IO::Compress is not fatpack friendly

[miyagawa]

This might not be the best place to discuss the issue, but:

CPAN::Common::Index depends on IO::Compress, which dependencies contain XS (Compress::Raw::Bzip2 and Compress::Raw::Zlib) https://metacpan.org/source/PMQS/IO-Compress-2.068/META.json#L35

They're part of core as of 5.10.0, but as I want to integrate CPAN::Common::Index to cpanm, that cannot be fatpacked back to 5.8.x.

I suppose the possible workaround would be:

• make the Compress::Raw::* a soft dependency in IO::Compress (maybe it is already, but i'm not sure)
• Use a system provided gzip command line in C::C::I
• else?

[dagolden]

As I mentioned in Berlin, we could also make IO::Compress itself optional and -- if not available (or XS Raw not available) -- mirror the uncompressed version of the index instead (or die for a compressed local package).

[eserte]

What about IO::Zlib? It's in core, uses XS code if it's available, and may fallback to external gzip if not.

[skaji]

I want to resolve this issue and to make CPAN::Common::Index fatpack friendly with perl 5.8.

Currently CPAN::Common::Index depends on 2 modules

• (a) IO::Compress (hence XS modules Compress::Raw::Bzip2 and Compress::Raw::Zlib)
• (b) Path::Tiny (hence XS modules Digest::SHA)

To make CPAN::Common::Index fatpack friendly, we need to eliminate these 2 dependencies.

As for IO::Compress

• (option a1) As suggested by @xdg, make IO::Compress itself optional, if not available, mirror the uncompressed version of the index instead (or die for a compressed local package)
• (option a2) As suggested by @eserte, use IO::Zlib (note: it seems that IO::Zlib assumes gzip files do not contain white spaces in their names)
• (option a3) Use external gzip command manually (with eg, File::Which, IPC::Run3)

As for Path::Tiny

• (option b1) Use File::Spec, File::Basename, etc, instead of Path::Tiny

I'm happy to create a pull request for these, but before that, I would like your comments. @xdg @miyagawa @eserte What do you think?

[eserte]

Theoretically IO::Zlib could be made shell meta character safe by using open "-|" list syntax, at least on platforms which supports this (sadly, on Windows this is still unsupported).

[xdg]

Someone could test Path::Tiny with older Digest and see what happens if Digest::SHA is unavailable.

I'm open to the possibility of not requiring a version of Digest/Digest::SHA that mandates 5.10 for fatpacking, but I'd want to think carefully about it. Note that the prereqs are not enforced in the code, only in the Makefile.PL.

[skaji]

@xdg Because CPAN::Common::Index::Mirror uses File::Spec and File::Basename directly, I think we can use File::Spec and File::Basename directly in CPAN::Common::Index::LocalPackage.

[xdg]

My thoughts about IO::Compress:

• external commands aren't portable
• IO::Zlib isn't core in 5.8
• I think all CPAN mirrors also offer uncompressed versions of the files
• I'd rather fall back to uncompressed files on 5.8 if IO::Compress et al. isn't available rather than do something unportable

[skaji]

@xdg Thank you for clarifying your thoughts. I understand portability should come first here, and I agree that external commands aren't portable.

Now I would like to work on (option a1).