Re: Socket Time-out Issues

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

Hi Mark,

By "negative response code" I assume you mean that the recv() API would 
return -1, right?  (Normally I hear the term "negative response code" in 
conjunction with IBM technologies like APPC or 5250, not with TCP/IP.)

It's true that sometimes recv() will return -1 if an error occurs. 
However, you can't rely on this always being the case -- especially over 
the Internet.

When the Java side times out and closes the connection, a TCP/IP packet 
containing the FIN flag (and probably also the RST flag) is sent from 
the Java program to your RPG program, and this is what triggers the 
recv() API to return -1.   But... what if that packet never arrives? 
What if a firewall blocks it?  Or a router gets unplugged, and therefore 
the packet can't be sent?  Or your Internet connection goes down?  Or 
someone cuts the network cable?

The point is -- these messages that demonstrate errors are handy, but 
you can never rely on them.  Your recv() API in your RPG program has no 
100% safe way to tell the difference between "nothing was sent", vs 
"connection is dead".

For that reason, you should ALWAYS implement timeouts on your sockets. 
Based on your business rules, determine how long it's acceptable to wait 
-- double that -- and if nothing is received in that time, assume that 
the connection is dead and start over.

Here's a link to an article I wrote that describes how to do timeouts on 
sockets in ILE RPG:
http://systeminetwork.com/article/timeouts-sockets-0

mgarton@xxxxxxxxxxxxxxx wrote:
> I have socket client written in Java that sends a message to a socket
> server running on the iSeries written in RPG.  The socket server is the
> spawning socket server based on Scott Klements code.   I am having a
> problem where the client times out but the server doesn't realize it.  The
> client sends a message and times out after 40 seconds if it doesn't receive
> a response.  The server receives a message, gets data, and sends a
> response. Usually it only take a second or two.  On the send of the
> response, from the server, I check the response code.  If the response code
> is negative, I assume the client didn't get the response and back out the
> change.  The java developer assures me that once the timeout is reached,
> the socket connection is ended by the client.  I would expect to get a
> negative response code on the send from the server, but that is not always
> the case.  This week we had some system issues causing the server to send
> responses two or three minutes later.  I would have expected the pipe to
> have been broken in that amount of time.
>
> Am I wrong to expect a negative response code on the send from the server?
> Is there anything that I can tweak so the server recognizes the pipe is
> broken by the client so that it will get a negative response code?
>
> Thanks,
> Mark Garton