fix(command): wait for all stdout and stderr streams to complete correctly

internal/command/start.go

@@ -9,8 +9,9 @@ import (
 )
 
 // Start launches a command and streams stdout and stderr to channels.
-// All the channels returned are ready only and won't be closed
-// if the command fails later.
+// stdoutLines and stderrLines channels will be closed when there is no more
+// output to read, in order for the caller to catch all lines even after the
+// command has finished. The waitError channel returned will never be closed.
 func (c *Cmder) Start(cmd *exec.Cmd) (
 	stdoutLines, stderrLines <-chan string,
 	waitError <-chan error, startErr error,
@@ -38,6 +39,7 @@ func start(cmd execCmd) (stdoutLines, stderrLines <-chan string,
 	if err != nil {
 		_ = stdout.Close()
 		<-stdoutDone
+		close(stdoutLinesCh)
 		return nil, nil, nil, err
 	}
 	go streamToChannel(stderrReady, stderrDone, stderr, stderrLinesCh)
@@ -45,9 +47,11 @@ func start(cmd execCmd) (stdoutLines, stderrLines <-chan string,
 	err = cmd.Start()
 	if err != nil {
 		_ = stdout.Close()
-		_ = stderr.Close()
 		<-stdoutDone
+		close(stdoutLinesCh)
+		_ = stderr.Close()
 		<-stderrDone
+		close(stderrLinesCh)
 		return nil, nil, nil, err
 	}
 
@@ -55,8 +59,10 @@ func start(cmd execCmd) (stdoutLines, stderrLines <-chan string,
 	go func() {
 		err := cmd.Wait()
 		<-stdoutDone
-		<-stderrDone
+		close(stdoutLinesCh)
 		_ = stdout.Close()
+		<-stderrDone
+		close(stderrLinesCh)
 		_ = stderr.Close()
 		waitErrorCh <- err
 	}()

internal/command/startnlog.go

@@ -18,31 +18,37 @@ func (c *Cmder) RunAndLog(ctx context.Context, command string, logger Logger) (e
 		return err
 	}
 
-	streamCtx, streamCancel := context.WithCancel(context.Background())
 	streamDone := make(chan struct{})
-	go streamLines(streamCtx, streamDone, logger, stdout, stderr)
+	go streamLines(streamDone, logger, stdout, stderr)
 
 	err = <-waitError
-	streamCancel()
 	<-streamDone
 	return err
 }
 
-func streamLines(ctx context.Context, done chan<- struct{},
-	logger Logger, stdout, stderr <-chan string,
+func streamLines(done chan<- struct{}, logger Logger,
+	stdout, stderr <-chan string,
 ) {
 	defer close(done)
 
-	var line string
-
 	for {
 		select {
-		case <-ctx.Done():
-			return
-		case line = <-stdout:
-			logger.Info(line)
-		case line = <-stderr:
-			logger.Error(line)
+		case line, ok := <-stdout:
+			if ok {
+				logger.Info(line)
+			}
+			if stderr == nil {
+				return
+			}
+			stdout = nil
+		case line, ok := <-stderr:
+			if ok {
+				logger.Error(line)
+			}
+			if stdout == nil {
+				return
+			}
+			stderr = nil
 		}
 	}
 }