python学习(九) 网络编程学习--简易网站服务器

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 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 = []

　　

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 = 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()

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 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)

　　# Construct a response and send it back to the client
　　self.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, # GET
　　self.path, # /hello
　　self.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.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) #
　　return env

填写app所需的回调函数

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

发送数据并且关闭连接

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()

主函数和参数解析，创建服务器

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()

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 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')
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 socket

SERVER_ADDRESS = (HOST, PORT) = '', 8888
REQUEST_QUEUE_SIZE = 1024

def grim_reaper(signum, frame):
    while True:
        try:
            pid, status = os.waitpid(
                -1,          # Wait for any child process
                 os.WNOHANG  # Do not block and return EWOULDBLOCK error
            )
        except OSError:
            return

        if pid == 0:  # no more zombies
            return

def handle_request(client_connection):
    request = client_connection.recv(1024)
    print(request.decode())
    http_response = b"""\
HTTP/1.1 200 OK

Hello, 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 interrupted
            if code == errno.EINTR:
                continue
            else:
                raise

        pid = os.fork()
        if pid == 0:  # child
            listen_socket.close()  # close child copy
            handle_request(client_connection)
            client_connection.close()
            os._exit(0)
        else:  # parent
            client_connection.close()  # close parent copy and loop over

if __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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