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Communicate errors

The Snaps SDK exposes a set of known errors that can be thrown from your Snap code without crashing the Snap. See the Snaps known errors reference for the full list of errors.

Import and throw errors​

To throw these known errors, first import them from the @metamask/snaps-sdk package, then throw them where needed. For example:

index.ts
import type { OnRpcRequestHandler } from "@metamask/snaps-sdk";
import { MethodNotFoundError } from "@metamask/snaps-sdk";

export const onRpcRequest: OnRpcRequestHandler = async ({ request }) => {
  switch (request.method) {
    case "hello":
      return "Hello World!";
  default:
    // Throw a known error to avoid crashing the Snap.
    throw new MethodNotFoundError();
  }
};

Pass data with the error​

The error class constructors exported by @metamask/snaps-sdk have the following signature:

class SnapJsonRpcError extends SnapError {
  new (message?: string, data?: Record<string, Json>)
}

Both parameters are optional. If you don't pass message, then a pre-determined message is used. If you don't pass data, then an empty object is passed.

data can be any JSON-serializable object.

Detect known errors in dapps​

Known errors are thrown back to the caller as JSON-RPC errors. They have a numeric code, a message string, and a data object.

The Snaps known errors reference lists all the known errors with their codes and intended usage.

Example​

See the @metamask/error-example-snap package for a full example of communicating errors.