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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"

        "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

}