FastAPI reads a declared body IN FULL before the first dependency, so
`POST /auth/password-login` drained an arbitrary upload from an anonymous
caller and only then answered 401. 70 of the 72 body-declaring routes
behaved the same way: one unauthenticated client could spend the
process's memory and time at will.
A raw ASGI middleware, not `@app.middleware("http")` — BaseHTTPMiddleware
cannot wrap `receive`, so it could only trust `Content-Length`, which a
client may omit (chunked) or understate. This refuses an oversized
declaration outright and counts the bytes of everything else as they
arrive, the same rule `capped_body` already applies per-route. Registered
directly inside the access log: a refusal is still logged with its
request id, but the session, CORS, the setup gate and every auth
dependency never run for a body that is already too large.
Two routes opt out, under one stated rule: an exemption is ONLY for a
route whose own cap is larger than the global one. That is why
`/api/diagnostics/events` is absent — it caps itself at 512 KiB, below
the ceiling, so exempting it could only widen what it accepts. The list
names route templates and a test resolves each against the live route
table, so a rename fails the gate instead of silently dropping an
exemption in prod.
The 413 is byte-identical to `capped_body`'s and the test compares the
two against each other rather than against a literal — two shapes for one
fact is how the `cancelled`/`canceled` bug happened.
peter
51daf3e388