Refactor method middleware (#9436)

* Refactor method middleware

* Vastly improve comments

app/scripts/lib/createMethodMiddleware.js

@@ -1,42 +0,0 @@
-
-const recordedWeb3Usage = {}
-
-/**
- * Returns a middleware that implements the following RPC methods:
- * - metamask_logInjectedWeb3Usage
- *
- * @param {Object} opts - The middleware options
- * @param {string} opts.origin - The origin for the middleware stack
- * @param {Function} opts.sendMetrics - A function for sending a metrics event
- * @returns {(req: any, res: any, next: Function, end: Function) => void}
- */
-export default function createMethodMiddleware ({ origin, sendMetrics }) {
-  return function methodMiddleware (req, res, next, end) {
-    switch (req.method) {
-
-      case 'metamask_logInjectedWeb3Usage': {
-
-        const { action, name } = req.params[0]
-
-        if (!recordedWeb3Usage[origin]) {
-          recordedWeb3Usage[origin] = {}
-        }
-        if (!recordedWeb3Usage[origin][name]) {
-          recordedWeb3Usage[origin][name] = true
-          sendMetrics({
-            action,
-            name,
-            customVariables: { origin },
-          })
-        }
-
-        res.result = true
-        break
-      }
-
-      default:
-        return next()
-    }
-    return end()
-  }
-}

app/scripts/lib/enums.js

@@ -14,6 +14,7 @@ const MESSAGE_TYPE = {
   ETH_GET_ENCRYPTION_PUBLIC_KEY: 'eth_getEncryptionPublicKey',
   ETH_SIGN: 'eth_sign',
   ETH_SIGN_TYPED_DATA: 'eth_signTypedData',
+  LOG_WEB3_USAGE: 'metamask_logInjectedWeb3Usage',
   PERSONAL_SIGN: 'personal_sign',
 }
 

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

@@ -0,0 +1,33 @@
+import handlers from './handlers'
+
+const handlerMap = handlers.reduce((map, handler) => {
+  map.set(handler.methodName, handler.implementation)
+  return map
+}, new Map())
+
+/**
+ * Returns a middleware that implements the RPC methods defined in the handlers
+ * directory.
+ *
+ * The purpose of this middleware is to create portable RPC method
+ * implementations that are decoupled from the rest of our background
+ * architecture.
+ *
+ * Handlers consume functions that hook into the background, and only depend
+ * on their signatures, not e.g. controller internals.
+ *
+ * Eventually, we'll want to extract this middleware into its own package.
+ *
+ * @param {Object} opts - The middleware options
+ * @param {string} opts.origin - The origin for the middleware stack
+ * @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) {
+  return function methodMiddleware (req, res, next, end) {
+    if (handlerMap.has(req.method)) {
+      return handlerMap.get(req.method)(req, res, next, end, opts)
+    }
+    return next()
+  }
+}

app/scripts/lib/rpc-method-middleware/handlers/index.js

@@ -0,0 +1,6 @@
+import logWeb3Usage from './log-web3-usage'
+
+const handlers = [
+  logWeb3Usage,
+]
+export default handlers

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

@@ -0,0 +1,57 @@
+import { MESSAGE_TYPE } from '../../enums'
+
+/**
+ * This RPC method is called by our inpage web3 proxy whenever window.web3 is
+ * accessed. We're collecting data on window.web3 usage so that we can warn
+ * website maintainers, and possibly our users, before we remove window.web3
+ * by November 16, 2020.
+ */
+
+const logWeb3Usage = {
+  methodName: MESSAGE_TYPE.LOG_WEB3_USAGE,
+  implementation: logWeb3UsageHandler,
+}
+export default logWeb3Usage
+
+const recordedWeb3Usage = {}
+
+/**
+ * @typedef {Object} LogWeb3UsageOptions
+ * @property {string} origin - The origin of the request.
+ * @property {Function} sendMetrics - A function that registers a metrics event.
+ */
+
+/**
+ * @typedef {Object} LogWeb3UsageParam
+ * @property {string} action - The action taken (get or set).
+ * @property {string} name - The window.web3 property name subject to the action.
+ */
+
+/**
+ * @param {import('json-rpc-engine').JsonRpcRequest<[LogWeb3UsageParam]>} req - The JSON-RPC request object.
+ * @param {import('json-rpc-engine').JsonRpcResponse<true>} res - The JSON-RPC response object.
+ * @param {Function} _next - The json-rpc-engine 'next' callback.
+ * @param {Function} end - The json-rpc-engine 'end' callback.
+ * @param {LogWeb3UsageOptions} options
+ */
+function logWeb3UsageHandler (
+  req, res, _next, end,
+  { origin, sendMetrics },
+) {
+  const { action, name } = req.params[0]
+
+  if (!recordedWeb3Usage[origin]) {
+    recordedWeb3Usage[origin] = {}
+  }
+  if (!recordedWeb3Usage[origin][name]) {
+    recordedWeb3Usage[origin][name] = true
+    sendMetrics({
+      action,
+      name,
+      customVariables: { origin },
+    })
+  }
+
+  res.result = true
+  return end()
+}

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

@@ -0,0 +1 @@
+export { default } from './createMethodMiddleware'

app/scripts/metamask-controller.js

@@ -28,7 +28,7 @@ import {
 import ComposableObservableStore from './lib/ComposableObservableStore'
 import AccountTracker from './lib/account-tracker'
 import createLoggerMiddleware from './lib/createLoggerMiddleware'
-import createMethodMiddleware from './lib/createMethodMiddleware'
+import createMethodMiddleware from './lib/rpc-method-middleware'
 import createOriginMiddleware from './lib/createOriginMiddleware'
 import createTabIdMiddleware from './lib/createTabIdMiddleware'
 import createOnboardingMiddleware from './lib/createOnboardingMiddleware'