Subversion Repositories openrisc

// 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"
        "syscall"
)

// Error records the name of a binary that failed to be 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 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 extra 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

        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)
                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)
                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
}

// 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 {
                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 {
                        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 {
                return err
        }

        for _, fd := range c.closeAfterStart {
                fd.Close()
        }

        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.Waitmsg
}

func (e *ExitError) Error() string {
        return e.Waitmsg.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
        msg, err := c.Process.Wait(0)

        var copyError error
        for _ = range c.goroutine {
                if err := <-c.errch; err != nil && copyError == nil {
                        copyError = err
                }
        }

        for _, fd := range c.closeAfterWait {
                fd.Close()
        }

        if err != nil {
                return err
        } else if !msg.Exited() || msg.ExitStatus() != 0 {
                return &ExitError{msg}
        }

        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.
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)
        c.closeAfterWait = append(c.closeAfterWait, pw)
        return pw, nil
}

// StdoutPipe returns a pipe that will be connected to the command's
// standard output when the command starts.
// The pipe will be closed automatically after Wait sees the command exit.
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.
// The pipe will be closed automatically after Wait sees the command exit.
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
}