sndio: address feedback from code review

* Add SampleRateMap with SampleRate keys rather than raw HashMap with
  u32 keys.
* Use FrameCount type alias rather than usize for buffer size.
* More robust error handling.
* Document InnerState state transitions.

Author: AaronM04

src/host/sndio/adapters.rs

@@ -1,11 +1,11 @@
-use crate::{Data, InputCallbackInfo, OutputCallbackInfo, Sample, SampleFormat};
+use crate::{Data, FrameCount, InputCallbackInfo, OutputCallbackInfo, Sample, SampleFormat};
 
 /// When given an input data callback that expects samples in the specified sample format, return
 /// an input data callback that expects samples in the I16 sample format. The `buffer_size` is in
 /// samples.
 pub(super) fn input_adapter_callback<D>(
     mut original_data_callback: D,
-    buffer_size: usize,
+    buffer_size: FrameCount,
     sample_format: SampleFormat,
 ) -> Box<dyn FnMut(&Data, &InputCallbackInfo) + Send + 'static>
 where
@@ -18,7 +18,7 @@ where
         }
         SampleFormat::F32 => {
             // Make the backing buffer for the Data used in the closure.
-            let mut adapted_buf = vec![0f32].repeat(buffer_size);
+            let mut adapted_buf = vec![0f32].repeat(buffer_size as usize);
             Box::new(move |data: &Data, info: &InputCallbackInfo| {
                 let data_slice: &[i16] = data.as_slice().unwrap(); // unwrap OK because data is always i16
                 let adapted_slice = &mut adapted_buf;
@@ -32,15 +32,15 @@ where
                 let adapted_data = unsafe {
                     Data::from_parts(
                         adapted_buf.as_mut_ptr() as *mut _,
-                        buffer_size,
+                        buffer_size as usize, // TODO: this is converting a FrameCount to a number of samples; invalid for stereo!
                         sample_format,
                     )
                 };
                 original_data_callback(&adapted_data, info);
             })
         }
         SampleFormat::U16 => {
-            let mut adapted_buf = vec![0u16].repeat(buffer_size);
+            let mut adapted_buf = vec![0u16].repeat(buffer_size as usize);
             Box::new(move |data: &Data, info: &InputCallbackInfo| {
                 let data_slice: &[i16] = data.as_slice().unwrap(); // unwrap OK because data is always i16
                 let adapted_slice = &mut adapted_buf;
@@ -54,7 +54,7 @@ where
                 let adapted_data = unsafe {
                     Data::from_parts(
                         adapted_buf.as_mut_ptr() as *mut _,
-                        buffer_size,
+                        buffer_size as usize, // TODO: this is converting a FrameCount to a number of samples; invalid for stereo!
                         sample_format,
                     )
                 };
@@ -69,7 +69,7 @@ where
 /// sample format. The `buffer_size` is in samples.
 pub(super) fn output_adapter_callback<D>(
     mut original_data_callback: D,
-    buffer_size: usize,
+    buffer_size: FrameCount,
     sample_format: SampleFormat,
 ) -> Box<dyn FnMut(&mut Data, &OutputCallbackInfo) + Send + 'static>
 where
@@ -82,15 +82,15 @@ where
         }
         SampleFormat::F32 => {
             // Make the backing buffer for the Data used in the closure.
-            let mut adapted_buf = vec![0f32].repeat(buffer_size);
+            let mut adapted_buf = vec![0f32].repeat(buffer_size as usize);
 
             Box::new(move |data: &mut Data, info: &OutputCallbackInfo| {
                 // Note: we construct adapted_data here instead of in the parent function because
                 // adapted_buf needs to be owned by the closure.
                 let mut adapted_data = unsafe {
                     Data::from_parts(
                         adapted_buf.as_mut_ptr() as *mut _,
-                        buffer_size,
+                        buffer_size as usize, // TODO: this is converting a FrameCount to a number of samples; invalid for stereo!
                         sample_format,
                     )
                 };
@@ -108,15 +108,15 @@ where
         }
         SampleFormat::U16 => {
             // Make the backing buffer for the Data used in the closure.
-            let mut adapted_buf = vec![0u16].repeat(buffer_size);
+            let mut adapted_buf = vec![0u16].repeat(buffer_size as usize);
 
             Box::new(move |data: &mut Data, info: &OutputCallbackInfo| {
                 // Note: we construct adapted_data here instead of in the parent function because
                 // adapted_buf needs to be owned by the closure.
                 let mut adapted_data = unsafe {
                     Data::from_parts(
                         adapted_buf.as_mut_ptr() as *mut _,
-                        buffer_size,
+                        buffer_size as usize, // TODO: this is converting a FrameCount to a number of samples; invalid for stereo!
                         sample_format,
                     )
                 };