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Hessian is a compact binary protocol for connecting web services.
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/*
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001-2004 Caucho Technology, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:
 *       "This product includes software developed by the
 *        Caucho Technology (http://www.caucho.com/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "Hessian", "Resin", and "Caucho" must not be used to
 *    endorse or promote products derived from this software without prior
 *    written permission. For written permission, please contact
 *    [email protected].
 *
 * 5. Products derived from this software may not be called "Resin"
 *    nor may "Resin" appear in their names without prior written
 *    permission of Caucho Technology.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL CAUCHO TECHNOLOGY OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
 * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * @author Scott Ferguson
 */

package com.caucho.hessian.mux;

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

/**
 * Hessian Mux, a peer-to-peer protocol.
 */
public class MuxServer {
  private Object READ_LOCK = new Object();
  private Object WRITE_LOCK = new Object();
  
  private InputStream is;
  private OutputStream os;
  private boolean isClient;

  private transient boolean isClosed;
  
  // channels that have data ready.
  private boolean inputReady[] = new boolean[4];

  // true if there's a thread already reading
  private boolean isReadLocked;
  // true if there's a thread already writing
  private boolean isWriteLocked;

  /**
   * Null argument constructor.
   */
  public MuxServer()
  {
  }

  /**
   * Create a new multiplexor with input and output streams.
   *
   * @param is the underlying input stream
   * @param os the underlying output stream
   * @param isClient true if this is the connection client.
   */
  public MuxServer(InputStream is, OutputStream os, boolean isClient)
  {
    init(is, os, isClient);
  }

  /**
   * Initialize the multiplexor with input and output streams.
   *
   * @param is the underlying input stream
   * @param os the underlying output stream
   * @param isClient true if this is the connection client.
   */
  public void init(InputStream is, OutputStream os, boolean isClient)
  {
    this.is = is;
    this.os = os;
    this.isClient = isClient;
  }

  /**
   * Gets the raw input stream.  Clients will normally not call
   * this.
   */
  public InputStream getInputStream()
  {
    return is;
  }

  /**
   * Gets the raw output stream.  Clients will normally not call
   * this.
   */
  public OutputStream getOutputStream()
  {
    return os;
  }

  /**
   * Starts a client call.
   */
  public boolean startCall(MuxInputStream in, MuxOutputStream out)
    throws IOException
  {
    int channel = isClient ? 2 : 3;

    return startCall(channel, in, out);
  }

  /**
   * Starts a client call.
   */
  public boolean startCall(int channel, MuxInputStream in, MuxOutputStream out)
    throws IOException
  {
    // XXX: Eventually need to check to see if the channel is used.
    // It's not clear whether this should cause a wait or an exception.
    
    in.init(this, channel);
    out.init(this, channel);

    return true;
  }
  
  /**
   * Reads a server request.
   */
  public boolean readRequest(MuxInputStream in, MuxOutputStream out)
    throws IOException
  {
    int channel = isClient ? 3 : 2;
    
    in.init(this, channel);
    out.init(this, channel);

    if (readChannel(channel) != null) {
      in.setInputStream(is);
      in.readToData(false);
      return true;
    }
    else
      return false;
  }

  /**
   * Grabs the channel for writing.
   *
   * @param channel the channel
   *
   * @return true if the channel has permission to write.
   */
  OutputStream writeChannel(int channel)
    throws IOException
  {
    while (os != null) {
      boolean canWrite = false;
      synchronized (WRITE_LOCK) {
        if (! isWriteLocked) {
          isWriteLocked = true;
          canWrite = true;
        }
        else {
          try {
            WRITE_LOCK.wait(5000);
          } catch (Exception e) {
          }
        }
      }

      if (canWrite) {
        os.write('C');
        os.write(channel >> 8);
        os.write(channel);
        
        return os;
      }
    }

    return null;
  }

  void yield(int channel)
    throws IOException
  {
    os.write('Y');
    freeWriteLock();
  }

  void flush(int channel)
    throws IOException
  {
    os.write('Y');
    os.flush();
    freeWriteLock();
  }

  void close(int channel)
    throws IOException
  {
    if (os != null) {
      os.write('Q');
      os.flush();
      freeWriteLock();
    }
  }
  
  /**
   * Frees the channel for writing.
   */
  void freeWriteLock()
  {
    synchronized (WRITE_LOCK) {
      isWriteLocked = false;
      WRITE_LOCK.notifyAll();
    }
  }

  /**
   * Reads data from a channel.
   *
   * @param channel the channel
   *
   * @return true if the channel is valid.
   */
  InputStream readChannel(int channel)
    throws IOException
  {
    while (! isClosed) {
      if (inputReady[channel]) {
        inputReady[channel] = false;
        return is;
      }

      boolean canRead = false;
      synchronized (READ_LOCK) {
        if (! isReadLocked) {
          isReadLocked = true;
          canRead = true;
        }
        else {
          try {
            READ_LOCK.wait(5000);
          } catch (Exception e) {
          }
        }
      }
      
      if (canRead) {
        try {
          readData();
        } catch (IOException e) {
          close();
        }
      }
    }

    return null;
  }

  boolean getReadLock()
  {
    synchronized (READ_LOCK) {
      if (! isReadLocked) {
        isReadLocked = true;
        return true;
      }
      else {
        try {
          READ_LOCK.wait(5000);
        } catch (Exception e) {
        }
      }
    }

    return false;
  }

  /**
   * Frees the channel for reading.
   */
  void freeReadLock()
  {
    synchronized (READ_LOCK) {
      isReadLocked = false;
      READ_LOCK.notifyAll();
    }
  }

  /**
   * Reads data until a channel packet 'C' or error 'E' is received.
   */
  private void readData()
    throws IOException
  {
    while (! isClosed) {
      int code = is.read();

      switch (code) {
      case ' ':
      case '\t':
      case '\n':
      case '\r':
        break;

      case 'C': {
        int channel = (is.read() << 8) + is.read();

        inputReady[channel] = true;
        return;
      }

      case 'E': {
        int channel = (is.read() << 8) + is.read();
        int status = (is.read() << 8) + is.read();

        inputReady[channel] = true;

        return;
      }

      case -1:
        close();
        return;
        
      default:
        // An error in the protocol.  Kill the connection.
        close();
        return;
      }
    }

    return;
  }

  /**
   * Close the mux
   */
  public void close()
    throws IOException
  {
    isClosed = true;
    
    OutputStream os = this.os;
    this.os = null;
    
    InputStream is = this.is;
    this.is = null;

    if (os != null)
      os.close();

    if (is != null)
      is.close();
  }
}