Added /usr/local/include/ykpiv to CGO include path for Linux

[sybrenstuvel]

On Ubuntu Linux (and derivatives, like the Mint Linux I'm using) the bundled version of yubico-piv-tool is 1.4.2, and is incompatible with this Go library (also see #16).

This PR makes it possible to build the latest version of yubico-piv-tool and install it to /usr/local. Without this change to the CGO parameters, the headers wouldn't be found in /usr/local/include/ykpiv.

It's still necessary to ensure /usr/local/lib is mentioned in /etc/ld.so.conf for the linker to find the library.

[sybrenstuvel]

By the way, an alternative approach would be, instead of adding /usr/include/ykpiv to the include directories, to just use #include <ykpiv/ykpiv.h>. This would let the compiler find the header file in /usr/include as well as /usr/local/include.

This would certainly work on Linux, but I don't know the implications for Windows.

[paultag]

Switching to /usr/local will break systems where you've installed it using a system installer. I like the include directories idea better - this change will fix one configuration but break every current user's configuration :)

Maybe we can test on a Windows box - iirc the SDK is dropped in the CWD and you build linking against those. Windows currently uses #cgo windows CFLAGS: -I./win/include/ykpiv/, so we could just change that to be #cgo windows CFLAGS: -I./win/include and fix the imports.

I like that idea much more, any chance we could rework this patch to do that? I'd absolutely merge something doing that. It's also more semantically correct.

[sybrenstuvel]

I can definitely rework the patch to do that, no problem :)

[paultag]

You rock, thank you!

[tianon]

https://packages.debian.org/sid/libykpiv-dev comes with pkg-config files (ykcs11.pc and ykpiv.pc) -- are those part of the upstream distribution too, or are those added by the Debian maintainers? (That could be another option to help insulate against the issue, ala // #cgo pkg-config: ...)

[paultag]

@tianon amazing idea if so!

[tianon]

ykpiv.pc does appear to be part of https://developers.yubico.com/yubico-piv-tool/Releases/yubico-piv-tool-1.7.0.tar.gz, at least! (not sure if that helps Windows, but it should help with /usr/local vs /usr)

[paultag]

Yeah I think tianon's right here 👍👍