UTAS needs a real request/response corpus before any Rust is written: it
is where protocol shape and FUT state start being coupled, so guessing is
worse here than it was for Blaze. The oracle truncates logged bodies at
~200 chars, and raising that cap would mean editing the behavioural
specification to make it easier to copy -- backwards. A proxy gets the
same evidence and leaves the oracle untouched.
THE DESIGN RULE: TEE, DO NOT REBUILD.
UTAS is plaintext HTTP/1.1 on ThreadingHTTPServer, so keep-alive,
pipelining and chunked transfer are all live. A proxy that parses a
request and re-emits it can corrupt the traffic it exists to observe --
and that corruption would present as a UTAS bug, pointing the
investigation in exactly the wrong direction. So bytes are copied
verbatim in both directions and a second copy goes to disk; transactions
are reconstructed later, offline, from that copy. A parser bug therefore
spoils the record and never the session.
Standalone, NOT in the container, so the same tool can later sit in front
of a Rust UTAS host and replay an identical captured request against both.
Two layers, as with the Blaze captures: raw/*.ofcap is exact bytes at mode
0600 and gitignored; sanitized/transactions.jsonl is the committed
artefact. Bodies are preserved EXACTLY and sanitised second -- only
known-secret headers and JSON keys are replaced, structure is never
reshaped, and every redaction is recorded in the transaction so a reader
knows what was touched.
Captured per transaction: connection id, sequence, relative and wall
time, elapsed ms, method, path, query, HTTP version, headers IN RECEIVED
ORDER as pairs (a dict would drop duplicates and ordering), raw body and
length for both directions, status, and observed keep-alive.
Verified as two independent properties, because they fail differently:
transparency (bytes through the proxy identical to bytes direct, Date
masked, with the mask asserted to have fired) and fidelity (parsed
transactions match what was sent, including a dechunked response and a
300-byte POST body). 5/5 mutations killed, including "record but do not
forward", "drop the last byte of every chunk" and "stop redacting".
scripts/test-utas-observe.py is committed alongside it: a capture tool
nobody can re-verify is not evidence.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
funman300
cdea85e214