Function computeStructHash

src/services/x402/client.ts:186–235

* Compute the EIP-712 struct hash for TransferWithAuthorization.

(authorization: {
  from: string
  to: string
  value: string
  validAfter: string
  validBefore: string
  nonce: string
})

 * Compute the EIP-712 struct hash for TransferWithAuthorization.
 */
function computeStructHash(authorization: {
  from: string
  to: string
  value: string
  validAfter: string
  validBefore: string
  nonce: string
}): Buffer {
  // ABI encode all fields as 32-byte words
  const encoded = Buffer.alloc(7 * 32)

  TRANSFER_WITH_AUTHORIZATION_TYPEHASH.copy(encoded, 0)

  // from address
  const fromBuf = Buffer.alloc(32)
  Buffer.from(authorization.from.replace('0x', ''), 'hex').copy(fromBuf, 12)
  fromBuf.copy(encoded, 32)

  // to address
  const toBuf = Buffer.alloc(32)
  Buffer.from(authorization.to.replace('0x', ''), 'hex').copy(toBuf, 12)
  toBuf.copy(encoded, 64)

  // value as uint256
  const valueBuf = Buffer.alloc(32)
  const value = BigInt(authorization.value)
  valueBuf.writeBigUInt64BE(value >> 192n, 0)
  valueBuf.writeBigUInt64BE((value >> 128n) & 0xffffffffffffffffn, 8)
  valueBuf.writeBigUInt64BE((value >> 64n) & 0xffffffffffffffffn, 16)
  valueBuf.writeBigUInt64BE(value & 0xffffffffffffffffn, 24)
  valueBuf.copy(encoded, 96)

  // validAfter as uint256
  const validAfterBuf = Buffer.alloc(32)
  validAfterBuf.writeBigUInt64BE(BigInt(authorization.validAfter), 24)
  validAfterBuf.copy(encoded, 128)

  // validBefore as uint256
  const validBeforeBuf = Buffer.alloc(32)
  validBeforeBuf.writeBigUInt64BE(BigInt(authorization.validBefore), 24)
  validBeforeBuf.copy(encoded, 160)

  // nonce as bytes32
  const nonceBuf = Buffer.from(authorization.nonce.replace('0x', ''), 'hex')
  const noncePadded = Buffer.alloc(32)
  nonceBuf.copy(noncePadded, 32 - nonceBuf.length)
  noncePadded.copy(encoded, 192)

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

/**
 * Sign an EIP-712 typed data hash with a secp256k1 private key.