linuxpimp20

hi. i've been reading about socket programming lately and want to get my hands dirty. Is there any exercises i could to to mess around with them? I don't have two linux boxes so i can't make a real connection but is it possible to connect back to myself connection 127.0.0.1? In that case would it be difficult to tell if i was successful or not? thanks for any replies in advance.

Polyphemus_

yap, you can connect to yourself via 127.0.0.1, but make sure you don't connect on the same port

linuxpimp20

to make sure im doing it right would it be just as simple has having two shells opened and sending the data to standard input?

Infinite Recursion

Have two shells open... one for the client and one for the server. Use 127.0.0.1 has the IP for both... just send and receive on unique ports... do not have them be the same and don't have them be a port that is already in use by a known service (ie httpd=80).

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Arevos

Eh? So far as I know, you just need a unique port for each listener. You can have multiple programs sending data to the same port/IP address.

Polyphemus_

yes, you can send data to the same port/IP address idd. Think of a webserver, it receives multiple requests on the same port.
The point we are mentioning though, is the client can't use the same port as the server on the same system.

Arevos

So you're saying that the client doesn't just connect to the server, it also listens for incoming connections, à la FTP?

Polyphemus_

Uhm, wel.. nope Just that two programs on the same system can't use one port at the same time (maybe with some kernel hacking, but you get the point ).

Arevos

I think you're getting confused with how TCP/IP works, or I'm just not understanding what you're getting at. Binding to a port only matters when you're listening. So, for instance, I have a HTTP server listening on port 80 on my computer. I couldn't start another HTTP server and tell it to listen on port 80, because that's already taken.

But I can point multiple browsers to my one HTTP server. I can have two clients connected to the same port at the same time on the same system. So your assertion that "the client can't use the same port as the server on the same system" doesn't make sense to me, because clients typically don't need to bind to a port. Only protocols like FTP, where the client also has to listen to incoming connections from the server, would this make any sense at all.

Polyphemus_

really? weird.. last time i tried i got an error the port was already in use.. and i didn't have to give arguments whether it was for input or output. maybe a java thingy?

I still have to learn much