dhali-js/src/dhali/createSignedClaim.js

A JavaScript library for managing XRPL payment channels and generating auth tokens for Dhali APIs

const HASH_PREFIX_PAYMENT_CHANNEL_CLAIM = 0x434c4d00;

/**
 * @private
 */
function _serializePaychanAuthorization(channelIdBytes, dropsBigInt) {
  if (!Buffer.isBuffer(channelIdBytes) || channelIdBytes.length !== 32) {
    throw new Error(
      `Invalid channelId length ${channelIdBytes.length}; must be 32 bytes.`,
    );
  }
  // 1) 4-byte prefix
  const prefix = Buffer.alloc(4);
  prefix.writeUInt32BE(HASH_PREFIX_PAYMENT_CHANNEL_CLAIM, 0);

  // 2) channelIdBytes (32 bytes)
  // 3) split drops into two 4-byte words
  const highBig = dropsBigInt >> 32n;
  const lowBig = dropsBigInt & 0xffffffffn;
  const high = Number(highBig);
  const low = Number(lowBig);
  const amountBuf = Buffer.alloc(8);
  amountBuf.writeUInt32BE(high, 0);
  amountBuf.writeUInt32BE(low, 4);

  return Buffer.concat([prefix, channelIdBytes, amountBuf]);
}

/**
 * Build the hex-string that you pass to an XRPL signer to sign a payment-channel claim.
 *
 * @param {string} channelIdHex 64-char hex string
 * @param {string} amountStr    integer string of drops
 * @returns {string} uppercase hex
 */
function buildPaychanAuthHexStringToBeSigned(channelIdHex, amountStr) {
  let channelIdBytes;

  channelIdBytes = Buffer.from(channelIdHex, "hex");

  if (channelIdBytes.length !== 32) {
    throw new Error(
      `Invalid channelId length ${channelIdBytes.length}; must be 32 bytes.`,
    );
  }

  let dropsBig;
  try {
    dropsBig = BigInt(amountStr);
  } catch {
    throw new Error("Invalid amount format.");
  }

  if (dropsBig < 0n) {
    throw new Error("Amount cannot be negative.");
  }

  const msg = _serializePaychanAuthorization(channelIdBytes, dropsBig);
  return msg.toString("hex").toUpperCase();
}

module.exports = {
  buildPaychanAuthHexStringToBeSigned,
  // exposed for testing
  _serializePaychanAuthorization,
};