Function computeDomainSeparator

src/services/x402/client.ts:148–181

* Compute EIP-712 domain separator hash.

(domain: {
  name: string
  version: string
  chainId: number
  verifyingContract: string
})

 * Compute EIP-712 domain separator hash.
 */
function computeDomainSeparator(domain: {
  name: string
  version: string
  chainId: number
  verifyingContract: string
}): Buffer {
  const EIP712_DOMAIN_TYPEHASH = createHash('sha3-256')
    .update(
      'EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)',
    )
    .digest()

  const nameHash = createHash('sha3-256').update(domain.name).digest()
  const versionHash = createHash('sha3-256').update(domain.version).digest()

  // ABI encode: typeHash + nameHash + versionHash + chainId + verifyingContract
  const encoded = Buffer.alloc(5 * 32)
  EIP712_DOMAIN_TYPEHASH.copy(encoded, 0)
  nameHash.copy(encoded, 32)
  versionHash.copy(encoded, 64)
  // chainId as uint256
  const chainIdBuf = Buffer.alloc(32)
  chainIdBuf.writeBigUInt64BE(BigInt(domain.chainId), 24)
  chainIdBuf.copy(encoded, 96)
  // verifyingContract as address (left-padded to 32 bytes)
  const addrBuf = Buffer.alloc(32)
  Buffer.from(domain.verifyingContract.replace('0x', ''), 'hex').copy(
    addrBuf,
    12,
  )
  addrBuf.copy(encoded, 128)

  return createHash('sha3-256').update(encoded).digest()
}

/**
 * Compute the EIP-712 struct hash for TransferWithAuthorization.