Re: How to retrieve a dns message from a bytebuffer

[Brian W. <bwe...@xb...>]

On Sep 1, 2011, at 2:57 PM, Periya.Data wrote:

> Hi,
>     I have a bytebuffer of size 2048 bytes. Its initial bytes have some custom data (upto 70th byte). From 71st byte, the DNS messages are there. I think I know the length of the DNS message (I am not yet sure about this).
> 
> How do I get one message at a time from the bytebuffer? 
> 
>  I am doing something like this:
> 
>         byte[] dns_msg_buf= new byte[1024];
>         bb.get(dns_msg_buf, 71, caplen);   // bb is a byte buffer with custom data and dns msgs. Caplen is the len.
>         Message dns_msg = new Message(dns_msg_buf);
>         System.out.println("Message size: " + dns_msg.numBytes());
> 
> dns_msg.numBytes => seems to be returning the size of the header only = which is 12 bytes. Is there a way to find the total length of the message = hdr + 4 message sections?

Message.numBytes() does return the size of the entire message; the provided "dig" helper program calls Message.toString(), which calls Message.numBytes(), and returns the full message size correctly.

The code looks correct, so I suspect that there's a problem with the data you're parsing.  The Message(byte []) constructor doesn't verify that the entire byte array was consumed by the parsing, so it probably wasn't.

Brian