Fix compile errors in backends

Firstly, fe37186 added the restriction that `Sink`s must be `Send`.
It turned out later that this restrictions was unnecessary, and
since some `Sink`s aren't `Send` yet, this restriction is lifted again.

librespot-org#601 refactored the `RodioSink` in order to make
it `Send`. These changes are partly reverted in favour of the initial
simpler design.

There were also some compile errors in the gstreamer backend which are
hereby solved.

playback/src/audio_backend/gstreamer.rs

@@ -1,7 +1,9 @@
 use super::{Open, Sink};
 use crate::audio::AudioPacket;
+
 use gst::prelude::*;
-use gst::*;
+use gstreamer as gst;
+use gstreamer_app as gst_app;
 use zerocopy::*;
 
 use std::sync::mpsc::{sync_channel, SyncSender};
@@ -52,14 +54,13 @@ impl Open for GstreamerSink {
         thread::spawn(move || {
             for data in rx {
                 let buffer = bufferpool.acquire_buffer(None);
-                if !buffer.is_err() {
-                    let mut okbuffer = buffer.unwrap();
-                    let mutbuf = okbuffer.make_mut();
+                if let Ok(mut buffer) = buffer {
+                    let mutbuf = buffer.make_mut();
                     mutbuf.set_size(data.len());
                     mutbuf
                         .copy_from_slice(0, data.as_bytes())
                         .expect("Failed to copy from slice");
-                    let _eat = appsrc.push_buffer(okbuffer);
+                    let _eat = appsrc.push_buffer(buffer);
                 }
             }
         });
@@ -69,8 +70,8 @@ impl Open for GstreamerSink {
             let watch_mainloop = thread_mainloop.clone();
             bus.add_watch(move |_, msg| {
                 match msg.view() {
-                    MessageView::Eos(..) => watch_mainloop.quit(),
-                    MessageView::Error(err) => {
+                    gst::MessageView::Eos(..) => watch_mainloop.quit(),
+                    gst::MessageView::Error(err) => {
                         println!(
                             "Error from {:?}: {} ({:?})",
                             err.get_src().map(|s| s.get_path_string()),

playback/src/audio_backend/mod.rs

@@ -11,9 +11,9 @@ pub trait Sink {
     fn write(&mut self, packet: &AudioPacket) -> io::Result<()>;
 }
 
-pub type SinkBuilder = fn(Option<String>) -> Box<dyn Sink + Send>;
+pub type SinkBuilder = fn(Option<String>) -> Box<dyn Sink>;
 
-fn mk_sink<S: Sink + Open + Send + 'static>(device: Option<String>) -> Box<dyn Sink + Send> {
+fn mk_sink<S: Sink + Open + 'static>(device: Option<String>) -> Box<dyn Sink> {
     Box::new(S::open(device))
 }
 

playback/src/audio_backend/rodio.rs

@@ -1,5 +1,4 @@
 use std::process::exit;
-use std::{convert::Infallible, sync::mpsc};
 use std::{io, thread, time};
 
 use cpal::traits::{DeviceTrait, HostTrait};
@@ -15,12 +14,12 @@ use crate::audio::AudioPacket;
 compile_error!("Rodio JACK backend is currently only supported on linux.");
 
 #[cfg(feature = "rodio-backend")]
-pub fn mk_rodio(device: Option<String>) -> Box<dyn Sink + Send> {
+pub fn mk_rodio(device: Option<String>) -> Box<dyn Sink> {
     Box::new(open(cpal::default_host(), device))
 }
 
 #[cfg(feature = "rodiojack-backend")]
-pub fn mk_rodiojack(device: Option<String>) -> Box<dyn Sink + Send> {
+pub fn mk_rodiojack(device: Option<String>) -> Box<dyn Sink> {
     Box::new(open(
         cpal::host_from_id(cpal::HostId::Jack).unwrap(),
         device,
@@ -43,8 +42,7 @@ pub enum RodioError {
 
 pub struct RodioSink {
     rodio_sink: rodio::Sink,
-    // will produce a TryRecvError on the receiver side when it is dropped.
-    _close_tx: mpsc::SyncSender<Infallible>,
+    _stream: rodio::OutputStream,
 }
 
 fn list_formats(device: &rodio::Device) {
@@ -152,29 +150,12 @@ fn create_sink(
 pub fn open(host: cpal::Host, device: Option<String>) -> RodioSink {
     debug!("Using rodio sink with cpal host: {}", host.id().name());
 
-    let (sink_tx, sink_rx) = mpsc::sync_channel(1);
-    let (close_tx, close_rx) = mpsc::sync_channel(1);
-
-    std::thread::spawn(move || match create_sink(&host, device) {
-        Ok((sink, stream)) => {
-            sink_tx.send(Ok(sink)).unwrap();
-
-            close_rx.recv().unwrap_err(); // This will fail as soon as the sender is dropped
-            debug!("drop rodio::OutputStream");
-            drop(stream);
-        }
-        Err(e) => {
-            sink_tx.send(Err(e)).unwrap();
-        }
-    });
-
-    // Instead of the second `unwrap`, better error handling could be introduced
-    let sink = sink_rx.recv().unwrap().unwrap();
+    let (sink, stream) = create_sink(&host, device).unwrap();
 
     debug!("Rodio sink was created");
     RodioSink {
         rodio_sink: sink,
-        _close_tx: close_tx,
+        _stream: stream,
     }
 }
 

playback/src/player.rs

@@ -50,7 +50,7 @@ struct PlayerInternal {
 
     state: PlayerState,
     preload: PlayerPreload,
-    sink: Box<dyn Sink + Send>,
+    sink: Box<dyn Sink>,
     sink_status: SinkStatus,
     sink_event_callback: Option<SinkEventCallback>,
     audio_filter: Option<Box<dyn AudioFilter + Send>>,
@@ -242,7 +242,7 @@ impl Player {
         sink_builder: F,
     ) -> (Player, PlayerEventChannel)
     where
-        F: FnOnce() -> Box<dyn Sink + Send> + Send + 'static,
+        F: FnOnce() -> Box<dyn Sink> + Send + 'static,
     {
         let (cmd_tx, cmd_rx) = mpsc::unbounded_channel();
         let (event_sender, event_receiver) = mpsc::unbounded_channel();

src/main.rs

@@ -105,7 +105,7 @@ fn print_version() {
 
 #[derive(Clone)]
 struct Setup {
-    backend: fn(Option<String>) -> Box<dyn Sink + Send + 'static>,
+    backend: fn(Option<String>) -> Box<dyn Sink + 'static>,
     device: Option<String>,
 
     mixer: fn(Option<MixerConfig>) -> Box<dyn Mixer>,