Handle zero rate/channels from hardware description gracefully

CoreAudio can report zero sample rate or channel count in the
hardware stream description during device transitions (e.g. device
unplug, default device change).  This is the #1 cubeb-coreaudio
crash signature, with ~240 crash pings per 30 days on macOS,
100% in the main (parent) process.

Previously, create_stream_description() would panic on zero rate
or channels.  Now:
- Validate rate and channel count in setup() immediately after
  reading the hardware description, returning an error with
  diagnostic logging when the values are invalid.  This catches
  the problem at the source, where we have full context (device
  info, stream pointer).
- Convert the asserts in create_stream_description() to
  debug_assert + error return, so programming errors are still
  caught in dev builds but users don't crash.
- The output path already had a zero-channel check ("observed in
  the wild"); extend it to also check rate, and add both checks
  to the input path.

Author: kinetiknz

src/backend/mod.rs

@@ -267,8 +267,22 @@ fn create_device_info(devid: AudioDeviceID, devtype: DeviceType) -> Option<devic
 }
 
 fn create_stream_description(stream_params: &StreamParams) -> Result<AudioStreamBasicDescription> {
-    assert!(stream_params.rate() > 0);
-    assert!(stream_params.channels() > 0);
+    debug_assert!(stream_params.rate() > 0);
+    debug_assert!(stream_params.channels() > 0);
+    if stream_params.rate() == 0 {
+        cubeb_log!(
+            "create_stream_description: invalid rate 0 (channels={})",
+            stream_params.channels()
+        );
+        return Err(Error::Error);
+    }
+    if stream_params.channels() == 0 {
+        cubeb_log!(
+            "create_stream_description: invalid channel count 0 (rate={})",
+            stream_params.rate()
+        );
+        return Err(Error::Error);
+    }
 
     let mut desc = AudioStreamBasicDescription::default();
 
@@ -3848,6 +3862,16 @@ impl<'ctx> CoreStreamData<'ctx> {
                 self.stm_ptr,
                 input_hw_desc
             );
+            // These have been observed in the wild.
+            if input_hw_desc.mSampleRate <= 0.0 || input_hw_desc.mChannelsPerFrame == 0 {
+                cubeb_log!(
+                    "({:p}) Invalid input hardware description: rate={}, channels={}",
+                    self.stm_ptr,
+                    input_hw_desc.mSampleRate,
+                    input_hw_desc.mChannelsPerFrame
+                );
+                return Err(Error::Error);
+            }
             // Notice: when we are using an aggregate device, input_hw_desc.mChannelsPerFrame is the
             // sum of all input channels of all devices added to the aggregate device.
             // Because we set the input device first on the aggregate device, the input device's
@@ -4056,11 +4080,13 @@ impl<'ctx> CoreStreamData<'ctx> {
                 output_hw_desc
             );
 
-            // This has been observed in the wild.
-            if output_hw_desc.mChannelsPerFrame == 0 {
+            // These have been observed in the wild.
+            if output_hw_desc.mSampleRate <= 0.0 || output_hw_desc.mChannelsPerFrame == 0 {
                 cubeb_log!(
-                    "({:p}) Output hardware description channel count is zero",
-                    self.stm_ptr
+                    "({:p}) Invalid output hardware description: rate={}, channels={}",
+                    self.stm_ptr,
+                    output_hw_desc.mSampleRate,
+                    output_hw_desc.mChannelsPerFrame
                 );
                 return Err(Error::Error);
             }