Fix iOS compilation error

.travis.yml

@@ -20,6 +20,8 @@ script:
 - cargo build --verbose
 - cargo test --verbose
 - cargo doc --verbose
+- cargo build --verbose --target aarch64-apple-ios
+- cargo test --verbose --target aarch64-apple-ios
 after_success: |
   [ $TRAVIS_BRANCH = master ] &&
   [ $TRAVIS_PULL_REQUEST = false ] &&

src/audio_unit/mod.rs

@@ -171,6 +171,29 @@ impl AudioUnit {
         }
     }
 
+    /// On successful initialization, the audio formats for input and output are valid
+    /// and the audio unit is ready to render. During initialization, an audio unit
+    /// allocates memory according to the maximum number of audio frames it can produce
+    /// in response to a single render call.
+    ///
+    /// Usually, the state of an audio unit (such as its I/O formats and memory allocations)
+    /// cannot be changed while an audio unit is initialized.
+    pub fn initialize(&mut self) -> Result<(), Error> {
+        unsafe { try_os_status!(sys::AudioUnitInitialize(self.instance)); }
+        Ok(())
+    }
+
+    /// Before you change an initialize audio unit’s processing characteristics,
+    /// such as its input or output audio data format or its sample rate, you must
+    /// first uninitialize it. Calling this function deallocates the audio unit’s resources.
+    ///
+    /// After calling this function, you can reconfigure the audio unit and then call
+    /// AudioUnitInitialize to reinitialize it.
+    pub fn uninitialize(&mut self) -> Result<(), Error> {
+        unsafe { try_os_status!(sys::AudioUnitUninitialize(self.instance)); }
+        Ok(())
+    }
+
     /// Sets the value for some property of the **AudioUnit**.
     ///
     /// To clear an audio unit property value, set the data paramater with `None::<()>`.
@@ -375,3 +398,20 @@ pub fn get_property<T>(
         Ok(data)
     }
 }
+
+#[cfg(target_os = "ios")]
+pub fn audio_session_get_property<T>(
+    id: u32,
+) -> Result<T, Error>
+{
+    let mut size = ::std::mem::size_of::<T>() as u32;
+    unsafe {
+        let mut data: T = ::std::mem::uninitialized();
+        let data_ptr = &mut data as *mut _ as *mut c_void;
+        let size_ptr = &mut size as *mut _;
+        try_os_status!(
+            sys::AudioSessionGetProperty(id, size_ptr, data_ptr)
+        );
+        Ok(data)
+    }
+}

src/audio_unit/render_callback.rs

@@ -8,6 +8,9 @@ use sys;
 pub use self::action_flags::ActionFlags;
 pub use self::data::Data;
 
+#[cfg(target_os = "ios")]
+use audio_unit::audio_session_get_property;
+
 
 /// When `set_render_callback` is called, a closure of this type will be used to wrap the given
 /// render callback function.
@@ -398,7 +401,7 @@ impl AudioUnit {
         // First, we'll retrieve the stream format so that we can ensure that the given callback
         // format matches the audio unit's format.
         let id = sys::kAudioUnitProperty_StreamFormat;
-        let asbd = try!(self.get_property(id, Scope::Output, Element::Output));
+        let asbd = try!(self.get_property(id, Scope::Input, Element::Output));
         let stream_format = super::StreamFormat::from_asbd(asbd)?;
 
         // If the stream format does not match, return an error indicating this.
@@ -471,7 +474,7 @@ impl AudioUnit {
         // First, we'll retrieve the stream format so that we can ensure that the given callback
         // format matches the audio unit's format.
         let id = sys::kAudioUnitProperty_StreamFormat;
-        let asbd = self.get_property(id, Scope::Input, Element::Input)?;
+        let asbd = self.get_property(id, Scope::Output, Element::Input)?;
         let stream_format = super::StreamFormat::from_asbd(asbd)?;
 
         // If the stream format does not match, return an error indicating this.
@@ -482,8 +485,20 @@ impl AudioUnit {
         // Pre-allocate a buffer list for input stream.
         //
         // First, get the current buffer size for pre-allocating the `AudioBuffer`s.
-        let id = sys::kAudioDevicePropertyBufferFrameSize;
-        let mut buffer_frame_size: u32 = self.get_property(id, Scope::Global, Element::Output)?;
+        #[cfg(target_os = "macos")]
+        let mut buffer_frame_size: u32 = {
+            let id = sys::kAudioDevicePropertyBufferFrameSize;
+            let buffer_frame_size: u32 = self.get_property(id, Scope::Global, Element::Output)?;
+            buffer_frame_size
+        };
+        #[cfg(target_os = "ios")]
+        let mut buffer_frame_size: u32 = {
+            let id = sys::kAudioSessionProperty_CurrentHardwareIOBufferDuration;
+            let seconds: f32 = super::audio_session_get_property(id)?;
+            let id = sys::kAudioSessionProperty_CurrentHardwareSampleRate;
+            let sample_rate: f64 = super::audio_session_get_property(id)?;
+            (sample_rate * seconds as f64).round() as u32
+        };
         let mut data: Vec<u8> = vec![];
         let sample_bytes = stream_format.sample_format.size_in_bytes();
         let n_channels = stream_format.channels_per_frame;
@@ -525,7 +540,7 @@ impl AudioUnit {
                 unsafe {
                     // Retrieve the up-to-date stream format.
                     let id = sys::kAudioUnitProperty_StreamFormat;
-                    let asbd = match super::get_property(audio_unit, id, Scope::Input, Element::Output) {
+                    let asbd = match super::get_property(audio_unit, id, Scope::Output, Element::Input) {
                         Err(err) => return err.to_os_status(),
                         Ok(asbd) => asbd,
                     };