package framer;

import java.io.IOException;
import java.io.OutputStream;

public interface Framer {
  /**
   * 添加成幀信息并將指定消息輸出到指定流
   * @param message
   * @param out
   * @throws IOException
   */
  void frameMsg(byte[] message, OutputStream out) throws IOException;

  /**
   * 掃描指定的流，從中抽取下一條信息
   * @return
   * @throws IOException
   */
  byte[] nextMsg() throws IOException;
}

package framer;

import java.io.*;

/**
 * @ClassName DelimFramer
 * @Description TODO
 * @Author Cays
 * @Date 2019/3/16 22:04
 * @Version 1.0
 **/
public class DelimFramer implements Framer {
  //輸入流
  private InputStream in;
  //定界符為換行符
  private static final byte DELIMITER='\n';

  public DelimFramer(InputStream in) {
    this.in = in;
  }

  @Override
  public void frameMsg(byte[] message, OutputStream out) throws IOException {
    //檢測信息中是否包含換行符
    for (byte b:message){
      if (b==DELIMITER){
        throw new IOException("Message contaions delimiter");
      }
    }
    //將成幀的信息輸出到流中
    out.write(message);
    //添加定界符
    out.write(DELIMITER);
    out.flush();
  }

  @Override
  public byte[] nextMsg() throws IOException {
    ByteArrayOutputStream messageBuffer=new ByteArrayOutputStream();
    int nextByte;
    //讀取流中的每一個字節，直到遇到定界符
    while ((nextByte=in.read())!=DELIMITER){
      if (nextByte==-1){
        //如果遇到定界符之前就到了流的終點
        if (messageBuffer.size()==0){
          return null;
        }else {
          //如果存入緩存區之前有數據，拋出異常
          throw new EOFException("Non-empty message without delimiter");
        }
      }
      //將無定界符的字節寫入消息緩存區
      messageBuffer.write(nextByte);
    }
    //將消息緩存區的內容以字節數組的形式返回
    return messageBuffer.toByteArray();
  }
}