feat(nip05): Namecoin .bit identifier resolution via ElectrumX

[mstrofnone]

Summary

Adds NIP-05 identifier resolution backed by Namecoin .bit names — the cypherpunk twin of DNS-based NIP-05.

A user can drop alice@example.bit, example.bit, d/example, or id/alice into anywhere Nip5.fetch(...) is called today, and dart-nostr will resolve it through a public Namecoin ElectrumX server instead of https://example.com/.well-known/nostr.json.

This is the Dart port of an already-shipping, multi-language ecosystem of .bit NIP-05 resolvers — see References below for the Kotlin / Swift / Go / JS / Rust ports this matches behaviour-for-behaviour.

API surface

Mirrors DnsIdentifier 1:1 so call sites don't have to branch:

	DNS NIP-05	Namecoin NIP-05
Detect	(n/a)	NamecoinIdentifier.isBit(id)
Fetch	DnsIdentifier.fetch(id)	NamecoinIdentifier.fetch(id, {client})
Verify	DnsIdentifier.verify(...)	NamecoinIdentifier.verify(..., {client})
Lookup URL	DnsIdentifier.verificationUrl(id)	NamecoinIdentifier.lookupUri(id)

Plus a thin dispatcher for callers that accept either form:

final pointer = await NostrIdentifier.fetch(input);
// .bit → NamecoinIdentifier.fetch
// otherwise → DnsIdentifier.fetch

NamecoinIdentifier.fetch returns the same DnsData type that DnsIdentifier.fetch returns, so any consumer that already handles a Future<DnsData?> works unchanged.

Accepted identifier shapes

Case-insensitive, optional nostr: URI prefix tolerated:

• alice@example.bit
• example.bit (uses the _ root entry)
• d/example (domain namespace)
• id/alice (identity namespace)

Name-value shapes supported

Both the simple and extended forms documented in namecoin/proposals ifa-0001 and the .bit NIP-05 draft:

// Simple form (root-only)
{ "nostr": "<64-hex-pubkey>" }

// Extended form (multi-user + relays)
{
  "nostr": {
    "names":  { "_": "<root-pubkey>", "alice": "<alice-pubkey>" },
    "relays": { "<alice-pubkey>": ["wss://relay.example.com/"] }
  }
}

// id/ namespace shape
{ "nostr": { "pubkey": "<hex>", "relays": ["wss://r.example.com/"] } }

Implementation

• Pure Dart, no new mandatory dependencies.
• WebSocket-over-TLS transport via dart:io WebSocket.connect, with a pluggable HttpClient for callers that need pinned-cert trust (the public Namecoin ElectrumX servers ship self-signed certs).
• Failover across 3 default servers (electrumx.testls.space:50004, nmc2.bitcoins.sk:57004, 46.229.238.187:57004). Definitive misses short-circuit; transport errors fall through.
• Name-script parsing handles direct push / OP_PUSHDATA1 / OP_PUSHDATA2. OP_PUSHDATA4 accepted defensively (Namecoin values fit in 520 bytes per consensus rules).
• Expiry check at NameExpireDepth = 36000 blocks (~250 days, matches consensus.nNameExpirationDepth in Namecoin Core).

The implementation is split into 5 small files under lib/src/namecoin/:

File	Purpose
script.dart	Build name-index script + parse NAME_UPDATE outputs
electrumx_server.dart	ElectrumxServer type + default server list
electrumx_client.dart	ElectrumxClient interface + DefaultElectrumxClient impl
identifier.dart	Parse .bit / d/ / id/ shapes (private)
value.dart	Extract pubkey + relays from name-value JSON (private)

Public surface exposed through lib/nostr.dart:

• NamecoinIdentifier / Nip5Namecoin (public-facing, mirrors DnsIdentifier)
• NostrIdentifier (dispatcher)
• ElectrumxClient / DefaultElectrumxClient (transport, pluggable)
• ElectrumxServer / defaultElectrumxServers
• NameNotFoundException / NameExpiredException / ElectrumxUnreachableException

Tests

29 new test cases in test/nips/nip_005_namecoin_test.dart:

Group	Cases	What it covers
isBit	4	Detection across .bit / d/ / id/ / nostr: shapes
parseIdentifier	7	All shape combinations + uppercase normalisation + edge cases
lookupUri	2	Pseudo-URI generation, error path
extractNostrFromValue	8	Simple, extended, id/, malformed, invalid pubkey
Namecoin script utilities	5	Hash determinism, NAME_UPDATE round-trip, PUSHDATA1/PUSHDATA2
Live Namecoin blockchain	3	m@testls.bit, testls.bit, non-existent — same pattern as damus@damus.io in nip_005_test.dart

449/449 tests pass (420 existing + 29 new). Run with:

dart test test/nips/nip_005_namecoin_test.dart

Live verification

Captured against the real Namecoin blockchain just before opening this PR:

$ dart run .scratch_verify.dart
--- m@testls.bit ---
  pubkey: 6cdebccabda1dfa058ab85352a79509b592b2bdfa0370325e28ec1cb4f18667d
  domain: testls.bit
  name:   m
--- testls.bit ---
  pubkey: 460c25e682fda7832b52d1f22d3d22b3176d972f60dcdc3212ed8c92ef85065c
--- nonexistent.bit ---
  result: null

Same pubkeys as the JS port (nostr-tools PR #533), the Go port (nostrlib-nip05-namecoin), and the Kotlin/Amethyst port — so any client mixing dart-nostr with one of those agrees byte-for-byte on identity.

Back-compat

• No breaking changes. Existing DnsIdentifier / Nip5 is untouched.
• All new types are additive: NamecoinIdentifier, Nip5Namecoin typedef, NostrIdentifier, ElectrumxClient, DefaultElectrumxClient, ElectrumxServer, defaultElectrumxServers, three exception types.
• web_socket_channel was already a transitive dependency (via nip_046); this PR uses dart:io WebSocket directly so no new lines in pubspec.yaml.
• Existing 420 tests still pass without modification.

Security properties

• No name-value inheritance from ancestor records. alice@sub.example.bit only consults d/example's names.alice, not _'s pubkey. (Tested explicitly.)
• Hex pubkey validation — rejects anything that isn't 64 hex chars before returning DnsData.
• NameNotFound/NameExpired short-circuit — definitive blockchain answers from one server propagate immediately rather than burning the rest of the failover list.
• Self-signed certs are opt-in. Default DefaultElectrumxClient uses platform trust; callers must explicitly inject an HttpClient with badCertificateCallback for the public test servers. (See _trustAllHttpClient in the test file for the pattern; production should pin specific cert fingerprints.)

References

This PR ports an already-shipping pattern. The Dart implementation matches:

• Go (canonical) — mstrofnone/nostrlib-nip05-namecoin — proposed nostr/nip05/namecoin subpackage for fiatjaf.com/nostr
• JS — nbd-wtf/nostr-tools PR #533 — nostr-tools/nip05namecoin subpackage
• Kotlin — vitorpamplona/amethyst PR #1547, PR #2595, PR #2612
• Swift — nostur-com/nostur-ios-public PR #60
• Rust — mikedilger/gossip PR #1018
• Spec — namecoin/proposals ifa-0001
• NIP-05 — nostr-protocol/nips/05.md

A follow-up PR will add the relay-resolver counterpart (wss://relay.example.bit/ → real wss endpoint with TLSA pin records). Posting that as a separate PR so each is independently reviewable.

Checklist

• dart analyze — no issues
• dart format — formatted
• dart test — 449/449 pass
• Live-verified on Namecoin chain via ElectrumX
• No new mandatory dependencies
• Public APIs documented (dartdoc on every method)
• Anti-inheritance security property tested

[ethicnology]

Hey @mstrofnone this is very appreciated !

I was going to implement it myself, at some point…

I'm busy this week but be sure I will review that over this week-end or the next one

[ethicnology]

merged in #44