refactor: Simplify RPC handling in SnapController (#3397)

Stop storing an RPC handler in the runtime for Snaps, instead just move
the handler code directly to `handleRequest`. Also removes the
`RequestQueue` previously used during the Snap starting up, instead we
let as many requests as needed wait for `startPromise`. This simplifies
RPC request routing significantly.

Recommend reviewing this with whitespace changes not displayed 😄

Author: FrederikBolding

packages/snaps-controllers/coverage.json

@@ -1,6 +1,6 @@
 {
-  "branches": 94.42,
-  "functions": 98.4,
-  "lines": 98.69,
-  "statements": 98.52
+  "branches": 94.97,
+  "functions": 98.38,
+  "lines": 98.76,
+  "statements": 98.59
 }

packages/snaps-controllers/src/snaps/RequestQueue.test.ts

@@ -4880,85 +4880,6 @@ describe('SnapController', () => {
       snapController.destroy();
     });
 
-    it('handlers will throw if there are too many pending requests before a snap has started', async () => {
-      const rootMessenger = getControllerMessenger();
-      const messenger = getSnapControllerMessenger(rootMessenger);
-      const fakeSnap = getPersistedSnapObject({ status: SnapStatus.Stopped });
-      const snapId = fakeSnap.id;
-      const snapController = getSnapController(
-        getSnapControllerOptions({
-          messenger,
-          state: {
-            snaps: {
-              [snapId]: fakeSnap,
-            },
-          },
-        }),
-      );
-
-      let resolveExecutePromise: any;
-      const deferredExecutePromise = new Promise((resolve) => {
-        resolveExecutePromise = resolve;
-      });
-
-      rootMessenger.registerActionHandler(
-        'ExecutionService:executeSnap',
-        async () => deferredExecutePromise,
-      );
-
-      // Fill up the request queue
-      const finishPromise = Promise.all(
-        new Array(100).fill(1).map(async (_, id) =>
-          snapController.handleRequest({
-            snapId,
-            origin: MOCK_ORIGIN,
-            handler: HandlerType.OnRpcRequest,
-            request: {
-              jsonrpc: '2.0',
-              method: 'bar',
-              params: {},
-              id,
-            },
-          }),
-        ),
-      );
-
-      await expect(
-        snapController.handleRequest({
-          snapId,
-          origin: MOCK_ORIGIN,
-          handler: HandlerType.OnRpcRequest,
-          request: {
-            jsonrpc: '2.0',
-            method: 'bar',
-            params: {},
-            id: 100,
-          },
-        }),
-      ).rejects.toThrow(
-        'Exceeds maximum number of requests waiting to be resolved, please try again.',
-      );
-
-      // Before processing the pending requests,
-      // we need an rpc message handler function to be returned
-      jest
-        .spyOn(messenger, 'call')
-        .mockImplementation(async (method, ..._args: unknown[]) => {
-          if (method === 'ExecutionService:executeSnap') {
-            return deferredExecutePromise;
-          } else if (method === 'ExecutionService:handleRpcRequest') {
-            return Promise.resolve(undefined);
-          }
-          return true;
-        });
-
-      // Resolve the promise that the pending requests are waiting for and wait for them to finish
-      resolveExecutePromise();
-      await finishPromise;
-
-      snapController.destroy();
-    });
-
     it('crashes the Snap on unhandled errors', async () => {
       const { manifest, sourceCode, svgIcon } =
         await getMockSnapFilesWithUpdatedChecksum({