flask启动流程01

flask 源码分析01：启动流程

1.WSGI简介

'''

Flask框架遵循wsgi协议

1.	WSGI 中有一个非常重要的概念：每个 python web 应用都是一个可调用（callable）的对象。在 flask 中，这个对象就是 app = Flask(__name__) 创建出来的 app

2.	要运行 web 应用，必须有 web server，比如我们熟悉的 apache、nginx ，或者 python 中的 gunicorn，
flask框架则应用到了werkzeug工具包提供的WSGIServer，监听在指定的端口，收到 HTTP 请求的时候解析为 WSGI 格式，然后调用 app 去执行处理的逻辑。

3. Server 和 Application 之间怎么通信，就是 WSGI 的功能。它规定了 app(environ, start_response) 的接口，server 会调用 application，并传给它两个参数：environ 包含了请求的所有信息，start_response 是 application 处理完之后需要调用的函数，参数是状态码、响应头部还有错误信息。


4. WSGI application 非常重要的特点是：它是可以嵌套的。换句话说，我可以写个 application，它做的事情就是调用另外一个 application，然后再返回（类似一个 proxy）。一般来说，嵌套的最后一层是业务应用，中间就是 middleware。这样的好处是，可以解耦业务逻辑和其他功能，比如限流、认证、序列化等都实现成不同的中间层，不同的中间层和业务逻辑是不相关的，可以独立维护；而且用户也可以动态地组合不同的中间层来满足不同的需求。

'''

2.实例化flask对象

from flask import Flask
app = Flask(__name__)

2.1静态属性

class Flask(object):

	# 请求响应
	request_class = Request
	response_class = Response
	
	# 配置文件
	config_class = Config
	
	# 秘钥
	secret_key = ConfigAttribute("SECRET_KEY")
	
	# 路由
	url_rule_class = Rule
	url_map_class = Map
	
	# session
	session_interface = SecureCookieSessionInterface()
	
	# 模板
	template_folder = None

2.2init初始化

def __init__(self,...):

	# 静态文件相关
	self.static_url_path = static_url_path
	self.static_folder = static_folder
	
	# 配置文件
	self.config = self.make_config(instance_relative_config)
	
	# 视图函数: 格式-----{endpoint:func名}
	self.view_functions = {}
	
	# 加载所有的@app.before_request的函数，格式{ None:[func1, func2...] }
	self.before_request_funcs = {}
	
	# 加载所有的@before_first_request的函数，格式[func3, func4...]
	self.before_first_request_funcs = []
	
	# 加载所有的@app.after_request的函数，格式{ None:[func1, func2...] }
	self.after_request_funcs = {}
	
	# 蓝图
	self.blueprints = {}
    self._blueprint_order = []
	
	# url
	self.url_map = self.url_map_class()

	# 添加静态文件路由
	if self.has_static_folder:
        assert (
            bool(static_host) == host_matching
        ), "Invalid static_host/host_matching combination"
        self.add_url_rule(
            self.static_url_path + "/<path:filename>",
            endpoint="static",
            host=static_host,
            view_func=self.send_static_file,
        )

3.秘钥处理

'''
app.secret_key = 'david'
'''
......

4.加载配置文件

'''
app.config.from_object(settings.py)
'''

class Config(dict):
	
	def from_object(self, obj):
		if isinstance(obj, string_types):
			obj = import_string(obj)
			
		# 遍历配置文件，并以键值对的形式存储
		for key in dir(obj):
			if key.isupper():
				self[key] = getattr(obj, key)

5.before_first_request

'''
@app.before_first_request
def func3():
	pass
	
@app.before_first_request
def func4():
	pass
'''

# 添加所有的@before_first_request的函数名到列表，格式[func3, func4...]
# self.before_first_request_funcs = []
@setupmethod
def before_first_request(self, f):
    self.before_first_request_funcs.append(f)
    return f

6.before_request

'''
@app.before_request
def func1():
	pass
	
@app.before_request
def func2():
	pass
	
'''

# 加载所有的@app.before_request的函数，格式{ None:[func1, func2...] }
# self.before_request_funcs = {}
@setupmethod
def before_request(self, f):
    self.before_request_funcs.setdefault(None, []).append(f)
    return f

7.after_request

'''
@app.after_request
def func5():
	pass
	
@app.after_request
def func6():
	pass
	
'''

# 加载所有的@app.before_request的函数，格式{ None:[func5, func6...] }
# self.before_request_funcs = {}
@setupmethod
def after_request(self, f):
    self.after_request_funcs.setdefault(None, []).append(f)
    return f

8.路由与视图

'''
@app.route('/index', methods=['GET', 'POST'], endpoint='index')
def index():
	pass
	
'''
# rule : url
def route(self, rule, **options):
    
	def decorator(f):
		endpoint = options.pop("endpoint", None)
		self.add_url_rule(rule, endpoint, f, **options)
		return f

	return decorator

@setupmethod
def add_url_rule(
    self,
    rule,
    endpoint=None,
    view_func=None,
    provide_automatic_options=None,
    **options
):

# 以下都是add_url_rule()内容》》》》》

8.1路由之endpoint

    if endpoint is None:
        endpoint = _endpoint_from_view_func(view_func)
    options["endpoint"] = endpoint

8.2路由之methods,不写默认是'GET'

    methods = options.pop("methods", None)

    # if the methods are not given and the view_func object knows its
    # methods we can use that instead.  If neither exists, we go with
    # a tuple of only ``GET`` as default.
    if methods is None:
        methods = getattr(view_func, "methods", None) or ("GET",)
    if isinstance(methods, string_types):
        raise TypeError(
            "Allowed methods have to be iterables of strings, "
            'for example: @app.route(..., methods=["POST"])'
        )
    methods = set(item.upper() for item in methods)

8.3路由之rule_map

	'''
	# 路由 werkzeug工具集提供的路由系统：werkzeug/routing.py(Rule, Map)
	url_rule_class = Rule
	url_map_class = Map
	
	self.url_map = self.url_map_class()
	
	# 视图函数: 格式----- view_functions = {endpoint:view_func}
	self.view_functions = {}
	
	'''
	
	
    rule = self.url_rule_class(rule, methods=methods, **options)

    self.url_map.add(rule)
    if view_func is not None:
        old_func = self.view_functions.get(endpoint)
        if old_func is not None and old_func != view_func:
            raise AssertionError(
                "View function mapping is overwriting an "
                "existing endpoint function: %s" % endpoint
            )
        self.view_functions[endpoint] = view_func

9.启动入口代码

# 应用启动的入口代码就是app.run()
from flask import Flask
app = Flask(__name__)
 
@app.route('/')
def hello_world():
	return 'Hello, World!'
 
if __name__ == '__main__':
	app.run()

# werkzeug.serving的run_simple
def run(self, host=None, port=None, debug=None, **options):
"""Runs the application on a local development server."""

	from werkzeug.serving import run_simple

	# 如果host 和 port 没有指定，设置 host 和 port 的默认值 127.0.0.1 和 5000
	if host is None:
		host = '127.0.0.1'
	if port is None:
		server_name = self.config['SERVER_NAME']
		if server_name and ':' in server_name:
			port = int(server_name.rsplit(':', 1)[1])
		else:
			port = 5000
 
	# 调用 werkzeug.serving 模块的 run_simple 函数，传入收到的参数
	# 注意第三个参数传进去的是 self，也就是要执行的 web application
	try:
		run_simple(host, port, self, **options)
	finally:
		self._got_first_request = False