[GD-General] Sockets question

[brian h. <bri...@py...>]

I'll probably figure this out 5 minutes after posting this, but hey, if 
I don't post the question, I won't figure it out.  Sacrifices to the 
coding gods and all that.

Anyway, I've traditionally written UDP servers such that when I need to 
respond to a client, I just do a sendto() using the address I grabbed 
via recvfrom().  This has always worked when I used the same socket for 
both the send and receive, i.e.

recvfrom( mySocket, ... );
sendto( mySocket, ... );

I've tried to generalize some things, and in the process I wanted to 
remove the constraint that I send data out on the same socket I 
received that data from, but it's not working.  i.e.

recvfrom( mySocket, &sa, ... );
sendto( defaultSocket, &sa, ... );

This isn't working.  sendto() doesn't fail, but the client never sees 
that return packet.  

The defaultSocket is just a kind of dummy socket I would like to keep 
around in case I want to just send random crap out on the wire without 
being forced to connect and/or bind first.

I'm assuming I'm making a major assumption here that isn't valid, but 
after rereading Stevens again, I can't figure out what I might be doing 
wrong.  I tried bind()ing the defaultSocket before use to an ephemeral 
port, and that didn't make any difference.  If I go back to using the 
same socket for send/receive, it works fine, but if I substitute a 
different socket, it stops working.

I can't see this being an illegal use of the sockets, since otherwise 
it would mean you could never sendto() a destination that you hadn't 
previously, say, connect()ed to or recvfrom()ed, which doesn't seem 
right at all.

Anyway, just to clarify:

//this works (pseudo code obviously)
mySocket = socket( ... );
bind( mySocket, myPort );
recvfrom( mySocket, &sa, ... );
sendto( mySocket, &sa .. );

//this doesn't (in that the client never sees a response)
mySocket = socket( ... );
bind( mySocket, myPort );
defaultSocket = socket( ... );
//doesn't matter if I bind defaultSocket() or not
recvfrom( mySocket, &sa, ... );
sendto( defaultSocket, &sa ... );

-Hook