secs-gem/interop/README.md

External cross-validation harnesses

Every harness in this directory exists so a reviewer doesn't have to take our word for it. Each one validates our C++ codec / framing / dispatch against an independent third-party implementation that read the SEMI standards without talking to us.

See ../VERIFICATION.md for the full test plan and the honest accounting of which proofs are external vs internal.

What's here

Validator	Independence	Coverage
host_vs_cpp_server.py + passive_equipment.py	secsgem-py 0.3.0 — Python reference impl	~24 + 4 checks: S1, S2, S5, S6, S7, S10 happy paths
raw_gem300_harness.py	secsgem-py with hand-crafted SecsStreamFunctions	3 checks: S3F17, S16F5, S16F27 (limited by SFDL grammar)
secs4j/Secs4jHostHarness.java	secs4java8 — Apache 2.0 Java impl by kenta-shimizu	55 checks across S1/S2/S3/S5/S6/S7/S10/S14/S16, including the full E40 body that defeated secsgem-py and unsolicited S6F11/S5F1 observation
tshark_validate.sh	Wireshark's built-in HSMS dissector	69 captured frames dissected with no malformed-packet warnings
spool_persistence_test.py	secsgem-py + a docker-restart loop	Restart-survives-spool integrity
⚙️ ../tests/test_e5_kat.cpp	SEMI E5 §9 encoding rules	196 known-answer byte assertions across every format code
⚙️ ../apps/fuzz_secs2_decode.cpp + fuzz_sml_parse.cpp	libFuzzer + ASan + UBSan	~70 000 + ~285 000 random inputs per minute, 0 crashes

The ⚙️ entries aren't in interop/ directly because they don't involve a network peer — they're either pure codec round-trips (KAT) or coverage-guided fuzzing. Listed here so the full external proof inventory lives in one place.

Running each validator

secsgem-py — secsgem-py active host → C++ server

docker compose up -d server
docker compose run --rm interop python3 /app/interop/host_vs_cpp_server.py \
    --host server --port 5000 --session-id 0

secsgem-py — C++ host → secsgem-py equipment

docker compose up -d equipment_py
docker compose run --rm builder /app/build/secs_interop_probe \
    --host equipment_py --port 5000 --device 0

secsgem-py — raw GEM 300 frames

docker compose up -d server
docker compose run --rm interop python3 /app/interop/raw_gem300_harness.py \
    --host server --port 5000 --session-id 0

secs4j — independent Java host → C++ server

bash interop/secs4j_validate.sh

Builds an eclipse-temurin:21-jdk sidecar with secs4java8 cloned + compiled at image build, then drives 55 checks against compose up server. See secs4j/Secs4jHostHarness.java for the list and secs4j/Dockerfile for the build.

tshark — Wireshark HSMS dissector

docker compose run --rm builder bash /app/interop/tshark_validate.sh

Captures a pcap of the demo flow, runs tshark -V with the HSMS dissector forced for the test port, asserts no malformed packets + that all expected control/data frames parse.

spool persistence — restart-survives test

bash interop/spool_persistence_test.py

Drops the host link mid-flight, kills the server, restarts it, and asserts the spooled S5F1 / S6F11 frames drain to the host on reconnect.

What these harnesses caught

Real bugs surfaced during interop development (now fixed):

1. Strict U-width parsing rejected U1-encoded identifiers. SEMI E5 declares DATAID, RPTID, VID, CEID, ALID, EXID etc. as U1 | U2 | U4 | U8; secsgem-py picks the smallest width that fits. Our scalar accessors were strict. Now lenient with range-checked downcasts (messages_helpers.hpp::any_unsigned_first).

2. PPBODY rejected when sent as ASCII. SEMI allows PPBODY to be ASCII | Binary | List; secsgem-py defaults to ASCII. Added the BINARY_OR_ASCII codegen type and the as_text_or_binary accessor.

3. Missing S1F23 / S1F24 (Collection Event Namelist). Added the wire schema, the vids_for(ceid) accessor, and the dispatch handler.

4. Missing S10F3 handler (host→equipment Terminal Display). Our server only registered S10F1; per SEMI E5 §13 those are opposite directions. Added the missing dispatch.

5. TSan use-after-free in act_exception_complete (test code, not library): held a pointer across fire_internal(RecoveryComplete) which deletes the entry. Found by the ThreadSanitizer lane on first run.

The C++ test suite stayed green through every one of these fixes — the changes were purely permissive widenings or additive features, no existing behaviour broke.

When to add a new validator

A new third-party SECS implementation, or a new dissector, or a new fuzzer target — anything that exercises our wire surface from an angle the existing five don't cover — is worth adding. The pattern is consistent:

1. New script / harness lives here (or a sidecar Docker context for non-Python validators).
2. Wired into .gitea/workflows/ci.yml as a separate job.
3. Listed in this README's table + in ../VERIFICATION.md.
4. Surfaced in the README's proof-of-feature-completeness table if it adds a meaningful new dimension.

Bug reports from a new validator → file at raphael@maenle.net with the wire trace, the validator's output, and the equipment YAML so we can reproduce.