Flask源码教程

Posted 2021-04-12 python学习教室

引言

我们知道web应用的本质就是：

1.浏览器发送一个HTTP请求2.服务器收到请求，处理业务逻辑，生成html、json等数据3.服务器把html、json等数据放在HTTP响应的body中发送给浏览器4.浏览器收到http响应

可以看到这一过程我们需要接受、解析HTTP请求和发送HTTP响应，如果这些都由我们自己来写的话，我们需要自己处理包括建立TCP连接（HTTP协议是建立在TCP之上）、解析原始HTTP请求等工作，这太麻烦了。所以我们需要：

1.一个HTTP服务器软件帮我们处理这些工作2.Web应用框架处理业务逻辑

而WSGI就是约定HTTP服务器软件和Web应用框架交互的协议

WSGI协议

WSGI协议主要包括两部分，服务端和应用框架端

具体来说，HTTP服务器把HTTP原始请求封装成一个dict对象，调用应用框架的如下函数，dict对象传给environ参数，并提供一个start_response回调函数。

应用框架处理完业务逻辑之后，回过头来调用start_response这个函数让HTTP服务器软件发送HTTP响应给浏览器

def application(environ, start_response): start_response('200 OK', [('Content-Type', 'text/html')]) return [b'<h1>Hello, web!</h1>']

Gunicon

gunicorn^[1]是一个用python写的实现了WSGI协议的HTTP Server

我们来看一下它是如何启动我们的项目的

# 创建虚拟环境virtualenv --python=python3 venv# 安装gunicornpip install gunicorn

# 查看我们的应用代码cat myapp.py def application(environ, start_response): start_response('200 OK', [('Content-Type', 'text/html')]) return [b'<h1>Hello, web!</h1>']

# 这行命令的意思是gunicorn从myapp这个模块中导入application这个对象# 相当于 from myapp import application# 然后开启四个worker来处理浏览器发送过来的http请求，调用application对象来执行gunicorn -w 4 myapp:application[2020-12-22 07:03:22 -0800] [50121] [INFO] Starting gunicorn 20.0.4[2020-12-22 07:03:22 -0800] [50121] [INFO] Listening at: http://127.0.0.1:8000 (50121)[2020-12-22 07:03:22 -0800] [50121] [INFO] Using worker: sync[2020-12-22 07:03:22 -0800] [50124] [INFO] Booting worker with pid: 50124[2020-12-22 07:03:22 -0800] [50125] [INFO] Booting worker with pid: 50125[2020-12-22 07:03:22 -0800] [50126] [INFO] Booting worker with pid: 50126[2020-12-22 07:03:22 -0800] [50127] [INFO] Booting worker with pid: 50127

我们自己来实现HTTP 服务器软件或者叫WSGI Server呢？

vim my_wsgi_server.py

# -*- coding: UTF-8 -*-import ioimport socketimport 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
 def serve_forever(self): listen_socket = self.listen_socket while True: # 轮询获取客户端的TCP连接 self.client_connection, client_address = listen_socket.accept() # 处理一个HTTP请求，然后关闭 self.handle_one_request()
 def handle_one_request(self): request_data = self.client_connection.recv(1024) self.request_data = request_data = request_data.decode('utf-8') # Print formatted request data a la 'curl -v' print(''.join( f'< {line}\n' for line in request_data.splitlines() ))
 self.parse_request(request_data)
 # 把原始的HTTP请求变成dict字典 env = self.get_environ()
 # 这里就是WSGI协议部分 # 传入包含请求信息的dict对象和回调函数start_response result = self.application(env, self.start_response)
 # 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'] = io.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', 'Mon, 15 Jul 2019 5:54:48 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 = f'HTTP/1.1 {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('utf-8') # Print formatted response data a la 'curl -v' print(''.join( f'> {line}\n' for line in response.splitlines() )) response_bytes = response.encode() self.client_connection.sendall(response_bytes) 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') # 获取python my_wsgi_server.py后面的第一个参数 app_path = sys.argv[1] module, application = app_path.split(':') # myapp module = __import__(module) # myapp.application application = getattr(module, application) # 创建http服务器 httpd = make_server(SERVER_ADDRESS, application) print(f'WSGIServer: Serving HTTP on port {PORT} ...\n')
 httpd.serve_forever()

python3 my_wsgi_server.py myapp:application

至此，你就成功用自己写的wsgi server运行了自己的应用代码

你还可以尝试用这个wsgi server运行flask

pip3 install flask

vim flask_app

from flask import Flask
flask_app = Flask(__name__)

@flask_app.route('/')def hello_world(): return "hello flask"
# python3 my_wsgi_server.py flask_app:flask_app

python3 my_wsgi_server.py flask_app:flask_app

访问8888端口

git clone [e-mail]:johnson329/flask_src.gitgit checkout 6723f55virtualenv --python=python3 venvsource venv/bin/activatepip3 install -r requirements.txtpython3 my_wsgi_server.py flask_app:flask_app

点击阅读原文获取查看Flask源码教程

参考

Let’s Build A Web Server. Part 1.^[2]

Let’s Build A Web Server. Part 2.^[3]

References

[1] gunicorn: https://gunicorn.org/
[2] Let’s Build A Web Server. Part 1.: https://ruslanspivak.com/lsbaws-part1/
[3] Let’s Build A Web Server. Part 2.: https://ruslanspivak.com/lsbaws-part2/