Falcon WSGI application with asyncio

README.md

Getting Started

$ pip install falcon
$ python3 app.py

alternatively with Gunicorn (for HTTP/1.1):

$ pip install gunicorn
$ gunicorn app:app

aggregator.py

from asyncio import Future, Task, coroutine as async, sleep
from random import randint


def retrieve(*uris, callback=None):
    res = Future()
    responses = []

    def conclude(response):
        responses.append(response)
        if callback:
            callback(response)
        if len(responses) == len(uris):
            res.set_result(responses)

    for uri in uris:
        task = Task(fetch(uri))
        task.add_done_callback(lambda task: conclude(task.result()))

    return res


@async
def fetch(uri):
    print("retrieving %s..." % uri)
    lag = yield from _http()
    lag = lag * 1000
    print("downloaded %s in %d ms" % (uri, lag))
    return "[%d ms] %s\n" % (lag, uri)


@async
def _http():
    lag = randint(2, 9) * 0.1
    yield from sleep(lag)
    return lag

app.py

import asyncio

import falcon

import aggregator

from wsgiref import simple_server


class Frontpage:

    def on_get(self, req, res):
        uris = ("http://example.org/foo", "http://example.org/bar",
                "http://example.org/baz")

        res.stream = ResponseStream(res.stream)
        service_requests = aggregator.retrieve(*uris,
                callback=res.stream.write) # XXX: race condition? `write` vs. `__iter__`
        loop = asyncio.get_event_loop()
        loop.run_until_complete(service_requests)


class ResponseStream:

    def __init__(self, output_stream):
        self.output_stream = output_stream
        self.chunks = []

    def write(self, chunk):
        self.chunks.append(chunk)

    def __iter__(self, *args, **kwargs):
        while True:
            try:
                chunk = self.chunks.pop(0) # XXX: inefficient?
                yield chunk.encode("utf8")
            except IndexError:
                break


app = falcon.API()
app.add_route("/", Frontpage())


if __name__ == "__main__":
    server = simple_server.make_server("localhost", 8000, app)
    server.serve_forever()