Added subprocess audio backend

Cargo.lock

@@ -908,6 +908,7 @@ dependencies = [
  "portaudio-rs 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "rodio 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "sdl2 0.32.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "shell-words 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -1725,6 +1726,11 @@ dependencies = [
  "byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "shell-words"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "signal-hook"
 version = "0.1.10"
@@ -2540,6 +2546,7 @@ dependencies = [
 "checksum sha-1 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "23962131a91661d643c98940b20fcaffe62d776a823247be80a48fcb8b6fce68"
 "checksum sha2 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "7b4d8bfd0e469f417657573d8451fb33d16cfe0989359b93baf3a1ffc639543d"
 "checksum shannon 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "7ea5b41c9427b56caa7b808cb548a04fb50bb5b9e98590b53f28064ff4174561"
+"checksum shell-words 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "39acde55a154c4cd3ae048ac78cc21c25f3a0145e44111b523279113dce0d94a"
 "checksum signal-hook 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)" = "4f61c4d59f3aaa9f61bba6450a9b80ba48362fd7d651689e7a10c453b1f6dc68"
 "checksum signal-hook-registry 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "913661ac8848a61e39684a3c3e7a7a14a4deec7f54b4976d0641e70dda3939b1"
 "checksum slab 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "17b4fcaed89ab08ef143da37bc52adbcc04d4a69014f4c1208d6b51f0c47bc23"

playback/Cargo.toml

@@ -20,6 +20,7 @@ version = "0.1.0"
 futures = "0.1"
 log = "0.4"
 byteorder = "1.3"
+shell-words = "0.1.0"
 
 alsa            = { version = "0.2.1", optional = true }
 portaudio-rs    = { version = "0.3.0", optional = true }

playback/src/audio_backend/mod.rs

@@ -46,6 +46,9 @@ use self::sdl::SdlSink;
 mod pipe;
 use self::pipe::StdoutSink;
 
+mod subprocess;
+use self::subprocess::SubprocessSink;
+
 pub const BACKENDS: &'static [(&'static str, fn(Option<String>) -> Box<dyn Sink>)] = &[
     #[cfg(feature = "alsa-backend")]
     ("alsa", mk_sink::<AlsaSink>),
@@ -60,6 +63,7 @@ pub const BACKENDS: &'static [(&'static str, fn(Option<String>) -> Box<dyn Sink>
     #[cfg(feature = "sdl-backend")]
     ("sdl", mk_sink::<SdlSink>),
     ("pipe", mk_sink::<StdoutSink>),
+    ("subprocess", mk_sink::<SubprocessSink>),
 ];
 
 pub fn find(name: Option<String>) -> Option<fn(Option<String>) -> Box<dyn Sink>> {

playback/src/audio_backend/subprocess.rs

@@ -0,0 +1,59 @@
+use super::{Open, Sink};
+use shell_words::split;
+use std::io::{self, Write};
+use std::mem;
+use std::process::{Child, Command, Stdio};
+use std::slice;
+
+pub struct SubprocessSink {
+    shell_command: String,
+    child: Option<Child>,
+}
+
+impl Open for SubprocessSink {
+    fn open(shell_command: Option<String>) -> SubprocessSink {
+        if let Some(shell_command) = shell_command {
+            SubprocessSink {
+                shell_command: shell_command,
+                child: None,
+            }
+        } else {
+            panic!("subprocess sink requires specifying a shell command");
+        }
+    }
+}
+
+impl Sink for SubprocessSink {
+    fn start(&mut self) -> io::Result<()> {
+        let args = split(&self.shell_command).unwrap();
+        self.child = Some(
+            Command::new(&args[0])
+                .args(&args[1..])
+                .stdin(Stdio::piped())
+                .spawn()?,
+        );
+        Ok(())
+    }
+
+    fn stop(&mut self) -> io::Result<()> {
+        if let Some(child) = &mut self.child.take() {
+            child.kill()?;
+            child.wait()?;
+        }
+        Ok(())
+    }
+
+    fn write(&mut self, data: &[i16]) -> io::Result<()> {
+        let data: &[u8] = unsafe {
+            slice::from_raw_parts(
+                data.as_ptr() as *const u8,
+                data.len() * mem::size_of::<i16>(),
+            )
+        };
+        if let Some(child) = &mut self.child {
+            let child_stdin = child.stdin.as_mut().unwrap();
+            child_stdin.write_all(data)?;
+        }
+        Ok(())
+    }
+}

playback/src/lib.rs

@@ -3,6 +3,7 @@ extern crate log;
 
 extern crate byteorder;
 extern crate futures;
+extern crate shell_words;
 
 #[cfg(feature = "alsa-backend")]
 extern crate alsa;