libpod: use io.Writer vs io.WriteCloser for attach streams

We never ever close the stream so we do not need the Close() function in
th ebackend, the caller should close when required which may no be the
case, i.e. when os.Stdout/err is used.
This should not be a breaking change as the io.Writer is a subset of
io.WriteCloser, therfore all code should still compile while allowing to
pass in Writers without Close().

This is useful for podman top where we exec ps in the container via
podman exec.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

libpod/container_top_linux.go

@@ -355,16 +355,10 @@ func (c *Container) execPSinContainer(args []string) ([]string, error) {
 	defer wPipe.Close()
 	defer rPipe.Close()
 
-	rErrPipe, wErrPipe, err := os.Pipe()
-	if err != nil {
-		return nil, err
-	}
-	defer wErrPipe.Close()
-	defer rErrPipe.Close()
-
+	var errBuf bytes.Buffer
 	streams := new(define.AttachStreams)
 	streams.OutputStream = wPipe
-	streams.ErrorStream = wErrPipe
+	streams.ErrorStream = &errBuf
 	streams.AttachOutput = true
 	streams.AttachError = true
 
@@ -375,13 +369,6 @@ func (c *Container) execPSinContainer(args []string) ([]string, error) {
 			stdout = append(stdout, scanner.Text())
 		}
 	}()
-	stderr := []string{}
-	go func() {
-		scanner := bufio.NewScanner(rErrPipe)
-		for scanner.Scan() {
-			stderr = append(stderr, scanner.Text())
-		}
-	}()
 
 	cmd := append([]string{"ps"}, args...)
 	config := new(ExecConfig)
@@ -390,15 +377,13 @@ func (c *Container) execPSinContainer(args []string) ([]string, error) {
 	if err != nil {
 		return nil, err
 	} else if ec != 0 {
-		return nil, fmt.Errorf("runtime failed with exit status: %d and output: %s", ec, strings.Join(stderr, " "))
+		return nil, fmt.Errorf("runtime failed with exit status: %d and output: %s", ec, errBuf.String())
 	}
 
 	if logrus.GetLevel() >= logrus.DebugLevel {
 		// If we're running in debug mode or higher, we might want to have a
 		// look at stderr which includes debug logs from conmon.
-		for _, log := range stderr {
-			logrus.Debugf("%s", log)
-		}
+		logrus.Debugf(errBuf.String())
 	}
 
 	return stdout, nil

libpod/define/config.go

@@ -51,9 +51,9 @@ const (
 // AttachStreams contains streams that will be attached to the container
 type AttachStreams struct {
 	// OutputStream will be attached to container's STDOUT
-	OutputStream io.WriteCloser
+	OutputStream io.Writer
 	// ErrorStream will be attached to container's STDERR
-	ErrorStream io.WriteCloser
+	ErrorStream io.Writer
 	// InputStream will be attached to container's STDIN
 	InputStream *bufio.Reader
 	// AttachOutput is whether to attach to STDOUT

pkg/bindings/containers/types.go

@@ -295,9 +295,9 @@ type ResizeExecTTYOptions struct {
 //go:generate go run ../generator/generator.go ExecStartAndAttachOptions
 type ExecStartAndAttachOptions struct {
 	// OutputStream will be attached to container's STDOUT
-	OutputStream *io.WriteCloser
+	OutputStream *io.Writer
 	// ErrorStream will be attached to container's STDERR
-	ErrorStream *io.WriteCloser
+	ErrorStream *io.Writer
 	// InputStream will be attached to container's STDIN
 	InputStream *bufio.Reader
 	// AttachOutput is whether to attach to STDOUT