OCPP 1.6: never restore a transaction onto connector 0

[tmenguy]

Fixes issue #2169

Problem

On a single-connector OCPP 1.6 charger, restarting Home Assistant (or reloading the entry) while a car is charging leaves Charge Control permanently unavailable after the next stop:

on my setup (3 wallbox pulsar plus socket) I got this:

wallbox_2_parking: StopTransaction for unknown transaction id=1790509373; cannot tell which of connectors [0, 1] it ends, holding their session state until the charger reports their status

And the id was not unknown. It was, falsely, recorded on two connectors:

1. After the restart, the first MeterValues for connector 1 restores the running transaction. That part works.
2. The first MeterValues for connector 0 finds (0, transaction_id) unset and restores it through get_ha_metric. For connector 0 its only candidate is the flattened sensor.<cpid>_transaction_id, which on a single-connector charger shows connector 1's session, so _active_tx becomes {1: id, 0: id}. On my chargers, they send connector-0 Meter Values regularly, my wallbox Pulsar answers every connector-less TriggerMessage MeterValues on connector 0
3. _resolve_stop_connector sees the id on two connectors and returns None, so the stop holds [0, 1].
4. The Pulsar sends Finishing before its StopTransaction, and nothing more until the car is unplugged. The one status that would have settled connector 1 has already gone by, so the hold never clears and the transaction-bound Charge Control switch stays unavailable. Connector 0 can never be settled by a status at all.

The same happens without a mid-session restart when the flattened sensor is unknown at start-up: the (0, transaction_id) metric then stays unset, and the first session afterwards is copied onto connector 0.

Before #2128 the duplicate was ok, because the stop went to the first match (connector 1) and the switch was not dependent on a transaction id. #2128's "never guess" rule.... turned it into a stuck charger.

Recovery today: unplug the car, send a connector-less TriggerMessage StatusNotification (the Pulsar then reports both connectors and connector 1 settles, it is a workaround I put in place in my system while waiting for this fix), or reload the entry while not charging.

Change

In on_meter_values, I set connector 0's transaction metric to 0 before the HA restore runs, so connector 0 never inherits a transaction. That is the value it already has in normal operation: when the flattened sensor reads 0 at start-up, the existing restore produces exactly this state. Nothing else changes:

• get_ha_metric keeps its fallback, which other measurands still rely on.

• The OCPP 1.6: allocate unique transaction ids and stop guessing on unknown StopTransaction #2128 hold and settle rules are untouched.

• The legacy active_transaction_id sync behaves as it already does whenever connector-0 samples arrive.

• A charger that puts a transactionId on connector-0 MeterValues (dunno if it exists? seems non-standard, but no proof of that) => done a fix for this case (code rabbit review shown it)

What I have not done:

• A hold created by a genuinely ambiguous stop still waits for the next status report. Chargers that report Finishing before StopTransaction could strand such a hold. Triggering a StatusNotification per held connector would settle it, but that is a separate behavior change.

Tests

Three tests in tests/test_v16_transaction_identity.py, all failing before the change:

• test_station_meter_values_do_not_restore_a_transaction: connector-0 MeterValues after a restart leave _active_tx[0] == 0.
• test_stop_after_a_restart_mid_session_is_attributed: the Pulsar's order (Charging → MeterValues conn 1 → Finishing → MeterValues conn 0 → StopTransaction) ends connector 1's session with nothing held.
• test_station_meter_values_do_not_pick_up_a_later_session: with no HA state at start-up, a later session does not end up on connector 0.

Before the change it reproduces the stuck hold exactly; with the change the stop is attributed to connector 1.

Summary by CodeRabbit

• Bug Fixes

  • Prevented station-level meter updates from incorrectly inheriting a connector’s transaction ID, improving transaction tracking for single-connector chargers and after restarts.

• Tests

  • Added regression coverage for transaction handling across restarts and multiple connectors.

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• custom_components/ocpp/ocppv16.py
• tests/test_v16_transaction_identity.py

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• custom_components/ocpp/ocppv16.py
• tests/test_v16_transaction_identity.py

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📝 Walkthrough

Walkthrough

on_meter_values now prevents connector 0 from adopting or restoring a transaction ID. Regression tests cover flattened Home Assistant state, connector 1 activity, and restart-related transaction handling.

Changes

OCPP 1.6 connector 0 transaction identity

Layer / File(s)	Summary
Connector 0 transaction identity custom_components/ocpp/ocppv16.py, tests/test_v16_transaction_identity.py	on_meter_values clears the incoming transaction ID for connector 0 and sets an unset ID to 0. Tests cover flattened Home Assistant state, connector 1 transaction activity, and restart handling.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 5924b

The transaction-identity change appears mergeable after normal checks: connector 0 remains outside active sessions, and connector 1 can recover its session after a restart.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to 565c0

The fix addresses the reported restart failure, but it may cause a supported single-connector stop request to report success without stopping an active charge. The effect is limited to an affected charger; no broader security exposure was established.

Retained concerns

• Medium · reliability · inferred: After a station-level reading, a single-connector stop request addressed to connector 0 can return success without sending RemoteStopTransaction while connector 1 has an active transaction.

Security review details

Security Blast Radius

• inferred — The identified control effect is scoped to a single-connector charger's transaction and remote-stop operation; the examined change does not establish cross-charger or cross-tenant reachability.

Trust Boundaries and Controls

• observed — MeterValues transaction IDs can influence per-connector active state through self-heal. Ambiguous stops are held instead of being applied to a potentially wrong connector; station-level status reports do not settle that hold.

Hardening Proposals

• proposed — Keep station-level transaction identity out of self-heal as well as sensor restoration, and preserve the connector-0 stop alias without allowing a no-op to masquerade as a stopped active transaction.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 2 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: preventing transaction restoration onto connector 0 in OCPP 1.6.

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @custom_components/ocpp/ocppv16.py:
- Line 1569: Update on_meter_values so connector 0’s transaction ID remains zero
throughout the handler, including the self-heal path that updates _metrics and
_active_tx; do not adopt a nonzero incoming transaction_id for connector 0. Add
a regression test where connector 0 MeterValues includes a nonzero
transaction_id.

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• custom_components/ocpp/ocppv16.py
• tests/test_v16_transaction_identity.py

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.30%. Comparing base (e4f7306) to head (5924b7f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2170      +/-   ##
==========================================
+ Coverage   97.25%   97.30%   +0.04%     
==========================================
  Files          12       12              
  Lines        4261     4265       +4     
==========================================
+ Hits         4144     4150       +6     
+ Misses        117      115       -2     

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