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.. _aiohttp-web-lowlevel:
Low Level Server
================
.. currentmodule:: aiohttp.web
This topic describes :mod:`aiohttp.web` based *low level* API.
Abstract
--------
Sometimes user don't need high-level concepts introduced in
:ref:`aiohttp-web`: applications, routers, middlewares and signals.
All what is needed is supporting asynchronous callable which accepts a
request and returns a response object.
This is done by introducing :class:`aiohttp.web.Server` class which
serves a *protocol factory* role for
:meth:`asyncio.loop.create_server` and bridges data
stream to *web handler* and sends result back.
Low level *web handler* should accept the single :class:`BaseRequest`
parameter and performs one of the following actions:
1. Return a :class:`Response` with the whole HTTP body stored in memory.
2. Create a :class:`StreamResponse`, send headers by
:meth:`StreamResponse.prepare` call, send data chunks by
:meth:`StreamResponse.write` and return finished response.
3. Raise :class:`HTTPException` derived exception (see
:ref:`aiohttp-web-exceptions` section).
All other exceptions not derived from :class:`HTTPException`
leads to *500 Internal Server Error* response.
4. Initiate and process Web-Socket connection by
:class:`WebSocketResponse` using (see :ref:`aiohttp-web-websockets`).
Run a Basic Low-Level Server
----------------------------
The following code demonstrates very trivial usage example::
import asyncio
from aiohttp import web
async def handler(request):
return web.Response(text="OK")
async def main():
server = web.Server(handler)
runner = web.ServerRunner(server)
await runner.setup()
site = web.TCPSite(runner, 'localhost', 8080)
await site.start()
print("======= Serving on http://127.0.0.1:8080/ ======")
# pause here for very long time by serving HTTP requests and
# waiting for keyboard interruption
await asyncio.sleep(100*3600)
asyncio.run(main())
In the snippet we have ``handler`` which returns a regular
:class:`Response` with ``"OK"`` in BODY.
This *handler* is processed by ``server`` (:class:`Server` which acts
as *protocol factory*). Network communication is created by
:ref:`runners API <aiohttp-web-app-runners-reference>` to serve
``http://127.0.0.1:8080/``.
The handler should process every request for every *path*, e.g.
``GET``, ``POST``, Web-Socket.
The example is very basic: it always return ``200 OK`` response, real
life code is much more complex usually.
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