antex

Hi, I'm having trouble figuring out how to do two things "simultaniously" over the same connection. Say I want to send 2 files to the same client or send 1 file and some text messages. The problem is that I use the send function to do both so I can't make sure that the client recv doesn't mix the file info with the text message (I'm using winsock). An example of the behavior I need is something similar to msn messenger (or any other chat software), there you can chat and send a file at the same time. Since I'm sending both messages and files with the send function, there is no way for the client recv function to know the difference because all it does is receiving the next bytes available over the connection.

I would really appreciate any help I can get because I don't see any solution at all.

vart

You can wrap your messages in some internal protocol
((MesType,MesLen,MesBody))
and parse these buffers on the receiver side applying actions according to MesType

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antex

Ok thanks. Is it a bad idea to let the first or first few bytes received from each call identify the type, or is that good enough for most purposes? But what if not all info gets extracted in one call, due to some connection problem or some kind of buffer problem, then the next piece of information won't be the identification bytes. How do I solve this? I really don't understand internal socket buffers or whatever they are called.

vart

Define some pattern for message start and message end (called start marker and end marker)
in my sample it was "((" and "))"
check for these markers before you start parsing the rest and after you finished parsing

if markers don't match - start scanning the stream till you find the start marker...

It you use TCP and not UDP you should not have problems with loosing data or receiveing unordered data...

__________________
If I have eight hours for cutting wood, I spend six sharpening my axe.

antex

Thank you very very much!

brewbuck

Why not just make another connection to the host? Imagine trying to have three conversations on a single phone line. You could come up with some complicated protocol to allow multiple people to all talk on the same line, but WHY?

vart

BTW - I think that is what Messagenger ICQ etc do, You can check the number of open ports on your comp when you start simple conversation in Messager, and compare it to the number of open ports when the file transfer starts... 1 port should be added to the list

__________________
If I have eight hours for cutting wood, I spend six sharpening my axe.

antex

Well, I didn't think about that at all, but that seem to be a good option and far easier to program too. Thank you both for your replies! I really appreciate you help!

abachler

You could try sending the text as OOB data, which is handled seperately from the normal data stream.

brewbuck

A Google search for "TCP OOB" turns up zillions of examples why using OOB transmission is a bad idea, not universally supported, not guaranteed to work, etc.