浅谈flask源码之请求过程

# 摘自Flask源码 app.py
class Flask(_PackageBoundObject):
  # 中间省略
  def __call__(self, environ, start_response):
    return self.wsgi_app(environ, start_response)
      
  def wsgi_app(self, environ, start_response):
    # environ: 一个包含全部HTTP请求信息的字典, 由WSGI Server解包HTTP请求生成
    # start_response: WSGI Server提供的函数, 调用可以发送响应的状态码和HTTP报文头,
    # 函数在返回前必须调用一次.
    :param environ: A WSGI environment.
    :param start_response: A callable accepting a status code,
      a list of headers, and an optional exception context to
      start the response.
    # 创建上下文
    ctx = self.request_context(environ)
    error = None
    try:
      try:
        # 把上下文压栈
        ctx.push()
        # 分发请求
        response = self.full_dispatch_request()
      except Exception as e:
        error = e
        response = self.handle_exception(e)
      except:
        error = sys.exc_info()[1]
        raise
      # 返回结果
      return response(environ, start_response)
    finally:
      if self.should_ignore_error(error):
        error = None
        # 上下文出栈
        ctx.auto_pop(error)

# 摘自Flask源码 app.py
class Flask(_PackageBoundObject):
  # 中间省略
  def full_dispatch_request(self):
    self.try_trigger_before_first_request_functions()
    try:
      request_started.send(self)
      rv = self.preprocess_request()
      if rv is None:
        rv = self.dispatch_request()
    except Exception as e:
      rv = self.handle_user_exception(e)
    return self.finalize_request(rv)

  def dispatch_request(self):
    req = _request_ctx_stack.top.request
    if req.routing_exception is not None:
      self.raise_routing_exception(req)
    rule = req.url_rule
    if getattr(rule, 'provide_automatic_options', False)       and req.method == 'OPTIONS':
      return self.make_default_options_response()
    return self.view_functions[rule.endpoint](**req.view_args)

  def finalize_request(self, rv, from_error_handler=False):
    response = self.make_response(rv)
    try:
      response = self.process_response(response)
      request_finished.send(self, response=response)
    except Exception:
      if not from_error_handler:
        raise
      self.logger.exception('Request finalizing failed with an '
                 'error while handling an error')
    return response

from flask import Flask
app = Flask(__name__)


@app.before_first_request
def before_first_request():
  print('before_first_request run')


@app.before_request
def before_request():
  print('before_request run')


@app.after_request
def after_request(param):
  print('after_request run')
  return param

@app.teardown_request
def teardown_request(param):
  print('teardown_request run')


@app.route('/')
def hello_world():
  return 'Hello World!'


if __name__ == '__main__':
  app.run()

# 摘自Flask源码 app.py
class Flask(_PackageBoundObject):
  # 中间省略
  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

# 摘自Flask源码 app.py
class Flask(_PackageBoundObject):
  # 中间省略
  # 定义view_functions
  self.view_functions = {}
  # 定义url_map
  self.url_map = Map()
  
  def add_url_rule(self, rule, endpoint=None, view_func=None,
           provide_automatic_options=None, **options):
    # 创建rule
    rule = self.url_rule_class(rule, methods=methods, **options)
    rule.provide_automatic_options = provide_automatic_options
    # 把rule添加到url_map
    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)
      # 把view_func 添加到view_functions字典
      self.view_functions[endpoint] = view_func

# 摘自Flask源码 ctx.py
class RequestContext(object):
  # 中间省略
  def push(self):
    top = _request_ctx_stack.top
    if top is not None and top.preserved:
      top.pop(top._preserved_exc)
    # 获取应用上下文
    app_ctx = _app_ctx_stack.top
    # 判断应用上下文是否存在并与当前应用一致
    if app_ctx is None or app_ctx.app != self.app:
      # 创建应用上下文并入栈
      app_ctx = self.app.app_context()
      app_ctx.push()
      self._implicit_app_ctx_stack.append(app_ctx)
    else:
      self._implicit_app_ctx_stack.append(None)

    if hasattr(sys, 'exc_clear'):
      sys.exc_clear()
    # 把请求上下文入栈
    _request_ctx_stack.push(self)

from flask import Flask, request, g, current_app
app = Flask(__name__)

@app.before_request
def before_request():
  print 'before_request run'
  g.name="Tom"
  
@app.after_request
def after_request(response):
  print 'after_request run'
  print(g.name)
  return response

@app.route('/')
def index():
  print(request.url)
  g.name = 'Cat'
  print(current_app.name)
  
if __name__ == '__main__':
  app.run()

# 摘自Flask源码 globals.py
from functools import partial
from werkzeug.local import LocalStack, LocalProxy


_request_ctx_stack = LocalStack()
_app_ctx_stack = LocalStack()
current_app = LocalProxy(_find_app)
request = LocalProxy(partial(_lookup_req_object, 'request'))
session = LocalProxy(partial(_lookup_req_object, 'session'))
g = LocalProxy(partial(_lookup_app_object, 'g'))