'''yencode''' is a [binary encoding]. [tcllib] provides an implementation.
** Documentation **
[http://core.tcl.tk/tcllib/doc/trunk/embedded/www/tcllib/files/modules/base64/yencode.html%|%official reference] (alternates [http://tcllib.sourceforge.net/doc/yencode.html%|%1] ,[http://docs.activestate.com/activetcl/8.5/tcllib/base64/yencode.html%|%2]):
** Tcllib yenc **
This package provides a Tcl-only implementation of the yEnc file encoding. This
is a recently introduced method of encoding binary files for transmission
through Usenet. This encoding packs binary data into a format that requires an
8-bit clean transmission layer but that escapes characters special to the
[NNTP] posting protocols. See http://www.yenc.org/ for details concerning the
algorithm.
----
[Pat Thoyts] wrote in [comp.lang.tcl]:
I found out about yenc encoding ... and it's not the same as uuencoding.
Hopefully you are not trying to decode yenc data using the
[uuencode]/[uudecode] code :) If you want a tcl yenc decoder I'm going to add
one to [tcllib]'s [base64] module shortly.
[LV] and in fact Pat has added (to the latest base64 module of tcllib) a
yencode set of functions.
In the meantime here is the core of this method:
======
namespace eval yencode {} ;# added by RS
proc yencode::yEncode {s} {
set r {}
binary scan $s c* d
foreach {c} $d {
set v [expr {($c + 42) % 256}]
if {$v == 0x00 || $v == 0x09 || $v == 0x0A
|| $v == 0x0D || $v == 0x3D} {
append r "="
set v [expr {($v + 42) % 256}]
}
append r [format %c $v]
}
return $r
}
proc yencode::yDecode {s} {
set r {}
set esc 0
binary scan $s c* d
foreach c $d {
if {$c == 61 && $esc == 0} {
set esc 1
continue
}
set v [expr {($c - 42) % 256}]
if {$esc} {
set v [expr {($v - 42) % 256}]
set esc 0
}
append r [format %c $v]
}
return $r
}
======
----
Someone recently posted a question on [comp.lang.tcl] asking about yenc
multi-part support in Tcl. Anyone know of such code?
----
I don't know of any support in tcl; but there is C-code available at
http://www.fpx.de/fp/Software/UUDeview/. It has a tcl interface layer. I
wasn't able to get that working myself (did not try very hard) but the
standalone application definitely converts multipart yenc files.
----
There is a bug in the example encode/decode code above that also exists in the
tcllib implementation. The yEnc 1.3 spec states that escaped characters should
have their ascii value further rotated by 64, not 42, so the escape character
rotation value should be by 64, not 42 as in the example code. This bug exists
in the current CVS v. 1.11 copy of the base64/yencode.tcl tcllib file.
I discovered this while trying to decode some externally yencoded data with
tcllib's yencode.tcl implementation. I was getting corrupt output from
ydecode. Making this change to my yencode.tcl file produces correctly decoded
output data from ::yencode::decode.
I would have posted to the sourceforge tracker, except that logins to
sourceforge are disabled at the moment.
[AK] 2003-12-10 09:40: Just tried to login and had no trouble.
[AK]: RE, can you please provide me with an example text which triggers the bug
? A patch showing exactly what to change would be good as well.
[AK] Ok, should be fixed in Tcllib CVS Head now, yencode 1.1.2.
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