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// Copyright 2009 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 exec runs external commands. It wraps os.StartProcess to make it
// easier to remap stdin and stdout, connect I/O with pipes, and do other
// adjustments.
package exec
import (
"bytes"
"errors"
"io"
"os"
"strconv"
"sync"
"syscall"
)
// Error records the name of a binary that failed to be executed
// and the reason it failed.
type Error struct {
Name string
Err error
}
func (e *Error) Error() string {
return "exec: " + strconv.Quote(e.Name) + ": " + e.Err.Error()
}
// Cmd represents an external command being prepared or run.
type Cmd struct {
// Path is the path of the command to run.
//
// This is the only field that must be set to a non-zero
// value.
Path string
// Args holds command line arguments, including the command as Args[0].
// If the Args field is empty or nil, Run uses {Path}.
//
// In typical use, both Path and Args are set by calling Command.
Args []string
// Env specifies the environment of the process.
// If Env is nil, Run uses the current process's environment.
Env []string
// Dir specifies the working directory of the command.
// If Dir is the empty string, Run runs the command in the
// calling process's current directory.
Dir string
// Stdin specifies the process's standard input. If Stdin is
// nil, the process reads from the null device (os.DevNull).
Stdin io.Reader
// Stdout and Stderr specify the process's standard output and error.
//
// If either is nil, Run connects the corresponding file descriptor
// to the null device (os.DevNull).
//
// If Stdout and Stderr are the same writer, at most one
// goroutine at a time will call Write.
Stdout io.Writer
Stderr io.Writer
// ExtraFiles specifies additional open files to be inherited by the
// new process. It does not include standard input, standard output, or
// standard error. If non-nil, entry i becomes file descriptor 3+i.
//
// BUG: on OS X 10.6, child processes may sometimes inherit unwanted fds.
// http://golang.org/issue/2603
ExtraFiles []*os.File
// SysProcAttr holds optional, operating system-specific attributes.
// Run passes it to os.StartProcess as the os.ProcAttr's Sys field.
SysProcAttr *syscall.SysProcAttr
// Process is the underlying process, once started.
Process *os.Process
// ProcessState contains information about an exited process,
// available after a call to Wait or Run.
ProcessState *os.ProcessState
err error // last error (from LookPath, stdin, stdout, stderr)
finished bool // when Wait was called
childFiles []*os.File
closeAfterStart []io.Closer
closeAfterWait []io.Closer
goroutine []func() error
errch chan error // one send per goroutine
}
// Command returns the Cmd struct to execute the named program with
// the given arguments.
//
// It sets Path and Args in the returned structure and zeroes the
// other fields.
//
// If name contains no path separators, Command uses LookPath to
// resolve the path to a complete name if possible. Otherwise it uses
// name directly.
//
// The returned Cmd's Args field is constructed from the command name
// followed by the elements of arg, so arg should not include the
// command name itself. For example, Command("echo", "hello")
func Command(name string, arg ...string) *Cmd {
aname, err := LookPath(name)
if err != nil {
aname = name
}
return &Cmd{
Path: aname,
Args: append([]string{name}, arg...),
err: err,
}
}
// interfaceEqual protects against panics from doing equality tests on
// two interfaces with non-comparable underlying types
func interfaceEqual(a, b interface{}) bool {
defer func() {
recover()
}()
return a == b
}
func (c *Cmd) envv() []string {
if c.Env != nil {
return c.Env
}
return os.Environ()
}
func (c *Cmd) argv() []string {
if len(c.Args) > 0 {
return c.Args
}
return []string{c.Path}
}
func (c *Cmd) stdin() (f *os.File, err error) {
if c.Stdin == nil {
f, err = os.Open(os.DevNull)
if err != nil {
return
}
c.closeAfterStart = append(c.closeAfterStart, f)
return
}
if f, ok := c.Stdin.(*os.File); ok {
return f, nil
}
pr, pw, err := os.Pipe()
if err != nil {
return
}
c.closeAfterStart = append(c.closeAfterStart, pr)
c.closeAfterWait = append(c.closeAfterWait, pw)
c.goroutine = append(c.goroutine, func() error {
_, err := io.Copy(pw, c.Stdin)
if err1 := pw.Close(); err == nil {
err = err1
}
return err
})
return pr, nil
}
func (c *Cmd) stdout() (f *os.File, err error) {
return c.writerDescriptor(c.Stdout)
}
func (c *Cmd) stderr() (f *os.File, err error) {
if c.Stderr != nil && interfaceEqual(c.Stderr, c.Stdout) {
return c.childFiles[1], nil
}
return c.writerDescriptor(c.Stderr)
}
func (c *Cmd) writerDescriptor(w io.Writer) (f *os.File, err error) {
if w == nil {
f, err = os.OpenFile(os.DevNull, os.O_WRONLY, 0)
if err != nil {
return
}
c.closeAfterStart = append(c.closeAfterStart, f)
return
}
if f, ok := w.(*os.File); ok {
return f, nil
}
pr, pw, err := os.Pipe()
if err != nil {
return
}
c.closeAfterStart = append(c.closeAfterStart, pw)
c.closeAfterWait = append(c.closeAfterWait, pr)
c.goroutine = append(c.goroutine, func() error {
_, err := io.Copy(w, pr)
return err
})
return pw, nil
}
func (c *Cmd) closeDescriptors(closers []io.Closer) {
for _, fd := range closers {
fd.Close()
}
}
// Run starts the specified command and waits for it to complete.
//
// The returned error is nil if the command runs, has no problems
// copying stdin, stdout, and stderr, and exits with a zero exit
// status.
//
// If the command fails to run or doesn't complete successfully, the
// error is of type *ExitError. Other error types may be
// returned for I/O problems.
func (c *Cmd) Run() error {
if err := c.Start(); err != nil {
return err
}
return c.Wait()
}
// Start starts the specified command but does not wait for it to complete.
func (c *Cmd) Start() error {
if c.err != nil {
c.closeDescriptors(c.closeAfterStart)
c.closeDescriptors(c.closeAfterWait)
return c.err
}
if c.Process != nil {
return errors.New("exec: already started")
}
type F func(*Cmd) (*os.File, error)
for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} {
fd, err := setupFd(c)
if err != nil {
c.closeDescriptors(c.closeAfterStart)
c.closeDescriptors(c.closeAfterWait)
return err
}
c.childFiles = append(c.childFiles, fd)
}
c.childFiles = append(c.childFiles, c.ExtraFiles...)
var err error
c.Process, err = os.StartProcess(c.Path, c.argv(), &os.ProcAttr{
Dir: c.Dir,
Files: c.childFiles,
Env: c.envv(),
Sys: c.SysProcAttr,
})
if err != nil {
c.closeDescriptors(c.closeAfterStart)
c.closeDescriptors(c.closeAfterWait)
return err
}
c.closeDescriptors(c.closeAfterStart)
c.errch = make(chan error, len(c.goroutine))
for _, fn := range c.goroutine {
go func(fn func() error) {
c.errch <- fn()
}(fn)
}
return nil
}
// An ExitError reports an unsuccessful exit by a command.
type ExitError struct {
*os.ProcessState
}
func (e *ExitError) Error() string {
return e.ProcessState.String()
}
// Wait waits for the command to exit.
// It must have been started by Start.
//
// The returned error is nil if the command runs, has no problems
// copying stdin, stdout, and stderr, and exits with a zero exit
// status.
//
// If the command fails to run or doesn't complete successfully, the
// error is of type *ExitError. Other error types may be
// returned for I/O problems.
func (c *Cmd) Wait() error {
if c.Process == nil {
return errors.New("exec: not started")
}
if c.finished {
return errors.New("exec: Wait was already called")
}
c.finished = true
state, err := c.Process.Wait()
c.ProcessState = state
var copyError error
for _ = range c.goroutine {
if err := <-c.errch; err != nil && copyError == nil {
copyError = err
}
}
c.closeDescriptors(c.closeAfterWait)
if err != nil {
return err
} else if !state.Success() {
return &ExitError{state}
}
return copyError
}
// Output runs the command and returns its standard output.
func (c *Cmd) Output() ([]byte, error) {
if c.Stdout != nil {
return nil, errors.New("exec: Stdout already set")
}
var b bytes.Buffer
c.Stdout = &b
err := c.Run()
return b.Bytes(), err
}
// CombinedOutput runs the command and returns its combined standard
// output and standard error.
func (c *Cmd) CombinedOutput() ([]byte, error) {
if c.Stdout != nil {
return nil, errors.New("exec: Stdout already set")
}
if c.Stderr != nil {
return nil, errors.New("exec: Stderr already set")
}
var b bytes.Buffer
c.Stdout = &b
c.Stderr = &b
err := c.Run()
return b.Bytes(), err
}
// StdinPipe returns a pipe that will be connected to the command's
// standard input when the command starts.
// The pipe will be closed automatically after Wait sees the command exit.
// A caller need only call Close to force the pipe to close sooner.
// For example, if the command being run will not exit until standard input
// is closed, the caller must close the pipe.
func (c *Cmd) StdinPipe() (io.WriteCloser, error) {
if c.Stdin != nil {
return nil, errors.New("exec: Stdin already set")
}
if c.Process != nil {
return nil, errors.New("exec: StdinPipe after process started")
}
pr, pw, err := os.Pipe()
if err != nil {
return nil, err
}
c.Stdin = pr
c.closeAfterStart = append(c.closeAfterStart, pr)
wc := &closeOnce{File: pw}
c.closeAfterWait = append(c.closeAfterWait, wc)
return wc, nil
}
type closeOnce struct {
*os.File
close sync.Once
closeErr error
}
func (c *closeOnce) Close() error {
c.close.Do(func() {
c.closeErr = c.File.Close()
})
return c.closeErr
}
// StdoutPipe returns a pipe that will be connected to the command's
// standard output when the command starts.
//
// Wait will close the pipe after seeing the command exit, so most callers
// need not close the pipe themselves; however, an implication is that
// it is incorrect to call Wait before all reads from the pipe have completed.
// For the same reason, it is incorrect to call Run when using StdoutPipe.
// See the example for idiomatic usage.
func (c *Cmd) StdoutPipe() (io.ReadCloser, error) {
if c.Stdout != nil {
return nil, errors.New("exec: Stdout already set")
}
if c.Process != nil {
return nil, errors.New("exec: StdoutPipe after process started")
}
pr, pw, err := os.Pipe()
if err != nil {
return nil, err
}
c.Stdout = pw
c.closeAfterStart = append(c.closeAfterStart, pw)
c.closeAfterWait = append(c.closeAfterWait, pr)
return pr, nil
}
// StderrPipe returns a pipe that will be connected to the command's
// standard error when the command starts.
//
// Wait will close the pipe after seeing the command exit, so most callers
// need not close the pipe themselves; however, an implication is that
// it is incorrect to call Wait before all reads from the pipe have completed.
// For the same reason, it is incorrect to use Run when using StderrPipe.
// See the StdoutPipe example for idiomatic usage.
func (c *Cmd) StderrPipe() (io.ReadCloser, error) {
if c.Stderr != nil {
return nil, errors.New("exec: Stderr already set")
}
if c.Process != nil {
return nil, errors.New("exec: StderrPipe after process started")
}
pr, pw, err := os.Pipe()
if err != nil {
return nil, err
}
c.Stderr = pw
c.closeAfterStart = append(c.closeAfterStart, pw)
c.closeAfterWait = append(c.closeAfterWait, pr)
return pr, nil
}