Add Label B0 AFN (FANS 1/A Logon) decoder plugin

[thepacket]

Adds a decoder for FANS 1/A AFN-Contact messages carried under label B0 (parallel to label A0, different operators / sub-networks).

Wire format

/SOUCAYA.AFN/FMHUAL984,.N78004,AA92FB,080809/FCPPIKCAYA,0F897

Surfaces ATSU, application, callsign, tail, ICAO 24-bit, UTC time, capability blocks (FCPP variant included in the descriptor alternation), and CRC.

npm run build passes.

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📥 Commits

Reviewing files that changed from the base of the PR and between 10f9f69 and f42380d.

📒 Files selected for processing (3)

• lib/MessageDecoder.ts
• lib/plugins/Label_B0_AFN.ts
• lib/plugins/official.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[kevinelliott]

Summary

Adds Label_B0_AFN for the FANS 1/A AFN-Contact (FN_CON / CPDLC logon request) message. Parses the /<ATSU>.AFN/FMH<callsign>,.<tail>,<icao24>,<HHMMSS>/<cap-block>... envelope and surfaces ATSU, callsign, tail, ICAO 24-bit address, UTC time, capability blocks, and trailing CRC. Registered in both lib/MessageDecoder.ts and lib/plugins/official.ts. Build passes per the description.

Verdict

Needs changes before merge. Solid envelope decomposition and capability-block parsing, but the formatted output has duplicated rows from antipatterns flagged in the project conventions, and there are no tests.

Must Fix

• No tests. Please add Label_B0_AFN.test.ts covering: (a) the wire-format example from the PR description, (b) a header without ICAO24 or time (the regex's optional groups), (c) multiple capability blocks, (d) no capability blocks. Use lib/plugins/Label_15.test.ts as a template.
• Duplicate Time row (project antipattern). Lines 108-112 call ResultFormatter.timestamp(...) which already pushes a {type:'time', code:'TIMESTAMP', label:'Message Timestamp'} item. Then lines 211-218 explicitly push another {type:'time', code:'TIME', label:'Logon Time (UTC)'} row using the same HHMMSS string. Two time rows for the same value. Pick one — either keep ResultFormatter.timestamp (preferred — uses canonical message_timestamp raw key and consistent formatting) and drop the explicit push, or drop the formatter call and only push the explicit row.
• Duplicate Callsign row (project antipattern). Line 98 calls ResultFormatter.flightNumber(decodeResult, callsign) which adds a Flight Number item. Then lines 195-201 push a separate {code:'CALLSIGN', label:'Callsign'} row with the same value. Two rows, same string. Use ResultFormatter.callsign(...) (which exists at lib/utils/result_formatter.ts line 93-101) instead of flightNumber(...), and drop the manual push — or vice versa.
• HHMMSS validation missing. Line 107: any 6-digit string passes through to DateTimeUtils.convertHHMMSSToTod. A malformed 999999 will produce a nonsensical time-of-day value silently. Validate hh<24, mm<60, ss<60 before calling the converter (see PR #413 line 71-74 for an example of the same check).

Should Fix

• Header regex tail group is too permissive. Line 83: (?<tail>[A-Z0-9-]{3,10})?. With no anchor, this can absorb the next-field separator if a comma is missing. The wire format always uses ,. to delimit callsign and tail; consider requiring the leading . and matching [A-Z0-9-]{3,10} only after it, e.g. \.(?<tail>[A-Z0-9-]{3,10}). As written the optional-comma + optional-dot pattern (,?\.?) accepts inputs the spec wouldn't.
• atsu_address raw key vs. existing ground_address. RawFields.ground_address already exists in the canonical interface (lib/DecoderPluginInterface.ts line 107). Using a new key atsu_address for the same concept fragments downstream consumers. Suggest using ground_address and adding a separate display label "ATSU Address" if you want the human-readable form to differ.
• capability_blocks raw value is the structured array. That's fine for downstream code, but the formatted output flattens each block into a one-row string "/FCPP → token1, token2". Worth considering whether the block's individual flags (e.g. capability bits) could be parsed into named fields rather than left as opaque tokens — even partial enrichment would make this more useful.
• Non-standard raw.icao_24bit. Other parts of the codebase don't have this key. Add to RawFields if it's going to land, or reuse a canonical alternative.
• Direction is hardcoded. "Downlink (aircraft → ground)" — this is correct for an FN_CON, but if/when B0 ever carries a logon-acknowledge from the ground side, the hardcoding will be wrong. Comment or guard.

Nits

• The descriptor says "AFN — ATS Facilities Notification (FANS 1/A CPDLC Logon)" but the formatted message-type row says "AFN Contact (FN_CON) — FANS 1/A CPDLC Logon Request" and the application row says "AFN (ATS Facilities Notification)". Three slightly different descriptions of the same thing in three places — consider unifying.
• parsedCaps.forEach((cap, i) => { const idx = i + 1; … type: \capability_block_${idx}`, code: `CAP${idx}` … })— emitting per-block typed rows means downstream type matching becomes a moving target. Suggest a single row with all blocks, or a stable row type likecapability_block` and an index column inside the value.
• "Application" row hardcodes "AFN (ATS Facilities Notification)" but the regex already requires .AFN/ literally — the row carries no information beyond what the descriptor already states. Consider dropping it.

Tests

Missing entirely. Suggested fixtures, beyond the four scenarios under Must Fix:

• Header with , but no ..
• Last capability block where the final token is exactly 4 hex chars (so flagPart is empty after CRC strip — the code currently leaves an empty string in the tokens array).
• Last capability block where the final token is < 5 chars (the ^[A-F0-9]{5,}$ guard skips CRC stripping — verify behavior).

Notes

• Registration: confirmed in both lib/MessageDecoder.ts (line 81) and lib/plugins/official.ts (line 67) at the PR HEAD.
• FANS 1/A consistency: this plugin shares CRC-stripping and tail-detection patterns with PRs #409 and #411. Please coordinate raw-key naming (crc vs crc_hex, tail vs air_address, ground_address vs atsu_address) across the trio before merging — landing them with three different conventions for the same fields will be painful to undo. See review on PR #411 for the suggested shared-helper approach.

Thanks @thepacket!