Web Server Tutorial

Welcome to a tutorial on how to create a simple web server with ASAB.

The code

#!/usr/bin/env python3
import asab
import asab.web
import aiohttp.web


class MyWebApplication(asab.Application):

        async def initialize(self):
                self.add_module(asab.web.Module)
                websvc = self.get_service("asab.WebService")
                websvc.WebApp.router.add_get('/', self.index)

        async def index(self, request):
                return aiohttp.web.Response(text='Hello, world.\n')


if __name__ == '__main__':
        app = MyWebApplication()
        app.run()

To start the application, store above code in a file app.py.

Use python3 app.py -w to run it.

The ASAB web server is now available at http://localhost:8080/.

Deeper look

#!/usr/bin/env python3
import asab

class MyWebApplication(asab.Application):

    async def initialize(self):
        pass

if __name__ == '__main__':
    app = MyWebApplication()
    app.run()

This is a standard ASAB code that declares the application class and establishes main() function for the application. The Application.initialize() method is an application lifecycle method that allows to extend standard initialization of the application with a custom code.

import asab.web
import aiohttp.web

The ASAB web server is a module of ASAB, that is available at asab.web for importing. ASAB web server is built on top of aiohttp.web library. You can freely use any functionality from aiohttp.web library, ASAB is designed to be as much compatible as possible.

self.add_module(asab.web.Module)

This is how you load the ASAB module into the application. The asab.web.Module provides a asab.WebService aka a web server.

websvc = self.get_service("asab.WebService")

This is how locate a service.

websvc.WebApp.router.add_get('/', self.index)

The web service websvc provides default web application WebApp, which in turn provides a router. The router is used to map URLs to respective handlers (self.index in this example). It means that if you access the web server with a path /, it will be handled by a self.index().

async def index(self, request):
    return aiohttp.web.Response(text='Hello, world.\n')

The index() method is a handler. A handler must be a coroutine that accepts a aiohttp.web.Request instance as its only argument and returns a aiohttp.web.Response instance or equivalent.

For more information, go to aiohttp.web handler manual page.