DownloadUtils.java

package games.strategy.engine.framework.map.download;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;

import games.strategy.debug.ClientLogger;

public class DownloadUtils {

  private static Map<URL, Integer> downloadLengthCache = new HashMap<>();


  static Optional<Integer> getDownloadLength(URL url) {
    if (!downloadLengthCache.containsKey(url)) {
      Optional<Integer> length = getDownloadLengthWithoutCache(url);
      if (length.isPresent()) {
        downloadLengthCache.put(url, length.get());
      } else {
        return Optional.empty();
      }
    }
    return Optional.of(downloadLengthCache.get(url));
  }

  private static Optional<Integer> getDownloadLengthWithoutCache(URL url) {
    try {
      HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
      int responseCode = httpConn.getResponseCode();
      // always check HTTP response code first
      if (responseCode == HttpURLConnection.HTTP_OK) {
        int length = httpConn.getContentLength();
        if (length <= 0) {
          return Optional.empty();
        } else {
          return Optional.of(httpConn.getContentLength());
        }
      } else {
        ClientLogger.logQuietly("Unexpected response code:  " + responseCode);
        return Optional.empty();
      }
    } catch (IOException e) {
      ClientLogger.logQuietly("Failed to connect to: " + url + ", to get download size. Ignoring this error and will "
          + "not display the map download size on the UI.", e);
      return Optional.empty();
    }
  }

  public static URL toURL(String url) {
    try {
      return new URL(url);
    } catch (MalformedURLException e) {
      throw new IllegalStateException("Invalid URL: " + url, e);
    }
  }

  public static void downloadFile(URL url, File targetFile) throws IOException {
    FileOutputStream fos = new FileOutputStream(targetFile);
    url = getUrlFollowingRedirects(url);
    ReadableByteChannel rbc = Channels.newChannel(url.openStream());
    fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
    fos.close();
  }

  public static void downloadFile(String urlString, File targetFile) throws IOException {
    downloadFile(getUrlFollowingRedirects(urlString), targetFile);
  }

  private static URL getUrlFollowingRedirects(String possibleRedirectionUrl) throws IOException {
    URL url = new URL(possibleRedirectionUrl);
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    int status = conn.getResponseCode();
    if (status == HttpURLConnection.HTTP_MOVED_TEMP || status == HttpURLConnection.HTTP_MOVED_PERM
        || status == HttpURLConnection.HTTP_SEE_OTHER) {
      // update the URL if we were redirected
      url = new URL(conn.getHeaderField("Location"));
    }
    return url;
  }

  private static URL getUrlFollowingRedirects(URL url) throws IOException {
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    int status = conn.getResponseCode();
    if (status == HttpURLConnection.HTTP_MOVED_TEMP || status == HttpURLConnection.HTTP_MOVED_PERM
        || status == HttpURLConnection.HTTP_SEE_OTHER) {
      // update the URL if we were redirected
      url = new URL(conn.getHeaderField("Location"));
    }
    return url;
  }

}