fastapi中的请求上下文

背景

fastapi专注于异步、中间件和依赖项的处理，无法在任意地方使用请求上下文。而Flask中，较为明显的优点，便是可以随处使用请求上下文还有对象g。

构造g对象

• 原理：基于contextvars来管理上下文

• 代码：

  点击查看代码

  from contextvars import ContextVar, Token
  from typing import Any, Dict
  
  from starlette.types import ASGIApp, Receive, Scope, Send
  
  
  class Globals:
      __slots__ = ("_vars", "_reset_tokens")
  
      _vars: Dict[str, ContextVar]
      _reset_tokens: Dict[str, Token]
  
      def __init__(self) -> None:
          object.__setattr__(self, "_vars", {})
          object.__setattr__(self, "_reset_tokens", {})
  
      def reset(self) -> None:
          for _name, var in self._vars.items():
              try:
                  var.reset(self._reset_tokens[_name])
              # ValueError will be thrown if the reset() happens in
              # a different context compared to the original set().
              # Then just set to None for this new context.
              except ValueError:
                  var.set(None)
  
      def _ensure_var(self, item: str) -> None:
          if item not in self._vars:
              self._vars[item] = ContextVar(f"globals:{item}", default=None)
              self._reset_tokens[item] = self._vars[item].set(None)
  
      def __getattr__(self, item: str) -> Any:
          return self._vars[item].get()
  
      def __setattr__(self, item: str, value: Any) -> None:
          self._ensure_var(item)
          self._vars[item].set(value)
  
  
  class GlobalsMiddleware:
      def __init__(self, app: ASGIApp) -> None:
          self.app = app
  
      async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
          if scope["type"] != "lifespan":
              g.reset()
          await self.app(scope, receive, send)
  
  
  g = Globals()
  

【注】：代码来源