Use feedback instead of metadata for keep-alive in RAOP

[postlund]

Short feature/function description I currently send metadata periodically in RAOP to keep the connection alive according to a post I found over at owntone. But there's actually a feedback endpoint dedicated for this purpose, so I should move over to that instead.

What needs to be done?

• Add a method in RTSP that sends feedback
• Call feedback method from keep-alive loop instead of set_metadata

Is this a breaking change? No

Anything else worth knowing? No

[Schlaubischlump]

The feedback endpoint is not available on older devices / firmware versions, is it ? What happens if a request is send to a device, which does not support the endpoint ?

It would be a good idea to either check the ANNOUNCE response to see if the feedback endpoint is available and only send it if required or send and OPTIONS request every 30 seconds as heartbeat like RAOP-Player does. OPTIONS is always available, no matter how outdated the firmware or device is.

[postlund]

Right, that might be true of course. Would be interesting to know when it was introduced. Anyways, it's probably hard to see if it's supported as it's a POST request. OPTIONS will contain POST if that's supported, but that might not necessary mean that the /feedback endpoint is available. I'm leaning towards using the feedback method as I find that to be cleaner and let potential problems emerge as an issue later.

[Schlaubischlump]

Good point, that makes it indeed very hard to detect if the 'feedback' endpoint is available. Sadly there is not much information about the endpoint out there. First time I read about it was around the time iOS 11.4 for the original Homepod came out. Maybe its part of the Airplay 2 protocol specification and not part of the original AirTunes v2. I'm not sure.

Like you said, keeping the future in mind, it might be best to just use it and see if it causes any problems down the road for any device.

[postlund]

I can confirm that the presence of POST does not necessarily mean that /feedback is supported. My old Yamaha receiver has AirPlay support (AirTunes v2 I presume) and it reports that POST is supported:

2021-05-31 14:01:35 DEBUG [pyatv.support.http]: Sending RTSP/1.0 message: b'OPTIONS * RTSP/1.0\r\nUser-Agent: AirPlay/540.31\r\nCSeq: 1\r\nDACP-ID: 27737845AA20C901\r\nActive-Remote: 1857361097\r\nClient-Instance: 27737845AA20C901\r\n\r\n'
2021-05-31 14:01:35 DEBUG [pyatv.support.http]: Received: b'RTSP/1.0 200 OK\r\nPublic: ANNOUNCE, SETUP, RECORD, PAUSE, FLUSH, TEARDOWN, OPTIONS, GET_PARAMETER, SET_PARAMETER, POST, GET\r\nServer: AirTunes/103.2\r\nCSeq: 1\r\n\r\n'

Sending feedback is not however:

2021-05-31 14:01:07 DEBUG [pyatv.support.http]: Sending RTSP/1.0 message: b'POST /feedback RTSP/1.0\r\nUser-Agent: AirPlay/540.31\r\nCSeq: 1\r\nDACP-ID: B5B21A57B164B24A\r\nActive-Remote: 2199282051\r\nClient-Instance: B5B21A57B164B24A\r\n\r\n'
2021-05-31 14:01:07 DEBUG [pyatv.support.http]: Received: b'RTSP/1.0 501 Not Implemented\r\nServer: AirTunes/103.2\r\nCSeq: 1\r\n\r\n'

So, that puts me in the spot that I need different methods of sending keep-alive messages depending on what is supported. I guess I can just try to call /feedback and use the response to determine what method to use.

[Schlaubischlump]

Is it even necessary to send a feedback request on these old devices ? In my experience only the homepod and homepod mini require the keep-alive signal. Shouldn't, check if feedback produces a valid response, otherwise do not send any more feedback signals be enough ?

[postlund]

Yeah, that sounds even more correct now when you say it. That's what I will do 👍 But first I'm gonna do some work on a fake device so I can get at least some basic functional tests up and running.

[postlund]

Fixed by #1119.