Honor Ctrl+C while waiting for user input (#1805)

Fixes #1800

RELEASE_NOTES=[BUGFIX] Honor Ctrl+C while waiting for user input

Signed-off-by: Dominik Schulz <dominik.schulz@gauner.org>

internal/cui/cui.go

@@ -15,6 +15,7 @@ func GetSelection(ctx context.Context, prompt string, choices []string) (string,
 	if ctxutil.IsAlwaysYes(ctx) || !ctxutil.IsInteractive(ctx) {
 		return "impossible", 0
 	}
+
 	for i, c := range choices {
 		fmt.Printf("[%  d] %s\n", i, c)
 	}

pkg/termio/ask.go

@@ -40,7 +40,7 @@ func AskForString(ctx context.Context, text, def string) (string, error) {
 	}
 
 	fmt.Fprintf(Stdout, "%s [%s]: ", text, def)
-	input, err := NewReader(Stdin).ReadLine()
+	input, err := NewReader(ctx, Stdin).ReadLine()
 	if err != nil {
 		return "", fmt.Errorf("failed to read user input: %w", err)
 	}
@@ -95,7 +95,7 @@ func AskForInt(ctx context.Context, text string, def int) (int, error) {
 		return def, nil
 	}
 
-	str, err := AskForString(ctx, text, strconv.Itoa(def))
+	str, err := AskForString(ctx, text+" (q to abort)", strconv.Itoa(def))
 	if err != nil {
 		return 0, err
 	}

pkg/termio/reader.go

@@ -2,30 +2,58 @@ package termio
 
 import (
 	"bytes"
+	"context"
 	"io"
 )
 
 // LineReader is an unbuffered line reader
 type LineReader struct {
-	r io.Reader
+	r   io.Reader
+	ctx context.Context
 }
 
 // NewReader creates a new line reader
-func NewReader(r io.Reader) *LineReader {
-	return &LineReader{r: r}
+func NewReader(ctx context.Context, r io.Reader) *LineReader {
+	return &LineReader{r: r, ctx: ctx}
 }
 
 // Read implements io.Reader
 func (lr LineReader) Read(p []byte) (int, error) {
 	return lr.r.Read(p)
 }
 
+// rr is a composite value to transport the result of Read through a channel
+type rr struct {
+	n   int
+	err error
+}
+
 // ReadLine reads one line w/o buffering
 func (lr LineReader) ReadLine() (string, error) {
 	out := &bytes.Buffer{}
 	buf := make([]byte, 1) // important: we must only read one byte at a time!
 	for {
-		n, err := lr.r.Read(buf)
+		// we wait for the user input in the background so we can use the
+		// select statement below to be able to immediately quit when the
+		// user presses Ctrl+C
+		msg := make(chan rr, 1)
+		go func() {
+			n, err := lr.r.Read(buf)
+			msg <- rr{n, err}
+		}()
+
+		var n int
+		var err error
+		// wait for a user input (or a signal to abort)
+		select {
+		case <-lr.ctx.Done():
+			return "", ErrAborted
+		case s := <-msg:
+			n = s.n
+			err = s.err
+		}
+
+		// process the user input
 		for i := 0; i < n; i++ {
 			if buf[i] == '\n' {
 				return out.String(), nil

pkg/termio/reader_test.go

@@ -1,6 +1,7 @@
 package termio
 
 import (
+	"context"
 	"io"
 	"strings"
 	"testing"
@@ -24,17 +25,19 @@ func TestReadLines(t *testing.T) {
 }
 
 func TestReadLineError(t *testing.T) {
+	ctx := context.Background()
 	stdin := strings.NewReader("fo")
-	lr := NewReader(iotest.TimeoutReader(stdin))
+	lr := NewReader(ctx, iotest.TimeoutReader(stdin))
 
 	line, err := lr.ReadLine()
 	assert.Error(t, err)
 	assert.Equal(t, "f", line)
 }
 
 func TestRead(t *testing.T) {
+	ctx := context.Background()
 	stdin := strings.NewReader(`foobarbazzabzabzab`)
-	lr := NewReader(stdin)
+	lr := NewReader(ctx, stdin)
 
 	b := make([]byte, 10)
 	n, err := lr.Read(b)
@@ -44,7 +47,8 @@ func TestRead(t *testing.T) {
 }
 
 func mustReadLine(r io.Reader) string {
-	line, err := NewReader(r).ReadLine()
+	ctx := context.Background()
+	line, err := NewReader(ctx, r).ReadLine()
 	if err != nil {
 		panic(err)
 	}