Re: Problem sending message length in ByteBuffer

[Niklas Therning]

+1


Maarten Bosteels wrote:

Hello all,

Right now we have the TextLineDecoder, which always works with a delimiter.
Wouldn't it be a good idea to add a PrefixedStringDecoder ?

Something like this:

public class PrefixedStringDecoder extends CumulativeProtocolDecoder {
  ...
  public PrefixedStringDecoder(int prefixLength, int maxDataLength,
Charset charset) {
    this.prefixLength = prefixLength;
    this.maxDataLength = maxDataLength;
    this.charset = charset;
  }

  protected boolean doDecode(IoSession session, ByteBuffer in,
ProtocolDecoderOutput out) throws Exception {
    if (in.prefixedDataAvailable(prefixLength, maxDataLength)) {
      String msg = in.getPrefixedString(prefixLength, charset.newDecoder());
      out.write(msg);
      return true;
    } else {
      return false;
    }
  }

Maarten

On Dec 4, 2007 8:51 AM, Niklas Therning <[EMAIL PROTECTED]> wrote:

guttikonda wrote:

Hi

   I am new to Mina.I have implemented a mina server to accept connections
from tcp/ip clients.The client only accepts network byte order messages with
message length.I figured that i can achieve it by using DataInputStream and
DataOutputStream readUTF() and writeUTF() methods respectively.

When receiving data from client i am successful in getting the correct one:
                                ByteBuffer rb = (ByteBuffer)msg;
              reader = new DataInputStream(rb.asInputStream());
              String inputMsg = reader.readUTF();

I want to achieve the same thing when sending the response.I have no idea
how i should wrap the DataOutputStream in my ByteBuffer to write it back to
the session.If i simply write my response string back it is not producing
the message length.Can anyone please help?

Maybe something like

ByteArrayOutputStream baos = new ByteArrayOutputStream();
DataOutputStream writer = new DataOutputStream(baos);
writer.writeUTF(msg);
session.write(ByteBuffer.wrap(baos.toByteArray());

would work?

BUT, you couldn't you simply use ByteBuffer.getPrefixedString(...) and
ByteBuffer.putPrefixedString(...) instead?

AND, you should be aware that the network layer may decide to deliver
your message in several packets. The result is that you cannot assume
that a ByteBuffer passed in to your IoHandler.messageReceived() method
contains a complete message. You should look into implementing a custom
ProtocolDecoder. There's a tutorial on this. The beauty of using
decoder/encoder is that you will only have to deal with Strings in your
IoHandler.

HTH
Niklas