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A framework for building RESTful web APIs.
There is a newer version: 2.2.2
/*
 * Copyright 2016 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.api.server.spi;

import com.google.appengine.api.modules.ModulesService;
import com.google.appengine.api.modules.ModulesServiceFactory;
import com.google.apphosting.api.ApiProxy;
import com.google.apphosting.api.ApiProxy.Environment;

/**
 * Utililty for runtime environment related operations, such as checking whether current Endpoints
 * backend is running on App Engine.
 */
public class EnvUtil {
  public static final String ENV_APPENGINE_RUNTIME = "com.google.appengine.runtime.environment";
  public static final String ENV_APPENGINE_PROD = "Production";
  private static final String ORIGINAL_APPENGINE_RUNTIME_ENV =
      System.getProperty(EnvUtil.ENV_APPENGINE_RUNTIME);
  public static final String DEFAULT_VERSION_HOSTNAME =
      "com.google.appengine.runtime.default_version_hostname";

  /**
   * Resets ENV_APPENGINE_RUNTIME to its original state. Used for testing usually.
   */
  public static void recoverAppEngineRuntime() {
    if (ORIGINAL_APPENGINE_RUNTIME_ENV != null) {
      System.setProperty(EnvUtil.ENV_APPENGINE_RUNTIME, ORIGINAL_APPENGINE_RUNTIME_ENV);
    } else {
      System.clearProperty(EnvUtil.ENV_APPENGINE_RUNTIME);
    }
  }

  /**
   * Returns whether this is an Endpoints backend running on App Engine. It can be either running
   * on App Engine production, or local machine using App Engine dev app server.
   */
  public static boolean isRunningOnAppEngine() {
    String property = System.getProperty(ENV_APPENGINE_RUNTIME);
    return property != null && !property.isEmpty();
  }

  /**
   * Returns whether this is an Endpoints backend running on App Engine in production.
   * {@code false} if the backend is local using App Engine dev server or if not running on App
   * Engine at all (Tornado backend).
   */
  public static boolean isRunningOnAppEngineProd() {
    String property = System.getProperty(ENV_APPENGINE_RUNTIME);
    return property != null && property.equals(ENV_APPENGINE_PROD);
  }

  /**
   * Returns hostname of an running Endpoints API. It can be 1) "localhost:PORT" if running on
   * development server, or 2) "app_id.appspot.com" if running on external app engine prod, or
   * 3) "app_id.googleplex.com" if running as Google 1st party Endpoints API, or 4) {@code null} if
   * not running on App Engine (e.g. Tornado Endpoints API).
   */
  public static String getAppHostName() {
    if (!isRunningOnAppEngine()) {
      return null;
    }
    Environment env = ApiProxy.getCurrentEnvironment();
    if (env != null) {  // if env is null, ModulesService calls will NPE
      ModulesService modules = ModulesServiceFactory.getModulesService();
      return modules.getVersionHostname(modules.getCurrentModule(), modules.getCurrentVersion());
    }
    return null;
  }
}