Reading an archive's "ZIP comment"

[Zbiggy]

I'm wondering: how can this be done in the script? I would use vfs::zip -
but if not possible, can be other way too.

Well, there is a procedure at http://wiki.tcl.tk/11846 - but an attempt to
use this raises an error: "not enough arguments for all format specifiers".

When I tried to use the proposed method sequentially line-by-line then - in
the end it reported:

#v+
% puts $cb(comment)
0
#v-

...which is wrong, of course.

Not being too familiar with ZIP-format details, I'm not sure, what's the
problem.
--
Z.

[Donal K. Fellows]

On 16/10/2011 23:04, Zbiggy wrote:
> I'm wondering: how can this be done in the script? I would use vfs::zip -
> but if not possible, can be other way too.
>
> Well, there is a procedure at http://wiki.tcl.tk/11846 - but an attempt to
> use this raises an error: "not enough arguments for all format specifiers".

Try the code at http://wiki.tcl.tk/3307#pagetoc2af086b9 which uses Tcl
8.6 (TclOO and the [zlib] command only though, so could be used with 8.5
with a bit of effort and external packages I suppose). It works with the
sample files I've tried, but they didn't have comments so I've only gone
with what's in the spec...

Donal.

[Zbiggy]

In comp.lang.tcl, Donal K. Fellows wrote:

> Try the code at http://wiki.tcl.tk/3307#pagetoc2af086b9 which uses Tcl
> 8.6 (TclOO and the [zlib] command only though, so could be used with 8.5
> with a bit of effort and external packages I suppose). It works with the
> sample files I've tried, but they didn't have comments so I've only gone
> with what's in the spec...

Well, it properly recognized the bytesize - but still cannot read
zipfile-comment:

#v+
% puts Comment:[$z comment]
Comment:
foreach n [$z names] {
puts "$n ([$z info $n disksize] bytes)"
}
asdd (7405 bytes)
%
#v-

[$z comment] seems to be empty (but the ZIP file is commented).
--
Z.

[Donal K. Fellows]

On 17/10/2011 18:29, Zbiggy wrote:
> Well, it properly recognized the bytesize - but still cannot read
> zipfile-comment:

[...]

> [$z comment] seems to be empty (but the ZIP file is commented).

I've never had a ZIP file with a comment, so I couldn't test. :-)

Donal.

[Zbiggy]

In comp.lang.tcl, Donal K. Fellows wrote:

> I've never had a ZIP file with a comment, so I couldn't test. :-)

Maybe you can create one? Usually: "zip -c archive.zip file file file..."
--
Z.

[Donal K. Fellows]

OK, I can read them with my class. :-) I can also read overall comments
(i.e., those created if you use the -z option). Hence I claim that my
code's doing the right thing. Whatever the problem is, it's not my code.

I do note that that class doesn't apply any encoding handling. It
probably ought to, but... well, you've got the source. :-D

Donal.

[Zbiggy]

In comp.lang.tcl, Donal K. Fellows wrote:

> OK, I can read them with my class. :-) I can also read overall comments
> (i.e., those created if you use the -z option). Hence I claim that my
> code's doing the right thing. Whatever the problem is, it's not my code.

Well, tried it again; like before, it returns no zipfile-comment. Although
it properly recognizes size and packed file name. Tried it using "Example of
use" from the mentioned page.

Slackware64 13.1, TCL/Tk 8.6b2

If your code really is correct - maybe there's a need for some more details,
how to use it? The example obviously won't return any zipfile-comment.
--
Z.

[hae]

Hi Zbiggy,

I used the method ReadDirectory in from the wiki page mentioned above
and created a zip file with winrar.exe that contains a comment. It
works for me.

Here is the code I used:

--------8<-------------8<----------------

set fd [open Readme.zip]

proc ReadDirectory {} {
variable fd

set off -22
while 1 {
seek $fd $off end
binary scan [read $fd 4] i sig
if {$sig == 0x06054b50} {
seek $fd $off end
break
}
incr off -1
}
binary scan [read $fd 22] issssiis sig disk cddisk nrecd nrec \
dirsize diroff clen
if {$clen > 0} {
set comment [read $fd $clen]
} else {
set comment ""
}
if {$disk != 0} {
error "multi-file zip not supported"
}
seek $fd $diroff
for {set i 0} {$i < $nrec} {incr i} {
binary scan [read $fd 46] issssssiiisssssii \
sig ver mver flag method time date crc csz usz n m k d ia
ea \
off
if {$sig != 0x02014b50} {
error "bad directory entry"
}
set name [read $fd $n]
set extra [read $fd $m]
if {$k == 0} {
set c ""
} else {
set c [read $fd $k]
}
set directory($name) [dict create timestamp [list $date $time]
\
size $csz disksize $usz offset $off method $method \
extra $extra comment $c]
}

puts comment='$comment'
parray directory
}

--------8<-------------8<----------------

Here is my test output:

(tclzip) 54 % source tclzip.tcl
(tclzip) 55 % ReadDirectory
comment='This is a zip comment!'
directory(Readme.txt) = timestamp {16212 16389} size 10 disksize 10
offset 0 method 0 extra {} comment {}
(tclzip) 56 %

[Donal K. Fellows]

On 19/10/2011 22:47, Zbiggy wrote:
> Well, tried it again; like before, it returns no zipfile-comment. Although
> it properly recognizes size and packed file name. Tried it using "Example of
> use" from the mentioned page.

There can be comments on both the overall archive and on the individual
files. (Under the assumption that $z holds the name of an instance of a
Zip object,) [$z comment] returns the whole archive comment, and [$z
comment $file] returns the comment associated with a particular file; I
tried to make the usage of the API as obvious as possible.

I tested it with ZIP files created with both my system 'zip' command
(which is how I tested the comments) and with Java's 'jar' tool. These
are independent implementations, so I assume that if I can read both of
their output, my code is correct. :-) Note however that Java's 'jar'
tool does not produce comments at all, so I couldn't check that
particular combination.

Perhaps your sample zip file just doesn't have any comments? Or maybe
they're packed somehow into the 'extra' info field, which I don't parse
at all. (The ZIP spec is really quite complicated when you get into the
details, and not everything is actually documented apparently.)

Donal.

[Zbiggy]

In comp.lang.tcl, hae wrote:

> I used the method ReadDirectory in from the wiki page mentioned above
> and created a zip file with winrar.exe that contains a comment. It
> works for me.

I made another attempt using this code - here's the result:

#v+
% ReadDirectory
comment=''
directory(asdd) = timestamp {15996 31078} size 3891 disksize 7405 offset 0
method 8 extra {UT˙ Mux
čd} comment {To jest test}
#v-

Then we can see still an empty comment - but, from the other side, it showed
comment in a dictionary "comment" contents, and some strange things in
"extra" field contents.

No idea, maybe my ZIP utility is flawed? It's Zip 3.0 (July 5th 2008). But,
from the other side: since Midnight Commander - and other tools - are able
to recognize the contents of zip-packages prepared using this utility - and
the comment, of course - I don't think, it's really flawed.

Still I can't understand the origin of the problem.
--
Z.

[Donal K. Fellows]

On 20/10/2011 11:51, Zbiggy wrote:
> I made another attempt using this code - here's the result:
>
> #v+
> % ReadDirectory
> comment=''
> directory(asdd) = timestamp {15996 31078} size 3891 disksize 7405 offset 0

> method 8 extra {...} comment {To jest test}

> #v-
>
> Then we can see still an empty comment - but, from the other side, it showed
> comment in a dictionary "comment" contents, and some strange things in
> "extra" field contents.

Ah! You've misunderstood the ZIP format. There are *two* *independent*
places for comments: the overall archive, and attached to each file in
the archive. In the case you're dealing with, the overall comment is not
there but there is a comment on the 'asdd' entry; with my code, doing
[$z comment asdd] will return it. Alternatively, pick the value out of
the dictionary with [dict get]; that's all that's going on.

It all seems a bit odd if you're only putting one file inside the ZIP, I
know, but it makes a lot more sense with multi-file archives.

Donal.

[Zbiggy]

In comp.lang.tcl, Donal K. Fellows wrote:

> There can be comments on both the overall archive and on the individual
> files.

Ah, now I see, that I totally confused "-c" and "-z" options of the ZIP
utility; actually, I was always commenting entire archive only, as it was
quite enough for me.

Thanks, not tried it again yet (in a few minutes) - but I'm pretty sure,
that my troubles are over. :D
--
Z.