If the pmr with ibm involved a comm trace, that should be on the system for
you to inspect.
Not picking on you or your product, but you need to analyze this with
something external to your own product.
Also verify that something in between is not stripping out some of the
traffic, or some attempt at a man in the middle proxy.
Jim

-----Original Message-----
From: JAVA400-L [mailto:java400-l-bounces@xxxxxxxxxxxx] On Behalf Of James
H. H. Lampert
Sent: Wednesday, June 13, 2018 12:32 PM
To: Java 400 List <java400-l@xxxxxxxxxxxx>
Subject: Anybody here know where I can get help with a TCP communication
problem?

We have a terminal emulator problem.

On a handful of hosts, our Java-based TN5250 emulator has a chronic problem
of sporadic crashing.

On the host where that happens the most, it happens both with and without
SSL. The owners of the host have filed a PMR, and the IBM analyst swears up
and down that we are sending 200kB (and larger) packets that are causing
buffer overruns.

We have data stream capture and buffer-dump diagnostics built into the
emulator, and we have yet to find a single case in which the last thing we
sent before the crash (or indeed, anything we sent) was even as much as
16kB, at least as an RFC 1205/2877 TN5250 data stream passed to the socket.

Moreover, according to the traces and dumps on our end, there are at least
as many cases in which the last traffic through the socket was sent FROM the
host TO the emulator.

Almost from the beginning, it has looked to me like some sort of network
issue. Except that IBM's own emulator is apparently immune.

It's driving me crazy. Every time I see new email from the customer with the
open PMR, my blood starts to boil. And none of the Google searches I've
tried, looking for some sort of list-server or board for help diagnosing
Java SSL problems have turned up anything even vaguely relevant (most seem
to be concerned either with certs, or with HTTPS, or both.

When we establish secure connection, we start with a static
SSLSocketFactory. This is instantiated using an SSLContext that has a very
basic TrustManager. We then, whenever a new secured socket is needed, get
the socket from the factory with a "createSocket(adr, port)"
method call. Perfectly straightforward, and it works just fine on the
overwhelming majority of hosts.

I don't understand what could make the Telnet server think it was getting a
200kB packet, when I can find no evidence that we've ever sent anything
remotely that big.

--
JHHL
--
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