Add RPC method handler hook selection (#12664)

Adds a property, `hookNames`, to each RPC method handler export in `app/scripts/lib/rpc-method-middleware` and a function, `selectHooks`, to select from them.

`createMethodMiddleware` receives a giant `opts` object that includes a bunch of different methods from `MetaMaskController` and its subcontrollers. Each method implementation only requires a subset of these methods to do its work. Because they need some kind of name, we call these methods "hooks". With this change, whenever an RPC method is called, `selectHooks` will be called to ensure that each method only receives the hooks that it needs in order to do its job.

This implementation is based on [work in `snaps-skunkworks`](https://github.com/MetaMask/snaps-skunkworks/blob/a3e1248/packages/rpc-methods/src/utils.ts#L17-L34) that will be merged in the near future.

app/scripts/lib/rpc-method-middleware/createMethodMiddleware.js

@@ -4,7 +4,7 @@ import handlers from './handlers';
 
 const handlerMap = handlers.reduce((map, handler) => {
   for (const methodName of handler.methodNames) {
-    map.set(methodName, handler.implementation);
+    map.set(methodName, handler);
   }
   return map;
 }, new Map());
@@ -23,7 +23,6 @@ const handlerMap = handlers.reduce((map, handler) => {
  * Eventually, we'll want to extract this middleware into its own package.
  *
  * @param {Object} opts - The middleware options
- * @param {Function} opts.sendMetrics - A function for sending a metrics event
  * @returns {(req: Object, res: Object, next: Function, end: Function) => void}
  */
 export default function createMethodMiddleware(opts) {
@@ -33,9 +32,32 @@ export default function createMethodMiddleware(opts) {
       return end(ethErrors.rpc.methodNotSupported());
     }
 
-    if (handlerMap.has(req.method)) {
+    const handler = handlerMap.get(req.method);
-      return handlerMap.get(req.method)(req, res, next, end, opts);
+    if (handler) {
+      const { implementation, hookNames } = handler;
+      return implementation(req, res, next, end, selectHooks(opts, hookNames));
     }
+
     return next();
   };
 }
+
+/**
+ * Returns the subset of the specified `hooks` that are included in the
+ * `hookNames` object. This is a Principle of Least Authority (POLA) measure
+ * to ensure that each RPC method implementation only has access to the
+ * API "hooks" it needs to do its job.
+ *
+ * @param {Record<string, unknown>} hooks - The hooks to select from.
+ * @param {Record<string, true>} hookNames - The names of the hooks to select.
+ * @returns {Record<string, unknown> | undefined} The selected hooks.
+ */
+function selectHooks(hooks, hookNames) {
+  if (hookNames) {
+    return Object.keys(hookNames).reduce((hookSubset, hookName) => {
+      hookSubset[hookName] = hooks[hookName];
+      return hookSubset;
+    }, {});
+  }
+  return undefined;
+}

app/scripts/lib/rpc-method-middleware/handlers/add-ethereum-chain.js

@@ -12,6 +12,14 @@ import { CHAIN_ID_TO_NETWORK_ID_MAP } from '../../../../../shared/constants/netw
 const addEthereumChain = {
   methodNames: [MESSAGE_TYPE.ADD_ETHEREUM_CHAIN],
   implementation: addEthereumChainHandler,
+  hookNames: {
+    addCustomRpc: true,
+    getCurrentChainId: true,
+    findCustomRpcBy: true,
+    updateRpcTarget: true,
+    requestUserApproval: true,
+    sendMetrics: true,
+  },
 };
 export default addEthereumChain;
 

app/scripts/lib/rpc-method-middleware/handlers/get-provider-state.js

@@ -9,6 +9,9 @@ import { MESSAGE_TYPE } from '../../../../../shared/constants/app';
 const getProviderState = {
   methodNames: [MESSAGE_TYPE.GET_PROVIDER_STATE],
   implementation: getProviderStateHandler,
+  hookNames: {
+    getProviderState: true,
+  },
 };
 export default getProviderState;
 

app/scripts/lib/rpc-method-middleware/handlers/log-web3-shim-usage.js

@@ -10,6 +10,11 @@ import { MESSAGE_TYPE } from '../../../../../shared/constants/app';
 const logWeb3ShimUsage = {
   methodNames: [MESSAGE_TYPE.LOG_WEB3_SHIM_USAGE],
   implementation: logWeb3ShimUsageHandler,
+  hookNames: {
+    sendMetrics: true,
+    getWeb3ShimUsageState: true,
+    setWeb3ShimUsageRecorded: true,
+  },
 };
 export default logWeb3ShimUsage;
 

app/scripts/lib/rpc-method-middleware/handlers/switch-ethereum-chain.js

@@ -15,6 +15,13 @@ import {
 const switchEthereumChain = {
   methodNames: [MESSAGE_TYPE.SWITCH_ETHEREUM_CHAIN],
   implementation: switchEthereumChainHandler,
+  hookNames: {
+    getCurrentChainId: true,
+    findCustomRpcBy: true,
+    setProviderType: true,
+    updateRpcTarget: true,
+    requestUserApproval: true,
+  },
 };
 export default switchEthereumChain;
 

app/scripts/lib/rpc-method-middleware/handlers/watch-asset.js

@@ -3,6 +3,9 @@ import { MESSAGE_TYPE } from '../../../../../shared/constants/app';
 const watchAsset = {
   methodNames: [MESSAGE_TYPE.WATCH_ASSET, MESSAGE_TYPE.WATCH_ASSET_LEGACY],
   implementation: watchAssetHandler,
+  hookNames: {
+    handleWatchAssetRequest: true,
+  },
 };
 export default watchAsset;