Merge pull request #52 from newrelic/fix-middleware-instrumentation

check if getModuleContext is async and instrument accordingly

lib/context.js

@@ -14,29 +14,50 @@ module.exports = function initialize(shim, ctx) {
   So, we proxy `_ENTRIES` and record a span whenever middleware modifies it.
   */
   shim.setFramework(shim.NEXT)
+  const isAsync = util.types.isAsyncFunction(ctx.getModuleContext)
   shim.wrap(ctx, 'getModuleContext', function middlewareRecorder(shim, getModuleContext) {
-    return function wrappedModuleContext() {
-      const result = getModuleContext.apply(this, arguments)
-      const handler = {
-        set(obj, prop, value) {
-          const nrObj = Object.assign(Object.create(null), value)
-          const middlewareName = prop.replace(/^middleware_pages/, '')
-          shim.record(nrObj, 'default', function mwRecord(shim, origMw, name, [args]) {
-            return {
-              name: `${shim._metrics.MIDDLEWARE}${shim._metrics.PREFIX}${middlewareName}`,
-              type: shim.MIDDLEWARE,
-              req: args.request,
-              route: middlewareName,
-              promise: true
-            }
-          })
-          obj[prop] = nrObj
-          return true
-        }
+    // define proxy handler that adds a set trap and re-assigns the middleware handler
+    // with a wrapped function to record the middleware handler execution.
+    const handler = {
+      set(obj, prop, value) {
+        const nrObj = Object.assign(Object.create(null), value)
+        const middlewareName = prop.replace(/^middleware_pages/, '')
+        shim.record(nrObj, 'default', function mwRecord(shim, origMw, name, [args]) {
+          return {
+            name: `${shim._metrics.MIDDLEWARE}${shim._metrics.PREFIX}${middlewareName}`,
+            type: shim.MIDDLEWARE,
+            req: args.request,
+            route: middlewareName,
+            promise: true
+          }
+        })
+        obj[prop] = nrObj
+        return true
+      }
+    }
+
+    /**
+     * Check if the context._ENTRIES object is a proxy, and make it one if not.
+     * @param {Object} moduleContext return of `getModuleContext`
+     */
+    function maybeApplyProxyHandler(moduleContext) {
+      if (!util.types.isProxy(moduleContext.context._ENTRIES)) {
+        moduleContext.context._ENTRIES = new Proxy(moduleContext.context._ENTRIES, handler)
       }
-      if (!util.types.isProxy(result.context._ENTRIES)) {
-        result.context._ENTRIES = new Proxy(result.context._ENTRIES, handler)
+    }
+
+    // In 12.1.1 `getModuleContext` became async
+    // see: https://github.com/vercel/next.js/pull/34437/files#diff-071a8410458475238acf837aa65ab1016398606a4d896d624db618b7fdb889c4
+    if (isAsync) {
+      return async function wrappedModuleContextPromise() {
+        const result = await getModuleContext.apply(this, arguments)
+        maybeApplyProxyHandler(result)
+        return result
       }
+    }
+    return function wrappedModuleContext() {
+      const result = getModuleContext.apply(this, arguments)
+      maybeApplyProxyHandler(result)
       return result
     }
   })