Remove the done and error callbacks. The error callback is in an
error message. The done callback is replace with spa_pending.
Make enum_params take a callback and data for the results. This allows
us to push the results one after another to the app and avoids ownership
issues of the passed data. We can then extend this to handle the async
case by doing a _wait call with a spa_pending+callback+data that will
be called when the _enum_params returns and async result.
Add a sync method.
All methods can now return SPA_RESULT_IS_ASYNC return values and you
can use spa_node_wait() to register a callback when they complete
with optional extra parameters. This makes it easier to sync and
handle the reply.
Make helper methods to simulate the sync enum_params behaviour for
sync nodes.
Let the transport generate the sequence number for pw_resource_sync()
and pw_proxy_sync(). That way we don't need to keep track of numbers
ourselves and we can match the reply to the request easily.
Add return values to events and method callbacks. This makes it
possible to pass any error or async return value.
Add sync/done/error in both directions so that both proxy and resource
and perform/reply sync and produce errors.
Return a SPA_ASYNC from remote method calls (and events), keep the
sequence number in the connection.
With the core sync/done we can remove the client-node done method and
it's internal sequence number along with the seq number in method calls.
We can also use the method/event async return value to perform a sync
with as the unique sequence number for this method.
Add sync method and done/error event to proxy and resource.
