python `網絡編程`和其他語言都是一樣的，服務器這塊步驟為：
`1. 創建套接字`
`2. 綁定地址`
`3. 監聽該描述符的所有請求`
`4. 有新的請求到了調用accept處理請求`
Python Web服務器網關接口（Python Web Server Gateway Interface，簡稱`“WSGI”`），可以保證同一個服務器響應不同應用框架的請求，WSGI的出現，讓開發者可以將網絡框架與網絡服務器的選擇分隔開來，例如，你可以使用Gunicorn或Nginx/uWSGI或Waitress服務器來運行Django、Flask或Pyramid應用。下面簡單實現一個機遇WSGI協議的服務器。
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 = []
定義了一個WSGIServer類，并且在類的init函數完成了套接字的創建、綁定、監聽等。
下面實現WSGIServer的輪詢檢測新的連接并處理連接：
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()
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實現處理請求的函數
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)
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解析請求
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()
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返回當前服務器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
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填寫app所需的回調函數
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
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發送數據并且關閉連接
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()
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主函數和參數解析，創建服務器
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()
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將上面的文件保存為webserver.py
下面搭建虛擬環境，并且安裝Pyramid、Flask和Django等框架開發的網絡應用。
$ [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
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編寫pyramidapp.py，主要是調用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()
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可以通過自己開發的網絡服務器來啟動上面的Pyramid應用。
`python webserver.py pyramidapp:app`
同樣可以創建Flask應用
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
上述代碼的工作原理：
`1 網絡框架提供一個命名為application的可調用對象`。
`2 服務器每次從HTTP客戶端接收請求之后，調用application。它會向可調用對象傳遞一個名叫environ的字典作為參數，其中包含了WSGI/CGI的諸多變量，以及一個名為start_response的可調用對象`。
`3 框架/應用生成HTTP狀態碼以及HTTP響應報頭（HTTP response headers），然后將二者傳遞至start_response，等待服務器保存。此外，框架/應用還將返回響應的正文。
服務器將狀態碼、響應報頭和響應正文組合成HTTP響應，并返回給客戶端`。
可以采用多進程的方式處理多個客戶端請求,將上述代碼稍作修改
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 函數為捕捉子進程退出的回調函數，父進程等待所有子進程退出后再退出，避免僵尸進程。由于子進程退出父進程捕獲到消息，調用grim_reaper處理，由于父進程之前阻塞在accept上，捕獲子進程銷毀消息后，父進程accept失敗，所以增加了errno.EINTR錯誤判斷，如果是由于信號中斷導致accept失敗，就讓父進程繼續調用accept即可。
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