Add Label AA CPDLC (FANS 1/A Uplink) decoder plugin

[thepacket]

Adds a decoder for FANS 1/A CPDLC uplinks carried under label AA.

Handles both ARINC-622 envelope forms:

• Double-dot qualifier: /USADCXA.AT1.JA788A222E042A4E61CF9D1A4D29A821D08932…
• Single-dot IMI+sublabel: /FUKJJYA.CR1B-16332201EFEA8E94A95287147

Registration-pattern cascade handles all-hex tails (HL-prefix Korean, B-prefix Taiwan/China, dashed European/Asian, US N-numbers, Japanese JA).

npm run build passes.

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📥 Commits

Reviewing files that changed from the base of the PR and between 10f9f69 and 4138571.

📒 Files selected for processing (3)

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

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[kevinelliott]

Summary

Adds Label_AA_CPDLC for FANS-1/A CPDLC carried under label AA. Handles two ARINC-622 envelope shapes: double-dot service-qualifier (/USADCXA.AT1.JA788A…) and single-dot IMI+sublabel (/FUKJJYA.CR1B-16332…). Surfaces ground address, IMI/qualifier, sublabel, tail, hex payload, and 4-hex CRC; preserves payload as cpdlc_payload_hex for downstream ASN.1 PER decode. Registered in both lib/MessageDecoder.ts and lib/plugins/official.ts. Build passes per the description.

Verdict

Needs changes before merge. The two-form envelope detection and tail-cascade approach are nicely thought out, but the lack of tests is a blocker, and a couple of edge cases need attention before this can ship alongside Label_B6_Forwardslash.

Must Fix

• No tests. This plugin is the most algorithmically interesting of the five — please add Label_AA_CPDLC.test.ts with at least: (a) a Form 1 message with a clean US/Japan/Korea registration, (b) a Form 2 CR response, (c) a Form 1 message with an all-hex-looking tail (the case the cascade was designed to handle), and (d) malformed inputs. Use lib/plugins/Label_15.test.ts as a template.
• HL/B-prefix tails missing the dash variant. The cascade at lines 115-121 has ^(HL\d{4}) for Korea but Korean civil tails are HL\d{4} without a dash, while ^([A-Z]-\d{4,5}) covers Chinese B-NNNN and Taiwanese B-NNNNN. What's missing: the unhyphenated Chinese registration form B\d{4,5} that some FANS 1/A messages emit. Add a probe for that, or document that the unhyphenated Chinese case is intentionally left to the fallback.
• Form 2 single-dot regex over-matches Form 1. The regex at line 78-79 (/^\/(?<ground>[A-Z0-9]{5,9})\.(?<imi>[A-Z]{2})(?<sublabel>[A-Z0-9])(?<rest>.+)$/) would match /USADCXA.AT1.JA788A… (ground=USADCXA, imi=AT, sublabel=1, rest=.JA788A…) if it ran first — but you correctly try doubleDot first. Please add a comment noting the order matters and consider an explicit guard to make the intent obvious to future readers (e.g. require Form 2's third position to not be .).

Should Fix

• Mixing unshift and push for formatted.items. Lines 182-207 use unshift(...) for the message-type / direction / form / ground-address rows, then lines 168 (ResultFormatter.tail) and 212-256 use push. The result is that tail (pushed at line 168, before the unshift block) ends up after the unshifted block. The visual order in formatted output will be: MSGTYP, DIR, FORM, GNDADDR, TAIL, IMI, SUBLBL, PAYLOAD, CRC, NOTE. That's coherent but accidental — please switch to all-push and reorder explicitly so the order is intentional and easy to audit.
• payload truncation in display. Line 230-232 — when payload > 96 chars, display is <first 48>…<last 48>. This is fine for human readability, but the truncated value still shows the literal Unicode ellipsis (…) without a clear "truncated" indicator. Suggest ${payload.substring(0, 48)}…[${payload.length - 96} more]…${payload.substring(payload.length - 48)} so consumers know how much was elided.
• raw.air_data is non-standard and overlaps with Label_A6_ADS. PR #409 introduces the same key. If both plugins are going to land, the key should be promoted to RawFields in lib/DecoderPluginInterface.ts or renamed (unparsed_body?) for clarity.
• raw.cpdlc_payload_bytes. Derived from cpdlc_payload_hex.length / 2 — fine, but redundant with the raw hex itself. Either drop it or also expose it for B0/A6 payloads to keep the FANS 1/A trio consistent.
• direction is set in raw but the key isn't on the canonical RawFields interface. Same comment as #409.

Nits

• imiDescriptions is only populated for AT1/ATN/CR. Consider extending with AT2/AT3 or noting that those exist (FANS 1/A has more than three IMIs).
• formatted.items row "Note" with "Payload is ASN.1 PER binary…" is consumer-facing UI text. It might be more idiomatic to expose this as part of the description or a single field rather than a distinct row.
• The formNote value 'Form 1 (qualifier.tail)' — the description says "qualifier.tail" but Form 1 actually has qualifier dot tail, where the qualifier and tail are separated by a dot. Suggest 'Form 1 (service-qualifier + tail)' or just 'Form 1' with the descriptor doing the explaining.

Tests

Missing entirely. Beyond the four scenarios listed under Must Fix, please add: empty body, body without leading /, double-dot envelope where the rest is too short to extract a payload + CRC.

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 and PRs #409 and #412 all duplicate the "extract tail from a hex stream" logic (with subtly different cascades and fallbacks) and all introduce overlapping non-standard raw keys (crc, crc_hex, air_data, cpdlc_payload_hex, ads_payload_hex). Strongly suggest landing a small shared helper (e.g. lib/utils/arinc622.ts) before merging the three so the FANS family stays coherent. The existing lib/plugins/Label_B6.ts is a placeholder and could be the home for the shared logic, or a new utils file.

Thanks @thepacket!