ProtocolUtils.java

/*
 * (C) Copyright 2013 Kurento (http://kurento.org/)
 *
 * 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 org.kurento.jsonrpc.internal;

import java.io.IOException;
import java.io.InputStream;

/**
 * @author Ivan Gracia (igracia@gsyc.es)
 * @version 1.0.0
 */
public final class ProtocolUtils {

  /**
   * Encodings accepted in JSON (UTF-8, UTF-16BE/LE, UTF-32BE/LE).
   */
  private static final String UTF8 = "UTF-8";
  private static final String UTF16BE = "UTF-16BE";
  private static final String UTF16LE = "UTF-16LE";
  private static final String UTF32BE = "UTF-32BE";
  private static final String UTF32LE = "UTF-32LE";

  /**
   * Reads inputStream (from request) and detects incoming JSON encoding.
   * 
   * @param inputStream
   *          Input Stream from request
   * @return String identifier for detected JSON (UTF8, UTF16LE, ...)
   * @throws IOException
   *           Exception while parsing JSON
   */
  public static String detectJsonEncoding(InputStream inputStream) throws IOException {
    inputStream.mark(4);
    int mask = 0;
    for (int count = 0; count < 4; count++) {
      int r = inputStream.read();
      if (r == -1) {
        break;
      }
      mask = mask << 1;
      mask |= r == 0 ? 0 : 1;
    }
    inputStream.reset();
    return match(mask);
  }

  /**
   * Match recovered mask to String identifier (UTF8, UTF16LE, ...).
   * 
   * @param mask
   *          Mask from detectJsonEncoding method
   * @return String identifier for the detected JSON encoding
   */
  private static String match(int mask) {
    switch (mask) {
      case 1:
        return UTF32BE;
      case 5:
        return UTF16BE;
      case 8:
        return UTF32LE;
      case 10:
        return UTF16LE;
      case 15:
        return UTF8;
      default:
        return null;
    }
  }

}