fix: support large output with --enable-live-ouput (#1139)

* fix: support large output with --enable-live-ouput

This replaces Scanner with ReadString to handle large amount of data returned by helm ouptut when executing diff action

- Changing pkg/helmexec/runner_test.go TestLiveOutput test, adding test with large amount of data, reproducing the issue before applying this fix
- Changing pkg/helmexec/runner.go Scanner with Readstring

Resolves https://github.com/helmfile/helmfile/issues/893

Signed-off-by: Franck Labatut <franck.labatut@ubisoft.com>

* fix: prevent data race

Signed-off-by: Franck Labatut <franck.labatut@ubisoft.com>

---------

Signed-off-by: Franck Labatut <franck.labatut@ubisoft.com>

pkg/helmexec/runner.go

@@ -127,13 +127,26 @@ func Output(ctx context.Context, c *exec.Cmd, stripArgsValuesOnExitError bool, l
 
 func LiveOutput(ctx context.Context, c *exec.Cmd, stripArgsValuesOnExitError bool, stdout io.Writer) ([]byte, error) {
 	reader, writer := io.Pipe()
-	scannerStopped := make(chan struct{})
+	ch := make(chan error)
+	doneCh := make(chan struct{})
 
 	go func() {
-		defer close(scannerStopped)
-		scanner := bufio.NewScanner(reader)
-		for scanner.Scan() {
-			fmt.Fprintln(stdout, scanner.Text())
+		defer close(doneCh)
+		reader := bufio.NewReader(reader)
+
+		for {
+			// prefer readstring over scanner to handle potential large output
+			// https://stackoverflow.com/a/29444042
+			line, err := reader.ReadString('\n')
+			if err != nil {
+				if err == io.EOF {
+					break
+				}
+				ch <- err
+			}
+
+			line = strings.TrimSuffix(line, "\n")
+			fmt.Fprintln(stdout, line)
 		}
 	}()
 
@@ -142,7 +155,6 @@ func LiveOutput(ctx context.Context, c *exec.Cmd, stripArgsValuesOnExitError boo
 	err := c.Start()
 
 	if err == nil {
-		ch := make(chan error)
 		go func() {
 			ch <- c.Wait()
 		}()
@@ -154,7 +166,7 @@ func LiveOutput(ctx context.Context, c *exec.Cmd, stripArgsValuesOnExitError boo
 			err = <-ch
 		}
 		_ = writer.Close()
-		<-scannerStopped
+		<-doneCh
 	}
 
 	if err != nil {

pkg/helmexec/runner_test.go

@@ -3,6 +3,7 @@ package helmexec
 import (
 	"bytes"
 	"context"
+	_ "embed"
 	"os/exec"
 	"reflect"
 	"strings"
@@ -48,6 +49,9 @@ func TestShellRunner_Execute(t *testing.T) {
 	}
 }
 
+//go:embed testdata/live-output-data.txt
+var liveOutputData string
+
 func TestLiveOutput(t *testing.T) {
 	tests := []struct {
 		name    string
@@ -55,6 +59,12 @@ func TestLiveOutput(t *testing.T) {
 		wantW   string
 		wantErr bool
 	}{
+		{
+			name:    "live_output_data",
+			cmd:     exec.Command("cat", "testdata/live-output-data.txt"),
+			wantW:   liveOutputData,
+			wantErr: false,
+		},
 		{
 			name:    "echo_template",
 			cmd:     exec.Command("echo", "template"),