Tornado streaming HTTP response as AsyncHTTPClient receives chunks

Question

I\'m trying to write a Tornado request handler which makes asynchronous HTTP requests, and returns data to the client as it receives it from it\'s async requests. Unfortunat

Answer 1

Decorate your method with gen.coroutine and yield a list of futures. Here's a simple example:

from tornado import gen, web, httpclient

class StreamingHandler(web.RequestHandler):
    @web.asynchronous
    @gen.coroutine
    def get(self):
        client = httpclient.AsyncHTTPClient()

        self.write('some opening')
        self.flush()

        requests = [
            httpclient.HTTPRequest(
                url='http://httpbin.org/delay/' + str(delay),
                streaming_callback=self.on_chunk
            ) for delay in [5, 4, 3, 2, 1]
        ]

        # `map()` doesn't return a list in Python 3
        yield list(map(client.fetch, requests))

        self.write('some closing')
        self.finish()

    def on_chunk(self, chunk):
        self.write('some chunk')
        self.flush()

Notice that even though the requests are yielded "backwards", the first chunk will still be received after about a second. If you sent them out synchronously, it'd take you 15 seconds. When you request them asynchronously, it takes you just 5.