Simplify the code that creates a tar passed to CopyToContainer (#416)

docker/docker.go

@@ -214,19 +214,22 @@ func (d *docker) CreateAttachConnection(name string) (net.Conn, error) {
 }
 
 func (d *docker) CopyToContainer(containerName, destination, fileName string, content io.Reader) error {
-	r, w := io.Pipe()
-	b, readErr := ioutil.ReadAll(content)
-	if readErr != nil {
-		return readErr
+	contents, err := ioutil.ReadAll(content)
+	if err != nil {
+		return err
 	}
-	t := tar.NewWriter(w)
-	go func() {
-		t.WriteHeader(&tar.Header{Name: fileName, Mode: 0600, Size: int64(len(b)), ModTime: time.Now()})
-		t.Write(b)
-		t.Close()
-		w.Close()
-	}()
-	return d.c.CopyToContainer(context.Background(), containerName, destination, r, types.CopyToContainerOptions{AllowOverwriteDirWithFile: true})
+	var buf bytes.Buffer
+	t := tar.NewWriter(&buf)
+	if err := t.WriteHeader(&tar.Header{Name: fileName, Mode: 0600, Size: int64(len(contents)), ModTime: time.Now()}); err != nil {
+		return err
+	}
+	if _, err := t.Write(contents); err != nil {
+		return err
+	}
+	if err := t.Close(); err != nil {
+		return err
+	}
+	return d.c.CopyToContainer(context.Background(), containerName, destination, &buf, types.CopyToContainerOptions{AllowOverwriteDirWithFile: true})
 }
 
 func (d *docker) CopyFromContainer(containerName, filePath string) (io.Reader, error) {