WSGIServer 例子, 理解什么是 WSGI

app_flask.py

from flask import Flask
from flask import Response
flask_app = Flask('flaskapp')


@flask_app.route('/hello')
def hello_world():
    return Response(
        'Hello world from Flask!\n',
        mimetype='text/plain'
    )

wsgi_app = flask_app.wsgi_app

app_pyramid.py

from pyramid.config import Configurator
from pyramid.response import Response


def hello_world(request):
    return Response(
        'Hello world from Pyramid!\n',
        content_type='text/plain',
    )

config = Configurator()
config.add_route('hello', '/hello')
config.add_view(hello_world, route_name='hello')
wsgi_app = config.make_wsgi_app()

app_tornado.py

import tornado.web
import tornado.wsgi


class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello world from Tornado!")

application = tornado.web.Application([
    (r"/hello", MainHandler),
])
wsgi_app = tornado.wsgi.WSGIAdapter(application)

test.py

#!/bin/env python


class Test():
    def __init__(self, app):
        self.app = app

    def handler(self):
        return self.app(self.set_headers)

    def set_headers(self, content):
        self.headers_set = content

    def get_headers(self):
        return self.headers_set


class App():
    def __call__(self, func):
        func("test")
        return "test" * 2


app = App()
test = Test(app)
print test.handler()
print test.get_headers()

tornado_WSGIAdapter.py

class WSGIAdapter(object):
    """Converts a `tornado.web.Application` instance into a WSGI application.

    Example usage::

        import tornado.web
        import tornado.wsgi
        import wsgiref.simple_server

        class MainHandler(tornado.web.RequestHandler):
            def get(self):
                self.write("Hello, world")

        if __name__ == "__main__":
            application = tornado.web.Application([
                (r"/", MainHandler),
            ])
            wsgi_app = tornado.wsgi.WSGIAdapter(application)
            server = wsgiref.simple_server.make_server('', 8888, wsgi_app)
            server.serve_forever()

    See the `appengine demo
    <https://github.com/tornadoweb/tornado/tree/stable/demos/appengine>`_
    for an example of using this module to run a Tornado app on Google
    App Engine.

    In WSGI mode asynchronous methods are not supported.  This means
    that it is not possible to use `.AsyncHTTPClient`, or the
    `tornado.auth` or `tornado.websocket` modules.

    .. versionadded:: 4.0
    """
    def __init__(self, application):
        if isinstance(application, WSGIApplication):
            self.application = lambda request: web.Application.__call__(
                application, request)
        else:
            self.application = application

    def __call__(self, environ, start_response):
        method = environ["REQUEST_METHOD"]
        uri = urllib_parse.quote(from_wsgi_str(environ.get("SCRIPT_NAME", "")))
        uri += urllib_parse.quote(from_wsgi_str(environ.get("PATH_INFO", "")))
        if environ.get("QUERY_STRING"):
            uri += "?" + environ["QUERY_STRING"]
        headers = httputil.HTTPHeaders()
        if environ.get("CONTENT_TYPE"):
            headers["Content-Type"] = environ["CONTENT_TYPE"]
        if environ.get("CONTENT_LENGTH"):
            headers["Content-Length"] = environ["CONTENT_LENGTH"]
        for key in environ:
            if key.startswith("HTTP_"):
                headers[key[5:].replace("_", "-")] = environ[key]
        if headers.get("Content-Length"):
            body = environ["wsgi.input"].read(
                int(headers["Content-Length"]))
        else:
            body = b""
        protocol = environ["wsgi.url_scheme"]
        remote_ip = environ.get("REMOTE_ADDR", "")
        if environ.get("HTTP_HOST"):
            host = environ["HTTP_HOST"]
        else:
            host = environ["SERVER_NAME"]
        connection = _WSGIConnection(method, start_response,
                                     _WSGIRequestContext(remote_ip, protocol))
                                     # wgsi 的 start_response 函数, 被封装在 connection.
                                     # 以 tornado 为例, start_response 最终是在 tornado.web.RequestHandler 
                                     # 的 flush 函数中执行.
        request = httputil.HTTPServerRequest(
            method, uri, "HTTP/1.1", headers=headers, body=body,
            host=host, connection=connection)
            # 用 HTTPServerRequest 封装 request.
        request._parse_body()
        self.application(request)   # 这里的 application 是 http application, 
                                    # 也就是 tornado.wsgi.WSGIAdapter(application)传入的 application;
                                    # 这里调用 http application 来处理 request.
                                    # 以 torando 为例, 此句会调用 _RequestDispatcher 类, 传入此applition 和
                                    # request, 因为 application 在初始化的时候指定了 path 和 RequestHandler,
                                    # 比如 [(r"/", MainHandler), ...], 所以根据 reqeust 中的 path就能知道对应
                                    # 的 RequststHander, 然后执行 RequestHandler, 传入 application 和 request,
                                    # 在 RequestHandler 里面会调用 self.request.connection.write_headers, 里面
                                    # 会执行 start_response 函数.
                                    
        if connection._error:
            raise connection._error
        if not connection._finished:
            raise Exception("request did not finish synchronously")
        return connection._write_buffer

WSGIServer.py

#!/bin/env python

# Tested with Python 2.7.9, Linux & Mac OS X


import socket
import StringIO
import sys
 
 
class WSGIServer(object):
 
    address_family = socket.AF_INET
    socket_type = socket.SOCK_STREAM
    request_queue_size = 1
 
    def __init__(self, server_address):
        # Create a listening socket
        self.listen_socket = listen_socket = socket.socket(
            self.address_family,
            self.socket_type
        )
        # Allow to reuse the same address
        listen_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        # Bind
        listen_socket.bind(server_address)
        # Activate
        listen_socket.listen(self.request_queue_size)
        # Get server host name and port
        host, port = self.listen_socket.getsockname()[:2]
        self.server_name = socket.getfqdn(host)
        self.server_port = port
        # Return headers set by Web framework/Web application
        self.headers_set = []
 
    def set_app(self, application):
        self.application = application   # self.application 是 wsgi app, 它里面有一个 http application.
 
    def serve_forever(self):
        listen_socket = self.listen_socket
        while True:
            # New client connection
            self.client_connection, client_address = listen_socket.accept()
            # Handle one request and close the client connection. Then
            # loop over to wait for another client connection
            self.handle_one_request()
 
    def handle_one_request(self):
        self.request_data = request_data = self.client_connection.recv(1024)
        # Print formatted request data a la 'curl -v'
        print(''.join(
            '< {line}\n'.format(line=line)
            for line in request_data.splitlines()
        ))
 
        self.parse_request(request_data)
 
        # Construct environment dictionary using request data
        env = self.get_environ()
 
        # It's time to call our application callable and get
        # back a result that will become HTTP response body
        result = self.application(env, self.start_response)   # 这句话最重要, 调用 wsgi app 的 __call__ 方法, 
                                                              # 传入 env 和 start_response, start_response 是
                                                              # 本地函数.
 
        # Construct a response and send it back to the client
        self.finish_response(result)
 
    def parse_request(self, text):
        request_line = text.splitlines()[0]
        request_line = request_line.rstrip('\r\n')
        # Break down the request line into components
        (self.request_method,  # GET
         self.path,            # /hello
         self.request_version  # HTTP/1.1
         ) = request_line.split()
 
    def get_environ(self):
        env = {}
        # The following code snippet does not follow PEP8 conventions
        # but it's formatted the way it is for demonstration purposes
        # to emphasize the required variables and their values
        #
        # Required WSGI variables
        env['wsgi.version']      = (1, 0)
        env['wsgi.url_scheme']   = 'http'
        env['wsgi.input']        = StringIO.StringIO(self.request_data)
        env['wsgi.errors']       = sys.stderr
        env['wsgi.multithread']  = False
        env['wsgi.multiprocess'] = False
        env['wsgi.run_once']     = False
        # Required CGI variables
        env['REQUEST_METHOD']    = self.request_method    # GET
        env['PATH_INFO']         = self.path              # /hello
        env['SERVER_NAME']       = self.server_name       # localhost
        env['SERVER_PORT']       = str(self.server_port)  # 8888
        return env
 
    def start_response(self, status, response_headers, exc_info=None):
        # Add necessary server headers
        server_headers = [
            ('Date', 'Tue, 31 Mar 2015 12:54:48 GMT'),
            ('Server', 'WSGIServer 0.2'),
        ]
        self.headers_set = [status, response_headers + server_headers]
        # To adhere to WSGI specification the start_response must return
        # a 'write' callable. We simplicity's sake we'll ignore that detail
        # for now.
        # return self.finish_response
 
    def finish_response(self, result):
        try:
            status, response_headers = self.headers_set
            response = 'HTTP/1.1 {status}\r\n'.format(status=status)
            for header in response_headers:
                response += '{0}: {1}\r\n'.format(*header)
            response += '\r\n'
            for data in result:
                response += data
            # Print formatted response data a la 'curl -v'
            print(''.join(
                '> {line}\n'.format(line=line)
                for line in response.splitlines()
            ))
            self.client_connection.sendall(response)
        finally:
            self.client_connection.close()
 
 
SERVER_ADDRESS = (HOST, PORT) = '', 8888
 
 
def make_server(server_address, application):
    server = WSGIServer(server_address)
    server.set_app(application)
    return server
 
 
if __name__ == '__main__':
    if len(sys.argv) < 2:
        sys.exit('Provide a WSGI application object as module:callable')
    app_path = sys.argv[1]
    module, application = app_path.split(':')
    module = __import__(module)
    application = getattr(module, application)
    httpd = make_server(SERVER_ADDRESS, application)
    print('WSGIServer: Serving HTTP on port {port} ...\n'.format(port=PORT))
    httpd.serve_forever()