code: public int skipToBoundary() throws IOException {
  		int count = 0;
  		while (true) {
  			byte b = readByte();
  			count++;
  			if (isBoundary(b)) {
  				break;
  			}
  		}
  		return count;
  	}
docs: 跳过边界表示
  
  @return 跳过的字节数