#972 Support for extracting floppy images from Winimage SFX files

[Gert Hulselmans]

MemScope is distributed in a Winimage SFX.
When you open the file with 7-zip, it can see the floppy image file (1.44MB), but it can't extract it.

The following is run from Linux:

$ unzip -Z MemScope-110.exe
Archive: MemScope-110.exe
Zip file size: 150635 bytes, number of entries: 1
warning [../Downloads/MemScope-110.exe]: 90156 extra bytes at beginning or within zipfile
(attempting to process anyway)
-rw-a-- 1.0 fat 1474560 bx defX 06-Apr-14 09:31 MemScope-110.IMA
1 file, 1474560 bytes uncompressed, 60222 bytes compressed: 95.9%

$ unzip ../Downloads/MemScope-110.exe
Archive: ../Downloads/MemScope-110.exe
M2K MemScope 1.10
Compliments of Micro 2000 (M2K)
www.micro2000.com
(800) 864-8008 (818) 547-0125
warning [../Downloads/MemScope-110.exe]: 90156 extra bytes at beginning or within zipfile
(attempting to process anyway)
file #1: bad zipfile offset (lseek): 180224

$ dd if=MemScope-110.exe of=MemScope.img.zip bs=90156 skip=1
0+1 records gelezen
0+1 records geschreven
60479 bytes (60 kB) gekopieerd, 0,000519201 s, 116 MB/s

$ file MemScope_dd.img
MemScope_dd.img: Zip archive data, at least v1.0 to extract

$ unzip -Z MemScope.img.zip
Archive: MemScope.img.zip
Zip file size: 60479 bytes, number of entries: 1
-rw-a-- 1.0 fat 1474560 bx defX 06-Apr-14 09:31 MemScope-110.IMA
1 file, 1474560 bytes uncompressed, 60222 bytes compressed: 95.9%

$ unzip MemScope.img.zip
Archive: MemScope.img.zip
M2K MemScope 1.10
Compliments of Micro 2000 (M2K)
www.micro2000.com
(800) 864-8008 (818) 547-0125
file #1: bad zipfile offset (lseek): 90112

Fixing the zip file:
$ zip -FF MemScope.img.zip --out MemScope-fixed.img.zip
Fix archive (-FF) - salvage what can
Found end record (EOCDR) - says expect single disk archive
Found archive comment
Scanning for entries...
copying: MemScope-110.IMA (60222 bytes)
Central Directory found...
EOCDR found ( 1 60354)...
gert@gert-kot:~/Bureaublad$ unzip MemScope-fixed.img.zip
Archive: MemScope-fixed.img.zip
M2K MemScope 1.10
Compliments of Micro 2000 (M2K)
www.micro2000.com
(800) 864-8008 (818) 547-0125
inflating: MemScope-110.IMA

Changed bytes, between original and fixed zip file:
$ cmp -l MemScope_dd_fixed.img.zip MemScope_dd_fixed2.img.zip
60323 54 0
60324 140 0
60325 1 0

Filesizes of the original and fixed zip file:
$ ls -l MemScope*.img.zip
-rw------- 1 gert gert 60479 2010-08-14 20:03 MemScope-fixed.img.zip
-rw-r--r-- 1 gert gert 60479 2010-08-14 19:56 MemScope.img.zip

I think the zip file is corrupted at the "Relative offset of local file header" field (offset 42) of the "ZIP central directory file header". I am not completely sure (just did some reading on wikipedia).

It would be nice, if 7-zip can automatically correct/extract the zip compressed floppy images from Winimage SFX files:
http://www.winimage.com/wima_sfx.htm

[Gert Hulselmans]

MemScope WinImage SFX

[Gert Hulselmans]

MemScope zip file retrieved from MemScope-110.exe (corrupted zip file)

[Gert Hulselmans]

fixed MemScope zip file

[Igor Pavlov]

I don't think what 7-zip must support file that don't follow ZIP specification.

[Gert Hulselmans]

Just wondering, why was unpacking of some TAR and ISO archives with incorrect headers added to 7-zip 9.18 beta?
And why doesn't the same logic apply to embedded zip archives with incorrect headers like the WinImage images?

9.18 beta 2010-11-02
-------------------------
- 7-Zip now can unpack some TAR and ISO archives with incorrect headers.

[Igor Pavlov]

I can open some "bad" archives, if I see error is simple and I know how to ignore it.
But ZIP format is so complex, so some errors are difficult to understand and difficult to process.

[Gert Hulselmans]

In case of WinImage embedded zip files, it doesn't seem to be that complex (you only need to set 4 bytes to zero).
You don't need to be able to open all "bad" archives.

[Igor Pavlov]

Zip format is complex and ZIp code is complex.
So it's diffictult to think about all things when I change something there.

I don't think that Winimage BUGs are so important.
Why don't you report to Winimage developers about their bugs?