Implement a DACP control interface

[aleszczynskig]

Is your feature request related to a problem? Please describe.
When using forked-daapd, it can connect via a DACP interface to the source device to enable hardware control of the source (playback controls/ volume controls). It is particularly useful when using spocon with a pipe connecting forked-daapd. Can you implement a DACP interface so that playback controls and volume can be controlled. The control details will need to be send to forked-daapd over the metadata pipe. I have included the command in the bottom section.

Describe the solution you'd like
Implement a DACP interface and share the details over the metadata pipe.

Describe alternatives you've considered
Nothing. I do not believe there are any other options currently.

Additional context

Taken from https://github.com/mikebrady/shairport-sync-metadata-reader

daid -- this is the source's DACP-ID (if it has one -- it's not guaranteed), useful if you want to remotely control the source. Use this string to identify the source's remote control on the network.
acre -- this is the source's Active-Remote token, necessary if you want to send commands to the source's remote control (if it has one).
dapo -- the payload is the port number (as text) of the source's remote control, to which commands should be sent. It is 3689 for iTunes but varies for iOS devices.

[devgianlu]

@aleszczynskig Do you have a capture (like piping the data from the DACP controller to a file) of what the input data would look like? I am struggling to understand what the device being controlled receives.

[aleszczynskig]

@devgianlu - sorry for the delay. Super busy at the moment. Unfortunately I do not have a capture. This project seems to offer an implementation though. I appreciate it is not in written in java however maybe this repo would provide some useful insight?

https://github.com/melloware/dacp-net

[devgianlu]

Wait a second, is the control interface a pipe or an HTTP server? I thought it was a pipe and the stuff I found on the internet didn't make sense, but they do if it's HTTP.

[aleszczynskig]

It's an HTTP interface. You provide the details of that interface over the metadata pipe so that forked-daapd or similar can establish a connection back to it.