com.google.appengine.tools.development.DevAppServerClassLoader Maven / Gradle / Ivy

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SDK for dev_appserver (local development) with some of the dependencies shaded (repackaged)
There is a newer version: 2.0.31
/*
 * Copyright 2021 Google LLC
 *
 * 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
 *
 *     https://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.appengine.tools.development;

import com.google.appengine.tools.info.AppengineSdk;
import java.net.URL;
import java.net.URLClassLoader;
import java.security.AllPermission;
import java.security.CodeSource;
import java.security.PermissionCollection;
import java.util.ArrayList;
import java.util.List;

/**
 * Isolates the DevAppServer and all of its dependencies into its own classloader.
 * This ClassLoader refuses to load anything off of the JVM's System ClassLoader
 * except for JRE classes (i.e. it ignores classpath and JAR manifest entries).
 *
 */
class DevAppServerClassLoader extends URLClassLoader {

  private final ClassLoader delegate;

  private static final String DEV_APP_SERVER_INTERFACE
      = "com.google.appengine.tools.development.DevAppServer";

  private static final String APP_CONTEXT_INTERFACE
      = "com.google.appengine.tools.development.AppContext";

  private static final String DEV_APP_SERVER_AGENT
      = "com.google.appengine.tools.development.agent.AppEngineDevAgent";

  /**
   * A system property defining a prefix where, if a class name begins with the prefix, the class
   * will be loaded by the system class loader. If unset, no classes are loaded by the system
   * class loader.
   */
  static final String SYSTEM_CLASS_PREFIX_PROPERTY =
      "com.google.appengine.system.class.prefix";

  /**
   * Creates a new {@code DevAppServerClassLoader}, which will load
   * libraries from the App Engine SDK.
   *
   * @param delegate A delegate ClassLoader from which a few shared
   * classes will be loaded (e.g. DevAppServer).
   */
  public static DevAppServerClassLoader newClassLoader(ClassLoader delegate) {
    // NB Doing shared, then impl, in order, allows us to prefer
    // returning shared classes when asked by other classloaders. This makes
    // it so that we don't have to have the impl and shared classes
    // be a strictly disjoint set.
    List libs = new ArrayList<>(AppengineSdk.getSdk().getSharedLibs());
    libs.addAll(AppengineSdk.getSdk().getImplLibs());
    // Needed by admin console servlets, which are loaded by this
    // ClassLoader
    libs.addAll(AppengineSdk.getSdk().getUserJspLibs());
    return new DevAppServerClassLoader(libs.toArray(new URL[libs.size()]), delegate);
  }

  // NB
  //
  // Isolating our code may seem seem like overkill, but it's really necessary
  // in terms of integration scenarios, such as with GWT. In general, we've
  // discovered that users tend to put all sorts of nasty things on the
  // system classpath, and it interferes with our ability to properly isolate
  // user code and assign correct permissions.

  DevAppServerClassLoader(URL[] urls, ClassLoader delegate) {
    super(urls, ClassLoaderUtil.getPlatformClassLoader());
    this.delegate = delegate;
  }

  @Override
  protected synchronized Class loadClass(String name, boolean resolve)
      throws ClassNotFoundException {

    // No class can begin with /// so the default value disables the extraPrefix logic.
    String systemClassPrefix = System.getProperty(SYSTEM_CLASS_PREFIX_PROPERTY, "///");

    if (name.startsWith(systemClassPrefix) || name.startsWith("org.jacoco.agent.")) {
      Class c = ClassLoader.getSystemClassLoader().loadClass(name);
      if (resolve) {
        resolveClass(c);
      }
      return c;
    }
    // Special-case a few classes that need to be shared.
    if (name.equals(DEV_APP_SERVER_INTERFACE)
        || name.equals(APP_CONTEXT_INTERFACE)
        || name.equals(DEV_APP_SERVER_AGENT)
        || name.startsWith("com.google.appengine.tools.info.")
        || name.startsWith("com.google.apphosting.utils.config.")) {
      Class c = delegate.loadClass(name);
      if (resolve) {
        resolveClass(c);
      }
      return c;
    }

    // Otherwise, we're safe to load anything returned from the JRE or from
    // ourselves.
    return super.loadClass(name, resolve);
  }

  @Override
  protected PermissionCollection getPermissions(CodeSource codesource) {
    PermissionCollection permissions = super.getPermissions(codesource);
    permissions.add(new AllPermission());
    return permissions;
  }
}