Get error "Undefined reference to cap_xxx" when link libwebsockets built from master.

[RSATom]

Don't sure, but maybe it worth consider add libcap as dependency to libwebsockets.pc?

[lws-team]

It should look and see if you have libcap headers, and add it automatically:

https://libwebsockets.org/git/libwebsockets/tree/CMakeLists.txt#n559
https://libwebsockets.org/git/libwebsockets/tree/lib/plat/unix/CMakeLists.txt#n93

Is your pkgconf for libcap installed somewhere unusual?

[RSATom]

Ah... It's possible it my fault, and I just don't have libcap-dev installed... Sorry, closing.

[RSATom]

But on other side, why it sill uses cap_xxx functions? Maybe it miss ifdef guard? Let me check.

[lws-team]

It should use them if it finds the header during cmake

[RSATom]

Yes, it's something weird there... But please don't care - I'll try to find reason myself.

[lws-team]

Let me know if something to fix :-)

[RSATom]

It's something really strange. I've installed libcap-dev package (I'm on ubuntu 20.04) and rebuilt libwebsockets (from today's master). After that I've got following libwebsockets.pc

prefix="/usr/local"
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include

Name: libwebsockets
Description: Websockets server and client library
Version: 4.0.99-v4.0.0-225-g886e9326

Libs: -L${libdir} -lwebsockets
Cflags: -I${includedir}

i.e. there are no libcap reference there.

[RSATom]

I can investigate it myself, but maybe you will find issue much quicker...
Thanks in advance.

[lws-team]

OK I will do the same test tomorrow and see what happens.

[RSATom]

Some more info, I get LIB_LIST_AT_END=m;cap;dl on cmake run, but still nothing in .pc file...

[RSATom]

I think I found the reason: https://github.com/warmcat/libwebsockets/blob/master/lib/CMakeLists.txt#L273
When libwebsockets.pc is generating, LIB_LIST_AT_END not used in any way...

[lws-team]

Thanks for digging into it... IIUI it just needs this?

diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 6ed6b50e8..1ac0bc646 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -287,7 +287,7 @@ Name: libwebsockets_static
 Description: Websockets server and client static library
 Version: ${CPACK_PACKAGE_VERSION_MAJOR}.${CPACK_PACKAGE_VERSION_MINOR}.${CPACK_PACKAGE_VERSION_PATCH}
 
-Libs: -L\${libdir} -lwebsockets_static
+Libs: -L\${libdir} -lwebsockets_static ${LIB_LIST_AT_END}
 Libs.private:
 Cflags: -I\${includedir}"
 )

[RSATom]

It's not only about libwebsockets_static.pc but also about libwebsockets.pc.
Also, don't think ${LIB_LIST_AT_END} will work, just because it's semicolon separated list (i.e something like m;cap;dl), but it should be something like -lm -lcap -ldl.
And it's possible there are other problem exists (I don't sure 100% since I'm not an expert in creating .pc files) - besides -l<libname> arguments, it's possible it will require -L<libpath> arguments too.

[RSATom]

Some new find: according to pkg-config docs there are better way add dependencies from extern libraries - use Requires line in .pc file.

[RSATom]

Some more experimenting. It works fine if I edit libwebsockets.pc to something like this:

prefix="/usr/local"
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include

Name: libwebsockets
Description: Websockets server and client library
Version: 4.0.99-v4.0.0-225-g886e9326
Requires: libcap >= 2.0

Libs: -L${libdir} -lwebsockets
Cflags: -I${includedir}

[lws-team]

I fiddled with it a bit but I was not smart enough to understand how to autogenerate the pkgconfig format from what cmake has. I settled from having that maintained separately for optional packages...

https://libwebsockets.org/git/libwebsockets/commit?id=c8baeccfd76d324c1454cb9b57bf01a95ad5b500

is this enough or more libs need to be taken care about?

[RSATom]

@lws-team yes, it looks like it will work. The only question if libcap v2.0 is really minimal required version. I just never worked with libcap, so don't sure.

[lws-team]

Well, version in Fedora 32 is 1.9... upstream is 2.38 I don't think it uses anything so new, I changed it to not specify a version relationship. That's legal https://dev.gentoo.org/~mgorny/pkg-config-spec.html#package-list

I'll close it for now then.