replace buffer copy loop with a scanner that handles carriage returns

builder/vagrant/driver_2_2.go

@@ -1,6 +1,7 @@
 package vagrant
 
 import (
+	"bufio"
 	"bytes"
 	"fmt"
 	"log"
@@ -8,7 +9,6 @@ import (
 	"os/exec"
 	"regexp"
 	"strings"
-	"time"
 
 	"github.com/hashicorp/go-version"
 )
@@ -190,16 +190,47 @@ func (d *Vagrant_2_2_Driver) Version() (string, error) {
 	return version, nil
 }
 
-func (d *Vagrant_2_2_Driver) vagrantCmd(args ...string) (string, string, error) {
-	var stdout, stderr bytes.Buffer
+// Copied and modified from Bufio; this will return data that contains a
+// carriage return, not just data that contains a newline.
+// This allows us to stream progress output from vagrant that would otherwise
+// be smothered. It is a bit noisy, but probably prefereable to suppressing
+// the output in a way that looks like Packer has hung.
+func ScanLinesInclCR(data []byte, atEOF bool) (advance int, token []byte, err error) {
+	if atEOF && len(data) == 0 {
+		return 0, nil, nil
+	}
+	if i := bytes.IndexByte(data, '\n'); i >= 0 {
+		// We have a full newline-terminated line.
+		return i + 1, data[0:i], nil
+	}
+	if i := bytes.IndexByte(data, '\r'); i >= 0 {
+		// We have a CR-terminated line.
+		return i + 1, data[0:i], nil
+	}
+	// If we're at EOF, we have a final, non-terminated line. Return it.
+	if atEOF {
+		return len(data), data, nil
+	}
+	// Request more data.
+	return 0, nil, nil
+}
 
+func (d *Vagrant_2_2_Driver) vagrantCmd(args ...string) (string, string, error) {
 	log.Printf("Calling Vagrant CLI: %#v", args)
 	cmd := exec.Command(d.vagrantBinary, args...)
 	cmd.Env = append(os.Environ(), fmt.Sprintf("VAGRANT_CWD=%s", d.VagrantCWD))
-	cmd.Stdout = &stdout
-	cmd.Stderr = &stderr
 
-	err := cmd.Start()
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		log.Printf("error getting err pipe")
+	}
+
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		log.Printf("error getting out pioe")
+	}
+
+	err = cmd.Start()
 	if err != nil {
 		return "", "", fmt.Errorf("Error starting vagrant command with args: %q",
 			strings.Join(args, " "))
@@ -208,44 +239,24 @@ func (d *Vagrant_2_2_Driver) vagrantCmd(args ...string) (string, string, error)
 	stdoutString := ""
 	stderrString := ""
 
-	donech := make(chan bool)
-
+	scanOut := bufio.NewScanner(stdout)
+	scanOut.Split(ScanLinesInclCR)
+	scanErr := bufio.NewScanner(stderr)
+	scanErr.Split(ScanLinesInclCR)
 	go func() {
-		for {
-			select {
-			case <-donech:
-				line := stdout.String()
-				if line != "" {
-					log.Printf("[vagrant driver] stdout: %s", line)
-				}
-				stdoutString += line
-				line = stderr.String()
-				if line != "" {
-					log.Printf("[vagrant driver] stderr: %s", line)
-				}
-				stderrString += line
-				break
-			default:
-				line, _ := stdout.ReadString('\n')
-				if line != "" {
-					log.Printf("[vagrant driver] stdout: %s", line)
-					stdoutString += line
-
-				}
-				line, _ = stderr.ReadString('\n')
-				if line != "" {
-					log.Printf("[vagrant driver] stderr: %s", line)
-					stderrString += line
-
-				}
-				time.Sleep(500)
-			}
+		for scanErr.Scan() {
+			line := scanErr.Text()
+			log.Printf("[vagrant driver] stderr: %s", line)
+			stderrString += line + "\n"
 		}
 	}()
 
-	err = cmd.Wait()
-
-	donech <- true
+	for scanOut.Scan() {
+		line := scanOut.Text()
+		log.Printf("[vagrant driver] stdout: %s", line)
+		stdoutString += line + "\n"
+	}
+	cmd.Wait()
 
 	if _, ok := err.(*exec.ExitError); ok {
 		err = fmt.Errorf("Vagrant error: %s", stderrString)

builder/vagrant/step_add_box.go

@@ -82,7 +82,8 @@ func (s *StepAddBox) Run(ctx context.Context, state multistep.StateBag) multiste
 		return multistep.ActionContinue
 	}
 
-	ui.Say("Adding box using vagrant box add..")
+	ui.Say("Adding box using vagrant box add ...")
+	ui.Message("(this can take some time if we need to download the box)")
 	addArgs := s.generateAddArgs()
 
 	log.Printf("[vagrant] Calling box add with following args %s", strings.Join(addArgs, " "))