine with the error set to ErrPasteIndicator.
func (t *Terminal) SetBracketedPasteMode(on bool) {
if on {
io.WriteString(t.c, "\x1b[?2004h")
} else {
io.WriteString(t.c, "\x1b[?2004l")
}
}
// stRingBuffer is a ring buffer of strings.
type stRingBuffer struct {
// entries contains max elements.
entries []string
max int
// head contains the index of the element most recently added to the ring.
head int
// size contains the number of elements in the ring.
size int
}
func (s *stRingBuffer) Add(a string) {
if s.entries == nil {
const defaultNumEntries = 100
s.entries = make([]string, defaultNumEntries)
s.max = defaultNumEntries
}
s.head = (s.head + 1) % s.max
s.entries[s.head] = a
if s.size < s.max {
s.size++
}
}
// NthPreviousEntry returns the value passed to the nth previous call to Add.
// If n is zero then the immediately prior value is returned, if one, then the
// next most recent, and so on. If such an element doesn't exist then ok is
// false.
func (s *stRingBuffer) NthPreviousEntry(n int) (value string, ok bool) {
if n >= s.size {
return "", false
}
index := s.head - n
if index < 0 {
index += s.max
}
return s.entries[index], true
}
// readPasswordLine reads from reader until it finds \n or io.EOF.
// The slice returned does not include the \n.
// readPasswordLine also ignores any \r it finds.
func readPasswordLine(reader io.Reader) ([]byte, error) {
var buf [1]byte
var ret []byte
for {
n, err := reader.Read(buf[:])
if n > 0 {
switch buf[0] {
case '\n':
return ret, nil
case '\r':
// remove \r from passwords on Windows
default:
ret = append(ret, buf[0])
}
continue
}
if err != nil {
if err == io.EOF && len(ret) > 0 {
return ret, nil
}
return ret, err
}
}
}