How to write javascript in client side to receive and parse `chunked` response in time?

Question

I'm using play framework, to generate chunked response. The code is:

class Test extends Controller {
    public static void chunk() throws InterruptedException {
        for (int i = 0; i < 10; i++) {
            String data = repeat("" + i, 1000);
            response.writeChunk(data);
            Thread.sleep(1000);
        }
    }
}

When I use browser to visit http://localhost:9000/test/chunk, I can see the data displayed increased every second. But, when I write a javascript function to receive and handle the data, found it will block until all data received.

The code is:

$(function(){
    $.ajax(
        "/test/chunked", 
        {
            "success": function(data, textStatus, xhr) {
                alert(textStatus);
            }
        }
    );
});

I can see a message box popped up after 10s, when all the data received.

How to get the stream and handle the data in time?

Answer 1

jQuery doesn't support that, but you can do that with plain XHR:

var xhr = new XMLHttpRequest()
xhr.open("GET", "/test/chunked", true)
xhr.onprogress = function () {
  console.log("PROGRESS:", xhr.responseText)
}
xhr.send()

This works in all modern browsers, including IE 10. W3C specification here.

The downside here is that xhr.responseText contains an accumulated response. You can use substring on it, but a better idea is to use the responseType attribute and use slice on an ArrayBuffer.

Answer 2

Soon we should be able to use ReadableStream API (MDN docs here). The code below seems to be working with Chrome Version 62.0.3202.94:

fetch(url).then(function (response) {
    let reader = response.body.getReader();
    let decoder = new TextDecoder();
    return readData();
    function readData() {
        return reader.read().then(function ({value, done}) {
            let newData = decoder.decode(value, {stream: !done});
            console.log(newData);
            if (done) {
                console.log('Stream complete');
                return;
            }
            return readData();
        });
    }
});