[Solved] Given this middleware code, what will be the response header 'X-Custom' value? from starlette.middleware.... Given this middleware code, what will be the response header 'X-Custom' value? | FastAPI

FastAPI - Middleware and Hooks

Given this middleware code, what will be the response header 'X-Custom' value?

from starlette.middleware.base import BaseHTTPMiddleware

class CustomHeaderMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request, call_next):
        response = await call_next(request)
        response.headers['X-Custom'] = 'Hello'
        return response

app.add_middleware(CustomHeaderMiddleware)

ANo 'X-Custom' header added

B'Hello'

CRaises an error because headers are immutable

D'CustomHeaderMiddleware'

Step-by-Step Solution

Solution:

Step 1: Analyze dispatch method behavior
The middleware waits for the response from the next handler, then adds a header 'X-Custom' with value 'Hello'.
Step 2: Confirm header modification
Response headers are mutable; adding 'X-Custom' with 'Hello' succeeds.
Final Answer:
'Hello' -> Option B
Quick Check:
Response header 'X-Custom' = 'Hello' [OK]

Quick Trick: Modify response headers after call_next(request) [OK]

Common Mistakes:

MISTAKES

Assuming headers are immutable and cause error
Forgetting to await call_next
Expecting middleware class name as header value

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Given this middleware code, what will be the response header 'X-Custom' value?

Step 1: Analyze dispatch method behavior

Step 2: Confirm header modification

Final Answer:

Quick Check:

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