RE: Socket Time-out Issues

Could it also be cause by the java client ends the job, due to timeout,
without execute the close() api?


-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Scott Klement
Sent: Tuesday, June 10, 2008 12:29 PM
To: RPG programming on the AS400 / iSeries
Subject: Re: Socket Time-out Issues

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

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