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I tried to come up with a good title, but seem to have failed. Here's my problem:

I'm reading data in from a socket. The data contained in the buffer is a serialized object. Once the data is completely read, I can then create an ObjectInputStream and use readObject to read in the data.

My problem is, since my socket class is reading in the bytes... how do I know when I have received the full object? There does not seem to be an end of object indicator, and I've tried looking for a breakout of the serialized bytecode to see if I can find length fields, but the serialization bytecode is not well explained anywhere I can find with Google.

The objects I'm receiving are hash maps (java.util.Map) if that makes a difference.

Here is part of the code I'm using:

long start = System.currentTimeMillis();
long end = start + (getTimeout() * 1000);   
m_Ipports.send(dataToSend);       
m_Waiting = true;        
while (m_Waiting) {
  // Data is read in a separate thread, and stored into the byte buffer m_DataIn
  if (System.currentTimeMillis() > end) {
    //throw new Exception("Timeout waiting for response.");             
    m_Waiting = false;  // hack to get it to work. Times out every time.
  }
  m_Ipports.doEvents();
}
ByteArrayInputStream bis = new ByteArrayInputStream(m_DataIn.toByteArray()); 
ObjectInputStream ois = new ObjectInputStream(bis);        
Object o = ois.readObject();             
Map m = (Map)o;

So, my question is, when I'm reading m_DataIn, how do I determine I've reached the end of the object?

NOTE: I cannot in any way modify the server that I am receiving these objects from. It's not my code.

Thanks.

Charles.

ChopperCharles
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3 Answers3

3

The stream that is sending the object needs to provide you with the number of bytes it will send. You will know you've finished reading the object when you've read the specified number of bytes.

cklab
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  • +1 Another reason to do this is you cannot read bytes which are for the next object. (They will be ignored and the next object corrupt) – Peter Lawrey Jun 14 '12 at 15:56
  • That's not an option, I cannot modify the server that is sending me data. – ChopperCharles Jun 14 '12 at 16:02
  • See if this example works: http://www.java2s.com/Code/Java/Network-Protocol/ObjectInputStreamandObjectOutputStreamfromSocket.htm. I don't see how you will know that you're done reading unless someone breaks the connection. – cklab Jun 14 '12 at 16:07
  • I think what I need is a class or method that will validate a serialized object -- or I need to build my own parser. But for that, I really need a better spec for the serialization byte code. The one nice thing is that I am guaranteed to receive only one serialized object from the server in response to my request. So I never have to worry about receiving more than one at a time... I just need a good way to determine I've reached the end of the stream without waiting for the timeout. – ChopperCharles Jun 14 '12 at 20:08
  • No it doesn't. `EOFException` is sufficient. – user207421 Apr 05 '17 at 10:31
2

Why are you reading bytes from the socket at all? Just attach the ObjectInputStream directly to the socket and read objects.

user207421
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  • Because I don't have that option. I'm using an IPPort SSL class made by www.nsoftware.com. I have two ways to read in data received over the wire. 1) the DataIn event fires, with a parameter containing the bytes read. I enter a wait loop (since I want it to be a synchronous read) and wait for an EOL (but, I don't have an EOL for an object right now). – ChopperCharles Jun 15 '12 at 05:37
  • 2) I can set an OUTPUT stream that the class will write to directly when data is received. I can use a ByteArrayOutputStream for that... but it's an OUTPUT stream, and to read data with readObject I need an INPUT stream. So I have to get the bytes and add them to a ByteArrayInputStream before I can do so with ObjectInputStream. I don't have direct access to the socket. – ChopperCharles Jun 15 '12 at 05:37
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    @ChopperCharles So you have a *major* problem. You are using an API that is designed to conceal the very stream that ObjectInputStream needs. You are either going to have to change the sending protocol so as to include a length-word prefix, as suggested by Peter Lawrey above, or else read the socket until EOS before you decode anything. I suggest you review your infrastructure. It's getting in the way rather than helping. There is nothing wrong with `javax.net.ssl.SSLSocket`. Your plans to decode the serialized stream yourself just show how much damage this IPPort damage is doing. – user207421 Jun 17 '12 at 12:11
0

Well, The IPWorks IPPortS (SSL) class is extremely useful for pretty much every other instance I've needed it. It makes SSL communications a breeze... like 4 lines of code and a couple of event handlers. The one issue was reading objects from a stream. Rather than go and implement my own solution using ssl sockets, I implemented my own input stream. Hopefully this will be of use to someone else someday.

Input stream class:

class NetworkInputStream extends InputStream {
  private int m_Offset = 0;  
  private ByteArrayOutputStream m_Buffer = null;

  Ipports m_Ipports = null;
  public NetworkInputStream(Ipports ipport) {
    m_Ipports = ipport;
    m_Buffer = new ByteArrayOutputStream();
    try { m_Ipports.receiveStream(m_Buffer); } catch (Exception e) {}
    m_Offset = 0;
  }
  public void waitForData() throws Exception {  
    if (dataAvailable() == 0) { 
      m_Buffer.reset();
      m_Offset = 0;
    }
    while (dataAvailable() == 0 && m_Ipports.isConnected()) {      
      m_Ipports.doEvents();
    }
  }
  private int dataAvailable() {
    return m_Buffer.size() - m_Offset;  
  }
  public int read(byte[] buffer, int offset, int length) throws IOException, IndexOutOfBoundsException {
    try {
      waitForData();
    } catch (Exception e) { 
      throw new IOException(e.getMessage()); }
    int bytesRead = -1;
    int dataAvailable = dataAvailable();
    if (dataAvailable > 0) {
      bytesRead = Math.min(dataAvailable, length);
      m_Buffer.toByteArray();
      System.arraycopy(m_Buffer.toByteArray(), m_Offset, buffer, offset, length);      
      m_Offset += bytesRead;
    }
    return bytesRead;
  }
  @Override
  public int read() throws IOException {
    byte[] buf  = new byte[] { 0x00 };
    int rval = read(buf, 0, 1);
    if (rval == -1) return rval;
    int cast = (int)buf[0] & 0xff;
    return cast;
  }
}

Usage:

m_Ipports.setSSLStartMode(Ipports.sslImplicit);
m_Ipports.setTimeout(60);
m_Ipports.setRemoteHost(host);
m_Ipports.setRemotePort(port);
m_Ipports.setConnected(true);

NetworkInputStream nis = new NetworkInputStream(m_Ipports);
m_Ipports.setAcceptData(true);
m_Ipports.send(dataToSend);   
ObjectInputStream ois = new ObjectInputStream(nis);
Object resp = ois.readObject();
m_Ipports.setAcceptData(false);
m_Ipports.setReceiveStream(null);
Map m = (Map)o;

I've omitted the event handlers for IPPortS, the only one you really need is:

  public void SSLServerAuthentication(IpportsSSLServerAuthenticationEvent e) {
    e.accept = true;
  }

Now, this assumes you will get ONE complete object in response to a request. That's how the server I'm interacting with works.

Charles.

ChopperCharles
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