Rail Discovery

Rail discovery

The platform serves a generated support matrix — which (fiat, crypto) pairs each provider can on/off-ramp — from packages/sdp-types/src/generated/ramp.generated.ts (ONRAMP_SUPPORT, OFFRAMP_SUPPORT, RAMP_FIAT_CURRENCIES). You do not hand-edit that file. You teach your provider to report its rails, then a script distills live provider responses into a committed per-provider snapshot and merges every provider's snapshot into the matrix.

Implement rail support in packages/sdp-payments; the codegen (apps/sdp-api/scripts/ramp-support.ts) owns snapshots and the generated matrix. Choose one source:

1. Upstream discovery API: add RAMP_RAIL_DUMPS.<id> in packages/sdp-payments/src/ramps/shared.ts; _discoverRails writes raw responses; distillRailSupport reads and normalizes them.
2. No discovery API: make _discoverRails a no-op and return an explicit, tested snapshot from distillRailSupport. Do not invent a network endpoint or dump.

Both paths declare <PROVIDER>_DECLARED_RAIL_SUPPORT for entity types and country support not discovered in the snapshot. Reference the existing providers under packages/sdp-payments/src/ramps/providers/ — single-dump, multi-endpoint, discovered-country-support, and static-support variants are all represented.

The data flow

_discoverRails ──fetch──▶ .ramp-support/raw/<id>/*.json        (gitignored raw dumps)
distillRailSupport ──parse──▶ .ramp-support/<id>.currency.json  (committed snapshot)
ramp-support:generate ──merge snapshots + declared consts──▶ ramp.generated.ts  (committed)

Raw dumps under .ramp-support/raw/ are gitignored — network scratch, safe to delete and re-fetch. The snapshot (.ramp-support/<id>.currency.json) and the generated .ts are both committed and must be regenerated together when your support changes.

Step 1 — choose the source

For discovery-backed support, add an entry to RAMP_RAIL_DUMPS in packages/sdp-payments/src/ramps/shared.ts, one per upstream response:

<id>: {
  currencies: { name: "<id>/currencies", file: dumpFile("<id>/currencies") },
},

name is what _discoverRails writes; file is what distillRailSupport reads back. For static support, skip the dump entry.

Step 2 — _discoverRails

HTTP only. Read sandbox creds from the passed env with requireEnv, fetch each upstream endpoint with the injected fetchJson, and writeDump the raw response. No parsing or mapping here. For static support, use a no-op method and read no credentials.

async _discoverRails({ env, fetchJson, writeDump }: Parameters<RampProvider["_discoverRails"]>[0]) {
  const apiKey = requireEnv(env, "<PROVIDER>_SANDBOX_API_KEY");
  await writeDump(
    RAMP_RAIL_DUMPS.<id>.currencies.name,
    await fetchJson(this.id, "GET /currencies", `https://.../currencies?apiKey=${apiKey}`)
  );
}

Use the provider's most public/anonymous discovery endpoints where possible (some upstreams expose anonymous paged catalog endpoints). _discoverRails is @internal — only the discovery script ever calls it.

Step 3 — distillRailSupport

Pure: map the dump(s), or an explicit static declaration, into the types from packages/sdp-payments/src/ramps/types.ts:

interface ProviderRailSupportSnapshot {
  onramp: ProviderDirectionSupportSnapshot;
  offramp: ProviderDirectionSupportSnapshot;
}

interface ProviderDirectionSupportSnapshot {
  currencies: Record<string, { min: string | null; max: string | null }>;
  cryptos: readonly CryptoRailId[];
  countrySupport?: RampCountrySupport; // only set if you discover it — see step 4
}

Return it wrapped in a ProviderRailSupportDistillation — the snapshot plus any codes you had to drop:

export function distill<Id>RailSupport(raw: unknown): ProviderRailSupportDistillation {
  // parse `raw`, build currencies/cryptos/countrySupport, collect drops
  return { snapshot, droppedCurrencyCodes, droppedCountryCodes };
}

Keep the mapping in a standalone distill<Id>RailSupport(raw) (as above) so it's unit-testable without HTTP; the class's distillRailSupport(readDump) method just reads the dump and calls it.

Mapping rules (helpers live in shared.ts):

• Crypto code → CryptoRailId — Solana assets only today: isSolanaCryptoAsset(code) then SOLANA_ASSET_TO_RAIL[code] (e.g. USDC → usdc.solana). Skip anything else.
• Fiat code → currency key — validate with isActiveIso4217CurrencyCode(code); codes that fail are dropped into droppedCurrencyCodes, not added to the snapshot. Uppercase ISO 4217 only.
• Country code — validate with isIso3166Alpha2CountryCode(code); failures go into droppedCountryCodes.
• Limits — { min, max } are major-unit decimal strings when the provider reports bounds; use unreportedCurrencyLimit() ({ min: null, max: null }) when it doesn't.
• Only populate countrySupport on the snapshot if you're genuinely discovering it from the dump (one existing provider derives per-currency country lists this way). If your provider doesn't report country coverage, leave it undefined here and declare it instead (step 4).

Step 4 — declare what you don't discover

Every provider needs a <PROVIDER>_DECLARED_RAIL_SUPPORT const satisfying ProviderDeclaredRailSupport, assigned to declaredRailSupport on the class:

export const <PROVIDER>_DECLARED_RAIL_SUPPORT = {
  onramp: {
    countrySupport: { coverage: "unreported" },
    entityTypes: ["individual"],
  },
  offramp: {
    countrySupport: { coverage: "unreported" },
    entityTypes: [],
  },
} as const satisfies ProviderDeclaredRailSupport;

entityTypes (CounterpartyEntityType[]) is always declared here — it's never discovered from a dump. countrySupport is discovered xor declared, per direction: if your snapshot sets countrySupport for a direction, leave it off the declared const for that direction; if it doesn't (the common case — declare { coverage: "unreported" }), it must be declared. ramp-support:generate throws if a direction ends up with both or neither.

Generate + verify

Fetching raw dumps hits live sandbox APIs, so it runs under Doppler. Regenerating from committed snapshots is pure and needs no creds:

# from apps/sdp-api — fetch raw dumps for every provider + distill their snapshots
pnpm --filter @sdp/api currencies:discover
# just your provider
pnpm --filter @sdp/api currencies:discover -- <id>
# re-distill existing dumps, or generate a static-provider snapshot whose distiller ignores dumps
pnpm --filter @sdp/api exec tsx scripts/ramp-support.ts discover <id> --offline

# regenerate ramp.generated.ts from the committed snapshots + declared consts
pnpm --filter @sdp/api ramp-support:generate

# CI gate: regenerate in memory and byte-diff against the committed file
pnpm --filter @sdp/api ramp-support:drift

Commit .ramp-support/<id>.currency.json and the regenerated ramp.generated.ts together (confirm your provider's row in RAMP_PROVIDER_SUPPORT_COUNTS looks sane). Never hand-edit the generated file. Never commit .ramp-support/raw/.

Rules

• HTTP only in _discoverRails — no DB, no business logic.
• distillRailSupport is pure over the dumps — no fetching. A malformed dump should throw, not silently yield empty support; unsupported currency/country codes get reported in droppedCurrencyCodes/droppedCountryCodes, not swallowed.
• No fallbacks: a missing cred throws via requireEnv.
• Strong typing: the declared-support const is as const satisfies ProviderDeclaredRailSupport; no any.
• Your provider must already be registered (register-provider) — the codegen iterates RAMP_PROVIDERS and will fail if a client is missing.
• Verify with pnpm --filter @sdp/api ramp-support:drift, plus @sdp/payments typecheck, lint, and tests.