Make FFI work on heroku cedar-14

[glitch003]

This small change adds a search path to the library lookup logic. It specifically adds the "/lib/x86_64-linux-gnu/" path which is where libraries live on heroku cedar-14.

This change keeps backwards compatibility with the existing search paths that were already present :)

[trostli]

nice. i just ran into this issue myself

[trostli]

Actually the other place where libraries live on Heroku is /app/vendor. Can you add that path too? That is where they are installed when using buildpacks

[glitch003]

@trostli sure, done

[trostli]

Thanks!

[tduehr]

That needs to be created specific to the platform currently being used rather than being hard coded to x86.

[danielpclark]

Shouldn't a server environment use values provided by ENV? This would allow any server or system to provide proper configurations which is easy enough to document.

# # Example
# ENV['FFI_LIBS'] = "/app/vendor/;/lib/x86_64-linux-gnu/"
path = ['/usr/lib/','/usr/local/lib/']
path += ENV['FFI_LIBS'].to_s.split(/[;,]/)
# # Path is now
# ['/usr/lib/', '/usr/local/lib/', '/app/vendor/', '/lib/x86_64-linux-gnu/']
path.find do |pth|
  File.exist?(pth + libname)
end

[trostli]

good suggestion @danielpclark

[gsdean]

is this getting merged?

[headius]

@gsdean I see @tduehr comment above but no follow-up commits, so I'm not sure if this is ready or not.

[larskanis]

There is another PR which modifies the search path logic: #616 . To be honest, I would rather remove these hardcoded paths than adding random new ones. See my comment here.

[tduehr]

Please rebase this if it's still an issue.

[dmtask]

When will this be finished?

[larskanis]

This will not be merged. We'll not add architecture specific paths that are wrong on all other architectures.

FFI is not responsible for fixing misconfigurations in the library setup. FFI respects the library paths that are provided by the operating system. This is /etc/ld.so.conf and LD_LIBRARY_PATH for instance on Linux. They should be used instead of hardcoded paths within FFI.

To the contrary we'll remove the static paths entirely in a future release or limit then to operating systems that really need them.