text: /**
   * Copyright 2010-present Facebook.
   *
   * 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.facebook.widget;
  
  import android.content.Context;
  import com.facebook.internal.FileLruCache;
  import com.facebook.internal.Utility;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.OutputStream;
  import java.net.MalformedURLException;
  import java.net.URL;
  
  class UrlRedirectCache {
      static final String TAG = UrlRedirectCache.class.getSimpleName();
      private static final String REDIRECT_CONTENT_TAG = TAG + "_Redirect";
  
      private volatile static FileLruCache urlRedirectCache;
  
      synchronized static FileLruCache getCache(Context context) throws IOException{
          if (urlRedirectCache == null) {
              urlRedirectCache = new FileLruCache(context.getApplicationContext(), TAG, new FileLruCache.Limits());
          }
          return urlRedirectCache;
      }
  
      static URL getRedirectedUrl(Context context, URL url) {
          if (url == null) {
              return null;
          }
  
          String urlString = url.toString();
          URL finalUrl = null;
          InputStreamReader reader = null;
          try {
              InputStream stream;
              FileLruCache cache = getCache(context);
              boolean redirectExists = false;
              while ((stream = cache.get(urlString, REDIRECT_CONTENT_TAG)) != null) {
                  redirectExists = true;
  
                  // Get the redirected url
                  reader = new InputStreamReader(stream);
                  char[] buffer = new char[128];
                  int bufferLength;
                  StringBuilder urlBuilder = new StringBuilder();
                  while ((bufferLength = reader.read(buffer, 0, buffer.length)) > 0) {
                      urlBuilder.append(buffer, 0, bufferLength);
                  }
                  Utility.closeQuietly(reader);
  
                  // Iterate to the next url in the redirection
                  urlString = urlBuilder.toString();
              }
  
              if (redirectExists) {
                  finalUrl = new URL(urlString);
              }
          } catch (MalformedURLException e) {
              // caching is best effort, so ignore the exception
          } catch (IOException ioe) {
          } finally {
              Utility.closeQuietly(reader);
          }
  
          return finalUrl;
      }
  
      static void cacheUrlRedirect(Context context, URL fromUrl, URL toUrl) {
          if (fromUrl == null || toUrl == null) {
              return;
          }
  
          OutputStream redirectStream = null;
          try {
              FileLruCache cache = getCache(context);
              redirectStream = cache.openPutStream(fromUrl.toString(), REDIRECT_CONTENT_TAG);
              redirectStream.write(toUrl.toString().getBytes());
          } catch (IOException e) {
              // Caching is best effort
          } finally {
              Utility.closeQuietly(redirectStream);
          }
      }
  }
  