Merge pull request #386 from alexmoon/alsa

Switch from vendored alsa-sys to alsa crate

Cargo.toml

@@ -27,8 +27,9 @@ asio-sys = { version = "0.1", path = "asio-sys", optional = true }
 parking_lot = "0.9"
 
 [target.'cfg(any(target_os = "linux", target_os = "dragonfly", target_os = "freebsd"))'.dependencies]
-alsa-sys = { version = "0.1", path = "alsa-sys" }
+alsa = "0.4.1"
-libc = "0.2"
+nix = "0.15.0"
+libc = "0.2.65"
 
 [target.'cfg(any(target_os = "macos", target_os = "ios"))'.dependencies]
 coreaudio-rs = { version = "0.9.1", default-features = false, features = ["audio_unit", "core_audio"] }

alsa-sys/.gitignore

@@ -1,3 +0,0 @@
-/target
-/Cargo.lock
-.cargo/

alsa-sys/Cargo.toml

@@ -1,14 +0,0 @@
-[package]
-name = "alsa-sys"
-version = "0.1.1"
-authors = ["Pierre Krieger <pierre.krieger1708@gmail.com>"]
-build = "build.rs"
-description = "Bindings for the ALSA project (Advanced Linux Sound Architecture)"
-license = "MIT"
-links = "alsa"
-
-[dependencies]
-libc = "0.2.7"
-
-[build-dependencies]
-pkg-config = "0.3"

alsa-sys/build.rs

@@ -1,5 +0,0 @@
-extern crate pkg_config;
-
-fn main() {
-    pkg_config::find_library("alsa").unwrap();
-}

src/host/alsa/enumerate.rs

@@ -1,139 +1,69 @@
 use super::alsa;
-use super::check_errors;
 use super::Device;
-use std::ffi::CString;
-use std::ptr;
 use {BackendSpecificError, DevicesError};
 
 /// ALSA implementation for `Devices`.
 pub struct Devices {
-    // we keep the original list so that we can pass it to the free function
+    hint_iter: alsa::device_name::HintIter,
-    global_list: *const *const u8,
-
-    // pointer to the next string ; contained within `global_list`
-    next_str: *const *const u8,
 }
 
 impl Devices {
     pub fn new() -> Result<Self, DevicesError> {
-        unsafe {
+        Ok(Devices {
-            // TODO: check in which situation this can fail.
+            hint_iter: alsa::device_name::HintIter::new_str(None, "pcm")?,
-            let card = -1; // -1 means all cards.
+        })
-            let iface = b"pcm\0"; // Interface identification.
-            let mut hints = ptr::null_mut(); // Array of device name hints.
-            let res = alsa::snd_device_name_hint(card, iface.as_ptr() as *const _, &mut hints);
-            if let Err(description) = check_errors(res) {
-                let err = BackendSpecificError { description };
-                return Err(err.into());
-            }
-            let hints = hints as *const *const u8;
-            let devices = Devices {
-                global_list: hints,
-                next_str: hints,
-            };
-            Ok(devices)
-        }
     }
 }
 
 unsafe impl Send for Devices {}
 unsafe impl Sync for Devices {}
 
-impl Drop for Devices {
-    #[inline]
-    fn drop(&mut self) {
-        unsafe {
-            alsa::snd_device_name_free_hint(self.global_list as *mut _);
-        }
-    }
-}
-
 impl Iterator for Devices {
     type Item = Device;
 
     fn next(&mut self) -> Option<Device> {
         loop {
-            unsafe {
+            match self.hint_iter.next() {
-                if (*self.next_str).is_null() {
+                None => return None,
-                    return None;
+                Some(hint) => {
-                }
+                    let name = hint.name;
 
-                let name = {
+                    let io = hint.direction;
-                    let n_ptr = alsa::snd_device_name_get_hint(
-                        *self.next_str as *const _,
-                        b"NAME\0".as_ptr() as *const _,
-                    );
-                    if !n_ptr.is_null() {
-                        let bytes = CString::from_raw(n_ptr).into_bytes();
-                        let string = String::from_utf8(bytes).unwrap();
-                        Some(string)
-                    } else {
-                        None
-                    }
-                };
 
-                let io = {
+                    if let Some(io) = io {
-                    let n_ptr = alsa::snd_device_name_get_hint(
+                        if io != alsa::Direction::Playback {
-                        *self.next_str as *const _,
-                        b"IOID\0".as_ptr() as *const _,
-                    );
-                    if !n_ptr.is_null() {
-                        let bytes = CString::from_raw(n_ptr).into_bytes();
-                        let string = String::from_utf8(bytes).unwrap();
-                        Some(string)
-                    } else {
-                        None
-                    }
-                };
-
-                self.next_str = self.next_str.offset(1);
-
-                if let Some(io) = io {
-                    if io != "Output" {
-                        continue;
-                    }
-                }
-
-                let name = match name {
-                    Some(name) => {
-                        // Ignoring the `null` device.
-                        if name == "null" {
                             continue;
                         }
-                        name
                     }
-                    _ => continue,
-                };
 
-                // trying to open the PCM device to see if it can be opened
+                    let name = match name {
-                let name_zeroed = CString::new(&name[..]).unwrap();
+                        Some(name) => {
+                            // Ignoring the `null` device.
+                            if name == "null" {
+                                continue;
+                            }
+                            name
+                        }
+                        _ => continue,
+                    };
 
-                // See if the device has an available output stream.
+                    // See if the device has an available output stream.
-                let mut playback_handle = ptr::null_mut();
+                    let has_available_output = {
-                let has_available_output = alsa::snd_pcm_open(
+                        let playback_handle =
-                    &mut playback_handle,
+                            alsa::pcm::PCM::new(&name, alsa::Direction::Playback, true);
-                    name_zeroed.as_ptr() as *const _,
+                        playback_handle.is_ok()
-                    alsa::SND_PCM_STREAM_PLAYBACK,
+                    };
-                    alsa::SND_PCM_NONBLOCK,
-                ) == 0;
-                if has_available_output {
-                    alsa::snd_pcm_close(playback_handle);
-                }
 
-                // See if the device has an available input stream.
+                    // See if the device has an available input stream.
-                let mut capture_handle = ptr::null_mut();
+                    let has_available_input = {
-                let has_available_input = alsa::snd_pcm_open(
+                        let capture_handle =
-                    &mut capture_handle,
+                            alsa::pcm::PCM::new(&name, alsa::Direction::Capture, true);
-                    name_zeroed.as_ptr() as *const _,
+                        capture_handle.is_ok()
-                    alsa::SND_PCM_STREAM_CAPTURE,
+                    };
-                    alsa::SND_PCM_NONBLOCK,
-                ) == 0;
-                if has_available_input {
-                    alsa::snd_pcm_close(capture_handle);
-                }
 
-                if has_available_output || has_available_input {
+                    if has_available_output || has_available_input {
-                    return Some(Device(name));
+                        return Some(Device(name));
+                    }
                 }
             }
         }
@@ -149,3 +79,10 @@ pub fn default_input_device() -> Option<Device> {
 pub fn default_output_device() -> Option<Device> {
     Some(Device("default".to_owned()))
 }
+
+impl From<alsa::Error> for DevicesError {
+    fn from(err: alsa::Error) -> Self {
+        let err: BackendSpecificError = err.into();
+        err.into()
+    }
+}

src/host/alsa/mod.rs

@@ -1,17 +1,17 @@
-extern crate alsa_sys as alsa;
+extern crate alsa;
 extern crate libc;
 
-use self::libc::c_long;
+use self::alsa::poll::Descriptors;
 use crate::{
     BackendSpecificError, BuildStreamError, ChannelCount, Data, DefaultStreamConfigError,
     DeviceNameError, DevicesError, PauseStreamError, PlayStreamError, SampleFormat, SampleRate,
     StreamConfig, StreamError, SupportedStreamConfig, SupportedStreamConfigRange,
     SupportedStreamConfigsError,
 };
+use std::cmp;
 use std::sync::Arc;
 use std::thread::{self, JoinHandle};
 use std::vec::IntoIter as VecIntoIter;
-use std::{cmp, ffi, io, ptr};
 use traits::{DeviceTrait, HostTrait, StreamTrait};
 
 pub use self::enumerate::{default_input_device, default_output_device, Devices};
@@ -94,7 +94,7 @@ impl DeviceTrait for Device {
         E: FnMut(StreamError) + Send + 'static,
     {
         let stream_inner =
-            self.build_stream_inner(conf, sample_format, alsa::SND_PCM_STREAM_CAPTURE)?;
+            self.build_stream_inner(conf, sample_format, alsa::Direction::Capture)?;
         let stream = Stream::new_input(Arc::new(stream_inner), data_callback, error_callback);
         Ok(stream)
     }
@@ -111,7 +111,7 @@ impl DeviceTrait for Device {
         E: FnMut(StreamError) + Send + 'static,
     {
         let stream_inner =
-            self.build_stream_inner(conf, sample_format, alsa::SND_PCM_STREAM_PLAYBACK)?;
+            self.build_stream_inner(conf, sample_format, alsa::Direction::Playback)?;
         let stream = Stream::new_output(Arc::new(stream_inner), data_callback, error_callback);
         Ok(stream)
     }
@@ -169,55 +169,41 @@ impl Device {
         &self,
         conf: &StreamConfig,
         sample_format: SampleFormat,
-        stream_type: alsa::snd_pcm_stream_t,
+        stream_type: alsa::Direction,
     ) -> Result<StreamInner, BuildStreamError> {
-        let name = ffi::CString::new(self.0.clone()).expect("unable to clone device");
+        let name = &self.0;
 
-        let handle = unsafe {
+        let handle = match alsa::pcm::PCM::new(name, stream_type, true).map_err(|e| (e, e.errno()))
-            let mut handle = ptr::null_mut();
+        {
-            match alsa::snd_pcm_open(
+            Err((_, Some(nix::errno::Errno::EBUSY))) => {
-                &mut handle,
+                return Err(BuildStreamError::DeviceNotAvailable)
-                name.as_ptr(),
-                stream_type,
-                alsa::SND_PCM_NONBLOCK,
-            ) {
-                -16 /* determined empirically */ => return Err(BuildStreamError::DeviceNotAvailable),
-                -22 => return Err(BuildStreamError::InvalidArgument),
-                e => if let Err(description) = check_errors(e) {
-                    let err = BackendSpecificError { description };
-                    return Err(err.into());
-                }
             }
-            handle
+            Err((_, Some(nix::errno::Errno::EINVAL))) => {
+                return Err(BuildStreamError::InvalidArgument)
+            }
+            Err((e, _)) => return Err(e.into()),
+            Ok(handle) => handle,
         };
-        let can_pause = unsafe {
+        let can_pause = {
-            let hw_params = HwParams::alloc();
+            let hw_params = set_hw_params_from_format(&handle, conf, sample_format)?;
-            set_hw_params_from_format(handle, &hw_params, conf, sample_format)
+            hw_params.can_pause()
-                .map_err(|description| BackendSpecificError { description })?;
+        };
+        let (buffer_len, period_len) = set_sw_params_from_format(&handle, conf)?;
 
-            alsa::snd_pcm_hw_params_can_pause(hw_params.0) == 1
+        handle.prepare()?;
-        };
-        let (buffer_len, period_len) = unsafe {
-            set_sw_params_from_format(handle, conf)
-                .map_err(|description| BackendSpecificError { description })?
-        };
-
-        if let Err(desc) = check_errors(unsafe { alsa::snd_pcm_prepare(handle) }) {
-            let description = format!("could not get handle: {}", desc);
-            let err = BackendSpecificError { description };
-            return Err(err.into());
-        }
 
         let num_descriptors = {
-            let num_descriptors = unsafe { alsa::snd_pcm_poll_descriptors_count(handle) };
+            let num_descriptors = handle.count();
             if num_descriptors == 0 {
                 let description = "poll descriptor count for stream was 0".to_string();
                 let err = BackendSpecificError { description };
                 return Err(err.into());
             }
-            num_descriptors as usize
+            num_descriptors
         };
 
+        handle.start()?;
+
         let stream_inner = StreamInner {
             channel: handle,
             sample_format,
@@ -228,12 +214,6 @@ impl Device {
             can_pause,
         };
 
-        if let Err(desc) = check_errors(unsafe { alsa::snd_pcm_start(handle) }) {
-            let description = format!("could not start stream: {}", desc);
-            let err = BackendSpecificError { description };
-            return Err(err.into());
-        }
-
         Ok(stream_inner)
     }
 
@@ -242,51 +222,33 @@ impl Device {
         Ok(self.0.clone())
     }
 
-    unsafe fn supported_configs(
+    fn supported_configs(
         &self,
-        stream_t: alsa::snd_pcm_stream_t,
+        stream_t: alsa::Direction,
     ) -> Result<VecIntoIter<SupportedStreamConfigRange>, SupportedStreamConfigsError> {
-        let mut handle = ptr::null_mut();
+        let name = &self.0;
-        let device_name = match ffi::CString::new(&self.0[..]) {
+
-            Ok(name) => name,
+        let handle = match alsa::pcm::PCM::new(name, stream_t, true).map_err(|e| (e, e.errno())) {
-            Err(err) => {
+            Err((_, Some(nix::errno::Errno::ENOENT)))
-                let description = format!("failed to retrieve device name: {}", err);
+            | Err((_, Some(nix::errno::Errno::EBUSY))) => {
-                let err = BackendSpecificError { description };
+                return Err(SupportedStreamConfigsError::DeviceNotAvailable)
-                return Err(err.into());
             }
+            Err((_, Some(nix::errno::Errno::EINVAL))) => {
+                return Err(SupportedStreamConfigsError::InvalidArgument)
+            }
+            Err((e, _)) => return Err(e.into()),
+            Ok(handle) => handle,
         };
 
-        match alsa::snd_pcm_open(
+        let hw_params = alsa::pcm::HwParams::any(&handle)?;
-            &mut handle,
-            device_name.as_ptr() as *const _,
-            stream_t,
-            alsa::SND_PCM_NONBLOCK,
-        ) {
-            -2 |
-            -16 /* determined empirically */ => return Err(SupportedStreamConfigsError::DeviceNotAvailable),
-            -22 => return Err(SupportedStreamConfigsError::InvalidArgument),
-            e => if let Err(description) = check_errors(e) {
-                let err = BackendSpecificError { description };
-                return Err(err.into())
-            }
-        }
-
-        let hw_params = HwParams::alloc();
-        match check_errors(alsa::snd_pcm_hw_params_any(handle, hw_params.0)) {
-            Err(description) => {
-                let err = BackendSpecificError { description };
-                return Err(err.into());
-            }
-            Ok(_) => (),
-        };
 
         // TODO: check endianess
-        const FORMATS: [(SampleFormat, alsa::snd_pcm_format_t); 3] = [
+        const FORMATS: [(SampleFormat, alsa::pcm::Format); 3] = [
             //SND_PCM_FORMAT_S8,
             //SND_PCM_FORMAT_U8,
-            (SampleFormat::I16, alsa::SND_PCM_FORMAT_S16_LE),
+            (SampleFormat::I16, alsa::pcm::Format::S16LE),
             //SND_PCM_FORMAT_S16_BE,
-            (SampleFormat::U16, alsa::SND_PCM_FORMAT_U16_LE),
+            (SampleFormat::U16, alsa::pcm::Format::U16LE),
             //SND_PCM_FORMAT_U16_BE,
             //SND_PCM_FORMAT_S24_LE,
             //SND_PCM_FORMAT_S24_BE,
@@ -296,7 +258,7 @@ impl Device {
             //SND_PCM_FORMAT_S32_BE,
             //SND_PCM_FORMAT_U32_LE,
             //SND_PCM_FORMAT_U32_BE,
-            (SampleFormat::F32, alsa::SND_PCM_FORMAT_FLOAT_LE),
+            (SampleFormat::F32, alsa::pcm::Format::FloatLE),
             //SND_PCM_FORMAT_FLOAT_BE,
             //SND_PCM_FORMAT_FLOAT64_LE,
             //SND_PCM_FORMAT_FLOAT64_BE,
@@ -324,36 +286,15 @@ impl Device {
 
         let mut supported_formats = Vec::new();
         for &(sample_format, alsa_format) in FORMATS.iter() {
-            if alsa::snd_pcm_hw_params_test_format(handle, hw_params.0, alsa_format) == 0 {
+            if hw_params.test_format(alsa_format).is_ok() {
                 supported_formats.push(sample_format);
             }
         }
 
-        let mut min_rate = 0;
+        let min_rate = hw_params.get_rate_min()?;
-        if let Err(desc) = check_errors(alsa::snd_pcm_hw_params_get_rate_min(
+        let max_rate = hw_params.get_rate_max()?;
-            hw_params.0,
-            &mut min_rate,
-            ptr::null_mut(),
-        )) {
-            let description = format!("unable to get minimum supported rate: {}", desc);
-            let err = BackendSpecificError { description };
-            return Err(err.into());
-        }
 
-        let mut max_rate = 0;
+        let sample_rates = if min_rate == max_rate || hw_params.test_rate(min_rate + 1).is_ok() {
-        if let Err(desc) = check_errors(alsa::snd_pcm_hw_params_get_rate_max(
-            hw_params.0,
-            &mut max_rate,
-            ptr::null_mut(),
-        )) {
-            let description = format!("unable to get maximum supported rate: {}", desc);
-            let err = BackendSpecificError { description };
-            return Err(err.into());
-        }
-
-        let sample_rates = if min_rate == max_rate
-            || alsa::snd_pcm_hw_params_test_rate(handle, hw_params.0, min_rate + 1, 0) == 0
-        {
             vec![(min_rate, max_rate)]
         } else {
             const RATES: [libc::c_uint; 13] = [
@@ -363,7 +304,7 @@ impl Device {
 
             let mut rates = Vec::new();
             for &rate in RATES.iter() {
-                if alsa::snd_pcm_hw_params_test_rate(handle, hw_params.0, rate, 0) == 0 {
+                if hw_params.test_rate(rate).is_ok() {
                     rates.push((rate, rate));
                 }
             }
@@ -375,30 +316,13 @@ impl Device {
             }
         };
 
-        let mut min_channels = 0;
+        let min_channels = hw_params.get_channels_min()?;
-        if let Err(desc) = check_errors(alsa::snd_pcm_hw_params_get_channels_min(
+        let max_channels = hw_params.get_channels_max()?;
-            hw_params.0,
-            &mut min_channels,
-        )) {
-            let description = format!("unable to get minimum supported channel count: {}", desc);
-            let err = BackendSpecificError { description };
-            return Err(err.into());
-        }
-
-        let mut max_channels = 0;
-        if let Err(desc) = check_errors(alsa::snd_pcm_hw_params_get_channels_max(
-            hw_params.0,
-            &mut max_channels,
-        )) {
-            let description = format!("unable to get maximum supported channel count: {}", desc);
-            let err = BackendSpecificError { description };
-            return Err(err.into());
-        }
 
         let max_channels = cmp::min(max_channels, 32); // TODO: limiting to 32 channels or too much stuff is returned
         let supported_channels = (min_channels..max_channels + 1)
             .filter_map(|num| {
-                if alsa::snd_pcm_hw_params_test_channels(handle, hw_params.0, num) == 0 {
+                if hw_params.test_channels(num).is_ok() {
                     Some(num as ChannelCount)
                 } else {
                     None
@@ -422,30 +346,28 @@ impl Device {
             }
         }
 
-        // TODO: RAII
-        alsa::snd_pcm_close(handle);
         Ok(output.into_iter())
     }
 
     fn supported_input_configs(
         &self,
     ) -> Result<SupportedInputConfigs, SupportedStreamConfigsError> {
-        unsafe { self.supported_configs(alsa::SND_PCM_STREAM_CAPTURE) }
+        self.supported_configs(alsa::Direction::Capture)
     }
 
     fn supported_output_configs(
         &self,
     ) -> Result<SupportedOutputConfigs, SupportedStreamConfigsError> {
-        unsafe { self.supported_configs(alsa::SND_PCM_STREAM_PLAYBACK) }
+        self.supported_configs(alsa::Direction::Playback)
     }
 
     // ALSA does not offer default stream formats, so instead we compare all supported formats by
     // the `SupportedStreamConfigRange::cmp_default_heuristics` order and select the greatest.
     fn default_config(
         &self,
-        stream_t: alsa::snd_pcm_stream_t,
+        stream_t: alsa::Direction,
     ) -> Result<SupportedStreamConfig, DefaultStreamConfigError> {
-        let mut formats: Vec<_> = unsafe {
+        let mut formats: Vec<_> = {
             match self.supported_configs(stream_t) {
                 Err(SupportedStreamConfigsError::DeviceNotAvailable) => {
                     return Err(DefaultStreamConfigError::DeviceNotAvailable);
@@ -480,17 +402,17 @@ impl Device {
     }
 
     fn default_input_config(&self) -> Result<SupportedStreamConfig, DefaultStreamConfigError> {
-        self.default_config(alsa::SND_PCM_STREAM_CAPTURE)
+        self.default_config(alsa::Direction::Capture)
     }
 
     fn default_output_config(&self) -> Result<SupportedStreamConfig, DefaultStreamConfigError> {
-        self.default_config(alsa::SND_PCM_STREAM_PLAYBACK)
+        self.default_config(alsa::Direction::Playback)
     }
 }
 
 struct StreamInner {
     // The ALSA channel.
-    channel: *mut alsa::snd_pcm_t,
+    channel: alsa::pcm::PCM,
 
     // When converting between file descriptors and `snd_pcm_t`, this is the number of
     // file descriptors that this `snd_pcm_t` uses.
@@ -513,8 +435,6 @@ struct StreamInner {
 }
 
 // Assume that the ALSA library is built with thread safe option.
-unsafe impl Send for StreamInner {}
-
 unsafe impl Sync for StreamInner {}
 
 #[derive(Debug, Eq, PartialEq)]
@@ -549,11 +469,17 @@ fn input_stream_worker(
 ) {
     let mut ctxt = StreamWorkerContext::default();
     loop {
-        match poll_descriptors_and_prepare_buffer(&rx, stream, &mut ctxt, error_callback) {
+        let flow = report_error(
+            poll_descriptors_and_prepare_buffer(&rx, stream, &mut ctxt),
+            error_callback,
+        )
+        .unwrap_or(PollDescriptorsFlow::Continue);
+
+        match flow {
             PollDescriptorsFlow::Continue => continue,
             PollDescriptorsFlow::Return => return,
             PollDescriptorsFlow::Ready {
-                available_frames,
+                available_frames: _,
                 stream_type,
             } => {
                 assert_eq!(
@@ -561,11 +487,8 @@ fn input_stream_worker(
                     StreamType::Input,
                     "expected input stream, but polling descriptors indicated output",
                 );
-                process_input(
+                report_error(
-                    stream,
+                    process_input(stream, &mut ctxt.buffer, data_callback),
-                    &mut ctxt.buffer,
-                    available_frames,
-                    data_callback,
                     error_callback,
                 );
             }
@@ -581,7 +504,13 @@ fn output_stream_worker(
 ) {
     let mut ctxt = StreamWorkerContext::default();
     loop {
-        match poll_descriptors_and_prepare_buffer(&rx, stream, &mut ctxt, error_callback) {
+        let flow = report_error(
+            poll_descriptors_and_prepare_buffer(&rx, stream, &mut ctxt),
+            error_callback,
+        )
+        .unwrap_or(PollDescriptorsFlow::Continue);
+
+        match flow {
             PollDescriptorsFlow::Continue => continue,
             PollDescriptorsFlow::Return => return,
             PollDescriptorsFlow::Ready {
@@ -605,6 +534,22 @@ fn output_stream_worker(
     }
 }
 
+fn report_error<T, E>(
+    result: Result<T, E>,
+    error_callback: &mut (dyn FnMut(StreamError) + Send + 'static),
+) -> Option<T>
+where
+    E: Into<StreamError>,
+{
+    match result {
+        Ok(val) => Some(val),
+        Err(err) => {
+            error_callback(err.into());
+            None
+        }
+    }
+}
+
 enum PollDescriptorsFlow {
     Continue,
     Return,
@@ -619,8 +564,7 @@ fn poll_descriptors_and_prepare_buffer(
     rx: &TriggerReceiver,
     stream: &StreamInner,
     ctxt: &mut StreamWorkerContext,
-    error_callback: &mut (dyn FnMut(StreamError) + Send + 'static),
+) -> Result<PollDescriptorsFlow, BackendSpecificError> {
-) -> PollDescriptorsFlow {
     let StreamWorkerContext {
         ref mut descriptors,
         ref mut buffer,
@@ -636,68 +580,45 @@ fn poll_descriptors_and_prepare_buffer(
     });
 
     // Add ALSA polling fds.
-    descriptors.reserve(stream.num_descriptors);
     let len = descriptors.len();
-    let filled = unsafe {
+    descriptors.resize(
-        alsa::snd_pcm_poll_descriptors(
+        stream.num_descriptors + len,
-            stream.channel,
+        libc::pollfd {
-            descriptors[len..].as_mut_ptr(),
+            fd: 0,
-            stream.num_descriptors as libc::c_uint,
+            events: 0,
-        )
+            revents: 0,
-    };
+        },
-    debug_assert_eq!(filled, stream.num_descriptors as libc::c_int);
+    );
-    unsafe {
+    let filled = stream.channel.fill(&mut descriptors[len..])?;
-        descriptors.set_len(len + stream.num_descriptors);
+    debug_assert_eq!(filled, stream.num_descriptors);
-    }
 
-    let res = unsafe {
+    // Don't timeout, wait forever.
-        // Don't timeout, wait forever.
+    let res = alsa::poll::poll(descriptors, -1)?;
-        libc::poll(
+    if res == 0 {
-            descriptors.as_mut_ptr(),
+        let description = String::from("`alsa::poll()` spuriously returned");
-            descriptors.len() as libc::nfds_t,
+        return Err(BackendSpecificError { description });
-            -1,
-        )
-    };
-    if res < 0 {
-        let description = format!("`libc::poll()` failed: {}", io::Error::last_os_error());
-        error_callback(BackendSpecificError { description }.into());
-        return PollDescriptorsFlow::Continue;
-    } else if res == 0 {
-        let description = String::from("`libc::poll()` spuriously returned");
-        error_callback(BackendSpecificError { description }.into());
-        return PollDescriptorsFlow::Continue;
     }
 
     if descriptors[0].revents != 0 {
         // The stream has been requested to be destroyed.
         rx.clear_pipe();
-        return PollDescriptorsFlow::Return;
+        return Ok(PollDescriptorsFlow::Return);
     }
 
-    let stream_type = match check_for_pollout_or_pollin(stream, descriptors[1..].as_mut_ptr()) {
+    let stream_type = match stream.channel.revents(&descriptors[1..])? {
-        Ok(Some(ty)) => ty,
+        alsa::poll::Flags::OUT => StreamType::Output,
-        Ok(None) => {
+        alsa::poll::Flags::IN => StreamType::Input,
+        _ => {
             // Nothing to process, poll again
-            return PollDescriptorsFlow::Continue;
+            return Ok(PollDescriptorsFlow::Continue);
-        }
-        Err(err) => {
-            error_callback(err.into());
-            return PollDescriptorsFlow::Continue;
         }
     };
     // Get the number of available samples for reading/writing.
-    let available_samples = match get_available_samples(stream) {
+    let available_samples = get_available_samples(stream)?;
-        Ok(n) => n,
-        Err(err) => {
-            let description = format!("Failed to query the number of available samples: {}", err);
-            error_callback(BackendSpecificError { description }.into());
-            return PollDescriptorsFlow::Continue;
-        }
-    };
 
     // Only go on if there is at least `stream.period_len` samples.
     if available_samples < stream.period_len {
-        return PollDescriptorsFlow::Continue;
+        return Ok(PollDescriptorsFlow::Continue);
     }
 
     // Prepare the data buffer.
@@ -705,37 +626,26 @@ fn poll_descriptors_and_prepare_buffer(
     buffer.resize(buffer_size, 0u8);
     let available_frames = available_samples / stream.num_channels as usize;
 
-    PollDescriptorsFlow::Ready {
+    Ok(PollDescriptorsFlow::Ready {
         stream_type,
         available_frames,
-    }
+    })
 }
 
 // Read input data from ALSA and deliver it to the user.
 fn process_input(
     stream: &StreamInner,
     buffer: &mut [u8],
-    available_frames: usize,
     data_callback: &mut (dyn FnMut(&Data) + Send + 'static),
-    error_callback: &mut dyn FnMut(StreamError),
+) -> Result<(), BackendSpecificError> {
-) {
+    stream.channel.io().readi(buffer)?;
-    let result = unsafe {
-        alsa::snd_pcm_readi(
-            stream.channel,
-            buffer.as_mut_ptr() as *mut _,
-            available_frames as alsa::snd_pcm_uframes_t,
-        )
-    };
-    if let Err(err) = check_errors(result as _) {
-        let description = format!("`snd_pcm_readi` failed: {}", err);
-        error_callback(BackendSpecificError { description }.into());
-        return;
-    }
     let sample_format = stream.sample_format;
     let data = buffer.as_mut_ptr() as *mut ();
     let len = buffer.len() / sample_format.sample_size();
     let data = unsafe { Data::from_parts(data, len, sample_format) };
     data_callback(&data);
+
+    Ok(())
 }
 
 // Request data from the user's function and write it via ALSA.
@@ -757,31 +667,28 @@ fn process_output(
         data_callback(&mut data);
     }
     loop {
-        let result = unsafe {
+        match stream.channel.io().writei(buffer) {
-            alsa::snd_pcm_writei(
+            Err(err) if err.errno() == Some(nix::errno::Errno::EPIPE) => {
-                stream.channel,
+                // buffer underrun
-                buffer.as_ptr() as *const _,
+                // TODO: Notify the user of this.
-                available_frames as alsa::snd_pcm_uframes_t,
+                let _ = stream.channel.try_recover(err, false);
-            )
+            }
-        };
+            Err(err) => {
-        if result == -libc::EPIPE as c_long {
+                error_callback(err.into());
-            // buffer underrun
+                continue;
-            // TODO: Notify the user of this.
+            }
-            unsafe { alsa::snd_pcm_recover(stream.channel, result as i32, 0) };
+            Ok(result) if result != available_frames => {
-        } else if let Err(err) = check_errors(result as _) {
+                let description = format!(
-            let description = format!("`snd_pcm_writei` failed: {}", err);
+                    "unexpected number of frames written: expected {}, \
-            error_callback(BackendSpecificError { description }.into());
+                     result {} (this should never happen)",
-            continue;
+                    available_frames, result,
-        } else if result as usize != available_frames {
+                );
-            let description = format!(
+                error_callback(BackendSpecificError { description }.into());
-                "unexpected number of frames written: expected {}, \
+                continue;
-                 result {} (this should never happen)",
+            }
-                available_frames, result,
+            _ => {
-            );
+                break;
-            error_callback(BackendSpecificError { description }.into());
+            }
-            continue;
-        } else {
-            break;
         }
     }
 }
@@ -841,237 +748,126 @@ impl Drop for Stream {
 
 impl StreamTrait for Stream {
     fn play(&self) -> Result<(), PlayStreamError> {
-        unsafe {
+        self.inner.channel.pause(false).ok();
-            alsa::snd_pcm_pause(self.inner.channel, 0);
-        }
-        // TODO: error handling
         Ok(())
     }
     fn pause(&self) -> Result<(), PauseStreamError> {
-        unsafe {
+        self.inner.channel.pause(true).ok();
-            alsa::snd_pcm_pause(self.inner.channel, 1);
-        }
-        // TODO: error handling
         Ok(())
     }
 }
 
-// Check whether the event is `POLLOUT` or `POLLIN`.
-//
-// If so, return the stream type associated with the event.
-//
-// Otherwise, returns `Ok(None)`.
-//
-// Returns an `Err` if the `snd_pcm_poll_descriptors_revents` call fails.
-fn check_for_pollout_or_pollin(
-    stream: &StreamInner,
-    stream_descriptor_ptr: *mut libc::pollfd,
-) -> Result<Option<StreamType>, BackendSpecificError> {
-    let (revent, res) = unsafe {
-        let mut revent = 0;
-        let res = alsa::snd_pcm_poll_descriptors_revents(
-            stream.channel,
-            stream_descriptor_ptr,
-            stream.num_descriptors as libc::c_uint,
-            &mut revent,
-        );
-        (revent, res)
-    };
-    if let Err(desc) = check_errors(res) {
-        let description = format!("`snd_pcm_poll_descriptors_revents` failed: {}", desc);
-        let err = BackendSpecificError { description };
-        return Err(err);
-    }
-
-    if revent as i16 == libc::POLLOUT {
-        Ok(Some(StreamType::Output))
-    } else if revent as i16 == libc::POLLIN {
-        Ok(Some(StreamType::Input))
-    } else {
-        Ok(None)
-    }
-}
-
 // Determine the number of samples that are available to read/write.
 fn get_available_samples(stream: &StreamInner) -> Result<usize, BackendSpecificError> {
-    let available = unsafe { alsa::snd_pcm_avail_update(stream.channel) };
+    match stream.channel.avail_update() {
-    if available == -32 {
+        Err(err) if err.errno() == Some(nix::errno::Errno::EPIPE) => {
-        // buffer underrun
+            // buffer underrun
-        // TODO: Notify the user some how.
+            // TODO: Notify the user some how.
-        Ok(stream.buffer_len)
+            Ok(stream.buffer_len)
-    } else if let Err(desc) = check_errors(available as libc::c_int) {
+        }
-        let description = format!("failed to get available samples: {}", desc);
+        Err(err) => Err(err.into()),
-        let err = BackendSpecificError { description };
+        Ok(available) => Ok(available as usize * stream.num_channels as usize),
-        Err(err)
-    } else {
-        Ok((available * stream.num_channels as alsa::snd_pcm_sframes_t) as usize)
     }
 }
 
-unsafe fn set_hw_params_from_format(
+fn set_hw_params_from_format<'a>(
-    pcm_handle: *mut alsa::snd_pcm_t,
+    pcm_handle: &'a alsa::pcm::PCM,
-    hw_params: &HwParams,
     config: &StreamConfig,
     sample_format: SampleFormat,
-) -> Result<(), String> {
+) -> Result<alsa::pcm::HwParams<'a>, BackendSpecificError> {
-    if let Err(e) = check_errors(alsa::snd_pcm_hw_params_any(pcm_handle, hw_params.0)) {
+    let hw_params = alsa::pcm::HwParams::any(pcm_handle)?;
-        return Err(format!("errors on pcm handle: {}", e));
+    hw_params.set_access(alsa::pcm::Access::RWInterleaved)?;
-    }
-    if let Err(e) = check_errors(alsa::snd_pcm_hw_params_set_access(
-        pcm_handle,
-        hw_params.0,
-        alsa::SND_PCM_ACCESS_RW_INTERLEAVED,
-    )) {
-        return Err(format!("handle not acessible: {}", e));
-    }
 
     let sample_format = if cfg!(target_endian = "big") {
         match sample_format {
-            SampleFormat::I16 => alsa::SND_PCM_FORMAT_S16_BE,
+            SampleFormat::I16 => alsa::pcm::Format::S16BE,
-            SampleFormat::U16 => alsa::SND_PCM_FORMAT_U16_BE,
+            SampleFormat::U16 => alsa::pcm::Format::U16BE,
-            SampleFormat::F32 => alsa::SND_PCM_FORMAT_FLOAT_BE,
+            SampleFormat::F32 => alsa::pcm::Format::FloatBE,
         }
     } else {
         match sample_format {
-            SampleFormat::I16 => alsa::SND_PCM_FORMAT_S16_LE,
+            SampleFormat::I16 => alsa::pcm::Format::S16LE,
-            SampleFormat::U16 => alsa::SND_PCM_FORMAT_U16_LE,
+            SampleFormat::U16 => alsa::pcm::Format::U16LE,
-            SampleFormat::F32 => alsa::SND_PCM_FORMAT_FLOAT_LE,
+            SampleFormat::F32 => alsa::pcm::Format::FloatLE,
         }
     };
 
-    if let Err(e) = check_errors(alsa::snd_pcm_hw_params_set_format(
+    hw_params.set_format(sample_format)?;
-        pcm_handle,
+    hw_params.set_rate(config.sample_rate.0, alsa::ValueOr::Nearest)?;
-        hw_params.0,
+    hw_params.set_channels(config.channels as u32)?;
-        sample_format,
-    )) {
-        return Err(format!("format could not be set: {}", e));
-    }
-    if let Err(e) = check_errors(alsa::snd_pcm_hw_params_set_rate(
-        pcm_handle,
-        hw_params.0,
-        config.sample_rate.0 as libc::c_uint,
-        0,
-    )) {
-        return Err(format!("sample rate could not be set: {}", e));
-    }
-    if let Err(e) = check_errors(alsa::snd_pcm_hw_params_set_channels(
-        pcm_handle,
-        hw_params.0,
-        config.channels as libc::c_uint,
-    )) {
-        return Err(format!("channel count could not be set: {}", e));
-    }
 
     // If this isn't set manually a overlarge buffer may be used causing audio delay
-    if let Err(e) = check_errors(alsa::snd_pcm_hw_params_set_buffer_time_near(
+    hw_params.set_buffer_time_near(100_000, alsa::ValueOr::Nearest)?;
-        pcm_handle,
-        hw_params.0,
-        &mut 100_000,
-        &mut 0,
-    )) {
-        return Err(format!("buffer time could not be set: {}", e));
-    }
 
-    if let Err(e) = check_errors(alsa::snd_pcm_hw_params(pcm_handle, hw_params.0)) {
+    pcm_handle.hw_params(&hw_params)?;
-        return Err(format!("hardware params could not be set: {}", e));
-    }
 
-    Ok(())
+    Ok(hw_params)
 }
 
-unsafe fn set_sw_params_from_format(
+fn set_sw_params_from_format(
-    pcm_handle: *mut alsa::snd_pcm_t,
+    pcm_handle: &alsa::pcm::PCM,
     config: &StreamConfig,
-) -> Result<(usize, usize), String> {
+) -> Result<(usize, usize), BackendSpecificError> {
-    let mut sw_params = ptr::null_mut(); // TODO: RAII
+    let sw_params = pcm_handle.sw_params_current()?;
-    if let Err(e) = check_errors(alsa::snd_pcm_sw_params_malloc(&mut sw_params)) {
+    sw_params.set_start_threshold(0)?;
-        return Err(format!("snd_pcm_sw_params_malloc failed: {}", e));
-    }
-    if let Err(e) = check_errors(alsa::snd_pcm_sw_params_current(pcm_handle, sw_params)) {
-        return Err(format!("snd_pcm_sw_params_current failed: {}", e));
-    }
-    if let Err(e) = check_errors(alsa::snd_pcm_sw_params_set_start_threshold(
-        pcm_handle, sw_params, 0,
-    )) {
-        return Err(format!(
-            "snd_pcm_sw_params_set_start_threshold failed: {}",
-            e
-        ));
-    }
 
     let (buffer_len, period_len) = {
-        let mut buffer = 0;
+        let (buffer, period) = pcm_handle.get_params()?;
-        let mut period = 0;
-        if let Err(e) = check_errors(alsa::snd_pcm_get_params(
-            pcm_handle,
-            &mut buffer,
-            &mut period,
-        )) {
-            return Err(format!("failed to initialize buffer: {}", e));
-        }
         if buffer == 0 {
-            return Err(format!("initialization resulted in a null buffer"));
+            return Err(BackendSpecificError {
-        }
+                description: "initialization resulted in a null buffer".to_string(),
-        if let Err(e) = check_errors(alsa::snd_pcm_sw_params_set_avail_min(
+            });
-            pcm_handle, sw_params, period,
-        )) {
-            return Err(format!("snd_pcm_sw_params_set_avail_min failed: {}", e));
         }
+        sw_params.set_avail_min(period as alsa::pcm::Frames)?;
         let buffer = buffer as usize * config.channels as usize;
         let period = period as usize * config.channels as usize;
         (buffer, period)
     };
 
-    if let Err(e) = check_errors(alsa::snd_pcm_sw_params(pcm_handle, sw_params)) {
+    pcm_handle.sw_params(&sw_params)?;
-        return Err(format!("snd_pcm_sw_params failed: {}", e));
-    }
 
-    alsa::snd_pcm_sw_params_free(sw_params);
     Ok((buffer_len, period_len))
 }
 
-/// Wrapper around `hw_params`.
+impl From<alsa::Error> for BackendSpecificError {
-struct HwParams(*mut alsa::snd_pcm_hw_params_t);
+    fn from(err: alsa::Error) -> Self {
-
+        BackendSpecificError {
-impl HwParams {
+            description: err.to_string(),
-    pub fn alloc() -> HwParams {
-        unsafe {
-            let mut hw_params = ptr::null_mut();
-            check_errors(alsa::snd_pcm_hw_params_malloc(&mut hw_params))
-                .expect("unable to get hardware parameters");
-            HwParams(hw_params)
         }
     }
 }
 
-impl Drop for HwParams {
+impl From<alsa::Error> for BuildStreamError {
-    fn drop(&mut self) {
+    fn from(err: alsa::Error) -> Self {
-        unsafe {
+        let err: BackendSpecificError = err.into();
-            alsa::snd_pcm_hw_params_free(self.0);
+        err.into()
-        }
     }
 }
 
-impl Drop for StreamInner {
+impl From<alsa::Error> for SupportedStreamConfigsError {
-    #[inline]
+    fn from(err: alsa::Error) -> Self {
-    fn drop(&mut self) {
+        let err: BackendSpecificError = err.into();
-        unsafe {
+        err.into()
-            alsa::snd_pcm_close(self.channel);
-        }
     }
 }
 
-#[inline]
+impl From<alsa::Error> for PlayStreamError {
-fn check_errors(err: libc::c_int) -> Result<(), String> {
+    fn from(err: alsa::Error) -> Self {
-    if err < 0 {
+        let err: BackendSpecificError = err.into();
-        unsafe {
+        err.into()
-            let s = ffi::CStr::from_ptr(alsa::snd_strerror(err))
+    }
-                .to_bytes()
+}
-                .to_vec();
+
-            let s = String::from_utf8(s).expect("Streaming error occured");
+impl From<alsa::Error> for PauseStreamError {
-            return Err(s);
+    fn from(err: alsa::Error) -> Self {
-        }
+        let err: BackendSpecificError = err.into();
+        err.into()
+    }
+}
+
+impl From<alsa::Error> for StreamError {
+    fn from(err: alsa::Error) -> Self {
+        let err: BackendSpecificError = err.into();
+        err.into()
     }
-
-    Ok(())
 }