Add support for rodiojack backend.

The underlying `librespot` library already supports the JACK audio backend via `rodio`.
Enabling it in `spotifyd` turns out to be dead simple--just needed to add the config enum elements to pass it through!

Cargo.toml

@@ -58,6 +58,7 @@ default = ["alsa_backend"]
 portaudio_backend = ["librespot-playback/portaudio-backend"]
 pulseaudio_backend = ["librespot-playback/pulseaudio-backend"]
 rodio_backend = ["librespot-playback/rodio-backend"]
+rodiojack_backend = ["librespot-playback/rodiojack-backend"]
 
 [package.metadata.deb]
 depends = "$auto, systemd, pulseaudio"

docs/src/installation/Feature-flags.md

@@ -59,4 +59,16 @@ cargo build --release --no-default-features --features="rodio_backend"
 
 On Linux you will need the development package for alsa and make/gcc. (`libasound2-dev`,`build-essential` on debian, `alsa-lib-devel`,`make`,`gcc` on fedora)
 
-[mpris-specification]: https://specifications.freedesktop.org/mpris-spec/latest/
+[mpris-specification]: https://specifications.freedesktop.org/mpris-spec/latest/
+
+### JACK Audio Connection Kit
+
+To use the [JACK](http://jackaudio.org) backend on Linux, compile with the `--features` flag to enable it:
+
+```bash
+cargo build --release --no-default-features --features="rodiojack_backend"
+```
+
+You will need the development packages for alsa, make/gcc, and JACK. (`libasound2-dev`, `build-essential`, and `libjack-dev` on Debian; `alsa-lib-devel`, `make`, `gcc`, and `jack-audio-connection-kit-devel` on Fedora.)
+
+> __Note__: when Spotifyd starts with this backend, it will create a JACK output device named `cpal_client_out` with two ports: `out_0` for the left channel and `out_1` for the right.

src/config.rs

@@ -24,7 +24,9 @@ const CONFIG_FILE_NAME: &str = "spotifyd.conf";
     feature = "pulseaudio_backend",
     feature = "portaudio_backend",
     feature = "alsa_backend",
-    feature = "rodio_backend"
+    feature = "rodio_backend",
+    feature = "rodiojack_backend",
+    feature = "jackaudio_backend",
 )))]
 compile_error!("At least one of the backend features is required!");
 static BACKEND_VALUES: &[&str] = &[
@@ -36,6 +38,10 @@ static BACKEND_VALUES: &[&str] = &[
     "portaudio",
     #[cfg(feature = "rodio_backend")]
     "rodio",
+    #[cfg(feature = "rodiojack_backend")]
+    "rodiojack",
+    #[cfg(feature = "jackaudio_backend")]
+    "jackaudio",
 ];
 
 /// The backend used by librespot
@@ -46,6 +52,7 @@ pub enum Backend {
     PortAudio,
     PulseAudio,
     Rodio,
+    RodioJack,
 }
 
 fn default_backend() -> Backend {
@@ -61,6 +68,7 @@ impl FromStr for Backend {
             "portaudio" => Ok(Backend::PortAudio),
             "pulseaudio" => Ok(Backend::PulseAudio),
             "rodio" => Ok(Backend::Rodio),
+            "rodiojack" => Ok(Backend::RodioJack),
             _ => unreachable!(),
         }
     }
@@ -73,6 +81,7 @@ impl ToString for Backend {
             Backend::PortAudio => "portaudio".to_string(),
             Backend::PulseAudio => "pulseaudio".to_string(),
             Backend::Rodio => "rodio".to_string(),
+            Backend::RodioJack => "rodiojack".to_string(),
         }
     }
 }