1 files changed, 377 insertions, 0 deletions
diff --git a/src/pkg/exec/exec.go b/src/pkg/exec/exec.go
new file mode 100644
index 000000000..3b20f2008
--- /dev/null
+++ b/src/pkg/exec/exec.go
@@ -0,0 +1,377 @@
+// 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"
+	"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
+	Error os.Error
+}
+
+func (e *Error) String() string {
+	return "exec: " + strconv.Quote(e.Name) + ": " + e.Error.String()
+}
+
+// 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 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 /dev/null.
+	//
+	// 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
+
+	// 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             os.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() os.Error
+	errch           chan os.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 os.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() os.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 os.Error) {
+	return c.writerDescriptor(c.Stdout)
+}
+
+func (c *Cmd) stderr() (f *os.File, err os.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 os.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() os.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 *os.Waitmsg. Other error types may be
+// returned for I/O problems.
+func (c *Cmd) Run() os.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() os.Error {
+	if c.err != nil {
+		return c.err
+	}
+	if c.Process != nil {
+		return os.NewError("exec: already started")
+	}
+
+	type F func(*Cmd) (*os.File, os.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)
+	}
+
+	var err os.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 os.Error, len(c.goroutine))
+	for _, fn := range c.goroutine {
+		go func(fn func() os.Error) {
+			c.errch <- fn()
+		}(fn)
+	}
+
+	return nil
+}
+
+// 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 *os.Waitmsg. Other error types may be
+// returned for I/O problems.
+func (c *Cmd) Wait() os.Error {
+	if c.Process == nil {
+		return os.NewError("exec: not started")
+	}
+	if c.finished {
+		return os.NewError("exec: Wait was already called")
+	}
+	c.finished = true
+	msg, err := c.Process.Wait(0)
+
+	var copyError os.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 msg
+	}
+
+	return copyError
+}
+
+// Output runs the command and returns its standard output.
+func (c *Cmd) Output() ([]byte, os.Error) {
+	if c.Stdout != nil {
+		return nil, os.NewError("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, os.Error) {
+	if c.Stdout != nil {
+		return nil, os.NewError("exec: Stdout already set")
+	}
+	if c.Stderr != nil {
+		return nil, os.NewError("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, os.Error) {
+	if c.Stdin != nil {
+		return nil, os.NewError("exec: Stdin already set")
+	}
+	if c.Process != nil {
+		return nil, os.NewError("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, os.Error) {
+	if c.Stdout != nil {
+		return nil, os.NewError("exec: Stdout already set")
+	}
+	if c.Process != nil {
+		return nil, os.NewError("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, os.Error) {
+	if c.Stderr != nil {
+		return nil, os.NewError("exec: Stderr already set")
+	}
+	if c.Process != nil {
+		return nil, os.NewError("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
+}