code review 4517134: exec: add Cmd methods StdinPipe, StdoutPipe, StderrPipe

src/pkg/exec/exec.go

 // 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 (
@@ skipping 47 matching lines @@
         //
         // 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
 
         err             os.Error // last error (from LookPath, stdin, stdout, stderr)
         process         *os.Process
         finished        bool // when Wait was called
         childFiles      []*os.File
-        closeAfterStart []*os.File
-        closeAfterWait  []*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.
 //
@@ skipping 220 matching lines @@
         }
         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.closeAfterStart, pw)
+        return pw, nil
+}
+
+// StdoutPipe returns a pipe that will be connected to the command's
+// standard output when the command starts.
+func (c *Cmd) StdoutPipe() (io.Reader, 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.closeAfterStart, pr)
+        return pr, nil
+}
+
+// StderrPipe returns a pipe that will be connected to the command's
+// standard error when the command starts.
+func (c *Cmd) StderrPipe() (io.Reader, 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.closeAfterStart, pr)
+        return pr, nil
+}