SIP-26: Non-EVM protocol support

SIPS/sip-26.md

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+---
+sip: 26
+title: Non-EVM protocol support
+status: Draft
+author: Daniel Rocha (@danroc), Frederik Bolding (@FrederikBolding), Alex Donesky (@adonesky1)
+created: 2024-08-28
+---
+
+## Abstract
+
+This SIP presents an architecture to enable Snaps to expose blockchain-specific
+methods to dapps, extending MetaMask's functionality to support a multichain
+ecosystem.
+
+## Motivation
+
+Currently, MetaMask is limited to EVM-compatible networks. This proposal aims
+to empower developers, both first- and third-party, to use Snaps to add native
+support for non-EVM-compatible chains within MetaMask.
+
+## Specification
+
+> Formal specifications are written in TypeScript.
+
+### Language
+
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
+"SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" written
+in uppercase in this document are to be interpreted as described in [RFC
+2119](https://www.ietf.org/rfc/rfc2119.txt).
+
+### High-Level architecture
+
+The diagram below represents a high-level architecture of how the RPC Router
+integrates inside MetaMask to allow Snaps to expose protocol methods to dapps
+and the MetaMask clients.
+
+![High-level architecture](../assets/sip-26/components-diagram.png)
+
+- **Account Snaps**: Snaps that implement the [Keyring API][keyring-api] and are responsible
+  for signing requests and managing accounts.
+
+- **Protocol Snaps**: Snaps that implement protocol methods that do not require
+  an account to be executed.
+
+- **RPC Router**: Native component that forwards RPC requests to the
+  appropriate Protocol Snap or Account Snap.
+
+- **Keyring Controller**: Native component responsible for forwarding signing
+  requests to the appropriate keyring implementation.
+
+- **Accounts Controller**: Native component responsible for managing accounts
+  inside MetaMask. It stores all non-sensitive account information.
+
+- **Snaps Keyring**: Native component that acts as a bridge between the
+  Keyring Controller and the Account Snaps.
+
+### Components
+
+Here is a brief description of the components involved in this architecture
+which will require to be implemented or modified.
+
+#### RPC Router
+
+The RPC Router will be a new native component responsible for routing JSON-RPC
+requests to the appropriate Snap or keyring.
+
+To route a request, the RPC Router MUST extract the method name and [CAIP-2 chainId][caip-2]
+from the request object. It then determines whether the method is supported by
+a Protocol Snap or an Account Snap, with Account Snaps taking precedence over
+Protocol Snaps.
+
+If the method is supported by an Account Snap, the RPC Router forwards the
+request to the Keyring Controller; otherwise, it forwards the request to the
+appropriate Protocol Snap.
+
+#### Snaps Keyring
+
+The Snaps Keyring is an existing native component that exposes the
+[snap_manageAccounts][snap-manage-accs] method, allowing Account Snaps to
+register, remove, and update accounts.
+
+For example, this code can be used by an Account Snap to register a new account
+with the Account Router:
+
+```typescript
+// This will notify the Account Router that a new account was created, and the
+// Account Router will register this account as available for signing requests
+// using the `eth_signTypedData_v4` method.
+await snap.request({
+  method: "snap_manageAccounts",
+  params: {
+    method: "notify:accountCreated",
+    params: {
+      account: {
+        id: "74bb3393-f267-48ee-855a-2ba575291ab0",
+        type: "eip155:eoa",
+        address: "0x1234567890123456789012345678901234567890",
+        methods: ["eth_signTypedData_v4"],
+        options: {},
+      },
+    },
+  },
+});
+```
+
+Similar events are available to notify about the removal and update of
+accounts: `notify:accountRemoved` and `notify:accountUpdated`.
+
+Additionally, the Snaps Keyring expects the Account Snap to implement the
+Keyring API so it can forward signing requests to it through the
+[`keyring_submitRequest`][submit-request] method.
+
+#### Account Snaps
+
+As part of the Keyring API, non-EVM Account Snaps MUST also implement support
+for the `keyring_resolveAccountAddress` RPC method defined below. It is used
+by the RPC Router to extract the address of the account that should handle
+the signing request from the request object.
+
+```typescript
+type ResolveAccountAddressRequest = {
+  method: "keyring_resolveAccountAddress";
+  params: {
+    scope: CaipChainId;
+    request: JsonRpcRequest;
+  };
+};
+```
+`scope` - The [CAIP-2][caip-2] chainId the request is targeting
+
+`request` - A `JsonRpcRequest` containing strictly JSON-serializable values.
+
+The implementation MUST return a value of the type `{ address: string }` or `null`.
+
+#### Protocol Snaps
+
+Protocol Snaps implement and expose methods that do not require an account to
+execute and MUST list their supported methods and notifications in their manifest file:
+
+```json5
+"initialPermissions": {
+  "endowment:protocol": {
+    "scopes": {
+      "<caip2_chainId>": {
+        "methods": [
+          // List of supported methods
+        ],
+        "notifications": [
+          // List of supported notifications
+        ]
+      }
+    }
+  }
+}
+```
+
+Additionally protocol Snaps MUST implement the `onProtocolRequest` handler:
+
+```typescript
+import { OnProtocolRequestHandler } from "@metamask/snap-sdk";
+
+export const onProtocolRequest: OnProtocolRequestHandler = async ({
+  origin,
+  scope,
+  request,
+}) => {
+  // Return protocol responses
+};
+```
+
+The interface for an `onProtocolRequest` handler function’s arguments is:
+
+```typescript
+interface OnProtocolRequestArguments {
+  origin: string;
+  scope: CaipChainId;
+  request: JsonRpcRequest;
+}
+```
+
+`origin` - The origin making the protocol request (i.e. a dapp).
+
+`scope` - The [CAIP-2][caip-2] chainId the request is targeting.
+
+`request` - A `JsonRpcRequest` containing strictly JSON-serializable values.
+
+Any JSON-serializable value is allowed as the return value for `onProtocolRequest`.
+
+## Copyright
+
+Copyright and related rights waived via [CC0](../LICENSE).
+
+[keyring-api]: https://github.com/MetaMask/accounts/tree/main/packages/keyring-api
+[snap-manage-accs]: https://docs.metamask.io/snaps/reference/snaps-api/#snap_manageaccounts
+[submit-request]: https://docs.metamask.io/snaps/reference/keyring-api/account-management/#keyring_submitrequest
+[caip-2]: https://github.com/ChainAgnostic/CAIPs/blob/main/CAIPs/caip-2.md