TCP/IP Stream and recv?

Javier París Fernández <>
Wed Feb 8 20:12:34 CET 2006


Hi,
On Wed, Feb 08, 2006 at 06:36:16PM +0000, Chris Campbell wrote:
> Hi,
> 
> This may be a misunderstanding of tcp but here goes.  The following
> client sends two messages to a client one after the other, then waits
> 5 seconds and exits.  The server waits for 1 second after accepting a
> connection, then does 1 call to recv.  It only retrieves the first
> message.  Is this Erlang specific or TCP behaviour?  My understanding
> of tcp is that it's a stream and recv may return both messages
> (ignoring fragmentation for the moment).

Yes, it works that way.

> I have only used tcp with single requests like HTTP so far. I'm now
> toying with something that will send messages back and forth hence why
> it's important to know if recv will pull a single message or it just
> pulls everything to make account for this in the protocol parser.

In your case it's due to the use of {packet, 4}, which is a feature
added in Erlang to support sending messages using tcp, insted of
having a continuous stream. If you want to receive everything in one 
call you hace to use either raw or 0.

Regards.




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