Add two more config functions

Author: diwic

src/config.rs

@@ -1,15 +1,43 @@
 //! Configuration file API
 //!
-//! For now, just contains two functions regarding the global configuration
+//! For now, just contains functions regarding the global configuration
 //! stored as a cache inside alsa-lib. Calling `update_free_global` might help
 //! against valgrind reporting memory leaks.
 use crate::{alsa};
 use super::error::*;
+use super::Output;
+use std::ptr;
 
-pub fn update() -> Result<()> {
-	acheck!(snd_config_update()).map(|_| ())
+pub fn update() -> Result<bool> {
+	acheck!(snd_config_update()).map(|x| x != 0)
 }
 
 pub fn update_free_global() -> Result<()> {
 	acheck!(snd_config_update_free_global()).map(|_| ())
+}
+
+/// [snd_config_t](https://alsa-project.org/alsa-doc/alsa-lib/group___config.html) wrapper
+pub struct Config(*mut alsa::snd_config_t);
+
+impl Drop for Config {
+    fn drop(&mut self) { unsafe { alsa::snd_config_unref(self.0) }; }
+}
+
+pub fn update_ref() -> Result<Config> {
+	let mut top = ptr::null_mut();
+	acheck!(snd_config_update_ref(&mut top)).map(|_| Config(top))
+}
+
+impl Config {
+    pub fn save(&self, o: &mut Output) -> Result<()> {
+        acheck!(snd_config_save(self.0, super::io::output_handle(o))).map(|_| ())
+    }
+}
+
+#[test]
+fn config_save() {
+	let c = update_ref().unwrap();
+    let mut outp = Output::buffer_open().unwrap();
+	c.save(&mut outp).unwrap();
+    println!("== Config save ==\n{}", outp);
 }

src/io.rs

@@ -22,7 +22,7 @@ impl Output {
         let b = unsafe {
             let mut q = ptr::null_mut();
             let s = alsa::snd_output_buffer_string(self.0, &mut q);
-            slice::from_raw_parts(q as *const u8, s as usize)
+            if s == 0 { &[] } else { slice::from_raw_parts(q as *const u8, s as usize) }
         };
         f(b)
     }