GUACAMOLE-2268: Gate VNC UTF-8 (Extended Clipboard) support behind config check.

[bbennett-ks]

SendClientCutTextUTF8 and rfbClient.GotXCutTextUTF8 are only available in libvncserver/libvncclient 0.9.15+.

This adds configure checks for the UTF-8 (Extended Clipboard) APIs and guards the affected call sites with #ifdefs. When unavailable, the VNC client falls back to the classic SendClientCutText path.

Testing

libvncserver version 0.9.15:

autoreconf -I
./configure
…
checking for rfbClient.requestedResize... yes
checking for rfbClient.GotXCutTextUTF8... yes
…

libvncserver version 0.9.15:

autoreconf -I
./configure
…
checking for rfbClient.requestedResize... yes
checking for rfbClient.GotXCutTextUTF8... no
…

[necouchman]

Just FYI - this is fine, and I will merge as-is, but this can be simpler - the AC_CHECK_MEMBERS macro will automatically define HAVE_RFBCLIENT_GOTXCUTTEXTUTF8 for you. For example, we use this with RDP support and the VerifyCertificateEx:

guacamole-server/configure.ac

Lines 985 to 991 in c802cdc

	# Updated certificate verification callback (introduced with 2.0.0, not present
	# in 2.0.0-rc4 or earlier)
	if test "x${have_freerdp}" = "xyes"
	then
	AC_CHECK_MEMBERS([freerdp.VerifyCertificateEx],,,
	[[#include <freerdp/freerdp.h>]])
	fi

Obviously the defines end up a little less nicely-named than what you have, but the configure.ac ends up a little simpler.

[bbennett-ks]

Thanks for the tip! I modeled the fix based on support for libVNCserver support for the requestedResize. I'll keep this in mind for next my.

FYI, I implemented similar support for libVNCServer support FinishedFrameBufferUpdate. Once I began to test it, I realized the the base libVNCServer in GitHub supported FinishedFrameBufferUpdate so config support was not necessary.