packer: Ui can return an error for Ask, returns one for interrupt

builder/common/multistep_debug.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"github.com/mitchellh/multistep"
 	"github.com/mitchellh/packer/packer"
+	"log"
 	"time"
 )
 
@@ -27,7 +28,12 @@ func MultistepDebugFn(ui packer.Ui) multistep.DebugPauseFn {
 
 		result := make(chan string, 1)
 		go func() {
-			result <- ui.Ask(message)
+			line, err := ui.Ask(message)
+			if err != nil {
+				log.Printf("Error asking for input: %s", err)
+			}
+
+			result <- line
 		}()
 
 		for {

packer/rpc/ui.go

@@ -17,13 +17,9 @@ type UiServer struct {
 	ui packer.Ui
 }
 
-func (u *Ui) Ask(query string) string {
-	var result string
-	if err := u.client.Call("Ui.Ask", query, &result); err != nil {
-		panic(err)
-	}
-
-	return result
+func (u *Ui) Ask(query string) (result string, err error) {
+	err = u.client.Call("Ui.Ask", query, &result)
+	return
 }
 
 func (u *Ui) Error(message string) {
@@ -44,9 +40,9 @@ func (u *Ui) Say(message string) {
 	}
 }
 
-func (u *UiServer) Ask(query string, reply *string) error {
-	*reply = u.ui.Ask(query)
-	return nil
+func (u *UiServer) Ask(query string, reply *string) (err error) {
+	*reply, err = u.ui.Ask(query)
+	return
 }
 
 func (u *UiServer) Error(message *string, reply *interface{}) error {

packer/rpc/ui_test.go

@@ -17,10 +17,10 @@ type testUi struct {
 	sayMessage     string
 }
 
-func (u *testUi) Ask(query string) string {
+func (u *testUi) Ask(query string) (string, error) {
 	u.askCalled = true
 	u.askQuery = query
-	return "foo"
+	return "foo", nil
 }
 
 func (u *testUi) Error(message string) {
@@ -58,7 +58,8 @@ func TestUiRPC(t *testing.T) {
 	uiClient := &Ui{client}
 
 	// Basic error and say tests
-	result := uiClient.Ask("query")
+	result, err := uiClient.Ask("query")
+	assert.Nil(err, "should not error")
 	assert.True(ui.askCalled, "ask should be called")
 	assert.Equal(ui.askQuery, "query", "should be correct")
 	assert.Equal(result, "foo", "should have correct result")

packer/ui.go

@@ -1,6 +1,7 @@
 package packer
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"log"
@@ -24,7 +25,7 @@ const (
 // world. This sort of control allows us to strictly control how output
 // is formatted and various levels of output.
 type Ui interface {
-	Ask(string) string
+	Ask(string) (string, error)
 	Say(string)
 	Message(string)
 	Error(string)
@@ -53,7 +54,7 @@ type ReaderWriterUi struct {
 	l      sync.Mutex
 }
 
-func (u *ColoredUi) Ask(query string) string {
+func (u *ColoredUi) Ask(query string) (string, error) {
 	return u.Ui.Ask(u.colorize(query, u.Color, true))
 }
 
@@ -83,7 +84,7 @@ func (u *ColoredUi) colorize(message string, color UiColor, bold bool) string {
 	return fmt.Sprintf("\033[%d;%d;40m%s\033[0m", attr, color, message)
 }
 
-func (u *PrefixedUi) Ask(query string) string {
+func (u *PrefixedUi) Ask(query string) (string, error) {
 	return u.Ui.Ask(fmt.Sprintf("%s: %s", u.SayPrefix, query))
 }
 
@@ -99,7 +100,7 @@ func (u *PrefixedUi) Error(message string) {
 	u.Ui.Error(fmt.Sprintf("%s: %s", u.SayPrefix, message))
 }
 
-func (rw *ReaderWriterUi) Ask(query string) string {
+func (rw *ReaderWriterUi) Ask(query string) (string, error) {
 	rw.l.Lock()
 	defer rw.l.Unlock()
 
@@ -110,7 +111,7 @@ func (rw *ReaderWriterUi) Ask(query string) string {
 	log.Printf("ui: ask: %s", query)
 	if query != "" {
 		if _, err := fmt.Fprint(rw.Writer, query+" "); err != nil {
-			panic(err)
+			return "", err
 		}
 	}
 
@@ -124,18 +125,12 @@ func (rw *ReaderWriterUi) Ask(query string) string {
 		result <- line
 	}()
 
-	for {
-		select {
-		case line := <-result:
-			return line
-		case <-sigCh:
-			fmt.Fprint(
-				rw.Writer,
-				"\nInterrupts are blocked while waiting for input. Press enter.")
-		}
+	select {
+	case line := <-result:
+		return line, nil
+	case <-sigCh:
+		return "", errors.New("interrupted")
 	}
-
-	return ""
 }
 
 func (rw *ReaderWriterUi) Say(message string) {