Step 3: Check Transaction Outputs

Now we use the registry to check transaction outputs. Replace check.ts with:

import { findRegistryCell, fetchRegistryPayload, preflightCheck } from "@ckb-firewall/sdk";

const RPC_URL = "https://testnet.ckb.dev";

const REGISTRY_SPEC = {
  codeHash:    "0x493f1700508125b0e281b8fb1d168b03bd5ef71480399dd59221224901a9cd09",
  hashType:    "type" as const,
  typeIdValue: "0x9be0ad6e4e5039a64d9725ff037057c16ef59f126e3bdd9841b802f0e0a112fe",
  required:    true,
};

const { txHash, index } = await findRegistryCell(RPC_URL, REGISTRY_SPEC);
const registry = await fetchRegistryPayload(RPC_URL, txHash, index);
console.log(`Registry loaded: ${registry.entries.length} active entries`);

// A clean recipient — not on the blacklist
const cleanOutput = { lockArgs: "0x331cdd72ff9f7f22c53f9710d6639ca46de3ac06" };

// A blacklisted recipient — on the testnet blacklist
const blockedOutput = { lockArgs: "0xababababababababababababababababababababab" };

function check(label: string, lockArgs: string) {
  const result = preflightCheck([{ lockArgs }], [registry]);
  if (result.ok) {
    console.log(`✓ ${label} → clean`);
  } else {
    console.log(`✗ ${label} → ${result.reason} (code ${result.code})`);
  }
}

check(cleanOutput.lockArgs, cleanOutput.lockArgs);
check(blockedOutput.lockArgs, blockedOutput.lockArgs);

Run it:

npx tsx check.ts

Expected output:

Registry loaded: 2 active entries
✓ 0x331cdd72... → clean
✗ 0xababababab... → BlacklistedLockArgs (code 11)

preflightCheck is synchronous and makes no network calls — it checks the output against the already-fetched registry. You call it once per transaction, passing all outputs at once. It returns on the first blocked output it finds.

Notice the structure of the blocked result: { ok: false, code: 11, reason: "BlacklistedLockArgs" }. The code and reason fields are narrowed by the discriminated union, so you can switch on result.code with full type safety — no casting required.

Continue to Step 4.