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expect.go
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expect.go
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/*
File summary: Simple version of expect in pure Go
Package: expect
Author: Lee McLoughlin
Copyright (C) 2016 LMMR Tech Ltd
*/
/*
Expect is pure Go (golang) version of the terminal interaction package Expect
common on many Linux systems
A very simple example that calls the rev program to reverse the text in each
line is:
exp, err := NewExpect("rev")
if err != nil {
fmt.Fprintf(os.Stderr, "NewExpect failed %s", err)
}
exp.SetTimeoutSecs(5)
exp.Send("hello\r")
// i will be the index of the argument that matched the input otherwise
// i will be a negative number showing match fail or error
i, found, err := exp.Expect("olleh")
if i == 0 {
fmt.Println("found", string(found))
} else {
fmt.Println("failed ", err)
}
exp.Send(EOF)
This package has only been tested on Linux
*/
package expect
import (
"bytes"
"errors"
"fmt"
"io"
"log"
"os"
"os/exec"
"regexp"
"runtime"
"syscall"
"time"
"github.com/kr/pty"
)
const (
// NotFound is returned by Expect for non-matching non-errors (include EOF)
NotFound = -1
// TimedOut is returned by Expect on a timeout (along with an error of ETimedOut)
TimedOut = -2
// NotStringOrRexgexp is returned if a paramter is not a string or a regexp
NotStringOrRexgexp = -3
)
var (
ETimedOut = errors.New("TimedOut")
ENotStringOrRexgexp = errors.New("Not string or regexp")
EReadError = errors.New("Read Error")
// Debug if true will generate vast amounts of internal logging
Debug = false
// ExpectInSize is the size of the channel between the expectReader and Expect.
// If you overflow this than expectReader will block.
ExpectInSize = 20 * 1024
// EOF is the terminal EOF character - NOT guaranteed to be correct on all
// systems nor if the program passed to expect connects to a different
// platform
EOF = "\004"
)
func init() {
// No good way to discover EOF so have to take a best guess
// Default (above) to control-D
if runtime.GOOS == "windows" {
EOF = "\032" // control-Z
}
}
// Remember: Expect.Close() will not end the process
// you have to send it an EOF
type Expect struct {
// *os.File is an anonymous field for the pty connected to the command.
// This allows you to treat *Expect as a *os.File
*os.File
cmd *exec.Cmd
cmdIn io.Reader // Internally I always read from cmdIn not File so cmdOut works
cmdOut io.Writer
timeout time.Duration
// Expect reads into here. On a successful match all data up the end of the
// match is deleted shrinking the buffer.
// See also Clear() and BufStr()
Buffer *bytes.Buffer
// expertReader reads from Cmd and sends to Expect over this Chan
bytesIn chan byteIn
// Send true to this chan to get the expectReader goroutine to end
endExpectReader chan bool
// Is the expectReader running?
expectReaderRunning bool
// On EOF being read from Cmd this is set (and ExpectReader is ended)
Eof bool
// Result is filled in asynchronously after the cmd exits
Result ExpectWaitResult
}
type ExpectWaitResult struct {
// IsValid is true if this has been set because wait returned
IsValid bool
ProcessState *os.ProcessState
Error error
}
// debugf logs only if Debug is true
func debugf(format string, args ...interface{}) {
if !Debug {
return
}
s := fmt.Sprintf(format, args...)
log.Print(s)
}
// NewExpect starts prog, passing any given args, in its own pty.
// Note that in order to be non-blocking while reading from the pty this sets
// the non-blocking flag and looks for EAGAIN on reads failing. This has only
// been tested on Linux systems.
// On prog exiting or being killed Result is filled in shortly after.
func NewExpect(prog string, arg ...string) (*Expect, error) {
return newExpectCommon(true, prog, arg...)
}
// NewExpectProc is similar to NewExpect except the created cmd is returned.
// It is expected that the cmd will exit normally otherwise it is left to
// the caller to kill it.
// In the event of an error starting the cmd it will be killed but not reaped.
// However the cmd ends it is important that the caller reap the process
// by calling cmd.Process.Wait() otherwise it can use up a process slot in
// the operating system.
// Note that Result is not filled in.
func NewExpectProc(prog string, arg ...string) (*Expect, *exec.Cmd, error) {
exp, err := newExpectCommon(false, prog, arg...)
return exp, exp.cmd, err
}
func newExpectCommon(reap bool, prog string, arg ...string) (*Expect, error) {
name := "NewExpect"
if reap {
name = "MewExpectProc"
}
var err error
exp := new(Expect)
exp.cmd = exec.Command(prog, arg...)
exp.File, err = pty.Start(exp.cmd)
if reap && exp.cmd.Process != nil {
go exp.expectReaper()
}
if err != nil {
if exp.cmd.Process != nil {
if err2 := exp.cmd.Process.Kill(); err2 != nil {
debugf("%s cannot kill %s on error: %s", name, prog, err)
}
}
return nil, err
}
// make the pty non blocking so when I read from it I dont jam up
fd := int(exp.File.Fd())
err = syscall.SetNonblock(fd, true)
if err != nil {
if err2 := exp.cmd.Process.Kill(); err2 != nil {
debugf("%s cannot kill %s on error: %s", name, prog, err)
}
return nil, err
}
exp.SetCmdOut(nil)
exp.Buffer = new(bytes.Buffer)
exp.bytesIn = make(chan byteIn, ExpectInSize)
exp.endExpectReader = make(chan bool, 2) // should be 1 but just in case have extra space
exp.expectReaderRunning = true
go exp.expectReader()
return exp, err
}
// expectReaper reaps the process if it ends for any reason and saves the
// Wait() result
func (exp *Expect) expectReaper() {
exp.Result.ProcessState, exp.Result.Error = exp.cmd.Process.Wait()
exp.Result.IsValid = true
}
// SetCmdOut if a non-nil io.Writer is passed it will be sent a copy of everything
// read by Expect() from the pty.
// Note that if you bypass expect and read directly from the *Expect this is
// will not be used
func (exp *Expect) SetCmdOut(cmdOut io.Writer) {
if cmdOut != nil {
exp.cmdOut = cmdOut
exp.cmdIn = io.TeeReader(exp.File, cmdOut)
} else {
exp.cmdIn = exp.File
exp.cmdOut = nil
}
}
// SetTimeout sets the timeout for future calls to Expect().
// The default value is zero which cause Expect() to wait forever.
func (exp *Expect) SetTimeout(timeout time.Duration) {
exp.timeout = timeout
}
// SetTimeoutSecs is a convenience wrapper around SetTimeout
func (exp *Expect) SetTimeoutSecs(timeout int) {
exp.SetTimeout(time.Duration(timeout) * time.Second)
}
// Expect keeps reading input till either a timeout occurs (if set), one of the
// strings/regexps passed matches the input, end of input occurs or an error.
// If a string/regexp match occurs the index of the successful argument and the matching bytes
// are returned. Otherwise an error value and error are returned.
// Note: on EOF the return value will be NotFound and the error will be nil as
// EOF is not considered an error. This is the only time those values will be returned.
// See also Expecti()
func (exp *Expect) Expect(reOrStrs ...interface{}) (int, []byte, error) {
// Check the args
for n, reOrStr := range reOrStrs {
switch reOrStr.(type) {
case string:
continue
case *regexp.Regexp:
continue
default:
debugf("Expect non string/regexp passed as arg %d", n)
return NotStringOrRexgexp, nil, ENotStringOrRexgexp
}
}
if exp.Eof {
debugf("already at EOF")
return NotFound, nil, nil
}
timedOut := make(<-chan time.Time)
if exp.timeout != 0 {
timedOut = time.After(exp.timeout)
}
if len(exp.Buffer.Bytes()) > 0 {
// Fake byte-less input to get the for/select loop to process any pending buffered
// input
exp.bytesIn <- byteIn{}
}
for {
select {
case <-timedOut:
debugf("Expect timedOut")
return TimedOut, nil, ETimedOut
case boe, ok := <-exp.bytesIn:
if !ok {
debugf("Expect read error")
exp.expectReaderRunning = false
exp.Eof = true
return NotFound, nil, EReadError
}
if boe.isEOF {
debugf("Expect eof")
exp.expectReaderRunning = false
exp.Eof = true
return NotFound, nil, nil
}
if boe.isByte {
b := boe.b
debugf("Expect got new byte %c", b)
if err := exp.Buffer.WriteByte(b); err != nil {
debugf("Expect failed to add to buffer: %s", err)
return NotFound, nil, EReadError
}
}
bufBytes := exp.Buffer.Bytes()
debugf("Expect buffer now:<<%s>>", string(bufBytes))
debugf("Expect check for regexps")
for n, reOrStr := range reOrStrs {
var start, end int
switch rs := reOrStr.(type) {
case string:
debugf("string passed: %s", rs)
start = bytes.Index(bufBytes, []byte(rs))
if start < 0 {
continue
}
end = start + len(rs)
debugf("string found")
case *regexp.Regexp:
debugf("re passed: %s", rs)
loc := rs.FindIndex(bufBytes)
if loc == nil {
continue
}
start, end = loc[0], loc[1]
debugf("re found")
}
// dont just assign a slice as I'm about to change the contents
// of bytes and the slice will end up referencing the new data
//found := bytes[start:end]
found := make([]byte, end-start)
copy(found, bufBytes[start:end])
debugf("Expect found %s (start %d, end %d)", string(found), start, end)
debugf("Expect reset buffer to the remaining input following the match")
debugf("Expect buffer before reset:<<%s>>", string(exp.Buffer.Bytes()))
newBuf := bufBytes[end:]
debugf("Expect remaining:<<%s>>", string(newBuf))
exp.Buffer.Reset()
exp.Buffer.Write(newBuf)
debugf("Expect buffer after reset:<<%s>>", string(exp.Buffer.Bytes()))
return n, found, nil
}
}
}
// I can never get here...
return NotFound, nil, nil
}
// byteOrEof is used between Expect and readToChan.
// If isEOF is false and isByte is false then there is no input. This is used
// to get Expect() to process left over buffer input.
type byteIn struct {
isEOF bool
isByte bool
b byte
}
// expectReader reads from the pty and sends either a byte or eof to Expect.
// if anything appears on endExpectReader this goroutine ends
func (exp *Expect) expectReader() {
debugf("expectReader starting")
buf := make([]byte, 1)
for {
select {
case <-exp.endExpectReader:
debugf("expectReader ending")
return
default:
n, err := exp.cmdIn.Read(buf)
debugf("expectReader read %d, %c, %s", n, buf[0], err)
if err != nil {
if unixIsEAGAIN(err) {
debugf("expectReader EAGAIN")
time.Sleep(100 * time.Millisecond) // reduce busy looping
continue
}
debugf("expectReader ending read error")
exp.bytesIn <- byteIn{isEOF: true}
return
}
if n == 0 {
// Not EAGAIN but no input
debugf("expectReader ending nothing read")
exp.bytesIn <- byteIn{isEOF: true}
return
}
if n < 0 {
continue
}
exp.bytesIn <- byteIn{isByte: true, b: buf[0]}
}
}
}
// Clear out any unprocessed input
func (exp *Expect) Clear() {
exp.Buffer.Reset()
}
// BufStr is the buffer of expect read data as a string
func (exp *Expect) BufStr() string {
return string(exp.Buffer.Bytes())
}
// Kill the command. Using an Expect after a Kill is undefined
func (exp *Expect) Kill() error {
exp.Buffer.Reset()
exp.Close()
if exp.expectReaderRunning {
exp.endExpectReader <- true
exp.expectReaderRunning = false
}
return exp.cmd.Process.Kill()
}
// Original expect compatibility
// Spawn is a wrapper to NewExpect(), for compatibility with the original expect
func Spawn(prog string, arg ...string) (*Expect, error) {
return NewExpect(prog, arg...)
}
// Send sends the string to the process, for compatibility with the original expect
func (exp *Expect) Send(s string) (int, error) {
return exp.Write([]byte(s))
}
// Sends string rune by rune with a delay before each.
// Note: the return is the number of bytes sent not the number of runes sent
func (exp *Expect) SendSlow(delay time.Duration, s string) (int, error) {
for _, rune := range s {
time.Sleep(delay)
bytes := []byte(string(rune))
n, err := exp.Write(bytes)
if err != nil {
return n, err
}
}
return len([]byte(s)), nil
}
// Expecti is a convenience wrapper around Expect() that only returns the index
// and not the found bytes or error. This is close to the original expect()
func (exp *Expect) Expecti(reOrStrs ...interface{}) int {
i, _, _ := exp.Expect(reOrStrs...)
return i
}
// Expectp is a convenience wrapper around Expect() that panics on no match
// (so will panic on eof)
func (exp *Expect) Expectp(reOrStrs ...interface{}) int {
i, _, _ := exp.Expect(reOrStrs...)
if i < 0 {
panic(fmt.Sprintf("%s", reOrStrs...))
}
return i
}
// LogUser true asks for all input read by Expect() to be copied to stdout.
// LogUser false (default) turns it off.
// For compatibility with the original expect
func (exp *Expect) LogUser(on bool) {
if on {
exp.SetCmdOut(os.Stdout)
} else {
exp.SetCmdOut(nil)
}
}
// Copied from the non-exported func in src/crypto/rand/eagain.go
func unixIsEAGAIN(err error) bool {
if pe, ok := err.(*os.PathError); ok {
if errno, ok := pe.Err.(syscall.Errno); ok && errno == syscall.EAGAIN {
return true
}
}
return false
}