import java.io.*;
import java.nio.*;
import java.nio.channels.*;

public class RequestHandler implements Handler {
  private ChannelIO channelIO;
  private ByteBuffer requestByteBuffer = null;  //存放HTTP請求的緩沖區(qū)

  private boolean requestReceived = false;  //是否已經(jīng)接收到了所有的HTTP請求
  private Request request = null;  //表示HTTP請求
  private Response response = null;  //表示HTTP響應

  RequestHandler(ChannelIO channelIO) {
    this.channelIO = channelIO;
  }

  /* 
   * 接收HTTP請求，如果已經(jīng)接收到了所有的HTTP請求數(shù)據(jù)，就返回true,否則返回false
   */
  private boolean receive(SelectionKey sk) throws IOException {
    ByteBuffer tmp = null;

    if (requestReceived)return true;  //如果已經(jīng)接收到所有HTTP請求數(shù)據(jù)，返回true
    
    //如果已經(jīng)讀到通道的末尾，或者已經(jīng)讀到HTTP請求數(shù)據(jù)的末尾標志“\r\n”，就返回true
    if ((channelIO.read() < 0) || Request.isComplete(channelIO.getReadBuf())) {
      requestByteBuffer = channelIO.getReadBuf();
      return (requestReceived = true);
    }
    return false;
  }

  /*
   * 通過Request類的parse()方法，解析requestByteBuffer中的HTTP請求數(shù)據(jù)，構造相應的Request對象 
   */
  private boolean parse() throws IOException {
    try {
      request = Request.parse(requestByteBuffer);
      return true;
    } catch (MalformedRequestException x) {  
      //如果HTTP請求的格式不正確，就發(fā)送錯誤信息
      response = new Response(Response.Code.BAD_REQUEST,
                          new StringContent(x));
    }
    return false;
  }

  /*
   * 創(chuàng)建HTTP響應 
   */
  private void build() throws IOException {
    Request.Action action = request.action();
    //僅僅支持GET和HEAD請求方式
    if ((action != Request.Action.GET) &&
            (action != Request.Action.HEAD)){
       response = new Response(Response.Code.METHOD_NOT_ALLOWED,
                          new StringContent("Method Not Allowed"));
    }else{
       response = new Response(Response.Code.OK,
                      new FileContent(request.uri()), action);
    }
  }
  
  /*  接收HTTP請求，發(fā)送HTTP響應 */
  public void handle(SelectionKey sk) throws IOException {
    try {
        if (request == null) { //如果還沒有接收到HTTP請求的所有數(shù)據(jù)
            //接收HTTP請求      
            if (!receive(sk))return;
            requestByteBuffer.flip();
     
            //如果成功解析了HTTP請求，就創(chuàng)建一個Response對象
            if (parse())build();
     
            try {
                response.prepare();  //準備HTTP響應的內(nèi)容
            } catch (IOException x) {
                response.release();  
                response = new Response(Response.Code.NOT_FOUND,
                                  new StringContent(x));
                response.prepare();
            }

            if (send()) {  
               //如果HTTP響應沒有發(fā)送完畢，則需要注冊寫就緒事件，
               //以便在寫就緒事件發(fā)生時繼續(xù)發(fā)送數(shù)據(jù)
               sk.interestOps(SelectionKey.OP_WRITE);
            } else {
               //如果HTTP響應發(fā)送完畢，就斷開底層的連接，并且釋放Response占用的資源
               channelIO.close();
               response.release();
            }
        } else {  //如果已經(jīng)接收到HTTP請求的所有數(shù)據(jù)
            if (!send()) {  //如果HTTP響應發(fā)送完畢
              channelIO.close();
              response.release();
            }
        }
    } catch (IOException x) {
        x.printStackTrace();
        channelIO.close();
        if (response !=  null) {
            response.release();
        }
    }
  }

  /* 發(fā)送HTTP響應，如果全部發(fā)送完畢，就返回false，否則返回true */  
  private boolean send() throws IOException {
    return response.send(channelIO);
  }
}


/****************************************************
 * 作者：孫衛(wèi)琴                                     *
 * 來源：<<Java網(wǎng)絡編程精解>>                       *
 * 技術支持網(wǎng)址：www.javathinker.org                *
 ***************************************************/