Async Http Client - Zero Bytes Copy

Zero Bytes Copy

When uploading or downloading bytes, it is important to try to avoid buffering bytes in memory.

Upload

On the upload side, the mechanism is enabled by default when setting the Request's body to a File:

AsyncHttpClient client = new AsyncHttpClient();
File file = new File("file.avi");
Future f = client.preparePut("http://localhost").setBody(file).execute();

If you can't use a File, the recommended way is to use a BodyGenerator. It is strongly recommended to avoid using InputStream as the library will unfortunately buffer the entire content in memory in order to set the content-lenght, which can cause out of memory error.

Download

On the download side, you can use the HttpResponseBodyPart.writeTo to avoid loading bytes in memory and unnecessary copy:

AsyncHttpClient client = new AsyncHttpClient();
File tmp = new File("zeroCopy.txt");
final FileOutputStream stream = new FileOutputStream(tmp);
Future f = client.prepareGet("http://localhost/largefile.avi").execute(new AsyncHandler() {
    public void onThrowable(Throwable t) { }

    public STATE onBodyPartReceived(HttpResponseBodyPart bodyPart) throws Exception {
        bodyPart.writeTo(stream);
        return STATE.CONTINUE;
    }

{ .... } });
Response resp = f.get();