We should scope these as narrowely as possible to avoid side effects.

Avoid having to buffer everything we want to discard, and instead do it
piece by piece. This is more efficient, and avoids hitting any limits on
the buffering.

Note that this is safe here because we already know we have all the
compressed data. It would not be safe for a general input stream.

It seems MFT h264 decoder does not support frame cropping. Which
means that if frame width or height is not multiple of 16 then
decoded output can potentially be used with wrong offset. This
code adds explicit parsing of SPS to extract cropping information
to use, and will apply cropping if reported size differs from
expected.

This is the standard method of finding it on Unix systems, so make sure
we use it. Still keep a fallback, though, for other systems, e.g.
Windows.

FFMPEG is needed by the RFB library, so all the details about it should
only be applied there and not for other components.

This is the standard method of finding it on Unix systems, so make sure
we use it. Still keep a fallback, though, for other systems, e.g.
Windows.

Modern cmake has better support for adding source files and libraries
incrementally, so let's use that to clean things up.

These checks depend on accessRights being set up, this has only happened
if we have done the QUERYING steps.

Properties should be initialized in order to avoid random values in
case they are used earlier than expected.

It's a bit field so it's easier to decode in hex.

The browsers allow users to make an exception for expired certificates,
so we should probably also.

Otherwise we can get crashes on NULL dereference. This should only
happen on reverse connections where we don't have a server address.

Ubuntu 20.04
gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
libx264-dev:amd64 2:0.155.2917+git0a84d98-2

[ 11%] Building CXX object common/rfb/CMakeFiles/rfb.dir/H264LibavDecoderContext.cxx.o
tigervnc/common/rfb/H264LibavDecoderContext.cxx: In member function ‘virtual bool rfb::H264LibavDecoderContext::initCodec()’:
tigervnc/common/rfb/H264LibavDecoderContext.cxx:50:40: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
   50 |   AVCodec *codec = avcodec_find_decoder(AV_CODEC_ID_H264);
      |                    ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
      |                                        |
      |                                        const AVCodec*
make[2]: *** [common/rfb/CMakeFiles/rfb.dir/build.make:895: common/rfb/CMakeFiles/rfb.dir/H264LibavDecoderContext.cxx.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:597: common/rfb/CMakeFiles/rfb.dir/all] Error 2
make: *** [Makefile:130: all] Error 2

Avoid duplication, and add logging for some more error conditions so
it's possible to see in the logs why a resize has failed or produced
unexpected results.

Linux implementation using ffmpeg

This is a regression from ad0f061. If a VMware cursor rect was split up
over multiple read()s then the stream would become corrupted as we set
the restore point at the wrong place.

The generally recommended way is to include it from source files, not
headers. We had a mix of both. Let's try to be consistent and follow the
recommended way.

Can be helpful to see what encodings were actually used during a
connection, and how they performed.

Gives a bit more context where this error happened.

Single CPU machines are extremely rare now, so let's avoid the hassle of
multiple code paths.

The certificates might still be fine using the system trust store, or
the user can make an exception. So let's just log and continue on.

This got very common after 960c7d2 where we now always have a default
value for these settings.

This fixes regression introduced by the extended clipboard extension.
Previously it was possible for the server to hold on to the CLIPBOARD
selection even if another application took ownership of PRIMARY. This is
important to handle the common use case of selecting something in order
to paste over it.

The new request based model doesn't readily support this as we assume
the client has lost its data once we push the new PRIMARY selection to
it. So to handle this we have the maintain a cache of the client's data,
and make sure to fill that cache before we do anything that might cause
the client to lose the data.

The call of gnutls_set_default_priority_append() expects a normal priority
string, which means it must not start with ':'.

Let's avoid making this too complex and force every user to know about
magical functions.

Allows the default value to be dynamically generated in a buffer that is
reused.

Our current architecture doesn't support waiting for a response here, so
don't even try or we'll just get an error.

The session might have died, or failed to initialise properly, so be
prepared for gnutls_bye() to be unable to do its job.

We would leak the security module below the top client VeNCrypt module,
meaning that those modules would not get a chance to shut down
gracefully.

It's perfectly safe to delete NULL pointers, so simplify things by
removing these checks.

CharArray should always be null-terminated. There is a potential
scenario where this all might lead to crash. In Password we call
memset(), passing length of the array we get with strlen(), but
this won't return correct value when the array is not properly
null-terminated.

This change makes it possible for re-synchronizing the remote cursor on
the vncviewer when in fullscreen mode. This is done by locally moving
the cursor position to what the server thinks it should be.

Now SDL games should work!

This change adds support for the VMware Mouse Position
pseudo-encoding[1], which is used to notify VNC clients when X11 clients
call `XWarpPointer()`[2]. This function is called by SDL (and other
similar libraries)  when they detect that the server does not support
native relative motion, like some RFB clients.

With this, RFB clients can choose to adjust the local cursor position
under certain circumstances to match what the server has set. For
instance, if pointer lock has been enabled on the client's machine and
the cursor is not being drawn locally, the local position of the cursor
is irrelevant, so the RFB client can use what the server sends as the
canonical absolute position of the cursor. This ultimately enables the
possibility of games (especially FPS games) to behave how users expect
(if the clients implement the corresponding change).

Part of: #619

1: https://github.com/rfbproto/rfbproto/blob/master/rfbproto.rst#vmware-cursor-position-pseudo-encoding
2: https://tronche.com/gui/x/xlib/input/XWarpPointer.html
3: https://hg.libsdl.org/SDL/file/28e3b60e2131/src/events/SDL_mouse.c#l804

Some of these were incorrectly calculated so the server or client would
wait too long before proceeding with decoding.

Change all of these to be a more explicit calculation to avoid such
issues in the future.

We computed a safe area if a client gave us a bogus one, but we didn't
actually use it. Fix this properly and make sure we don't pass on bad
coordinates further.

So the current clipboard state is properly reflected in the desktop
session.

This was out of sync with the client handling for no good reason.

The peer expects a response, so we should also be able to respond that
there is no clipboard data currently available.

The extended clipboard protocol has the ability for the peer to request
things to be sent automatically, without a request message. Make sure we
honor such settings.