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动手实现简单的WSGI服务器

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作为一个Django开发时常与uWSGI打交道，接触的项目也都是采用nginx+uWSGI+django的部署方式，此篇文章记录下对WSGI的学习。

什么是WSGI

WSGI，全称为“Web Server Gateway Interface”，即 Web 服务器网关接口。它是一个 Python 标准，定义了 Web 服务器与 Web 应用或框架之间的通信协议（规范）。
容易混淆的概念WSGI、uwsgi、uWSGI对比：

  • WSGI： Web服务器与Web框架间的通信协议（规范）
  • uwsgi：uWSGI服务器自有的协议，它用于定义传输信息的类型，每一个uwsgi packet前4byte为传输信息类型描述，用于与nginx等代理服务器通信，它与WSGI相比是两样东西。
  • uWSGI：uWSGI是实现了uwsgi和WSGI两种协议的Web服务器。

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上面可以看出WSGI、uwsgi是通信协议或者叫做规范，uWSGI是Web服务器

现实WSGI服务器demo

为了简化对WSGI的理解这里我们先看一个HTTP到WSGI服务器的实现。
参考Python源码中WSGI实现方式的示例lib/wsgiref/simeple_server.py
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import sys
import socket
from datetime import datetime, timezone


class WSGIServer():
    application = None

    def __init__(self, host, port) -> None:
        self.client_connection = None
        self.headers_set = None
        self.server_address = (host, port)
        self.request_data = None
        self.request_method = None
        self.path = None
        self.server_name = None
        self.server_port = None

    def get_environ(self):
        env = {}
        env['wsgi.version'] = (1, 0)
        env['wsgi.url_scheme'] = 'http'
        env['wsgi.input'] = self.request_data
        env['wsgi.errors'] = sys.stderr
        env['REQUEST_METHOD'] = self.request_method
        env['PATH_INFO'] = self.path
        env['SERVER_NAME'] = self.server_name
        env['SERVER_PORT'] = self.server_port
        return env

    def handle_one_request(self):
        sk = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sk.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        sk.bind(self.server_address)
        sk.listen(1)
        self.client_connection, client_address = sk.accept()
        request_data = self.request_data =  self.client_connection.recv(1024)
        self.request_method, self.path, self.request_version = self.parse_request(request_data)    #提取http协议请求头字段
        env = self.get_environ()
        result = self.application(env, self.start_response)    #调用application
        self.finish_response(result)    #将python对象转换为http协议二进制数据使用socket发送
        self.client_connection.close()

    def start_response(self, status, response_headers, exc_info=None):
        now = datetime.now(timezone.utc).strftime("%a, %d %b %Y %H:%M:%S GMT")
        server_headers = [('Date', now), ('Server', 'WSGIServerCustomer 0.1')]
        self.headers_set = [status, response_headers+server_headers]

    def finish_response(self, result):
        try:
            status, response_headers = self.headers_set
            response = f'{self.request_version} {status}\r\n'
            for header in response_headers:
                response += '{0}: {1}\r\n'.format(*header)
            response += '\r\n'
            for data in result:
                response += data.decode()
            print(''.join('<{line}\n'.format(line=line) for line in response.splitlines()))
            self.client_connection.sendall(response.encode())
        finally:
            self.client_connection.close()

    def parse_request(self, data):
        print(''.join('>{line}\n'.format(line=line.decode()) for line in data.splitlines()))
        data = data.splitlines()[0]
        return data.decode().split()

    def get_app(self):
        return self.application

    def set_app(self,application):
        self.application = application

# 实现一个application
def demo_app(environ, start_response):
    from io import StringIO
    stdout = StringIO()
    print("Hello world!", file=stdout)
    print(file=stdout)
    # h = sorted(environ.items())
    # for k,v in h:
    #     print(k,'=',repr(v), file=stdout)
    start_response("200 OK", [('Content-Type','text/plain; charset=utf-8')])
    return [stdout.getvalue().encode("utf-8")]


def make_server(host, port, app):
    server = WSGIServer(host, port)
    server.set_app(app)
    return server


if __name__ == '__main__':
    httpd =  make_server('', 8000, demo_app)
    # 只处理一次请求
    httpd.handle_one_request()

运行效果展示

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实现 WSGI服务器 application分离

下面我们将WSGI服务器与Application分离，Application使用Flask.wsgi_app
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# !/usr/bin/env python
# -*- coding: utf-8 -*-
# @Author  : neighbour7
# @File    : wsgi_server.py

import sys
import socket
from datetime import datetime, timezone


class WSGIServer():
    application = None

    def __init__(self, host, port) -> None:
        self.client_connection = None
        self.headers_set = None
        self.server_address = (host, port)
        self.request_data = None
        self.request_method = None
        self.path = None
        self.server_name = None
        self.server_port = None

    def get_environ(self):
        env = {}
        env['wsgi.version'] = (1, 0)
        env['wsgi.url_scheme'] = 'http'
        env['wsgi.input'] = self.request_data
        env['wsgi.errors'] = sys.stderr
        env['REQUEST_METHOD'] = self.request_method
        env['PATH_INFO'] = self.path
        env['SERVER_NAME'] = self.server_name
        env['SERVER_PORT'] = self.server_port
        return env

    def handle_one_request(self):
        sk = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sk.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        sk.bind(self.server_address)
        sk.listen(1)
        self.client_connection, client_address = sk.accept()
        request_data = self.request_data =  self.client_connection.recv(1024)
        self.request_method, self.path, self.request_version = self.parse_request(request_data)    #提取http协议请求头字段
        env = self.get_environ()
        result = self.application(env, self.start_response)    #调用application
        self.finish_response(result)    #将python对象转换为http协议二进制数据使用socket发送
        self.client_connection.close()

    def start_response(self, status, response_headers, exc_info=None):
        now = datetime.now(timezone.utc).strftime("%a, %d %b %Y %H:%M:%S GMT")
        server_headers = [('Date', now), ('Server', 'WSGIServerCustomer 0.1')]
        self.headers_set = [status, response_headers+server_headers]

    def finish_response(self, result):
        try:
            status, response_headers = self.headers_set
            response = f'{self.request_version} {status}\r\n'
            for header in response_headers:
                response += '{0}: {1}\r\n'.format(*header)
            response += '\r\n'
            for data in result:
                response += data.decode()
            print(''.join('>{line}\n'.format(line=line) for line in response.splitlines()))
            self.client_connection.sendall(response.encode())
        finally:
            self.client_connection.close()

    def parse_request(self, data):
        data = data.splitlines()[0]
        return data.decode().split()

    def get_app(self):
        return self.application

    def set_app(self,application):
        self.application = application

# 实现一个application
def demo_app(environ, start_response):
    from io import StringIO
    stdout = StringIO()
    print("Hello world!", file=stdout)
    print(file=stdout)
    h = sorted(environ.items())
    for k,v in h:
        print(k,'=',repr(v), file=stdout)
    start_response("200 OK", [('Content-Type','text/plain; charset=utf-8')])
    return [stdout.getvalue().encode("utf-8")]


def make_server(host, port, app):
    server = WSGIServer(host, port)
    server.set_app(app)
    return server


if __name__ == '__main__':
    httpd =  make_server('', 8000, demo_app)
    # 只处理一次请求
    httpd.handle_one_request()
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# !/usr/bin/env python
# -*- coding: utf-8 -*-
# @Author  : neighbour7
# @File    : flaskapp.py

from flask import Flask, Response

flask_app = Flask('flaskapp')


@flask_app.route('/hello')
def hello_world():

    return "Hello World!"

app = flask_app.wsgi_app

Flask.wsgi_app 中接收两个参数(environ, start_response)，源码如下：
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运行效果展示
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总结

通过上面的例子明白WSGI实际上就是将HTTP(FastCGI、uwsgi)等协议转化为Python的可执行对象Application
WSGI 抽象了底层的网络通信细节，让开发者能够专注于编写 Web 应用逻辑，而不必处理网络层面的复杂性。

参考：

自己动手开发网络服务器（二）：实现ＷＳＧＩ服务
WSGI，uWSGI和uwsgi区别详解
wsgiref/simple_server.py