Do not hard error if libfuse is not present

[probonopd]

We could use dlopen ("/usr/lib64/libfuse.so.2", RTLD_LAZY); like on http://www.dwheeler.com/program-library/Program-Library-HOWTO/x172.html to print a nice message saying you can extract or mount the ISO if libfuse is not present.

Message:
It looks like libfuse is not installed on your system. To run this AppImage, you can loop-mount it or extract its contents, e.g. 7zx. See https://github.com/probonopd/AppImageKit/wiki/FUSE for more information.

[RazZziel]

Very interesting. According to the manual, dlopen("libfuse.so.2", RTLD_LAZY); would be more advisable, because it'd look for the library in the standard paths, although a fallback could be setup to find the library for instance in /tmp/libfuse.so.2, where we can download it without messing up the system, specially on 32bit AppImages on 64bit systems, where 32bit libfuse.so.2 is difficult to install.

[hideout]

nice dlopen sounds good for that problem

2016-03-30 7:30 GMT+02:00 Ismael Barros² notifications@github.com:

Very interesting. According to the manual, dlopen("libfuse.so.2",
RTLD_LAZY); would be more advisable, because it'd look for the library in
the standard paths, although a fallback could be setup to find the library
for instance in /tmp/libfuse.so.2, where we can download it without messing
up the system, specially on 32bit AppImages on 64bit systems, where 32bit
libfuse.so.2 is difficult to install.

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#123 (comment)

[probonopd]

dlopen("libfuse.so.2", RTLD_LAZY); would be more advisable

Correct. Anyone volunteers to do a PR?

[crayxt]

Will this cover the case when user is not a member of fuse group?

[RazZziel]

I don't think so, but at least we can warn the user

[probonopd]

KDevelop IRC thinks this would be a good idea, since a good error message helps in these cases.

[probonopd]

Here is an example of how to do this:
https://github.com/Efreak/apt-cacher-ng/blob/bb751da674c03ea81f0b4381c606b537c853b679/fs/httpfs.cc#L783-L807

Now, how do I get this into https://github.com/probonopd/appimagetool/blob/master/runtime.c? Probably it has to go into squashfuse... hl.c looks similar to the one linked above in that it calls fuse_main() but we are using ll.c iirc - so probably we need to dlsym significantly more than in the example above.

[darealshinji]

I have an idea:
You could build the main part of the runtime as a shared library (everything requiring libfuse). Create a header file from it (xxd -i AppImage.so > AppImage_so.h), include it in the the now smaller runtime binary, and when running the binary it will dump the library into a temporary file and try to dlopen() it. If it fails because libfuse is missing, print something useful.

[probonopd]

Cool idea but makes the code larger and more complex, and is not so clean (clutters /tmp).

What do you think, could we somehow cleverly use weak symbols?

[darealshinji]

I gave it a try: https://github.com/darealshinji/AppImageKit/tree/dlopen
The binaries are linked against libdl and not libfuse, but I didn't check if the runtime actually works when you build an AppImage with it.

[probonopd]

Can you upload a build here? Thanks.

[darealshinji]

build.zip

[probonopd]

@darealshinji hats off, it works 👍 💯 🥇

Please send PR.

[darealshinji]

Whoa, nice. Can you check what happens if libfuse is not present? Right now the invoked macros will call exit(1). I don't know if that's ok. Also, what kind of error message do you want? Something including a link to the wiki maybe?

[probonopd]

This is the error message that appears when the library is not available:

me@host:~$ ./XChat_IRC-x86_64.AppImage 
dlopen(): error loading libfuse.so.2
execv error: No such file or directory

But even in this case, this works:

me@host:~$ ./XChat_IRC-x86_64.AppImage --appimage-extract

So as the message, how about this?

[probonopd]

When libfuse is not present, we currently get

me@host:~$ /home/me/Downloads/appimagetool-x86_64.AppImage 
dlopen(): error loading libfuse.so.2
AppImages require FUSE to run. 
You might still be able to extract the contents of this AppImage 
if you run it with the --appimage-extract option. 
See https://github.com/probonopd/AppImageKit/wiki/FUSE 
for more information

execv error: No such file or directory

Can you get rid of the execv error: No such file or directory?

[darealshinji]

#365

[TheAssassin]

This has been solved in #365.

[DevRelMalima]

Try run this
me@host:~$ /home/me/Downloads/appimagetool-x86_64.AppImage --appimage-extract

this should work