Remove dead code in snaps-rpc-methods (#2050)

Remove some dead code in snaps-rpc-methods and increase testing coverage
of error cases. Also changes an error to throw using the proper JSON-RPC
error code.

Author: FrederikBolding

packages/snaps-rpc-methods/jest.config.js

@@ -10,10 +10,10 @@ module.exports = deepmerge(baseConfig, {
   ],
   coverageThreshold: {
     global: {
-      branches: 89.92,
+      branches: 92.91,
       functions: 100,
-      lines: 98.19,
-      statements: 96.78,
+      lines: 99.19,
+      statements: 97.5,
     },
   },
 });

packages/snaps-rpc-methods/src/permitted/common/snapInstallation.ts

@@ -447,4 +447,76 @@ describe('implementation', () => {
       jsonrpc: '2.0',
     });
   });
+
+  it('throws if params is not an object', async () => {
+    const { implementation } = requestSnapsHandler;
+
+    const hooks = getMockHooks();
+
+    const engine = new JsonRpcEngine();
+    engine.push((req, res, next, end) => {
+      const result = implementation(
+        req as JsonRpcRequest<RequestSnapsParams>,
+        res as PendingJsonRpcResponse<RequestSnapsResult>,
+        next,
+        end,
+        hooks,
+      );
+
+      result?.catch(end);
+    });
+
+    const response = (await engine.handle({
+      jsonrpc: '2.0',
+      id: 1,
+      method: 'wallet_requestSnaps',
+      params: [],
+    })) as JsonRpcSuccess<RequestSnapsResult>;
+
+    expect(response).toStrictEqual({
+      error: {
+        code: -32602,
+        message: '"params" must be an object.',
+        stack: expect.any(String),
+      },
+      id: 1,
+      jsonrpc: '2.0',
+    });
+  });
+
+  it('throws if params is an empty object', async () => {
+    const { implementation } = requestSnapsHandler;
+
+    const hooks = getMockHooks();
+
+    const engine = new JsonRpcEngine();
+    engine.push((req, res, next, end) => {
+      const result = implementation(
+        req as JsonRpcRequest<RequestSnapsParams>,
+        res as PendingJsonRpcResponse<RequestSnapsResult>,
+        next,
+        end,
+        hooks,
+      );
+
+      result?.catch(end);
+    });
+
+    const response = (await engine.handle({
+      jsonrpc: '2.0',
+      id: 1,
+      method: 'wallet_requestSnaps',
+      params: {},
+    })) as JsonRpcSuccess<RequestSnapsResult>;
+
+    expect(response).toStrictEqual({
+      error: {
+        code: -32602,
+        message: 'Request must have at least one requested snap.',
+        stack: expect.any(String),
+      },
+      id: 1,
+      jsonrpc: '2.0',
+    });
+  });
 });

packages/snaps-rpc-methods/src/permitted/requestSnaps.test.ts

@@ -24,8 +24,6 @@ import { hasProperty, isObject } from '@metamask/utils';
 
 import { WALLET_SNAP_PERMISSION_KEY } from '../restricted/invokeSnap';
 import type { MethodHooksObject } from '../utils';
-import type { InstallSnapsHook } from './common/snapInstallation';
-import { handleInstallSnaps } from './common/snapInstallation';
 
 const hookNames: MethodHooksObject<RequestSnapsHooks> = {
   installSnaps: true,
@@ -50,7 +48,9 @@ export type RequestSnapsHooks = {
   /**
    * Installs the requested snaps if they are permitted.
    */
-  installSnaps: InstallSnapsHook;
+  installSnaps: (
+    requestedSnaps: RequestSnapsParams,
+  ) => Promise<RequestSnapsResult>;
 
   /**
    * Initiates a permission request for the requesting origin.
@@ -185,8 +185,12 @@ async function requestSnapsImplementation(
   }
 
   try {
-    if (!Object.keys(requestedSnaps).length) {
-      throw new Error('Request must have at least one requested snap.');
+    if (Object.keys(requestedSnaps).length === 0) {
+      return end(
+        rpcErrors.invalidParams({
+          message: 'Request must have at least one requested snap.',
+        }),
+      );
     }
 
     const requestedPermissions = {
@@ -202,7 +206,7 @@ async function requestSnapsImplementation(
         WALLET_SNAP_PERMISSION_KEY
       ] as RequestSnapsResult;
     } else if (hasRequestedSnaps(existingPermissions, requestedSnaps)) {
-      res.result = await handleInstallSnaps(requestedSnaps, installSnaps);
+      res.result = await installSnaps(requestedSnaps);
     } else {
       const mergedPermissionsRequest = getSnapPermissionsRequest(
         existingPermissions,