Harbor: multiple sources for same mount

[shizmob]

Hi! First of all, thank you for writing Liquidsoap, I've been investigating it for usage in my own radio and it seems very useful and thorough.

One feature I'm looking to implement is Icecast proxying/multiplexing: multiple people can connect to the same mount, and it will only relay the (meta)data for one of them according to some decision process (first-connected in my case). This is to facilitate hand-off between DJs and between a DJ and the AFK streamer.

I was looking through the documentation and source code, and it looked like to me that Harbor is hardcoded to only accept a single input per mount point. Is this assessment true, and/or could what I'm looking for be implemented in some other way?

[toots]

Hi,

Thanks for the nice words!

If I understand what you are doing well, then the right way to implement this in liquidsoap would be to assign each DJ their own harbor input and to decide later which of their stream is played, for instance in a switch or a fallback. Here's a quick example with 2 DJs:

dj1 = input.harbor("dj1")
dj2 = input.harbor("dj2")

live_source = fallback(track_sensitive=false,[dj1,dj2])

Hope that helps!

I'll close this here but feel free to continue the conversation in the issue if you need more details.

[shizmob]

Hi, thanks! I've considered that solution, but the main problem is that it will always prioritize dj1 over dj2 if I'm understanding it right, while I'd like to prioritize whoever connected first (DJs trying to mess with eachother does happen, and it'd be bad if one could just intrude in another one's stream simply by virtue of being earlier in the list).

[smimram]

I guess it should be doable to add that behavior to switch.

[toots]

You can code it:

is_connected = ref ""

def on_connect(name,_) =
  if !is_connected == "" then
    is_connected := name
  end
end

# Partial application limitation here..
def on_disconnect(name) =
  def fn() =
    if !is_connected == name then
      is_connected := ""
    end
  end
  fn
end

dj1 = input.harbor(on_connect=on_connect("dj1"),
                   on_disconnect=on_disconnect("dj1"),
                   "dj1")

dj2 = input.harbor(on_connect=on_connect("dj2"),
                   on_disconnect=on_disconnect("dj2"),
                   "dj2")

s = switch(track_sensitive=false, [
   ({!is_connected == "dj1"},dj1),
   ({!is_connected == "dj2"},dj2)
])

[shizmob]

Doesn't that essentially break if dj2 connects before dj1 disconnects, since dj1's on_disconnect call will reset it to ""? I guess a list could be used instead...

[toots]

Doesn't that essentially break if dj2 connects before dj1 disconnects, since dj1's on_disconnect call will reset it to ""? I guess a list could be used instead...

Ha true! Let's try another way:

connected = ref []

def on_connect(name,_) =
  if not list.mem(name,!connected) then
    connected := list.rev(list.add(name,list.rev(!connected)))
  end
end

# Partial application limitation here..
def on_disconnect(name) =
  def fn() =
    list.remove(name,!connected)
  end
  fn
end

dj1 = input.harbor(on_connect=on_connect("dj1"),
                   on_disconnect=on_disconnect("dj1"),
                   "dj1")

dj2 = input.harbor(on_connect=on_connect("dj2"),
                   on_disconnect=on_disconnect("dj2"),
                   "dj2")

s = switch(track_sensitive=false, [
   ({list.hd(default="",!connected) == "dj1"},dj1),
   ({list.hd(default="",!connected) == "dj2"},dj2)
])

I haven't tested the code but that should give you an idea.

The general philosophy we're trying to stick with for liquidsoap is to implement simple, elementary operators and build complex cases from them. As @dbaelde once quoted from someone else (?): "simple things should be simple but complex things should be possible".. 🙂