added express plugin

config.js

@@ -15,6 +15,8 @@
  */
 'use strict';
 
+var path = require('path');
+
 // Default configuration
 module.exports = {
   trace: {
@@ -38,7 +40,9 @@ module.exports = {
     // An empty object means that no modules will be automatically traced at
     // all.
     // This field is experimental.
-    plugins: {},
+    plugins: {
+      express: path.join(__dirname, 'src/plugins/plugin-express.js')
+    },
 
     // Valid entries are:
     // 'express', 'hapi', 'http', 'restify'

src/hooks/index.js

@@ -37,8 +37,6 @@ var fs = require('fs');
 // Note: the order in which filenames are defined in the hooks determines the
 // order in which they are loaded.
 var toInstrument = Object.create(null, {
-  'express': { enumerable: true, value: { file: './userspace/hook-express.js',
-      patches: {} } },
   'grpc': { enumerable: true, value: { file: './userspace/hook-grpc.js',
       patches: {} } },
   'hapi': { enumerable: true, value: { file: './userspace/hook-hapi.js',

src/plugins/plugin-express.js

@@ -0,0 +1,70 @@
+'use strict';
+var shimmer = require('shimmer');
+var methods = require('methods').concat('use', 'route', 'param', 'all');
+
+var SUPPORTED_VERSIONS = '4.x';
+
+function patchModuleRoot(express, api) {
+  var labels = api.labels;
+  function applicationActionWrap(method) {
+    return function expressActionTrace() {
+      if (!this._google_trace_patched && !this._router) {
+        this._google_trace_patched = true;
+        this.use(middleware);
+      }
+      return method.apply(this, arguments);
+    };
+  }
+
+  function middleware(req, res, next) {
+    var options = {
+      name: req.path,
+      traceContext: req.get(api.constants.TRACE_CONTEXT_HEADER_NAME),
+      url: req.originalUrl,
+      skipFrames: 3
+    };
+    api.runInRootSpan(options, function(transaction) {
+      if (!transaction) {
+        next();
+        return;
+      }
+
+      // Set outgoing trace context.
+      res.set(api.constants.TRACE_CONTEXT_HEADER_NAME,
+        transaction.getTraceContext());
+
+      api.wrapEmitter(req);
+      api.wrapEmitter(res);
+
+      var url = req.protocol + '://' + req.hostname + req.originalUrl;
+      transaction.addLabel(labels.HTTP_METHOD_LABEL_KEY, req.method);
+      transaction.addLabel(labels.HTTP_URL_LABEL_KEY, url);
+      transaction.addLabel(labels.HTTP_SOURCE_IP, req.connection.remoteAddress);
+
+      // wrap end
+      var originalEnd = res.end;
+      res.end = function(chunk, encoding) {
+        res.end = originalEnd;
+        var returned = res.end(chunk, encoding);
+
+        if (req.route && req.route.path) {
+          transaction.addLabel('express/request.route.path', req.route.path);
+        }
+        transaction.addLabel(labels.HTTP_RESPONSE_CODE_LABEL_KEY, res.statusCode);
+        transaction.endSpan();
+        return returned;
+      };
+
+      next();
+    });
+  }
+
+  methods.forEach(function(method) {
+    shimmer.wrap(express.application, method, applicationActionWrap);
+  });
+  express._plugin_patched = true;
+}
+
+module.exports = [
+  { versions: SUPPORTED_VERSIONS, patch: patchModuleRoot }
+];