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