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From sebb <seb...@gmail.com>
Subject Re: Help putting TelnetClient into binary mode?
Date Tue, 09 Dec 2014 13:10:09 GMT
On 9 December 2014 at 02:15, Andrew Kolbus <andrew.kolbus@gmail.com> wrote:
> I am using the TelnetClient from commons-net 3.3 in JDK 8.  When I try to
> receive xmodem data over a telnet session, some bytes do not make it through
> to my code.
>
> Example:
> The remote device sends this (confirmed using windows network monitor):
> 01 01 FE [...] C0 00 FF FF FF 00 00 00 00 27 27 00 [...] (133 byte
> xmodem-crc packet)
>
> However, from the telnet client, I get this:
> 01 01 FE [...] C0 00 FF 00 00 00 27 27 00 [...] (130 bytes total)
>
> From what I have read, this is related to NVT.  It looks like it is
> converting [FF FF] to [FF] (removing one byte), and just outright removing
> [FF 00] (removing another two bytes for a total of three).

Yes, that is what the RFC mandates:

https://tools.ietf.org/html/rfc856#section-5

In binary mode, IAC (FF) is still required to be recognised.

> I tried using telnetClient.addOptionHandler(new
> SimpleOptionHandler(TelnetOption.BINARY, true, true, true, true));, but that
> did not change the data I received.
>
> A sample of the code I used to discover the issue is attached.  Is there a
> way to get the TelnetClient to pass all data through?

No, that would violate the RFC.

https://tools.ietf.org/html/rfc856#section-5

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