Add Label A0 AFN (ATS Facilities Notification) decoder plugin

[thepacket]

Adds a decoder for FANS 1/A AFN (Context Management / CPDLC logon) downlinks carried under label A0.

Handles all three observed envelope variants:

/LPAFAYA.AFN/FMHIBE0105,.EC-NVR,,093150/FAK4,GCCC,LPAFAYAF015
/PIKCPYA.AFN/FMHVIR8Y,.G-VPRD,,095426/FCASNNCPXA,0E7A6
/SNNCPXA.AFN/FMHVIR8Y,.G-VPRD/FAK0,EISN/FARADS,2/FARATC,0B5E0

npm run build passes.

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📥 Commits

Reviewing files that changed from the base of the PR and between 10f9f69 and dd15df9.

📒 Files selected for processing (3)

• lib/MessageDecoder.ts
• lib/plugins/Label_A0_AFN.ts
• lib/plugins/official.ts

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🧪 Generate unit tests (beta)

• Create PR with unit tests

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[kevinelliott]

Summary

Adds a Label_A0_AFN plugin for FANS 1/A AFN logon downlinks. Handles three observed envelope variants. Registered correctly.

Verdict

Changes requested — useful coverage, but the implementation diverges from project conventions in several places, doesn't use ResultFormatter, has unstable raw keys, and ships without tests.

Must Fix

• No tests. Please add coverage for each of the three documented variants from the PR description, plus a malformed envelope and an empty-body case.
• Plugin bypasses ResultFormatter almost entirely. Where helpers exist (tail, groundAddress, arrivalAirport, timestamp) they should be used so downstream consumers get the same raw.* keys and formatted.items shape as every other plugin. Currently you write decodeResult.raw.tail = … directly, push your own code:'TAIL' row, etc. — equivalent, but inconsistent.
• raw.message_timestamp is set to a HH:MM:SSZ string. Per RawFields, message_timestamp is numeric (seconds since midnight or epoch). This will type-mismatch downstream consumers. Use ResultFormatter.timestamp(decodeResult, DateTimeUtils.convertHHMMSSToTod(timeTok)) and validate hh<24, mm<60, ss<60 first.

Should Fix

• Sequence-detection heuristic is brittle. aircraft.match(/^([A-Z0-9]+?)(\d{4})$/) strips trailing 4 digits from any aircraft token of length ≥8 — so a tail like N12340105 would have 0105 peeled off as a "sequence". Variants 2 and 3 have no sequence — relying on length alone to disambiguate is risky. Drive this off the variant context (whether the post-envelope CSV block exists) instead.
• Dead code / no-op. Line 76: const consumed = env[0].length + (seq ? -0 : 0); — + -0 is a no-op and the comment "env[0] already included seq digits" contradicts it. Delete the conditional, just use env[0].length. Also lines 78–80: const remainder = remainderRaw.startsWith(',') ? remainderRaw : remainderRaw; — the two branches are identical. Remove.
• Non-standard raw keys. application, aircraft_address, message_sequence, reason_code, header_extra, capability_blocks, capability_code, atc_center_icao, ground_facility_full, ground_facility_address, ground_facility_version are bespoke. Consider namespacing under afn: { … } so these don't collide with future plugins, and document them in RawFields if they’re intended to be public.
• raw.arrival_icao is set to the ATC centre ICAO (line 138). The ATC centre is not the flight’s arrival airport. Drop this — it pollutes the standard arrival_icao slot.
• Ground-facility "version" parser (/^([A-Z0-9]+?)(F\d{2,4})$/) over-fits a single observed example (LPAFAYAF015). Without source documentation this should be exposed verbatim, not synthesised.
• Capability-block multi-shape rendering is asymmetric: when there is one block you emit individual rows; when there are multiple you collapse to BLK1/BLK2 with ·-joined values. That makes consumers branch on count. Pick one shape (recommend always per-token rows with an index suffix).
• HHMMSS validation. if (timeTok && /^\d{6}$/.test(timeTok)) accepts 999999. Validate ranges.

Nits

• appl === 'AFN' ? 'AFN (ATS Facilities Notification)' : appl — given this plugin's qualifiers().labels = ['A0'] and the regex anchors AFN semantically, you can probably hard-fail on non-AFN applications.
• decodeResult.raw.tail is set as an assignment, then later rendered via formatted.items.push({code:'TAIL'…}) rather than via ResultFormatter.tail(...).
• The leading let { ground, appl, aircraft } = env.groups; mutates aircraft. Consider naming the original aircraftRaw for clarity.

Tests

Missing. See Must Fix.

Notes

• Registration LGTM (MessageDecoder pluginClasses + official.ts re-export).
• CodeRabbit rate-limited; that comment can be ignored.

Thanks @thepacket!