blob: ac5dd4afe2f95294f67971423ed4310b4ba29b4a [file] [log] [blame]
// Copyright 2017 The Chromium OS 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 run
import (
const (
stderrTimeout time.Duration = time.Second // time to wait for stderr on command failure
// firstLineReader reads and returns the first line from a reader, discarding the rest.
// It's useful for consuming stderr from asynchronous commands.
type firstLineReader struct {
sch chan string
ech chan error
// newFirstLineReader returns a new reader for getting the first line from r.
func newFirstLineReader(r io.Reader) *firstLineReader {
f := &firstLineReader{make(chan string, 1), make(chan error, 1)}
go func() {
if ln, err := bufio.NewReader(r).ReadString('\n'); err != nil {
f.ech <- err
} else {
f.sch <- strings.TrimSpace(ln)
io.Copy(ioutil.Discard, r)
return f
// getLine returns the first line that was read, waiting up to timeout for the line.
// If an error or timeout is encountered, an error is returned, and for
// convenience the returned string also contains the error message.
func (f *firstLineReader) getLine(timeout time.Duration) (string, error) {
select {
case s := <-f.sch:
return s, nil
case err := <-f.ech:
return err.Error(), err
case <-time.After(timeout):
err := errors.New("read timed out")
return err.Error(), err
// appendToError waits up to timeout for the first line and returns a new error containing both
// origErr and the line. If no line is available, origErr is returned unchanged.
func (f *firstLineReader) appendToError(origErr error, timeout time.Duration) error {
s, err := f.getLine(timeout)
if err != nil || s == "" {
return origErr
return fmt.Errorf("%v: %v", origErr, s)