packer: RemoteCommand.StderrChan

packer/communicator.go

@@ -40,10 +40,30 @@ type RemoteCommand struct {
 
 	exitChans    []chan<- int
 	exitChanLock sync.Mutex
+	errChans     []chan<- string
+	errChanLock  sync.Mutex
 	outChans     []chan<- string
 	outChanLock  sync.Mutex
 }
 
+// StderrStream returns a channel that will be sent all the
+func (r *RemoteCommand) StderrChan() <-chan string {
+	r.errChanLock.Lock()
+	defer r.errChanLock.Unlock()
+
+	// If no channels have been made, make that slice and start
+	// the goroutine to read and send to them
+	if r.errChans == nil {
+		r.errChans = make([]chan<- string, 0, 5)
+		go r.channelReader(r.Stderr, &r.errChans, &r.errChanLock)
+	}
+
+	// Create the channel, append it to the channels we care about
+	errChan := make(chan string, 10)
+	r.errChans = append(r.errChans, errChan)
+	return errChan
+}
+
 // StdoutStream returns a channel that will be sent all the output
 // of stdout as it comes. The output isn't guaranteed to be a full line.
 // When the channel is closed, the process is exited.

packer/communicator_test.go

@@ -31,6 +31,29 @@ func TestRemoteCommand_ExitChan(t *testing.T) {
 	}
 }
 
+func TestRemoteCommand_StderrChan(t *testing.T) {
+	expected := "DATA!!!"
+
+	stderrBuf := new(bytes.Buffer)
+	stderrBuf.WriteString(expected)
+
+	rc := &RemoteCommand{}
+	rc.Stderr = stderrBuf
+
+	errChan := rc.StderrChan()
+
+	results := new(bytes.Buffer)
+	for data := range errChan {
+		results.WriteString(data)
+	}
+
+	if results.String() != expected {
+		t.Fatalf(
+			"outputs didn't match:\ngot:\n%s\nexpected:\n%s",
+			results.String(), stderrBuf.String())
+	}
+}
+
 func TestRemoteCommand_StdoutChan(t *testing.T) {
 	expected := "DATA!!!"