Introduces a mitmproxy-based recording HTTP/HTTPS sidecar that any CI
job can opt into to cache LLM-provider responses across runs. Unlike
the in-process VCR persister at tests/_vcr_redis_persister.py — which
can only intercept HTTP traffic from the same Python process where it
was loaded — this sidecar operates at the network layer, so it works
for any e2e job whose system-under-test runs in a Docker container
(every job under e2e_*, proxy_*, etc.).
Components
- tests/e2e_cassette_proxy/cache_key.py: pure-function cache-key
derivation. Hashes (method, scheme, host, path, sorted query,
allowlisted headers, canonical-JSON body); strips auth, tracing,
and SDK-metadata headers so equivalent requests collide regardless
of run-to-run noise.
- tests/e2e_cassette_proxy/redis_store.py: thin Redis wrapper that
stores one (request, response) pair per key as MessagePack
(JSON+base64 fallback). Caps per-key payload size, drops oversize
responses with a log line, and never blocks the request path on
Redis errors.
- tests/e2e_cassette_proxy/addon.py: mitmproxy addon that ties the
two together. Hosts on the passthrough list (localhost, the proxy
itself) are never cached; non-2xx upstream responses are not
persisted.
- tests/e2e_cassette_proxy/Dockerfile: pinned python:3.12-slim base +
pinned mitmproxy 11.0.2 + pinned redis-py + pinned msgpack.
- tests/e2e_cassette_proxy/trust_ca.sh: helper for SUT containers to
trust the proxy CA in every Python / curl / boto3 / node trust
store at once.
- tests/e2e_cassette_proxy/README.md: usage guide + opt-in checklist
for other e2e jobs.
CI integration
- New reusable command 'start_cassette_proxy' in .circleci/config.yml.
Builds the image, runs the sidecar wired to the project Redis, fetches
the proxy CA, and exports CASSETTE_PROXY_URL / CASSETTE_PROXY_CA into
$BASH_ENV for downstream steps.
- e2e_openai_endpoints is wired up as the canonical demo: two-line opt-in
pattern documented in the README.
- Job logs include a 'Cassette-proxy stats' step that dumps the
hit/miss/store summary via 'docker logs cassette-proxy | grep
[E2ECASS]'.
Tests
- 31 hermetic unit tests under tests/test_litellm/e2e_cassette_proxy:
- test_cache_key.py: 14 tests pinning equivalence-class behavior of
the key derivation (auth header, tracing header, JSON key order,
query order, host case all collapse; method/path/body/allowlisted
headers / query-param values do not).
- test_redis_store.py: 9 tests covering set/get round-trip, default
TTL, binary body round-trip, oversize-payload rejection, corrupt-
blob eviction, and graceful behavior when the Redis client raises.
- test_addon.py: 8 tests using a fake-mitmproxy flow to exercise
the addon end-to-end (passthrough miss, persist on 2xx, hit on
canonicalized-equivalent re-request, no-persist on 5xx, host
passthrough, replay-only 599-on-miss, record-only never serves
cache).
- 31/31 pass.
Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>
