Added subprocess audio backend

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(())
+    }
+}