Re: Anybody here know where I can get help with a TCP communication problem?

Are you checking the open source code for tn5250 or tn5250j for helpful
clues?

On Wed, Jun 13, 2018 at 10:32 AM, James H. H. Lampert <
jamesl-6/ELSmrcqeUu8xhjR5IN5AC/[email protected]> wrote:

> 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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>


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