For flatpaks we need to be able to support older v0 protocol clients.
To handle this we have:
- the connection detects an old client when it receives the first
message. It can do this by checking the sequence number, on old
versions it contains the message size and is never 0, on new
clients the sequence number is 0.
- We add a new signal at the start of the connection with the detected
version number. This installs the right version of the core proxy.
We also move the binding of the client until the hello message is
received. This way we can have a new client connect (portal),
hand over the connection to an old client, which then removes the
client binding again in the hello request with a v0 version.
There are some changes to the passing of fds in v0 vs v3 which need
to investigated some more.
- bump version of our interfaces to 3. This makes it possible to
have v0 and v3 protocol marshal functions.
- Add version number in the proxy. This is mostly automatically done
internally based on the version numbers the library is compiled
with. Where the version number was in the API before, it is now
actually used to look up the right protocol marshal functions. For
Proxies there is usually just 1 version, the current one. It is the
server that will support different versions.
- Add v0 compat marshal functions to convert from and to v0 format.
This has some complications. v0 has a type map it keeps in sync
with the server. For this we have a static type map with mappings
to our own v3 types. Pods are mostly the same except for objects
that used to have arbitrary pods in v0 vs spa_pod_prop in v3. Also
convert between v0 spa_pod_prop and v3 spa_pod_choice.
Formats and commands are also slightly different so handle those
mappings as well.
We only have marshal functions for the server side (resource)
v0 functions.
- Add v0 compatible client-node again. It's a bit tricky to map, v0
client-node basically lets the server to the mixing and teeing
and just does the processing of the internal node.
