python type_error ai_generated true

TypeError: 'coroutine' object is not callable

ID: python/fastapi-middleware-missing-await

Also available as: JSON · Markdown · 中文
80%Fix Rate
88%Confidence
0Evidence
2024-05-20First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.x active — — —

Root Cause

FastAPI middleware function is defined as async but not awaited when calling the next middleware or request handler.

generic

中文

FastAPI中间件函数定义为异步，但在调用下一个中间件或请求处理器时未使用await。

Workarounds

  1. 95% success Ensure middleware function uses await when calling call_next 
    @app.middleware('http')
async def add_process_time_header(request: Request, call_next):
    response = await call_next(request)
    return response
  2. 70% success Use synchronous middleware with proper decorator 
    @app.middleware('http')
def sync_middleware(request: Request, call_next):
    response = call_next(request)
    return response

Dead Ends

Common approaches that don't work:

  1. Adding @app.middleware('http') without async def 80% fail

    FastAPI expects an async function for middleware; synchronous functions cause different errors.

  2. Removing async keyword from middleware function 75% fail

    Middleware becomes synchronous but FastAPI still treats it as async, leading to runtime issues.