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Snaps exports

A snap can export the following methods.

onRpcRequest​

To communicate with dapps and other snaps, a snap must implement its own JSON-RPC API by exporting onRpcRequest. Whenever the snap receives a JSON-RPC request, the onRpcRequest handler method is called.

important

If your snap can do something useful without receiving and responding to JSON-RPC requests, such as providing transaction insights, you can skip exporting onRpcRequest. However, if you want to do something such as manage the user's keys for a particular protocol and create a dapp that sends transactions for that protocol via your snap, for example, you must specify an RPC API.

Parameters​

An object containing:

  • origin - The origin as a string.
  • request - The JSON-RPC request.

Returns​

A promise containing the return of the implemented method.

Example​

import { OnRpcRequestHandler } from '@metamask/snaps-types';

export const onRpcRequest: OnRpcRequestHandler = async ({
  origin,
  request,
}) => {
  switch (request.method) {
    case 'hello':
      return 'world!';

    default:
      throw new Error('Method not found.');
  }
};

onTransaction​

To provide transaction insights before a user signs a transaction, a snap must export onTransaction. Whenever there's a contract interaction, and a transaction is submitted using the MetaMask extension, MetaMask calls this method. MetaMask passes the raw unsigned transaction payload to the onTransaction handler method.

note

For MetaMask to call the snap's onTransaction method, you must request the endowment:transaction-insight permission.

Parameters​

An object containing:

  • transaction - The raw transaction payload.
  • chainId - The CAIP-2 chain ID.
  • transactionOrigin - The transaction origin if allowTransactionOrigin is set to true.

Returns​

A content object displayed using custom UI, alongside the confirmation for the transaction that onTransaction was called with.

Example​

import { OnTransactionHandler } from '@metamask/snaps-types';
import { panel, heading, text } from '@metamask/snaps-ui';

export const onTransaction: OnTransactionHandler = async ({
  transaction,
  chainId,
  transactionOrigin,
}) => {
  const insights = /* Get insights */;
  return {
    content: panel([
      heading('My Transaction Insights'),
      text('Here are the insights:'),
      ...(insights.map((insight) => text(insight.value)))
    ])
  };
};

onCronjob​

To run periodic actions for the user (cron jobs), a snap must export onCronjob. This method is called at the specified times with the specified payloads defined in the endowment:cronjob permission.

note

For MetaMask to call the snap's onCronjob method, you must request the endowment:cronjob permission.

Parameters​

An object containing an RPC request specified in the endowment:cronjob permission.

Example​

import { OnCronjobHandler } from '@metamask/snaps-types';

export const onCronjob: OnCronjobHandler = async ({ request }) => {
  switch (request.method) {
    case 'exampleMethodOne':
      return snap.request({
        method: 'snap_notify',
        params: {
          type: 'inApp',
          message: `Hello, world!`,
        },
      });

    default:
      throw new Error('Method not found.');
  }
};