metamask-extension/app/scripts/lib/rpc-method-middleware/handlers/watch-asset.js

import { ERC1155, ERC721 } from '@metamask/controller-utils';
import { ethErrors } from 'eth-rpc-errors';
import { MESSAGE_TYPE } from '../../../../../shared/constants/app';

const watchAsset = {
  methodNames: [MESSAGE_TYPE.WATCH_ASSET, MESSAGE_TYPE.WATCH_ASSET_LEGACY],
  implementation: watchAssetHandler,
  hookNames: {
    handleWatchAssetRequest: true,
  },
};
export default watchAsset;

/**
 * @typedef {object} WatchAssetOptions
 * @property {Function} handleWatchAssetRequest - The wallet_watchAsset method implementation.
 */

/**
 * @typedef {object} WatchAssetParam
 * @property {string} type - The type of the asset to watch.
 * @property {object} options - Watch options for the asset.
 */

/**
 * @param {import('json-rpc-engine').JsonRpcRequest<WatchAssetParam>} req - The JSON-RPC request object.
 * @param {import('json-rpc-engine').JsonRpcResponse<true>} res - The JSON-RPC response object.
 * @param {Function} _next - The json-rpc-engine 'next' callback.
 * @param {Function} end - The json-rpc-engine 'end' callback.
 * @param {WatchAssetOptions} options
 */
async function watchAssetHandler(
  req,
  res,
  _next,
  end,
  { handleWatchAssetRequest },
) {
  try {
    const {
      params: { options: asset, type },
      origin,
    } = req;

    const { tokenId } = asset;

    if (
      [ERC721, ERC1155].includes(type) &&
      tokenId !== undefined &&
      typeof tokenId !== 'string'
    ) {
      return end(
        ethErrors.rpc.invalidParams({
          message: `Expected parameter 'tokenId' to be type 'string'. Received type '${typeof tokenId}'`,
        }),
      );
    }

    await handleWatchAssetRequest(asset, type, origin);
    res.result = true;
    return end();
  } catch (error) {
    return end(error);
  }
}