python `网络编程`和其他语言都是一样的，服务器这块步骤为：
`1. 创建套接字`
`2. 绑定地址`
`3. 监听该描述符的所有请求`
`4. 有新的请求到了调用accept处理请求`
Python Web服务器网关接口（Python Web Server Gateway Interface，简称`“WSGI”`），可以保证同一个服务器响应不同应用框架的请求，WSGI的出现，让开发者可以将网络框架与网络服务器的选择分隔开来，例如，你可以使用Gunicorn或Nginx/uWSGI或Waitress服务器来运行Django、Flask或Pyramid应用。下面简单实现一个机遇WSGI协议的服务器。
import socket
from io import StringIO
import sysclass WSGIServer(object):address_family = socket.AF_INETsocket_type = socket.SOCK_STREAMrequest_queue_size = 1def __init__(self, server_address):# Create a listening socketself.listen_socket = listen_socket = socket.socket(self.address_family,self.socket_type)# Allow to reuse the same addresslisten_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)# Bindlisten_socket.bind(server_address)# Activatelisten_socket.listen(self.request_queue_size)# Get server host name and porthost, port = self.listen_socket.getsockname()[:2]self.server_name = socket.getfqdn(host)self.server_port = port# Return headers set by Web framework/Web applicationself.headers_set = []
定义了一个WSGIServer类，并且在类的init函数完成了套接字的创建、绑定、监听等。
下面实现WSGIServer的轮询检测新的连接并处理连接：
def set_app(self, application):self.application = applicationdef serve_forever(self):listen_socket = self.listen_socketwhile True:# New client connectionself.client_connection, client_address = listen_socket.accept()# Handle one request and close the client connection. Then# loop over to wait for another client connectionself.handle_one_request()
实现处理请求的函数
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 dataenv = self.get_environ()# It's time to call our application callable and get# back a result that will become HTTP response bodyresult = self.application(env, self.start_response)# Construct a response and send it back to the clientself.finish_response(result)
解析请求
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, # GETself.path, # /helloself.request_version # HTTP/1.1) = request_line.split()
返回当前服务器wsgi版本等信息
def get_environ(self):env = {} env['wsgi.version'] = (1, 0)env['wsgi.url_scheme'] = 'http'env['wsgi.input'] = StringIO.StringIO(self.request_data)env['wsgi.errors'] = sys.stderrenv['wsgi.multithread'] = Falseenv['wsgi.multiprocess'] = Falseenv['wsgi.run_once'] = False# Required CGI variablesenv['REQUEST_METHOD'] = self.request_method # GETenv['PATH_INFO'] = self.path # /helloenv['SERVER_NAME'] = self.server_name # localhostenv['SERVER_PORT'] = str(self.server_port) # 8888return env
填写app所需的回调函数
def start_response(self, status, response_headers, exc_info=None):# Add necessary server headersserver_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
发送数据并且关闭连接
def finish_response(self, result):try:status, response_headers = self.headers_setresponse = '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()
主函数和参数解析，创建服务器
SERVER_ADDRESS = (HOST, PORT) = '', 8888def make_server(server_address, application):server = WSGIServer(server_address)server.set_app(application)return serverif __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()
将上面的文件保存为webserver.py
下面搭建虚拟环境，并且安装Pyramid、Flask和Django等框架开发的网络应用。
$ [sudo] pip install virtualenv $ mkdir ~/envs $ virtualenv ~/envs/lsbaws/ $ cd ~/envs/lsbaws/ $ ls bin include lib $ source bin/activate (lsbaws) $ pip install pyramid (lsbaws) $ pip install flask (lsbaws) $ pip install django
编写pyramidapp.py，主要是调用pyramidapp接口生成app
from pyramid.config import Configurator from pyramid.response import Responsedef 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') app = config.make_wsgi_app()
可以通过自己开发的网络服务器来启动上面的Pyramid应用。
`python webserver.py pyramidapp:app`
同样可以创建Flask应用
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')app = flask_app.wsgi_app
上述代码的工作原理：
`1 网络框架提供一个命名为application的可调用对象`。
`2 服务器每次从HTTP客户端接收请求之后，调用application。它会向可调用对象传递一个名叫environ的字典作为参数，其中包含了WSGI/CGI的诸多变量，以及一个名为start_response的可调用对象`。
`3 框架/应用生成HTTP状态码以及HTTP响应报头（HTTP response headers），然后将二者传递至start_response，等待服务器保存。此外，框架/应用还将返回响应的正文。
服务器将状态码、响应报头和响应正文组合成HTTP响应，并返回给客户端`。
可以采用多进程的方式处理多个客户端请求,将上述代码稍作修改
import errno
import os
import signal
import socketSERVER_ADDRESS = (HOST, PORT) = '', 8888
REQUEST_QUEUE_SIZE = 1024def grim_reaper(signum, frame):while True:try:pid, status = os.waitpid(-1, # Wait for any child processos.WNOHANG # Do not block and return EWOULDBLOCK error)except OSError:returnif pid == 0: # no more zombiesreturndef handle_request(client_connection):request = client_connection.recv(1024)print(request.decode())http_response = b"""\
HTTP/1.1 200 OKHello, World!
"""client_connection.sendall(http_response)def serve_forever():listen_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)listen_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)listen_socket.bind(SERVER_ADDRESS)listen_socket.listen(REQUEST_QUEUE_SIZE)print('Serving HTTP on port {port} ...'.format(port=PORT))signal.signal(signal.SIGCHLD, grim_reaper)while True:try:client_connection, client_address = listen_socket.accept()except IOError as e:code, msg = e.args# restart 'accept' if it was interruptedif code == errno.EINTR:continueelse:raisepid = os.fork()if pid == 0: # childlisten_socket.close() # close child copyhandle_request(client_connection)client_connection.close()os._exit(0)else: # parentclient_connection.close() # close parent copy and loop overif __name__ == '__main__':serve_forever()
grim_reaper 函数为捕捉子进程退出的回调函数，父进程等待所有子进程退出后再退出，避免僵尸进程。由于子进程退出父进程捕获到消息，调用grim_reaper处理，由于父进程之前阻塞在accept上，捕获子进程销毁消息后，父进程accept失败，所以增加了errno.EINTR错误判断，如果是由于信号中断导致accept失败，就让父进程继续调用accept即可。
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