Extract getDevServerURL into reusable module

Summary:
Many RN devtools (inspector, source maps, etc.) rely on packager.
This refactors individual SourceCode.scriptURL parsing into one function
that will be easier to change in the future.

Reviewed By: javache

Differential Revision: D3348465

fbshipit-source-id: 5a55939ea59e1517cb63bcbe4963f57f02ab15f3

Author: frantic

Libraries/Inspector/ElementProperties.js

@@ -20,11 +20,11 @@ var Text = require('Text');
 var TouchableHighlight = require('TouchableHighlight');
 var TouchableWithoutFeedback = require('TouchableWithoutFeedback');
 var View = require('View');
-var {SourceCode} = require('NativeModules');
 var {fetch} = require('fetch');
 
 var flattenStyle = require('flattenStyle');
 var mapWithSeparator = require('mapWithSeparator');
+var getDevServer = require('getDevServer');
 
 var ElementProperties = React.createClass({
   propTypes: {
@@ -97,10 +97,7 @@ var ElementProperties = React.createClass({
   },
 
   _openFile: function(fileName: string, lineNumber: number) {
-    var match = SourceCode.scriptURL && SourceCode.scriptURL.match(/^https?:\/\/.*?\//);
-    var baseURL = match ? match[0] : 'http://localhost:8081/';
-
-    fetch(baseURL + 'open-stack-frame', {
+    fetch(getDevServer().url + 'open-stack-frame', {
       method: 'POST',
       body: JSON.stringify({file: fileName, lineNumber}),
     });

Libraries/JavaScriptAppEngine/Initialization/ExceptionsManager.js

@@ -35,12 +35,15 @@ function reportException(e: Error, isFatal: bool) {
 }
 
 function symbolicateAndUpdateStack(id, message, stack) {
+  const getDevServer = require('getDevServer');
   const {fetch} = require('fetch');
-  const {SourceCode, ExceptionsManager} = require('NativeModules');
-  const match = SourceCode.scriptURL && SourceCode.scriptURL.match(/^https?:\/\/.*?\//);
-  const endpoint = (match && match[0] : 'http://localhost:8081/') + 'symbolicate';
+  const {ExceptionsManager} = require('NativeModules');
+  const devServer = getDevServer();
+  if (!devServer.bundleLoadedFromServer) {
+    return;
+  }
 
-  fetch(endpoint, { method: 'POST', body: JSON.stringify({stack}) })
+  fetch(devServer.url + 'symbolicate', { method: 'POST', body: JSON.stringify({stack}) })
     .then(response => response.json())
     .then(response =>
       ExceptionsManager.updateExceptionMessage(message, response.stack, id))

Libraries/JavaScriptAppEngine/Initialization/getDevServer.js

@@ -0,0 +1,40 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @providesModule getDevServer
+ * @flow
+ */
+'use strict';
+
+const {SourceCode} = require('NativeModules');
+
+let _cachedDevServerURL: ?string;
+const FALLBACK = 'http://localhost:8081/';
+
+type DevServerInfo = {
+  url: string;
+  bundleLoadedFromServer: boolean;
+};
+
+/**
+ * Many RN development tools rely on the development server (packager) running
+ * @return URL to packager with trailing slash
+ */
+function getDevServer(): DevServerInfo {
+  if (_cachedDevServerURL === undefined) {
+    const match = SourceCode.scriptURL && SourceCode.scriptURL.match(/^https?:\/\/.*?\//);
+    _cachedDevServerURL = match ? match[0] : null;
+  }
+
+  return {
+    url: _cachedDevServerURL || FALLBACK,
+    bundleLoadedFromServer: _cachedDevServerURL !== null,
+  };
+}
+
+module.exports = getDevServer;