image/gif: encoded images incompatible with some viewers

[powerman]

What version of Go are you using (go version)?

go version go1.10.3 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/powerman/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/powerman/go"
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="x86_64-pc-linux-gnu-gcc"
CXX="x86_64-pc-linux-gnu-g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build380688713=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Just gif.Decode and then gif.Encode: https://play.golang.org/p/AMc63K13IHZ

What did you expect to see?

Encoded image must be valid.

What did you see instead?

Some image viewers and browsers show encoded image correctly, some (gqview, geeqie, qiv, xloadimage…) show broken image.

More details with attached image examples are here: BestImageViewer/geeqie#621

[minaevmike]

Hi @powerman . I think that your problem is similar to this one. Imagemagick tools works fine with this image. Am i right, that all of this viewers is based on gtk library?
Also there is an open bug for gdk-pixbuf https://gitlab.gnome.org/GNOME/gdk-pixbuf/issues/55

[powerman]

Thanks @minaevmike, you probably right, it's the same issue. I didn't tried every viewer, but from two tried by geeqie author one doesn't use GTK:

$ xloadimage out.gif                                                                           
out.gif is a 96x96 GIF image with 256 colors
Error reading GIF file: pixel stack overflow in PUSH_PIXEL()
$ ldd =xloadimage                                                                              
	linux-vdso.so.1 (0x000076c96ea14000)
	libX11.so.6 => /usr/lib64/libX11.so.6 (0x000076c96dfe5000)
	libtiff.so.5 => /usr/lib64/libtiff.so.5 (0x000076c96dd69000)
	libjpeg.so.62 => /usr/lib64/libjpeg.so.62 (0x000076c96dafd000)
	libpng16.so.16 => /usr/lib64/libpng16.so.16 (0x000076c96d8c2000)
	libm.so.6 => /lib64/libm.so.6 (0x000076c96d57a000)
	libc.so.6 => /lib64/libc.so.6 (0x000076c96d1b5000)
	libdl.so.2 => /lib64/libdl.so.2 (0x000076c96cfb1000)
	libxcb.so.1 => /usr/lib64/libxcb.so.1 (0x000076c96cd82000)
	libz.so.1 => /lib64/libz.so.1 (0x000076c96cb6a000)
	/lib64/ld-linux-x86-64.so.2 (0x000076c96e7f2000)
	libXau.so.6 => /usr/lib64/libXau.so.6 (0x000076c96c966000)
	libXdmcp.so.6 => /usr/lib64/libXdmcp.so.6 (0x000076c96c760000)
	libbsd.so.0 => /usr/lib64/libbsd.so.0 (0x000076c96c54a000)
	librt.so.1 => /lib64/librt.so.1 (0x000076c96c342000)
	libpthread.so.0 => /lib64/libpthread.so.0 (0x000076c96c122000)

So, while it looks like there is a bug in gdk-pixbuf, and probably a bug in some basic library used by xloadimage, still, it doesn't looks like a good idea to have image/gif generate files which can't be read by noticeable amount of existing viewers (all based on GTK plust all based on same basic lib as used by xloadimage, at least - to me this sounds "noticeable amount"). I'm pretty sure it is possible to generate gif files in some other way, more usual for all these viewers, because all(?) other non-Go tools which create gif files doesn't have this issue.

[bcmills]

(CC: @robpike for image/, @nigeltao for image/gif)

[robpike]

No idea. With no information about the actual issue, it's hard to do anything useful.

[makew0rld]

I believe this is the same issue as #33748. See this comment and ones below it that explain why this is happening.

[gopherbot]

Change https://golang.org/cl/354710 mentions this issue: compress/lzw: output a Clear code first, per GIF spec