feature(coreaudio): implement channel names

simplify unsafe structure

Author: nico-franco-gomez

src/host/coreaudio/macos/device.rs

@@ -31,8 +31,8 @@ use objc2_core_audio::{
     kAudioDevicePropertyLatency, kAudioDevicePropertyNominalSampleRate,
     kAudioDevicePropertySafetyOffset, kAudioDevicePropertyStreamConfiguration,
     kAudioDevicePropertyStreamFormat, kAudioObjectPropertyClass, kAudioObjectPropertyElementMain,
-    kAudioObjectPropertyScopeGlobal, kAudioObjectPropertyScopeInput,
-    kAudioObjectPropertyScopeOutput,
+    kAudioObjectPropertyElementName, kAudioObjectPropertyScopeGlobal,
+    kAudioObjectPropertyScopeInput, kAudioObjectPropertyScopeOutput,
 };
 use objc2_core_audio_types::{
     AudioBuffer, AudioBufferList, AudioStreamBasicDescription, AudioValueRange,
@@ -357,6 +357,10 @@ impl DeviceTrait for Device {
             timeout,
         )
     }
+
+    fn get_channel_name(&self, channel_index: u16, input: bool) -> Result<String, Error> {
+        Device::get_channel_name(self, channel_index, input)
+    }
 }
 
 #[derive(Clone)]
@@ -690,6 +694,24 @@ impl Device {
             .map(|mut configs| configs.next().is_some())
             .unwrap_or(false)
     }
+
+    fn get_channel_name(&self, channel_index: u16, input: bool) -> Result<String, Error> {
+        if input && !self.supports_input() {
+            return Err(Error::with_message(
+                ErrorKind::InvalidInput,
+                "Device does not support input",
+            ));
+        }
+
+        if !input && !self.supports_output() {
+            return Err(Error::with_message(
+                ErrorKind::InvalidInput,
+                "Device does not support output",
+            ));
+        }
+
+        get_channel_name_for_device(self.audio_device_id, channel_index, input)
+    }
 }
 
 impl Device {
@@ -1116,3 +1138,45 @@ pub(crate) fn get_device_buffer_frame_size(
     )?;
     Ok(frames as usize)
 }
+
+fn get_channel_name_for_device(
+    device_id: AudioDeviceID,
+    channel_index: u16,
+    input: bool,
+) -> Result<String, Error> {
+    let mut channel_name: *mut CFString = std::ptr::null_mut();
+    let mut data_size = size_of::<*mut CFString>() as u32;
+
+    let property_address = AudioObjectPropertyAddress {
+        mSelector: kAudioObjectPropertyElementName,
+        mScope: if input {
+            kAudioObjectPropertyScopeInput
+        } else {
+            kAudioObjectPropertyScopeOutput
+        },
+        // Channels numbers start on 1 here
+        mElement: channel_index as u32 + 1,
+    };
+
+    let status = unsafe {
+        AudioObjectGetPropertyData(
+            device_id,
+            NonNull::from(&property_address),
+            0,
+            null(),
+            NonNull::from(&mut data_size),
+            NonNull::from(&mut channel_name).cast(),
+        )
+    };
+    check_os_status(status)?;
+
+    if !channel_name.is_null() {
+        let raw_name = unsafe { CFRetained::from_raw(NonNull::new(channel_name).unwrap()) };
+        Ok(raw_name.to_string())
+    } else {
+        Err(Error::with_message(
+            ErrorKind::Other,
+            "channel name is null",
+        ))
+    }
+}