HttpUnsuccessfulResponseHandler.java

/*
 * Copyright (c) 2010 Google Inc.
 *
 * 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.client.http;

import java.io.IOException;

/**
 * Interface which handles abnormal HTTP responses (in other words not 2XX).
 *
 * <p>
 * For example, this might be used to refresh an OAuth 2 token:
 * </p>
 *
 * <pre>
  public static class RefreshTokenHandler implements HttpUnsuccessfulResponseHandler {
    public boolean handleResponse(
        HttpRequest request, HttpResponse response, boolean retrySupported) throws IOException {
      if (response.getStatusCode() == HttpStatusCodes.STATUS_CODE_UNAUTHORIZED) {
        refreshToken();
      }
      return false;
    }
  }
 * </pre>
 *
 * <p>
 * Sample usage with a request factory:
 * </p>
 *
 * <pre>
  public static HttpRequestFactory createRequestFactory(HttpTransport transport) {
    final RefreshTokenHandler handler = new RefreshTokenHandler();
    return transport.createRequestFactory(new HttpRequestInitializer() {
      public void initialize(HttpRequest request) {
        request.setUnsuccessfulResponseHandler(handler);
      }
    });
  }
 * </pre>
 *
 * <p>
 * More complex usage example:
 * </p>
 *
 * <pre>
  public static HttpRequestFactory createRequestFactory2(HttpTransport transport) {
    final RefreshTokenHandler handler = new RefreshTokenHandler();
    return transport.createRequestFactory(new HttpRequestInitializer() {
      public void initialize(HttpRequest request) {
        request.setUnsuccessfulResponseHandler(new HttpUnsuccessfulResponseHandler() {
          public boolean handleResponse(
              HttpRequest request, HttpResponse response, boolean retrySupported)
              throws IOException {
            return handler.handleResponse(request, response, retrySupported);
          }
        });
      }
    });
  }
 * </pre>
 *
 * @author moshenko@google.com (Jacob Moshenko)
 * @since 1.4
 */
public interface HttpUnsuccessfulResponseHandler {

  /**
   * Handler that will be invoked when an abnormal response is received. There are a few simple
   * rules that one must follow:
   * <ul>
   * <li>If you modify the request object or modify its execute interceptors in a way that should
   * resolve the error, you must return true to issue a retry.</li>
   * <li>Do not read from the content stream, this will prevent the eventual end user from having
   * access to it.</li>
   * </ul>
   *
   * @param request Request object that can be read from for context or modified before retry
   * @param response Response to process
   * @param supportsRetry Whether there will actually be a retry if this handler return {@code
   *        true}. Some handlers may want to have an effect only when there will actually be a retry
   *        after they handle their event (e.g. a handler that implements exponential backoff).
   * @return Whether or not this handler has made a change that will require the request to be
   *         re-sent.
   */
  boolean handleResponse(HttpRequest request, HttpResponse response, boolean supportsRetry)
      throws IOException;
}