Stable GnuPG interface, git should use GPGME

["Bernhard E. Reiter" <bernhard.reiter@intevation.de>]

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Dear Git-Devs,

git uses an pipe-and-exec approach to running a GnuPG binary 
as writen in the documentation [1]:

    gpg.program
           Use this custom program instead of "gpg" found on $PATH when making
           or verifying a PGP signature. The program must support the same
           command-line interface as GPG

please consider using libgpgme interfacing to GnuPG, because the gpg 
command-line interface is not considered an official API to GnuPG by the 
GnuPG-devs and thus potentially unstable. 

== Details

I'm involved in GnuPG development. For most applications using libgpgme is the 
way what GnuPG-devs would recommend, also see 

  https://wiki.gnupg.org/APIs .

GnuPG devs are making a good effort of trying to keep the command-line 
interface stable, though it is not for sure. Git is only using a small part 
of the interface, so the risk when keeping the current way is small. 
Still I believe git's stability and usability would profit when moving to 
libgpgme, especially with the coming move to GnuPG 2.2, better diagnosing 
messages and for cross-plattform usage.

== Usability problem with `gpg2` vs `gpg`

My use case today was signing and git by default found the `gpg` binary by 
default and the command failed. The reason is that I have `gpg2` installed 
and most applications use it right away. So git failed signing because 
the .gnupg configuration of the user was not ready for the old `gpg` which is 
still installed on Debian GNU/Linux for purposes of the operating system. If 
git would have used libgpgme, gpgme would have choosen the most uptodate 
version of `gpg` available (or configured) without me intervening via 
gpg.program. Now because of this problem you could adding a check for `gpg2` 
and fallback to `gpg`, but even better would be to move to libgpgme. >:)

Best Regards and thanks for maintaining Git as Free Software,
Bernhard

== how to respond

ps: Please copy me on replies as I am not on git@vger.kernel.org. 
pps: I've copied gnupg-devel@ so they can see I've send this report, you don't 
have to.


[1] 
https://github.com/git/git/blob/3bc53220cb2dcf709f7a027a3f526befd021d858/Documentation/config.txt
search for 'gpg.program'.

-- 
www.intevation.de/~bernhard (CEO)     +49 541 33 508 3-3
Intevation GmbH, Osnabrück, Germany; Amtsgericht Osnabrück, HRB 18998
Owned and run by Frank Koormann, Bernhard Reiter, Dr. Jan-Oliver Wagner

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