This fixes several integer overflow problems in the POD parser, as well
as fixing a returns-twice warning from GCC and integer truncation
problems in SPA_FLAG_CLEAR and SPA_ROUND_DOWN_N. The integer overflows
can result in a tiny POD being treated as a huge one, causing
out-of-bounds reads.
Extend version 3 protocol with message footers, which are for passing
around global state data that is not addressed to a specific object.
The extension is backward compatible with previous v3 clients, and won't
e.g. result to error spam in logs.
The footer is a single SPA POD, appended after the main message POD.
Because both the protocol message and the message POD record their
length, it's possible to append trailing data. Earlier clients will
ignore any data trailing the message POD.
The footer POD contains a sequence [Id opcode, Struct {...}]*,
so there is room to extend with new opcodes later as necessary.
There are separate marshal/demarshal routines for messages aimed at
resources and proxies.
The pw_remote object is really a wrapper around the pw_core_proxy.
The events it emits are also available in the core proxy and are
generally awkward to use.
With some clever new pw_core_proxy_* methods and a pw_core_connect
to create the core_proxy, we can convert all code away from pw_remote.
This is a first step in this conversion, using the pw_remote behind
the scenes. It leaks into some places because it really needs to become
its own struct in a next step.
Make the protocol client connect call async with a callback when it
completes.
Move the connect methods into separate files, add an empty connect
method that will use the screencast portal to get a pipewire fd.
Use the remote intention to get the connect method.
Add some better error reporting.
