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_extract_endpoint_context() caches the context dict per endpoint function and returned the cached dict itself. The request handler (and the WebSocket handler) then set endpoint_ctx["path"] on it, mutating the shared cached object. When the same endpoint function is used by more than one route (or the same route handles concurrent requests), the path stored in a RequestValidationError / ResponseValidationError could be overwritten by another request, so error messages and logs reported the wrong route. Return a copy of the cached context so each request gets its own dict.
ege-arhan
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Sep 22, 2026
ege-arhan
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The .copy() fixes the shared mutation, but the cache key id(func) (fastapi/routing.py:275-298, _endpoint_context_cache: dict[int, EndpointContext]) is still unsafe: the dict holds only ctx, no reference to func, so after GC the id can be recycled by a different endpoint and return stale file/line (CPython reuses ids aggressively when short-lived endpoint funcs are created/deleted, e.g. in tests). It also grows unbounded. Suggestion: validate the cached entry against func identity on hit (or key by weak reference to func) instead of trusting the bare id().
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_extract_endpoint_context() caches the context dict per endpoint function and returned the cached dict itself. The request handler (and the WebSocket handler) then set endpoint_ctx["path"] on it, mutating the shared cached object.
When the same endpoint function is used by more than one route (or the same route handles concurrent requests), the path stored in a RequestValidationError / ResponseValidationError could be overwritten by another request, so error messages and logs reported the wrong route.
Return a copy of the cached context so each request gets its own dict.
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