Both libplctag drivers carried Port on their tag-create params and consumed it
nowhere. The runtimes set Tag.Gateway to the bare host, and libplctag does not
fail on a portless gateway — it substitutes 44818. So an authored port was not
ignored in the harmless sense; the connection was silently REDIRECTED to whatever
answers on the default port. On a plant network that is another PLC, and the
driver would read its tags and report them Good.
This is the root cause of #534's four AbLegacy integration failures, and the
explanation for every observation in that issue: with each PCCC family moved to
its own port (44819/44820/44821), the driver still dialled 44818 and kept talking
to the AB CIP fixture's ControlLogix container. Hence PCCC-against-ControlLogix
errors under every server-path / client-cip-path permutation — the permutations
were never reaching a PCCC server at all.
Established by a direct libplctag 1.5.2 probe outside the repo, which answered
#534's open question: PCCC works fine against ab_server for all three families,
with path="1,0" AND with path=null (only path="" throws ErrorBadData). Since the
library could reach the simulators and the driver could not, the difference had
to be in our Tag construction, and Gateway was the only field that differed.
Same probe confirmed libplctag accepts host:port in the gateway attribute, which
is what the fix emits.
AbCip has the identical defect and is fixed alongside. It has never been
observable there: every AbCip fixture profile binds 44818, so no test that driver
has could distinguish "uses the authored port" from "always uses 44818". A
fixture that only ever exercises the default value cannot falsify a rule about
non-default values, however many tests point at it.
The port is now emitted unconditionally rather than only when non-default, so the
value does not depend on libplctag's own default; a port <= 0 still falls back to
the bare host rather than producing "host:0".
The load-bearing guard is the AbLegacy integration suite, which addresses each
family on a non-default port and cannot pass unless the port is honoured — 4/4
green, having never once passed before. Unit tests in both drivers pin the
composition for machines with no fixtures. Falsified both ways: reverting the
runtime line reddens all 4 integration tests; dropping the port > 0 guard reddens
exactly the two fallback cases.
AbCip integration 10/13 (3 pre-existing skips), AbCip unit 345, AbLegacy unit 219.
Claude-Session: https://claude.ai/code/session_015p7wGqy3YpZNCpDzTpGMKo
Joseph Doherty
01538464b7