font extract Panic: Index Out of Range in cz2.go:69 During CZ2 Decompression on Modified Font Files

[abdalgani1]

Hi team,
I'm reporting a reproducible runtime panic in the font extract command when processing CZ2 font images (.cz files) generated or modified via font edit. The error occurs specifically during the decompression step in CZ2 files, and it happens consistently on files with exact-length data boundaries. This prevents extracting images or info from edited fonts, blocking workflows like font modification for game localization (e.g., adding Arabic glyphs to Japanese fonts in LucaSystem-based games like Kanon steam).

Im using mac. and this problem only happen in the fonts i edit by the tool. when i add arabic characters, it will output everthing correctly but when i try to make png and txt to see the result it just make this error

/Users/abdalganiallaham/Downloads/LuckSystem_mac_x86_64/LuckSystem_mac font extract -s /Users/abdalganiallaham/Documents/Games/Kanon/files/newarfont/ゴシック24 -S /Users/abdalganiallaham/Documents/Games/Kanon/files/newarfont/info24.txt -o /Users/abdalganiallaham/Documents/Games/Kanon/files/newarfont/new.png -O /Users/abdalganiallaham/Documents/Games/Kanon/files/newarfont/new.txt
fontExtract called
panic: runtime error: index out of range [4607423] with length 4607423

goroutine 1 [running]:
lucksystem/czimage.(*Cz2Image).decompress(0xc00018e630)
/home/runner/work/LuckSystem/LuckSystem/czimage/cz2.go:69 +0x345
lucksystem/czimage.(*Cz2Image).GetImage(0xc00018e630, 0x1eec2e, 0x1eec2f)
/home/runner/work/LuckSystem/LuckSystem/czimage/cz2.go:84 +0x4e
lucksystem/font.LoadLucaFont(0xc000200000, 0x45451, 0x45452, 0xc000246000, 0x1eec2e, 0x1eec2f, 0x0)
/home/runner/work/LuckSystem/LuckSystem/font/font.go:75 +0xd4
lucksystem/font.LoadLucaFontFile(0x205be18d7, 0x48, 0x205be1887, 0x4c, 0x1)
/home/runner/work/LuckSystem/LuckSystem/font/font.go:60 +0x1b1
lucksystem/cmd.glob..func4(0x17acf00, 0xc000175600, 0x0, 0x8)
/home/runner/work/LuckSystem/LuckSystem/cmd/fontExtract.go:25 +0xce
github.com/spf13/cobra.(*Command).execute(0x17acf00, 0xc000175580, 0x8, 0x8, 0x17acf00, 0xc000175580)
/home/runner/go/pkg/mod/github.com/spf13/cobra@v1.5.0/command.go:876 +0x2ec
github.com/spf13/cobra.(*Command).ExecuteC(0x17ac280, 0xc000134010, 0xa, 0xa)
/home/runner/go/pkg/mod/github.com/spf13/cobra@v1.5.0/command.go:990 +0x375
github.com/spf13/cobra.(*Command).Execute(...)
/home/runner/go/pkg/mod/github.com/spf13/cobra@v1.5.0/command.go:918
lucksystem/cmd.Execute()
/home/runner/work/LuckSystem/LuckSystem/cmd/root.go:39 +0x3a
main.main()
/home/runner/work/LuckSystem/LuckSystem/main.go:12 +0x25

if i used font that have only arabic support and no english or japanease it will work by showing only arabic characters in the photo but by font support all. it will give correct sized file. but never work. i tried to cut last bit but didnt work.

[abdalgani1]

i tried older version also to make sure maybe old version will work. so i tried v2.3.0 which first supported kanon. and it give me diffrent resualts. it didnt even allow me to make a font form the first!!!

/Users/abdalganiallaham/Downloads/LuckSystem_mac_x86_64(1)/LuckSystem_mac font edit -s /Users/abdalganiallaham/Documents/Games/Kanon/files/fonts1/ゴシック24 -S /Users/abdalganiallaham/Documents/Games/Kanon/files/fontinfo/info24 -f /Users/abdalganiallaham/Documents/Games/Yomogi-Regular.ttf -o /Users/abdalganiallaham/Documents/Games/Kanon/files/fonts1/ゴシック24_arnew.cz -O /Users/abdalganiallaham/Documents/Games/Kanon/files/fontinfo/info24_arnew.txt -r
fontEdit called
panic: runtime error: index out of range [4607939] with length 4607939

goroutine 1 [running]:
lucksystem/czimage.(*Cz2Image).decompress(0xc000162630)
/home/runner/work/LuckSystem/LuckSystem/czimage/cz2.go:69 +0x345
lucksystem/czimage.(*Cz2Image).GetImage(0xc000162630, 0x201d37, 0x201d38)
/home/runner/work/LuckSystem/LuckSystem/czimage/cz2.go:84 +0x4e
lucksystem/font.LoadLucaFont(0xc000200000, 0x45451, 0x45452, 0xc000246000, 0x201d37, 0x201d38, 0x0)
/home/runner/work/LuckSystem/LuckSystem/font/font.go:75 +0xd4
lucksystem/font.LoadLucaFontFile(0x205aba884, 0x43, 0x205aba837, 0x49, 0x1)
/home/runner/work/LuckSystem/LuckSystem/font/font.go:60 +0x1b1
lucksystem/cmd.glob..func3(0x17acc60, 0xc00011e420, 0x0, 0xb)
/home/runner/work/LuckSystem/LuckSystem/cmd/fontEdit.go:27 +0xf0
github.com/spf13/cobra.(*Command).execute(0x17acc60, 0xc00011e370, 0xb, 0xb, 0x17acc60, 0xc00011e370)
/home/runner/go/pkg/mod/github.com/spf13/cobra@v1.5.0/command.go:876 +0x2ec
github.com/spf13/cobra.(*Command).ExecuteC(0x17ac260, 0xc00001e0f0, 0xd, 0xd)
/home/runner/go/pkg/mod/github.com/spf13/cobra@v1.5.0/command.go:990 +0x375
github.com/spf13/cobra.(*Command).Execute(...)
/home/runner/go/pkg/mod/github.com/spf13/cobra@v1.5.0/command.go:918
lucksystem/cmd.Execute()
/home/runner/work/LuckSystem/LuckSystem/cmd/root.go:39 +0x3a
main.main()
/home/runner/work/LuckSystem/LuckSystem/main.go:12 +0x25

[wetor]

CZ2 format images are currently unavailable.
It is recommended to create font files in CZ1 or CZ0 format. LucaSystem generally allows the use of fonts in other formats (even if they are different from the original format)

If possible, I would like you to upload a few sample files of CZ2 (although it will not be fixed in the short term)

[abdalgani1]

aaaa thats whyyyy i seeeee.
i will try to make new cz1 or even cz0 by the tool hopping it will work.
Thank you for info. and for the hope. i was almost about to give up..

having anything work in the game really important because its mean game will be translated to arabic or no
i will upload samples of cz2 with there info files. and take your time to add support for it.

https://www.mediafire.com/file/eznu9g1u804mzhr/Cz2+font+samples.zip/file

[abdalgani1]

aa. that dont want to work. all what i wanted to get the font photo and draw arabic latters instead of kanjis... aahhh

[abdalgani1]

what I noticed after a lot of tries: export cz2 gives wrong photo. It makes it for some reason have an extra empty column on the right. This makes the resolution of the photo wrong. For example, normal size 30 photo should have a resolution of 2232 x 3104 but the tool gives 2232 x 3136, which is exactly the difference of the one extra column. Also, it cuts the letters in the first line a little bit. You can see that.

When I try to import the correct photo with the correct resolution it gives me an error:
I1026 16:55:19.773162 43574 cz2.go:117] 图片大小不匹配，应该为 w3136 h2232
So the tool doesn't allow me to import it.

I don't know if that will help, but I thought to say it.

[abdalgani1]

so about cz1 font work on cz2. thats only partally correct. unfortunately

putting cz1 font will work only if you switch the font from the game. i mean game have 5 fonts. the default font should be not the font you edited. for example main font is gothtic so i should edit mincho. (also mincho have advantage to edit on mac because in mac any ten ten like in ゴ sometimes in terminal it will read as コ + ten ten. which will make game dont work )

then game will work then you will change the font and yeahhh cz1 font working!!!! but the latters really mess. so you need to edit font to match original info file.
because info file from little busters dont work. it will show empty text.
also you need to delete game save every time you forget to change the font back....... because font only work if its not selected as main
i think i can make tool fix when you run it it will fix save file without loosing your progress. but its binary so idk really

thats so much hard

so you need to edit the photo to match info file. but!!! using info file from not working cz2 font made by the tool may work! so you can insert latters that have diffrent width like arabic without any problems! but i will do more testing to know the limitations of that or even if it possible.

any way if it work then there is 100 way to add arabic support

edit:
making direct font cz1 in the tool will not work. becasue the new font will crash the game. you need to extract it first and then take old original png. and cut new latters from new broken font and paste them in the original png.
if you copy all the new photo to the old it will not work. you need to copy only the part you changed

then cz1 font will work on both LB_EN normally and kanon with some limitations

by this way i added correct arabic support to LB_EN

edit2:
the characters in kanon now working after i took exported photo from kanon font, cut the kanjis and then paste them in little busters png.
as i said using the png directly from kanon will not work even if it converted to cz1. but editing it will make work in both games

using this method for some reason made the game run directly from the edited font. and no need to delete the save. which amaizing

edit3:
any info file made by the tool dont work. and mess everything
i forgot to say that i added arabic support in cz2 games but its not that good. because i need info file. so in cz1 games i made perfect arabic support

[yoremi-trad-fr]

I couldn't test it at home because I don't have the LB game, but if you send me your modified font, I could test it on my end. In the meantime, this fix is provided by Claude in the lzw.go file.

Fix for CZ2 decompressLZW2 off-by-one bug (Issue #32)
Root cause
In czimage/lzw.go, function decompressLZW2() (line 114-123), the boundary check happens after reading the LZW code but before processing it:
go// CURRENT CODE (buggy)
for {
flag := bitIO.ReadBit(1)
if flag == 0 {
element = int(bitIO.ReadBit(15))
} else {
element = int(bitIO.ReadBit(18))
}
if bitIO.ByteOffset() > dataSize { // ← check AFTER read, BEFORE process
break // ← last valid code is silently dropped!
}
// ... process element ...
}
The last valid LZW code of each compressed block is read but never processed. The decompressed buffer ends up shorter than Width × Height, which triggers the panic in cz2.go:69:
panic: runtime error: index out of range [4607423] with length 4607423
On original game files the bug is silent because the lost code happens to produce padding bytes that aren't needed. After font edit recompresses the image with new dimensions (e.g., after adding Arabic glyphs), the block boundaries shift and the lost code now contains essential pixel data → buffer too short → panic.
Proof on the supplied Kanon file (ゴシック16)
Even on the original unmodified file, the bug is present — each block loses exactly 1 LZW code at the boundary:
Block[0]: codes_read=261886 codes_processed=261885 last_code_lost=True
decompressed=1238943 vs expected=1238943 diff=0 ← lucky: lost code was padding

Block[1]: codes_read=196626 codes_processed=196625 last_code_lost=True
decompressed=876129 vs expected=876129 diff=0 ← lucky: lost code was padding
After font edit changes the image dimensions, the recompressed blocks have different boundaries and the lost code is no longer padding → crash.
Fix
Move the boundary check before reading the code. This matches the reference implementation in lbee-utils (Rust):
In file czimage/lzw.go, replace lines 114-123:
go element := 0
for {
flag := bitIO.ReadBit(1)
if flag == 0 {
element = int(bitIO.ReadBit(15))
} else {
element = int(bitIO.ReadBit(18))
}
if bitIO.ByteOffset() > dataSize {
break
}
With:
go element := 0
for {
if bitIO.ByteOffset() >= dataSize-1 {
break
}
flag := bitIO.ReadBit(1)
if flag == 0 {
element = int(bitIO.ReadBit(15))
} else {
element = int(bitIO.ReadBit(18))
}
The condition >= dataSize-1 ensures at least 2 bytes remain before reading (minimum LZW code = 1 bit flag + 15 bits data = 16 bits = 2 bytes).
That's the only change needed. The rest of the function stays identical.
Testing
After applying the fix, the following should work without panic:
bash# 1. Edit font (add Arabic glyphs)
lucksystem font edit
-s ゴシック24 -S info24
-f arabic_font.ttf
-o ゴシック24_ar -O info24_ar.txt
-c arabic_charset.txt -a -r

2. Re-extract the edited font (previously crashed here)

lucksystem font extract
-s ゴシック24_ar -S info24_ar.txt
-o test.png -O test_charset.txt