prefetch-tracking.py

import asyncio

# next client id
client = 1

async def handler(r, w):
    line = await r.readline()
    try:
        method, path, version = line.split(b' ', 2)
    except:
        w.close()
        return
    # consume request
    while True:
        line = await r.readline()
        if not line or line == b'\r\n':
            break
    # dispatch
    if path == b'/':
        await handle_index(r, w)
    elif path == b'/theme.css':
        await handle_theme(r, w)
    w.close()

async def handle_index(r, w):
    w.write(b'HTTP/1.1 200 OK\r\n')
    w.write(b'Content-Type: text/html; charset=utf-8\r\n')
    w.write(b'Link: <theme.css>; rel="prefetch", as="stylesheet"\r\n')
    w.write(b'\r\n')
    w.write(b'Hello world!')
    await w.drain()

async def handle_theme(r, w):
    global client
    current = client
    client += 1
    w.write(b'HTTP/1.1 200 OK\r\n')
    w.write(b'Content-Type: text/css\r\n')
    w.write(b'\r\n')
    print('connected client{}'.format(current))
    # keep connection alive by slowly sending spaces
    while True:
        w.write(b' ')
        try:
            await w.drain()
        except:
            break
        await asyncio.sleep(1)
    print('disconnected client{}'.format(current))

async def main(host='127.0.0.1', port=8666):
    s = await asyncio.start_server(handler, host, port)
    print('Serving at http://{}:{}'.format(host, port))
    await s.serve_forever()

try:
    asyncio.run(main())
except KeyboardInterrupt:
    pass