streams.py

import asyncio
from aiohttp import web
import subprocess


async def uptime_handler(request):
    # http://HOST:PORT/?interval=90

    # Without the Content-Type, most (all?) browsers will not render
    # partially downloaded content. Note, the response type is
    # StreamResponse not Response.
    resp = web.StreamResponse(status=200,
                              reason='OK',
                              headers={'Content-Type': 'text/html'})

    # The StreamResponse is a FSM. Enter it with a call to prepare.
    await resp.prepare(request)

    counter = 0
    while counter < 10:
        try:
            # Technically, subprocess blocks, so this is a dumb call
            # to put in an async example. But, it's a tiny block and
            # still mocks instantaneous for this example.
            await resp.write(b"<strong>")
            await resp.write(subprocess.check_output('uptime'))
            await resp.write(b"</strong><br>\n")

            # This also yields to the scheduler, but your server
            # probably won't do something like this.
            await asyncio.sleep(1)
            counter += 1
        except Exception as e:
            # So you can observe on disconnects and such.
            print(repr(e))
            raise
    print("End")
    return resp


async def build_server(loop, address, port):
    # For most applications -- those with one event loop --
    # you don't need to pass around a loop object. At anytime,
    # you can retrieve it with a call to asyncio.get_event_loop().
    # Internally, aiohttp uses this pattern a lot. But, sometimes
    # "explicit is better than implicit." (At other times, it's
    # noise.)
    app = web.Application(loop=loop)
    app.router.add_route('GET', "/uptime", uptime_handler)

    return await loop.create_server(app.make_handler(), address, port)


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(build_server(loop, 'localhost', 9999))
    print("Server ready!")

    try:
        loop.run_forever()
    except KeyboardInterrupt:
        print("Shutting Down!")
        loop.close()