Various code improvements (#777)

* Remove deprecated use of std::u16::MAX
* Use `FromStr` for fallible `&str` conversions
* DRY up strings into constants
* Change `as_ref().map()` into `as_deref()`
* Use `Duration` for time constants and functions
* Optimize `Vec` with response times
* Move comments for `rustdoc` to parse

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 - [audio, playback] Moved `VorbisDecoder`, `VorbisError`, `AudioPacket`, `PassthroughDecoder`, `PassthroughError`, `AudioError`, `AudioDecoder` and the `convert` module from `librespot-audio` to `librespot-playback`. The underlying crates `vorbis`, `librespot-tremor`, `lewton` and `ogg` should be used directly. (breaking)
+- [audio, playback] Use `Duration` for time constants and functions (breaking)
 - [connect, playback] Moved volume controls from `librespot-connect` to `librespot-playback` crate
 - [connect] Synchronize player volume with mixer volume on playback
 - [playback] Store and pass samples in 64-bit floating point

audio/src/fetch/mod.rs

@@ -18,70 +18,70 @@ use tokio::sync::{mpsc, oneshot};
 use self::receive::{audio_file_fetch, request_range};
 use crate::range_set::{Range, RangeSet};
 
+/// The minimum size of a block that is requested from the Spotify servers in one request.
+/// This is the block size that is typically requested while doing a `seek()` on a file.
+/// Note: smaller requests can happen if part of the block is downloaded already.
 const MINIMUM_DOWNLOAD_SIZE: usize = 1024 * 16;
-// The minimum size of a block that is requested from the Spotify servers in one request.
-// This is the block size that is typically requested while doing a seek() on a file.
-// Note: smaller requests can happen if part of the block is downloaded already.
 
+/// The amount of data that is requested when initially opening a file.
+/// Note: if the file is opened to play from the beginning, the amount of data to
+/// read ahead is requested in addition to this amount. If the file is opened to seek to
+/// another position, then only this amount is requested on the first request.
 const INITIAL_DOWNLOAD_SIZE: usize = 1024 * 16;
-// The amount of data that is requested when initially opening a file.
-// Note: if the file is opened to play from the beginning, the amount of data to
-// read ahead is requested in addition to this amount. If the file is opened to seek to
-// another position, then only this amount is requested on the first request.
 
-const INITIAL_PING_TIME_ESTIMATE_SECONDS: f64 = 0.5;
+/// The ping time that is used for calculations before a ping time was actually measured.
-// The pig time that is used for calculations before a ping time was actually measured.
+const INITIAL_PING_TIME_ESTIMATE: Duration = Duration::from_millis(500);
 
-const MAXIMUM_ASSUMED_PING_TIME_SECONDS: f64 = 1.5;
+/// If the measured ping time to the Spotify server is larger than this value, it is capped
-// If the measured ping time to the Spotify server is larger than this value, it is capped
+/// to avoid run-away block sizes and pre-fetching.
-// to avoid run-away block sizes and pre-fetching.
+const MAXIMUM_ASSUMED_PING_TIME: Duration = Duration::from_millis(1500);
 
-pub const READ_AHEAD_BEFORE_PLAYBACK_SECONDS: f64 = 1.0;
+/// Before playback starts, this many seconds of data must be present.
-// Before playback starts, this many seconds of data must be present.
+/// Note: the calculations are done using the nominal bitrate of the file. The actual amount
-// Note: the calculations are done using the nominal bitrate of the file. The actual amount
+/// of audio data may be larger or smaller.
-// of audio data may be larger or smaller.
+pub const READ_AHEAD_BEFORE_PLAYBACK: Duration = Duration::from_secs(1);
 
-pub const READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS: f64 = 2.0;
+/// Same as `READ_AHEAD_BEFORE_PLAYBACK`, but the time is taken as a factor of the ping
-// Same as READ_AHEAD_BEFORE_PLAYBACK_SECONDS, but the time is taken as a factor of the ping
+/// time to the Spotify server. Both `READ_AHEAD_BEFORE_PLAYBACK` and
-// time to the Spotify server.
+/// `READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS` are obeyed.
-// Both, READ_AHEAD_BEFORE_PLAYBACK_SECONDS and READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS are
+/// Note: the calculations are done using the nominal bitrate of the file. The actual amount
-// obeyed.
+/// of audio data may be larger or smaller.
-// Note: the calculations are done using the nominal bitrate of the file. The actual amount
+pub const READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS: f32 = 2.0;
-// of audio data may be larger or smaller.
 
-pub const READ_AHEAD_DURING_PLAYBACK_SECONDS: f64 = 5.0;
+/// While playing back, this many seconds of data ahead of the current read position are
-// While playing back, this many seconds of data ahead of the current read position are
+/// requested.
-// requested.
+/// Note: the calculations are done using the nominal bitrate of the file. The actual amount
-// Note: the calculations are done using the nominal bitrate of the file. The actual amount
+/// of audio data may be larger or smaller.
-// of audio data may be larger or smaller.
+pub const READ_AHEAD_DURING_PLAYBACK: Duration = Duration::from_secs(5);
 
-pub const READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS: f64 = 10.0;
+/// Same as `READ_AHEAD_DURING_PLAYBACK`, but the time is taken as a factor of the ping
-// Same as READ_AHEAD_DURING_PLAYBACK_SECONDS, but the time is taken as a factor of the ping
+/// time to the Spotify server.
-// time to the Spotify server.
+/// Note: the calculations are done using the nominal bitrate of the file. The actual amount
-// Note: the calculations are done using the nominal bitrate of the file. The actual amount
+/// of audio data may be larger or smaller.
-// of audio data may be larger or smaller.
+pub const READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS: f32 = 10.0;
 
-const PREFETCH_THRESHOLD_FACTOR: f64 = 4.0;
+/// If the amount of data that is pending (requested but not received) is less than a certain amount,
-// If the amount of data that is pending (requested but not received) is less than a certain amount,
+/// data is pre-fetched in addition to the read ahead settings above. The threshold for requesting more
-// data is pre-fetched in addition to the read ahead settings above. The threshold for requesting more
+/// data is calculated as `<pending bytes> < PREFETCH_THRESHOLD_FACTOR * <ping time> * <nominal data rate>`
-// data is calculated as
+const PREFETCH_THRESHOLD_FACTOR: f32 = 4.0;
-// <pending bytes> < PREFETCH_THRESHOLD_FACTOR * <ping time> * <nominal data rate>
 
-const FAST_PREFETCH_THRESHOLD_FACTOR: f64 = 1.5;
+/// Similar to `PREFETCH_THRESHOLD_FACTOR`, but it also takes the current download rate into account.
-// Similar to PREFETCH_THRESHOLD_FACTOR, but it also takes the current download rate into account.
+/// The formula used is `<pending bytes> < FAST_PREFETCH_THRESHOLD_FACTOR * <ping time> * <measured download rate>`
-// The formula used is
+/// This mechanism allows for fast downloading of the remainder of the file. The number should be larger
-// <pending bytes> < FAST_PREFETCH_THRESHOLD_FACTOR * <ping time> * <measured download rate>
+/// than `1.0` so the download rate ramps up until the bandwidth is saturated. The larger the value, the faster
-// This mechanism allows for fast downloading of the remainder of the file. The number should be larger
+/// the download rate ramps up. However, this comes at the cost that it might hurt ping time if a seek is
-// than 1 so the download rate ramps up until the bandwidth is saturated. The larger the value, the faster
+/// performed while downloading. Values smaller than `1.0` cause the download rate to collapse and effectively
-// the download rate ramps up. However, this comes at the cost that it might hurt ping-time if a seek is
+/// only `PREFETCH_THRESHOLD_FACTOR` is in effect. Thus, set to `0.0` if bandwidth saturation is not wanted.
-// performed while downloading. Values smaller than 1 cause the download rate to collapse and effectively
+const FAST_PREFETCH_THRESHOLD_FACTOR: f32 = 1.5;
-// only PREFETCH_THRESHOLD_FACTOR is in effect. Thus, set to zero if bandwidth saturation is not wanted.
 
+/// Limit the number of requests that are pending simultaneously before pre-fetching data. Pending
+/// requests share bandwidth. Thus, havint too many requests can lead to the one that is needed next
+/// for playback to be delayed leading to a buffer underrun. This limit has the effect that a new
+/// pre-fetch request is only sent if less than `MAX_PREFETCH_REQUESTS` are pending.
 const MAX_PREFETCH_REQUESTS: usize = 4;
-// Limit the number of requests that are pending simultaneously before pre-fetching data. Pending
+
-// requests share bandwidth. Thus, havint too many requests can lead to the one that is needed next
+/// The time we will wait to obtain status updates on downloading.
-// for playback to be delayed leading to a buffer underrun. This limit has the effect that a new
+const DOWNLOAD_TIMEOUT: Duration = Duration::from_secs(1);
-// pre-fetch request is only sent if less than MAX_PREFETCH_REQUESTS are pending.
 
 pub enum AudioFile {
     Cached(fs::File),
@@ -131,10 +131,10 @@ impl StreamLoaderController {
         })
     }
 
-    pub fn ping_time_ms(&self) -> usize {
+    pub fn ping_time(&self) -> Duration {
-        self.stream_shared.as_ref().map_or(0, |shared| {
+        Duration::from_millis(self.stream_shared.as_ref().map_or(0, |shared| {
-            shared.ping_time_ms.load(atomic::Ordering::Relaxed)
+            shared.ping_time_ms.load(atomic::Ordering::Relaxed) as u64
-        })
+        }))
     }
 
     fn send_stream_loader_command(&self, command: StreamLoaderCommand) {
@@ -170,7 +170,7 @@ impl StreamLoaderController {
             {
                 download_status = shared
                     .cond
-                    .wait_timeout(download_status, Duration::from_millis(1000))
+                    .wait_timeout(download_status, DOWNLOAD_TIMEOUT)
                     .unwrap()
                     .0;
                 if range.length
@@ -271,10 +271,10 @@ impl AudioFile {
         let mut initial_data_length = if play_from_beginning {
             INITIAL_DOWNLOAD_SIZE
                 + max(
-                    (READ_AHEAD_DURING_PLAYBACK_SECONDS * bytes_per_second as f64) as usize,
+                    (READ_AHEAD_DURING_PLAYBACK.as_secs_f32() * bytes_per_second as f32) as usize,
-                    (INITIAL_PING_TIME_ESTIMATE_SECONDS
+                    (INITIAL_PING_TIME_ESTIMATE.as_secs_f32()
                         * READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS
-                        * bytes_per_second as f64) as usize,
+                        * bytes_per_second as f32) as usize,
                 )
         } else {
             INITIAL_DOWNLOAD_SIZE
@@ -405,17 +405,19 @@ impl Read for AudioFileStreaming {
         let length_to_request = match *(self.shared.download_strategy.lock().unwrap()) {
             DownloadStrategy::RandomAccess() => length,
             DownloadStrategy::Streaming() => {
-                // Due to the read-ahead stuff, we potentially request more than the actual reqeust demanded.
+                // Due to the read-ahead stuff, we potentially request more than the actual request demanded.
-                let ping_time_seconds =
+                let ping_time_seconds = Duration::from_millis(
-                    0.0001 * self.shared.ping_time_ms.load(atomic::Ordering::Relaxed) as f64;
+                    self.shared.ping_time_ms.load(atomic::Ordering::Relaxed) as u64,
+                )
+                .as_secs_f32();
 
                 let length_to_request = length
                     + max(
-                        (READ_AHEAD_DURING_PLAYBACK_SECONDS * self.shared.stream_data_rate as f64)
+                        (READ_AHEAD_DURING_PLAYBACK.as_secs_f32()
-                            as usize,
+                            * self.shared.stream_data_rate as f32) as usize,
                         (READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS
                             * ping_time_seconds
-                            * self.shared.stream_data_rate as f64) as usize,
+                            * self.shared.stream_data_rate as f32) as usize,
                     );
                 min(length_to_request, self.shared.file_size - offset)
             }
@@ -449,7 +451,7 @@ impl Read for AudioFileStreaming {
             download_status = self
                 .shared
                 .cond
-                .wait_timeout(download_status, Duration::from_millis(1000))
+                .wait_timeout(download_status, DOWNLOAD_TIMEOUT)
                 .unwrap()
                 .0;
         }

audio/src/fetch/receive.rs

@@ -1,8 +1,9 @@
 use std::cmp::{max, min};
 use std::io::{Seek, SeekFrom, Write};
 use std::sync::{atomic, Arc};
-use std::time::Instant;
+use std::time::{Duration, Instant};
 
+use atomic::Ordering;
 use byteorder::{BigEndian, WriteBytesExt};
 use bytes::Bytes;
 use futures_util::StreamExt;
@@ -16,7 +17,7 @@ use crate::range_set::{Range, RangeSet};
 
 use super::{AudioFileShared, DownloadStrategy, StreamLoaderCommand};
 use super::{
-    FAST_PREFETCH_THRESHOLD_FACTOR, MAXIMUM_ASSUMED_PING_TIME_SECONDS, MAX_PREFETCH_REQUESTS,
+    FAST_PREFETCH_THRESHOLD_FACTOR, MAXIMUM_ASSUMED_PING_TIME, MAX_PREFETCH_REQUESTS,
     MINIMUM_DOWNLOAD_SIZE, PREFETCH_THRESHOLD_FACTOR,
 };
 
@@ -57,7 +58,7 @@ struct PartialFileData {
 }
 
 enum ReceivedData {
-    ResponseTimeMs(usize),
+    ResponseTime(Duration),
     Data(PartialFileData),
 }
 
@@ -74,7 +75,7 @@ async fn receive_data(
 
     let old_number_of_request = shared
         .number_of_open_requests
-        .fetch_add(1, atomic::Ordering::SeqCst);
+        .fetch_add(1, Ordering::SeqCst);
 
     let mut measure_ping_time = old_number_of_request == 0;
 
@@ -86,14 +87,11 @@ async fn receive_data(
         };
 
         if measure_ping_time {
-            let duration = Instant::now() - request_sent_time;
+            let mut duration = Instant::now() - request_sent_time;
-            let duration_ms: u64;
+            if duration > MAXIMUM_ASSUMED_PING_TIME {
-            if 0.001 * (duration.as_millis() as f64) > MAXIMUM_ASSUMED_PING_TIME_SECONDS {
+                duration = MAXIMUM_ASSUMED_PING_TIME;
-                duration_ms = (MAXIMUM_ASSUMED_PING_TIME_SECONDS * 1000.0) as u64;
-            } else {
-                duration_ms = duration.as_millis() as u64;
             }
-            let _ = file_data_tx.send(ReceivedData::ResponseTimeMs(duration_ms as usize));
+            let _ = file_data_tx.send(ReceivedData::ResponseTime(duration));
             measure_ping_time = false;
         }
         let data_size = data.len();
@@ -127,7 +125,7 @@ async fn receive_data(
 
     shared
         .number_of_open_requests
-        .fetch_sub(1, atomic::Ordering::SeqCst);
+        .fetch_sub(1, Ordering::SeqCst);
 
     if result.is_err() {
         warn!(
@@ -149,7 +147,7 @@ struct AudioFileFetch {
 
     file_data_tx: mpsc::UnboundedSender<ReceivedData>,
     complete_tx: Option<oneshot::Sender<NamedTempFile>>,
-    network_response_times_ms: Vec<usize>,
+    network_response_times: Vec<Duration>,
 }
 
 // Might be replaced by enum from std once stable
@@ -237,7 +235,7 @@ impl AudioFileFetch {
 
             // download data from after the current read position first
             let mut tail_end = RangeSet::new();
-            let read_position = self.shared.read_position.load(atomic::Ordering::Relaxed);
+            let read_position = self.shared.read_position.load(Ordering::Relaxed);
             tail_end.add_range(&Range::new(
                 read_position,
                 self.shared.file_size - read_position,
@@ -267,26 +265,23 @@ impl AudioFileFetch {
 
     fn handle_file_data(&mut self, data: ReceivedData) -> ControlFlow {
         match data {
-            ReceivedData::ResponseTimeMs(response_time_ms) => {
+            ReceivedData::ResponseTime(response_time) => {
-                trace!("Ping time estimated as: {} ms.", response_time_ms);
+                trace!("Ping time estimated as: {}ms", response_time.as_millis());
+
+                // prune old response times. Keep at most two so we can push a third.
+                while self.network_response_times.len() >= 3 {
+                    self.network_response_times.remove(0);
+                }
 
                 // record the response time
-                self.network_response_times_ms.push(response_time_ms);
+                self.network_response_times.push(response_time);
-
-                // prune old response times. Keep at most three.
-                while self.network_response_times_ms.len() > 3 {
-                    self.network_response_times_ms.remove(0);
-                }
 
                 // stats::median is experimental. So we calculate the median of up to three ourselves.
-                let ping_time_ms: usize = match self.network_response_times_ms.len() {
+                let ping_time = match self.network_response_times.len() {
-                    1 => self.network_response_times_ms[0] as usize,
+                    1 => self.network_response_times[0],
-                    2 => {
+                    2 => (self.network_response_times[0] + self.network_response_times[1]) / 2,
-                        ((self.network_response_times_ms[0] + self.network_response_times_ms[1])
-                            / 2) as usize
-                    }
                     3 => {
-                        let mut times = self.network_response_times_ms.clone();
+                        let mut times = self.network_response_times.clone();
                         times.sort_unstable();
                         times[1]
                     }
@@ -296,7 +291,7 @@ impl AudioFileFetch {
                 // store our new estimate for everyone to see
                 self.shared
                     .ping_time_ms
-                    .store(ping_time_ms, atomic::Ordering::Relaxed);
+                    .store(ping_time.as_millis() as usize, Ordering::Relaxed);
             }
             ReceivedData::Data(data) => {
                 self.output
@@ -390,7 +385,7 @@ pub(super) async fn audio_file_fetch(
 
         file_data_tx,
         complete_tx: Some(complete_tx),
-        network_response_times_ms: Vec::new(),
+        network_response_times: Vec::with_capacity(3),
     };
 
     loop {
@@ -408,10 +403,8 @@ pub(super) async fn audio_file_fetch(
         }
 
         if fetch.get_download_strategy() == DownloadStrategy::Streaming() {
-            let number_of_open_requests = fetch
+            let number_of_open_requests =
-                .shared
+                fetch.shared.number_of_open_requests.load(Ordering::SeqCst);
-                .number_of_open_requests
-                .load(atomic::Ordering::SeqCst);
             if number_of_open_requests < MAX_PREFETCH_REQUESTS {
                 let max_requests_to_send = MAX_PREFETCH_REQUESTS - number_of_open_requests;
 
@@ -424,14 +417,15 @@ pub(super) async fn audio_file_fetch(
                 };
 
                 let ping_time_seconds =
-                    0.001 * fetch.shared.ping_time_ms.load(atomic::Ordering::Relaxed) as f64;
+                    Duration::from_millis(fetch.shared.ping_time_ms.load(Ordering::Relaxed) as u64)
+                        .as_secs_f32();
                 let download_rate = fetch.session.channel().get_download_rate_estimate();
 
                 let desired_pending_bytes = max(
                     (PREFETCH_THRESHOLD_FACTOR
                         * ping_time_seconds
-                        * fetch.shared.stream_data_rate as f64) as usize,
+                        * fetch.shared.stream_data_rate as f32) as usize,
-                    (FAST_PREFETCH_THRESHOLD_FACTOR * ping_time_seconds * download_rate as f64)
+                    (FAST_PREFETCH_THRESHOLD_FACTOR * ping_time_seconds * download_rate as f32)
                         as usize,
                 );
 

audio/src/lib.rs

@@ -11,6 +11,6 @@ mod range_set;
 pub use decrypt::AudioDecrypt;
 pub use fetch::{AudioFile, StreamLoaderController};
 pub use fetch::{
-    READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS, READ_AHEAD_BEFORE_PLAYBACK_SECONDS,
+    READ_AHEAD_BEFORE_PLAYBACK, READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS, READ_AHEAD_DURING_PLAYBACK,
-    READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS, READ_AHEAD_DURING_PLAYBACK_SECONDS,
+    READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS,
 };

connect/src/spirc.rs

@@ -88,7 +88,7 @@ const CONTEXT_TRACKS_HISTORY: usize = 10;
 const CONTEXT_FETCH_THRESHOLD: u32 = 5;
 
 const VOLUME_STEPS: i64 = 64;
-const VOLUME_STEP_SIZE: u16 = 1024; // (std::u16::MAX + 1) / VOLUME_STEPS
+const VOLUME_STEP_SIZE: u16 = 1024; // (u16::MAX + 1) / VOLUME_STEPS
 
 pub struct Spirc {
     commands: mpsc::UnboundedSender<SpircCommand>,

core/src/channel.rs

@@ -23,6 +23,8 @@ component! {
     }
 }
 
+const ONE_SECOND_IN_MS: usize = 1000;
+
 #[derive(Debug, Hash, PartialEq, Eq, Copy, Clone)]
 pub struct ChannelError;
 
@@ -74,8 +76,11 @@ impl ChannelManager {
         self.lock(|inner| {
             let current_time = Instant::now();
             if let Some(download_measurement_start) = inner.download_measurement_start {
-                if (current_time - download_measurement_start).as_millis() > 1000 {
+                if (current_time - download_measurement_start).as_millis()
-                    inner.download_rate_estimate = 1000 * inner.download_measurement_bytes
+                    > ONE_SECOND_IN_MS as u128
+                {
+                    inner.download_rate_estimate = ONE_SECOND_IN_MS
+                        * inner.download_measurement_bytes
                         / (current_time - download_measurement_start).as_millis() as usize;
                     inner.download_measurement_start = Some(current_time);
                     inner.download_measurement_bytes = 0;

playback/src/audio_backend/alsa.rs

@@ -2,7 +2,7 @@ use super::{Open, Sink, SinkAsBytes};
 use crate::config::AudioFormat;
 use crate::convert::Converter;
 use crate::decoder::AudioPacket;
-use crate::player::{NUM_CHANNELS, SAMPLES_PER_SECOND, SAMPLE_RATE};
+use crate::{NUM_CHANNELS, SAMPLES_PER_SECOND, SAMPLE_RATE};
 use alsa::device_name::HintIter;
 use alsa::pcm::{Access, Format, Frames, HwParams, PCM};
 use alsa::{Direction, Error, ValueOr};
@@ -10,8 +10,9 @@ use std::cmp::min;
 use std::ffi::CString;
 use std::io;
 use std::process::exit;
+use std::time::Duration;
 
-const BUFFERED_LATENCY: f32 = 0.125; // seconds
+const BUFFERED_LATENCY: Duration = Duration::from_millis(125);
 const BUFFERED_PERIODS: Frames = 4;
 
 pub struct AlsaSink {
@@ -57,7 +58,8 @@ fn open_device(dev_name: &str, format: AudioFormat) -> Result<(PCM, Frames), Box
     // latency = period_size * periods / (rate * bytes_per_frame)
     // For stereo samples encoded as 32-bit float, one frame has a length of eight bytes.
     let mut period_size = ((SAMPLES_PER_SECOND * format.size() as u32) as f32
-        * (BUFFERED_LATENCY / BUFFERED_PERIODS as f32)) as Frames;
+        * (BUFFERED_LATENCY.as_secs_f32() / BUFFERED_PERIODS as f32))
+        as Frames;
     {
         let hwp = HwParams::any(&pcm)?;
         hwp.set_access(Access::RWInterleaved)?;
@@ -80,7 +82,7 @@ impl Open for AlsaSink {
     fn open(device: Option<String>, format: AudioFormat) -> Self {
         info!("Using Alsa sink with format: {:?}", format);
 
-        let name = match device.as_ref().map(AsRef::as_ref) {
+        let name = match device.as_deref() {
             Some("?") => {
                 println!("Listing available Alsa outputs:");
                 list_outputs();
@@ -162,6 +164,8 @@ impl SinkAsBytes for AlsaSink {
 }
 
 impl AlsaSink {
+    pub const NAME: &'static str = "alsa";
+
     fn write_buf(&mut self) {
         let pcm = self.pcm.as_mut().unwrap();
         let io = pcm.io_bytes();

playback/src/audio_backend/gstreamer.rs

@@ -2,7 +2,7 @@ use super::{Open, Sink, SinkAsBytes};
 use crate::config::AudioFormat;
 use crate::convert::Converter;
 use crate::decoder::AudioPacket;
-use crate::player::{NUM_CHANNELS, SAMPLE_RATE};
+use crate::{NUM_CHANNELS, SAMPLE_RATE};
 
 use gstreamer as gst;
 use gstreamer_app as gst_app;
@@ -139,3 +139,7 @@ impl SinkAsBytes for GstreamerSink {
         Ok(())
     }
 }
+
+impl GstreamerSink {
+    pub const NAME: &'static str = "gstreamer";
+}

playback/src/audio_backend/jackaudio.rs

@@ -2,7 +2,7 @@ use super::{Open, Sink};
 use crate::config::AudioFormat;
 use crate::convert::Converter;
 use crate::decoder::AudioPacket;
-use crate::player::NUM_CHANNELS;
+use crate::NUM_CHANNELS;
 use jack::{
     AsyncClient, AudioOut, Client, ClientOptions, Control, Port, ProcessHandler, ProcessScope,
 };
@@ -81,3 +81,7 @@ impl Sink for JackSink {
         Ok(())
     }
 }
+
+impl JackSink {
+    pub const NAME: &'static str = "jackaudio";
+}

playback/src/audio_backend/mod.rs

@@ -90,6 +90,8 @@ use self::gstreamer::GstreamerSink;
 
 #[cfg(any(feature = "rodio-backend", feature = "rodiojack-backend"))]
 mod rodio;
+#[cfg(any(feature = "rodio-backend", feature = "rodiojack-backend"))]
+use self::rodio::RodioSink;
 
 #[cfg(feature = "sdl-backend")]
 mod sdl;
@@ -104,23 +106,23 @@ use self::subprocess::SubprocessSink;
 
 pub const BACKENDS: &[(&str, SinkBuilder)] = &[
     #[cfg(feature = "rodio-backend")]
-    ("rodio", rodio::mk_rodio), // default goes first
+    (RodioSink::NAME, rodio::mk_rodio), // default goes first
     #[cfg(feature = "alsa-backend")]
-    ("alsa", mk_sink::<AlsaSink>),
+    (AlsaSink::NAME, mk_sink::<AlsaSink>),
     #[cfg(feature = "portaudio-backend")]
-    ("portaudio", mk_sink::<PortAudioSink>),
+    (PortAudioSink::NAME, mk_sink::<PortAudioSink>),
     #[cfg(feature = "pulseaudio-backend")]
-    ("pulseaudio", mk_sink::<PulseAudioSink>),
+    (PulseAudioSink::NAME, mk_sink::<PulseAudioSink>),
     #[cfg(feature = "jackaudio-backend")]
-    ("jackaudio", mk_sink::<JackSink>),
+    (JackSink::NAME, mk_sink::<JackSink>),
     #[cfg(feature = "gstreamer-backend")]
-    ("gstreamer", mk_sink::<GstreamerSink>),
+    (GstreamerSink::NAME, mk_sink::<GstreamerSink>),
     #[cfg(feature = "rodiojack-backend")]
     ("rodiojack", rodio::mk_rodiojack),
     #[cfg(feature = "sdl-backend")]
-    ("sdl", mk_sink::<SdlSink>),
+    (SdlSink::NAME, mk_sink::<SdlSink>),
-    ("pipe", mk_sink::<StdoutSink>),
+    (StdoutSink::NAME, mk_sink::<StdoutSink>),
-    ("subprocess", mk_sink::<SubprocessSink>),
+    (SubprocessSink::NAME, mk_sink::<SubprocessSink>),
 ];
 
 pub fn find(name: Option<String>) -> Option<SinkBuilder> {

playback/src/audio_backend/pipe.rs

@@ -34,3 +34,7 @@ impl SinkAsBytes for StdoutSink {
         Ok(())
     }
 }
+
+impl StdoutSink {
+    pub const NAME: &'static str = "pipe";
+}

playback/src/audio_backend/portaudio.rs

@@ -2,7 +2,7 @@ use super::{Open, Sink};
 use crate::config::AudioFormat;
 use crate::convert::Converter;
 use crate::decoder::AudioPacket;
-use crate::player::{NUM_CHANNELS, SAMPLE_RATE};
+use crate::{NUM_CHANNELS, SAMPLE_RATE};
 use portaudio_rs::device::{get_default_output_index, DeviceIndex, DeviceInfo};
 use portaudio_rs::stream::*;
 use std::io;
@@ -57,7 +57,7 @@ impl<'a> Open for PortAudioSink<'a> {
 
         portaudio_rs::initialize().unwrap();
 
-        let device_idx = match device.as_ref().map(AsRef::as_ref) {
+        let device_idx = match device.as_deref() {
             Some("?") => {
                 list_outputs();
                 exit(0)
@@ -178,3 +178,7 @@ impl<'a> Drop for PortAudioSink<'a> {
         portaudio_rs::terminate().unwrap();
     }
 }
+
+impl<'a> PortAudioSink<'a> {
+    pub const NAME: &'static str = "portaudio";
+}

playback/src/audio_backend/pulseaudio.rs

@@ -2,7 +2,7 @@ use super::{Open, Sink, SinkAsBytes};
 use crate::config::AudioFormat;
 use crate::convert::Converter;
 use crate::decoder::AudioPacket;
-use crate::player::{NUM_CHANNELS, SAMPLE_RATE};
+use crate::{NUM_CHANNELS, SAMPLE_RATE};
 use libpulse_binding::{self as pulse, stream::Direction};
 use libpulse_simple_binding::Simple;
 use std::io;
@@ -55,7 +55,7 @@ impl Sink for PulseAudioSink {
             return Ok(());
         }
 
-        let device = self.device.as_ref().map(|s| (*s).as_str());
+        let device = self.device.as_deref();
         let result = Simple::new(
             None,                // Use the default server.
             APP_NAME,            // Our application's name.
@@ -104,3 +104,7 @@ impl SinkAsBytes for PulseAudioSink {
         }
     }
 }
+
+impl PulseAudioSink {
+    pub const NAME: &'static str = "pulseaudio";
+}

playback/src/audio_backend/rodio.rs

@@ -1,5 +1,6 @@
 use std::process::exit;
-use std::{io, thread, time};
+use std::time::Duration;
+use std::{io, thread};
 
 use cpal::traits::{DeviceTrait, HostTrait};
 use thiserror::Error;
@@ -8,7 +9,7 @@ use super::Sink;
 use crate::config::AudioFormat;
 use crate::convert::Converter;
 use crate::decoder::AudioPacket;
-use crate::player::{NUM_CHANNELS, SAMPLE_RATE};
+use crate::{NUM_CHANNELS, SAMPLE_RATE};
 
 #[cfg(all(
     feature = "rodiojack-backend",
@@ -203,8 +204,12 @@ impl Sink for RodioSink {
         // 44100 elements --> about 27 chunks
         while self.rodio_sink.len() > 26 {
             // sleep and wait for rodio to drain a bit
-            thread::sleep(time::Duration::from_millis(10));
+            thread::sleep(Duration::from_millis(10));
         }
         Ok(())
     }
 }
+
+impl RodioSink {
+    pub const NAME: &'static str = "rodio";
+}

playback/src/audio_backend/sdl.rs

@@ -2,9 +2,10 @@ use super::{Open, Sink};
 use crate::config::AudioFormat;
 use crate::convert::Converter;
 use crate::decoder::AudioPacket;
-use crate::player::{NUM_CHANNELS, SAMPLE_RATE};
+use crate::{NUM_CHANNELS, SAMPLE_RATE};
 use sdl2::audio::{AudioQueue, AudioSpecDesired};
-use std::{io, thread, time};
+use std::time::Duration;
+use std::{io, thread};
 
 pub enum SdlSink {
     F32(AudioQueue<f32>),
@@ -86,7 +87,7 @@ impl Sink for SdlSink {
             ($queue: expr, $size: expr) => {{
                 // sleep and wait for sdl thread to drain the queue a bit
                 while $queue.size() > (NUM_CHANNELS as u32 * $size as u32 * SAMPLE_RATE) {
-                    thread::sleep(time::Duration::from_millis(10));
+                    thread::sleep(Duration::from_millis(10));
                 }
             }};
         }
@@ -112,3 +113,7 @@ impl Sink for SdlSink {
         Ok(())
     }
 }
+
+impl SdlSink {
+    pub const NAME: &'static str = "sdl";
+}

playback/src/audio_backend/subprocess.rs

@@ -62,3 +62,7 @@ impl SinkAsBytes for SubprocessSink {
         Ok(())
     }
 }
+
+impl SubprocessSink {
+    pub const NAME: &'static str = "subprocess";
+}

playback/src/config.rs

@@ -2,9 +2,9 @@ use super::player::db_to_ratio;
 use crate::convert::i24;
 pub use crate::dither::{mk_ditherer, DithererBuilder, TriangularDitherer};
 
-use std::convert::TryFrom;
 use std::mem;
 use std::str::FromStr;
+use std::time::Duration;
 
 #[derive(Clone, Copy, Debug, Hash, PartialOrd, Ord, PartialEq, Eq)]
 pub enum Bitrate {
@@ -41,10 +41,10 @@ pub enum AudioFormat {
     S16,
 }
 
-impl TryFrom<&String> for AudioFormat {
+impl FromStr for AudioFormat {
-    type Error = ();
+    type Err = ();
-    fn try_from(s: &String) -> Result<Self, Self::Error> {
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        match s.to_uppercase().as_str() {
+        match s.to_uppercase().as_ref() {
             "F64" => Ok(Self::F64),
             "F32" => Ok(Self::F32),
             "S32" => Ok(Self::S32),
@@ -133,8 +133,8 @@ pub struct PlayerConfig {
     pub normalisation_method: NormalisationMethod,
     pub normalisation_pregain: f64,
     pub normalisation_threshold: f64,
-    pub normalisation_attack: f64,
+    pub normalisation_attack: Duration,
-    pub normalisation_release: f64,
+    pub normalisation_release: Duration,
     pub normalisation_knee: f64,
 
     // pass function pointers so they can be lazily instantiated *after* spawning a thread
@@ -152,8 +152,8 @@ impl Default for PlayerConfig {
             normalisation_method: NormalisationMethod::default(),
             normalisation_pregain: 0.0,
             normalisation_threshold: db_to_ratio(-1.0),
-            normalisation_attack: 0.005,
+            normalisation_attack: Duration::from_millis(5),
-            normalisation_release: 0.1,
+            normalisation_release: Duration::from_millis(100),
             normalisation_knee: 1.0,
             passthrough: false,
             ditherer: Some(mk_ditherer::<TriangularDitherer>),
@@ -184,7 +184,7 @@ impl Default for VolumeCtrl {
 }
 
 impl VolumeCtrl {
-    pub const MAX_VOLUME: u16 = std::u16::MAX;
+    pub const MAX_VOLUME: u16 = u16::MAX;
 
     // Taken from: https://www.dr-lex.be/info-stuff/volumecontrols.html
     pub const DEFAULT_DB_RANGE: f64 = 60.0;

playback/src/convert.rs

@@ -34,8 +34,21 @@ impl Converter {
         }
     }
 
+    /// To convert PCM samples from floating point normalized as `-1.0..=1.0`
+    /// to 32-bit signed integer, multiply by 2147483648 (0x80000000) and
+    /// saturate at the bounds of `i32`.
     const SCALE_S32: f64 = 2147483648.;
+
+    /// To convert PCM samples from floating point normalized as `-1.0..=1.0`
+    /// to 24-bit signed integer, multiply by 8388608 (0x800000) and saturate
+    /// at the bounds of `i24`.
     const SCALE_S24: f64 = 8388608.;
+
+    /// To convert PCM samples from floating point normalized as `-1.0..=1.0`
+    /// to 16-bit signed integer, multiply by 32768 (0x8000) and saturate at
+    /// the bounds of `i16`. When the samples were encoded using the same
+    /// scaling factor, like the reference Vorbis encoder does, this makes
+    /// conversions transparent.
     const SCALE_S16: f64 = 32768.;
 
     pub fn scale(&mut self, sample: f64, factor: f64) -> f64 {

playback/src/decoder/lewton_decoder.rs

@@ -6,6 +6,7 @@ use lewton::samples::InterleavedSamples;
 use std::error;
 use std::fmt;
 use std::io::{Read, Seek};
+use std::time::Duration;
 
 pub struct VorbisDecoder<R: Read + Seek>(OggStreamReader<R>);
 pub struct VorbisError(lewton::VorbisError);
@@ -24,7 +25,7 @@ where
     R: Read + Seek,
 {
     fn seek(&mut self, ms: i64) -> Result<(), AudioError> {
-        let absgp = ms * 44100 / 1000;
+        let absgp = Duration::from_millis(ms as u64 * crate::SAMPLE_RATE as u64).as_secs();
         match self.0.seek_absgp_pg(absgp as u64) {
             Ok(_) => Ok(()),
             Err(err) => Err(AudioError::VorbisError(err.into())),

playback/src/decoder/passthrough_decoder.rs

@@ -1,8 +1,10 @@
 // Passthrough decoder for librespot
 use super::{AudioDecoder, AudioError, AudioPacket};
+use crate::SAMPLE_RATE;
 use ogg::{OggReadError, Packet, PacketReader, PacketWriteEndInfo, PacketWriter};
 use std::fmt;
 use std::io::{Read, Seek};
+use std::time::Duration;
 use std::time::{SystemTime, UNIX_EPOCH};
 
 fn get_header<T>(code: u8, rdr: &mut PacketReader<T>) -> Result<Box<[u8]>, PassthroughError>
@@ -96,7 +98,10 @@ impl<R: Read + Seek> AudioDecoder for PassthroughDecoder<R> {
         self.stream_serial += 1;
 
         // hard-coded to 44.1 kHz
-        match self.rdr.seek_absgp(None, (ms * 44100 / 1000) as u64) {
+        match self.rdr.seek_absgp(
+            None,
+            Duration::from_millis(ms as u64 * SAMPLE_RATE as u64).as_secs(),
+        ) {
             Ok(_) => {
                 // need to set some offset for next_page()
                 let pck = self.rdr.read_packet().unwrap().unwrap();

playback/src/dither.rs

@@ -61,7 +61,7 @@ impl Ditherer for TriangularDitherer {
     }
 
     fn name(&self) -> &'static str {
-        "Triangular"
+        Self::NAME
     }
 
     fn noise(&mut self) -> f64 {
@@ -69,6 +69,10 @@ impl Ditherer for TriangularDitherer {
     }
 }
 
+impl TriangularDitherer {
+    pub const NAME: &'static str = "tpdf";
+}
+
 pub struct GaussianDitherer {
     cached_rng: ThreadRng,
     distribution: Normal<f64>,
@@ -84,7 +88,7 @@ impl Ditherer for GaussianDitherer {
     }
 
     fn name(&self) -> &'static str {
-        "Gaussian"
+        Self::NAME
     }
 
     fn noise(&mut self) -> f64 {
@@ -92,6 +96,10 @@ impl Ditherer for GaussianDitherer {
     }
 }
 
+impl GaussianDitherer {
+    pub const NAME: &'static str = "gpdf";
+}
+
 pub struct HighPassDitherer {
     active_channel: usize,
     previous_noises: [f64; NUM_CHANNELS],
@@ -110,7 +118,7 @@ impl Ditherer for HighPassDitherer {
     }
 
     fn name(&self) -> &'static str {
-        "Triangular, High Passed"
+        Self::NAME
     }
 
     fn noise(&mut self) -> f64 {
@@ -122,6 +130,10 @@ impl Ditherer for HighPassDitherer {
     }
 }
 
+impl HighPassDitherer {
+    pub const NAME: &'static str = "tpdf_hp";
+}
+
 pub fn mk_ditherer<D: Ditherer + 'static>() -> Box<dyn Ditherer> {
     Box::new(D::new())
 }
@@ -130,9 +142,9 @@ pub type DithererBuilder = fn() -> Box<dyn Ditherer>;
 
 pub fn find_ditherer(name: Option<String>) -> Option<DithererBuilder> {
     match name.as_deref() {
-        Some("tpdf") => Some(mk_ditherer::<TriangularDitherer>),
+        Some(TriangularDitherer::NAME) => Some(mk_ditherer::<TriangularDitherer>),
-        Some("gpdf") => Some(mk_ditherer::<GaussianDitherer>),
+        Some(GaussianDitherer::NAME) => Some(mk_ditherer::<GaussianDitherer>),
-        Some("tpdf_hp") => Some(mk_ditherer::<HighPassDitherer>),
+        Some(HighPassDitherer::NAME) => Some(mk_ditherer::<HighPassDitherer>),
         _ => None,
     }
 }

playback/src/lib.rs

@@ -12,3 +12,7 @@ mod decoder;
 pub mod dither;
 pub mod mixer;
 pub mod player;
+
+pub const SAMPLE_RATE: u32 = 44100;
+pub const NUM_CHANNELS: u8 = 2;
+pub const SAMPLES_PER_SECOND: u32 = SAMPLE_RATE as u32 * NUM_CHANNELS as u32;

playback/src/mixer/alsamixer.rs

@@ -241,6 +241,8 @@ impl Mixer for AlsaMixer {
 }
 
 impl AlsaMixer {
+    pub const NAME: &'static str = "alsa";
+
     fn switched_off(&self) -> bool {
         if !self.has_switch {
             return false;

playback/src/mixer/mod.rs

@@ -53,11 +53,11 @@ fn mk_sink<M: Mixer + 'static>(config: MixerConfig) -> Box<dyn Mixer> {
     Box::new(M::open(config))
 }
 
-pub fn find<T: AsRef<str>>(name: Option<T>) -> Option<MixerFn> {
+pub fn find(name: Option<&str>) -> Option<MixerFn> {
-    match name.as_ref().map(AsRef::as_ref) {
+    match name {
-        None | Some("softvol") => Some(mk_sink::<SoftMixer>),
+        None | Some(SoftMixer::NAME) => Some(mk_sink::<SoftMixer>),
         #[cfg(feature = "alsa-backend")]
-        Some("alsa") => Some(mk_sink::<AlsaMixer>),
+        Some(AlsaMixer::NAME) => Some(mk_sink::<AlsaMixer>),
         _ => None,
     }
 }

playback/src/mixer/softmixer.rs

@@ -42,6 +42,10 @@ impl Mixer for SoftMixer {
     }
 }
 
+impl SoftMixer {
+    pub const NAME: &'static str = "softmixer";
+}
+
 struct SoftVolumeApplier {
     volume: Arc<AtomicU64>,
 }

playback/src/player.rs

@@ -13,8 +13,8 @@ use tokio::sync::{mpsc, oneshot};
 
 use crate::audio::{AudioDecrypt, AudioFile, StreamLoaderController};
 use crate::audio::{
-    READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS, READ_AHEAD_BEFORE_PLAYBACK_SECONDS,
+    READ_AHEAD_BEFORE_PLAYBACK, READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS, READ_AHEAD_DURING_PLAYBACK,
-    READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS, READ_AHEAD_DURING_PLAYBACK_SECONDS,
+    READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS,
 };
 use crate::audio_backend::Sink;
 use crate::config::{Bitrate, NormalisationMethod, NormalisationType, PlayerConfig};
@@ -26,9 +26,7 @@ use crate::decoder::{AudioDecoder, AudioError, AudioPacket, PassthroughDecoder,
 use crate::metadata::{AudioItem, FileFormat};
 use crate::mixer::AudioFilter;
 
-pub const SAMPLE_RATE: u32 = 44100;
+use crate::{NUM_CHANNELS, SAMPLES_PER_SECOND};
-pub const NUM_CHANNELS: u8 = 2;
-pub const SAMPLES_PER_SECOND: u32 = SAMPLE_RATE as u32 * NUM_CHANNELS as u32;
 
 const PRELOAD_NEXT_TRACK_BEFORE_END_DURATION_MS: u32 = 30000;
 pub const DB_VOLTAGE_RATIO: f64 = 20.0;
@@ -297,14 +295,8 @@ impl Player {
             debug!("Normalisation Method: {:?}", config.normalisation_method);
 
             if config.normalisation_method == NormalisationMethod::Dynamic {
-                debug!(
+                debug!("Normalisation Attack: {:?}", config.normalisation_attack);
-                    "Normalisation Attack: {:.0} ms",
+                debug!("Normalisation Release: {:?}", config.normalisation_release);
-                    config.normalisation_attack * 1000.0
-                );
-                debug!(
-                    "Normalisation Release: {:.0} ms",
-                    config.normalisation_release * 1000.0
-                );
                 debug!("Normalisation Knee: {:?}", config.normalisation_knee);
             }
         }
@@ -973,12 +965,12 @@ impl Future for PlayerInternal {
                             let notify_about_position = match *reported_nominal_start_time {
                                 None => true,
                                 Some(reported_nominal_start_time) => {
-                                    // only notify if we're behind. If we're ahead it's probably due to a buffer of the backend and we;re actually in time.
+                                    // only notify if we're behind. If we're ahead it's probably due to a buffer of the backend and we're actually in time.
                                     let lag = (Instant::now() - reported_nominal_start_time)
                                         .as_millis()
                                         as i64
                                         - stream_position_millis as i64;
-                                    lag > 1000
+                                    lag > Duration::from_secs(1).as_millis() as i64
                                 }
                             };
                             if notify_about_position {
@@ -1219,6 +1211,16 @@ impl PlayerInternal {
                                                 + shaped_limiter_strength * self.limiter_factor;
                                     };
 
+                                    // Cast the fields here for better readability
+                                    let normalisation_attack =
+                                        self.config.normalisation_attack.as_secs_f64();
+                                    let normalisation_release =
+                                        self.config.normalisation_release.as_secs_f64();
+                                    let limiter_release_counter =
+                                        self.limiter_release_counter as f64;
+                                    let limiter_attack_counter = self.limiter_attack_counter as f64;
+                                    let samples_per_second = SAMPLES_PER_SECOND as f64;
+
                                     // Always check for peaks, even when the limiter is already active.
                                     // There may be even higher peaks than we initially targeted.
                                     // Check against the normalisation factor that would be applied normally.
@@ -1228,21 +1230,19 @@ impl PlayerInternal {
                                         if self.limiter_release_counter > 0 {
                                             // A peak was encountered while releasing the limiter;
                                             // synchronize with the current release limiter strength.
-                                            self.limiter_attack_counter = (((SAMPLES_PER_SECOND
+                                            self.limiter_attack_counter = (((samples_per_second
-                                                as f64
+                                                * normalisation_release)
-                                                * self.config.normalisation_release)
+                                                - limiter_release_counter)
-                                                - self.limiter_release_counter as f64)
+                                                / (normalisation_release / normalisation_attack))
-                                                / (self.config.normalisation_release
-                                                    / self.config.normalisation_attack))
                                                 as u32;
                                             self.limiter_release_counter = 0;
                                         }
 
                                         self.limiter_attack_counter =
                                             self.limiter_attack_counter.saturating_add(1);
-                                        self.limiter_strength = self.limiter_attack_counter as f64
+
-                                            / (SAMPLES_PER_SECOND as f64
+                                        self.limiter_strength = limiter_attack_counter
-                                                * self.config.normalisation_attack);
+                                            / (samples_per_second * normalisation_attack);
 
                                         if abs_sample > self.limiter_peak_sample {
                                             self.limiter_peak_sample = abs_sample;
@@ -1256,12 +1256,10 @@ impl PlayerInternal {
                                             // the limiter reached full strength. For that reason
                                             // start the release by synchronizing with the current
                                             // attack limiter strength.
-                                            self.limiter_release_counter = (((SAMPLES_PER_SECOND
+                                            self.limiter_release_counter = (((samples_per_second
-                                                as f64
+                                                * normalisation_attack)
-                                                * self.config.normalisation_attack)
+                                                - limiter_attack_counter)
-                                                - self.limiter_attack_counter as f64)
+                                                * (normalisation_release / normalisation_attack))
-                                                * (self.config.normalisation_release
-                                                    / self.config.normalisation_attack))
                                                 as u32;
                                             self.limiter_attack_counter = 0;
                                         }
@@ -1270,17 +1268,14 @@ impl PlayerInternal {
                                             self.limiter_release_counter.saturating_add(1);
 
                                         if self.limiter_release_counter
-                                            > (SAMPLES_PER_SECOND as f64
+                                            > (samples_per_second * normalisation_release) as u32
-                                                * self.config.normalisation_release)
-                                                as u32
                                         {
                                             self.reset_limiter();
                                         } else {
-                                            self.limiter_strength = ((SAMPLES_PER_SECOND as f64
+                                            self.limiter_strength = ((samples_per_second
-                                                * self.config.normalisation_release)
+                                                * normalisation_release)
-                                                - self.limiter_release_counter as f64)
+                                                - limiter_release_counter)
-                                                / (SAMPLES_PER_SECOND as f64
+                                                / (samples_per_second * normalisation_release);
-                                                    * self.config.normalisation_release);
                                         }
                                     }
                                 }
@@ -1806,18 +1801,18 @@ impl PlayerInternal {
             // Request our read ahead range
             let request_data_length = max(
                 (READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS
-                    * (0.001 * stream_loader_controller.ping_time_ms() as f64)
+                    * stream_loader_controller.ping_time().as_secs_f32()
-                    * bytes_per_second as f64) as usize,
+                    * bytes_per_second as f32) as usize,
-                (READ_AHEAD_DURING_PLAYBACK_SECONDS * bytes_per_second as f64) as usize,
+                (READ_AHEAD_DURING_PLAYBACK.as_secs_f32() * bytes_per_second as f32) as usize,
             );
             stream_loader_controller.fetch_next(request_data_length);
 
             // Request the part we want to wait for blocking. This effecively means we wait for the previous request to partially complete.
             let wait_for_data_length = max(
                 (READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS
-                    * (0.001 * stream_loader_controller.ping_time_ms() as f64)
+                    * stream_loader_controller.ping_time().as_secs_f32()
-                    * bytes_per_second as f64) as usize,
+                    * bytes_per_second as f32) as usize,
-                (READ_AHEAD_BEFORE_PLAYBACK_SECONDS * bytes_per_second as f64) as usize,
+                (READ_AHEAD_BEFORE_PLAYBACK.as_secs_f32() * bytes_per_second as f32) as usize,
             );
             stream_loader_controller.fetch_next_blocking(wait_for_data_length);
         }

src/main.rs

@@ -17,6 +17,8 @@ use librespot::playback::config::{
     AudioFormat, Bitrate, NormalisationMethod, NormalisationType, PlayerConfig, VolumeCtrl,
 };
 use librespot::playback::dither;
+#[cfg(feature = "alsa-backend")]
+use librespot::playback::mixer::alsamixer::AlsaMixer;
 use librespot::playback::mixer::mappings::MappedCtrl;
 use librespot::playback::mixer::{self, MixerConfig, MixerFn};
 use librespot::playback::player::{db_to_ratio, Player};
@@ -24,17 +26,14 @@ use librespot::playback::player::{db_to_ratio, Player};
 mod player_event_handler;
 use player_event_handler::{emit_sink_event, run_program_on_events};
 
-use std::convert::TryFrom;
+use std::env;
+use std::io::{stderr, Write};
 use std::path::Path;
+use std::pin::Pin;
 use std::process::exit;
 use std::str::FromStr;
-use std::{env, time::Instant};
+use std::time::Duration;
-use std::{
+use std::time::Instant;
-    io::{stderr, Write},
-    pin::Pin,
-};
-
-const MILLIS: f64 = 1000.0;
 
 fn device_id(name: &str) -> String {
     hex::encode(Sha1::digest(name.as_bytes()))
@@ -189,176 +188,216 @@ struct Setup {
 }
 
 fn get_setup(args: &[String]) -> Setup {
+    const AP_PORT: &str = "ap-port";
+    const AUTOPLAY: &str = "autoplay";
+    const BACKEND: &str = "backend";
+    const BITRATE: &str = "b";
+    const CACHE: &str = "c";
+    const CACHE_SIZE_LIMIT: &str = "cache-size-limit";
+    const DEVICE: &str = "device";
+    const DEVICE_TYPE: &str = "device-type";
+    const DISABLE_AUDIO_CACHE: &str = "disable-audio-cache";
+    const DISABLE_DISCOVERY: &str = "disable-discovery";
+    const DISABLE_GAPLESS: &str = "disable-gapless";
+    const DITHER: &str = "dither";
+    const EMIT_SINK_EVENTS: &str = "emit-sink-events";
+    const ENABLE_VOLUME_NORMALISATION: &str = "enable-volume-normalisation";
+    const FORMAT: &str = "format";
+    const HELP: &str = "h";
+    const INITIAL_VOLUME: &str = "initial-volume";
+    const MIXER_CARD: &str = "mixer-card";
+    const MIXER_INDEX: &str = "mixer-index";
+    const MIXER_NAME: &str = "mixer-name";
+    const NAME: &str = "name";
+    const NORMALISATION_ATTACK: &str = "normalisation-attack";
+    const NORMALISATION_GAIN_TYPE: &str = "normalisation-gain-type";
+    const NORMALISATION_KNEE: &str = "normalisation-knee";
+    const NORMALISATION_METHOD: &str = "normalisation-method";
+    const NORMALISATION_PREGAIN: &str = "normalisation-pregain";
+    const NORMALISATION_RELEASE: &str = "normalisation-release";
+    const NORMALISATION_THRESHOLD: &str = "normalisation-threshold";
+    const ONEVENT: &str = "onevent";
+    const PASSTHROUGH: &str = "passthrough";
+    const PASSWORD: &str = "password";
+    const PROXY: &str = "proxy";
+    const SYSTEM_CACHE: &str = "system-cache";
+    const USERNAME: &str = "username";
+    const VERBOSE: &str = "verbose";
+    const VERSION: &str = "version";
+    const VOLUME_CTRL: &str = "volume-ctrl";
+    const VOLUME_RANGE: &str = "volume-range";
+    const ZEROCONF_PORT: &str = "zeroconf-port";
+
     let mut opts = getopts::Options::new();
     opts.optflag(
-        "h",
+        HELP,
         "help",
         "Print this help menu.",
     ).optopt(
-        "c",
+        CACHE,
         "cache",
         "Path to a directory where files will be cached.",
         "PATH",
     ).optopt(
         "",
-        "system-cache",
+        SYSTEM_CACHE,
         "Path to a directory where system files (credentials, volume) will be cached. Can be different from cache option value.",
         "PATH",
     ).optopt(
         "",
-        "cache-size-limit",
+        CACHE_SIZE_LIMIT,
         "Limits the size of the cache for audio files.",
         "SIZE"
-    ).optflag("", "disable-audio-cache", "Disable caching of the audio data.")
+    ).optflag("", DISABLE_AUDIO_CACHE, "Disable caching of the audio data.")
-    .optopt("n", "name", "Device name.", "NAME")
+    .optopt("n", NAME, "Device name.", "NAME")
-    .optopt("", "device-type", "Displayed device type.", "TYPE")
+    .optopt("", DEVICE_TYPE, "Displayed device type.", "TYPE")
     .optopt(
-        "b",
+        BITRATE,
         "bitrate",
         "Bitrate (kbps) {96|160|320}. Defaults to 160.",
         "BITRATE",
     )
     .optopt(
         "",
-        "onevent",
+        ONEVENT,
         "Run PROGRAM when a playback event occurs.",
         "PROGRAM",
     )
-    .optflag("", "emit-sink-events", "Run program set by --onevent before sink is opened and after it is closed.")
+    .optflag("", EMIT_SINK_EVENTS, "Run program set by --onevent before sink is opened and after it is closed.")
-    .optflag("v", "verbose", "Enable verbose output.")
+    .optflag("v", VERBOSE, "Enable verbose output.")
-    .optflag("V", "version", "Display librespot version string.")
+    .optflag("V", VERSION, "Display librespot version string.")
-    .optopt("u", "username", "Username to sign in with.", "USERNAME")
+    .optopt("u", USERNAME, "Username to sign in with.", "USERNAME")
-    .optopt("p", "password", "Password", "PASSWORD")
+    .optopt("p", PASSWORD, "Password", "PASSWORD")
-    .optopt("", "proxy", "HTTP proxy to use when connecting.", "URL")
+    .optopt("", PROXY, "HTTP proxy to use when connecting.", "URL")
-    .optopt("", "ap-port", "Connect to AP with specified port. If no AP with that port are present fallback AP will be used. Available ports are usually 80, 443 and 4070.", "PORT")
+    .optopt("", AP_PORT, "Connect to AP with specified port. If no AP with that port are present fallback AP will be used. Available ports are usually 80, 443 and 4070.", "PORT")
-    .optflag("", "disable-discovery", "Disable discovery mode.")
+    .optflag("", DISABLE_DISCOVERY, "Disable discovery mode.")
     .optopt(
         "",
-        "backend",
+        BACKEND,
         "Audio backend to use. Use '?' to list options.",
         "NAME",
     )
     .optopt(
         "",
-        "device",
+        DEVICE,
         "Audio device to use. Use '?' to list options if using alsa, portaudio or rodio.",
         "NAME",
     )
     .optopt(
         "",
-        "format",
+        FORMAT,
         "Output format {F64|F32|S32|S24|S24_3|S16}. Defaults to S16.",
         "FORMAT",
     )
     .optopt(
         "",
-        "dither",
+        DITHER,
         "Specify the dither algorithm to use - [none, gpdf, tpdf, tpdf_hp]. Defaults to 'tpdf' for formats S16, S24, S24_3 and 'none' for other formats.",
         "DITHER",
     )
     .optopt("", "mixer", "Mixer to use {alsa|softvol}.", "MIXER")
     .optopt(
         "m",
-        "mixer-name",
+        MIXER_NAME,
         "Alsa mixer control, e.g. 'PCM' or 'Master'. Defaults to 'PCM'.",
         "NAME",
     )
     .optopt(
         "",
-        "mixer-card",
+        MIXER_CARD,
         "Alsa mixer card, e.g 'hw:0' or similar from `aplay -l`. Defaults to DEVICE if specified, 'default' otherwise.",
         "MIXER_CARD",
     )
     .optopt(
         "",
-        "mixer-index",
+        MIXER_INDEX,
         "Alsa index of the cards mixer. Defaults to 0.",
         "INDEX",
     )
     .optopt(
         "",
-        "initial-volume",
+        INITIAL_VOLUME,
         "Initial volume in % from 0-100. Default for softvol: '50'. For the Alsa mixer: the current volume.",
         "VOLUME",
     )
     .optopt(
         "",
-        "zeroconf-port",
+        ZEROCONF_PORT,
         "The port the internal server advertised over zeroconf uses.",
         "PORT",
     )
     .optflag(
         "",
-        "enable-volume-normalisation",
+        ENABLE_VOLUME_NORMALISATION,
         "Play all tracks at the same volume.",
     )
     .optopt(
         "",
-        "normalisation-method",
+        NORMALISATION_METHOD,
         "Specify the normalisation method to use {basic|dynamic}. Defaults to dynamic.",
         "METHOD",
     )
     .optopt(
         "",
-        "normalisation-gain-type",
+        NORMALISATION_GAIN_TYPE,
         "Specify the normalisation gain type to use {track|album}. Defaults to album.",
         "TYPE",
     )
     .optopt(
         "",
-        "normalisation-pregain",
+        NORMALISATION_PREGAIN,
         "Pregain (dB) applied by volume normalisation. Defaults to 0.",
         "PREGAIN",
     )
     .optopt(
         "",
-        "normalisation-threshold",
+        NORMALISATION_THRESHOLD,
         "Threshold (dBFS) to prevent clipping. Defaults to -1.0.",
         "THRESHOLD",
     )
     .optopt(
         "",
-        "normalisation-attack",
+        NORMALISATION_ATTACK,
         "Attack time (ms) in which the dynamic limiter is reducing gain. Defaults to 5.",
         "TIME",
     )
     .optopt(
         "",
-        "normalisation-release",
+        NORMALISATION_RELEASE,
         "Release or decay time (ms) in which the dynamic limiter is restoring gain. Defaults to 100.",
         "TIME",
     )
     .optopt(
         "",
-        "normalisation-knee",
+        NORMALISATION_KNEE,
         "Knee steepness of the dynamic limiter. Defaults to 1.0.",
         "KNEE",
     )
     .optopt(
         "",
-        "volume-ctrl",
+        VOLUME_CTRL,
         "Volume control type {cubic|fixed|linear|log}. Defaults to log.",
         "VOLUME_CTRL"
     )
     .optopt(
         "",
-        "volume-range",
+        VOLUME_RANGE,
         "Range of the volume control (dB). Default for softvol: 60. For the Alsa mixer: what the control supports.",
         "RANGE",
     )
     .optflag(
         "",
-        "autoplay",
+        AUTOPLAY,
         "Automatically play similar songs when your music ends.",
     )
     .optflag(
         "",
-        "disable-gapless",
+        DISABLE_GAPLESS,
         "Disable gapless playback.",
     )
     .optflag(
         "",
-        "passthrough",
+        PASSTHROUGH,
         "Pass raw stream to output, only works for pipe and subprocess.",
     );
 
@@ -374,17 +413,17 @@ fn get_setup(args: &[String]) -> Setup {
         }
     };
 
-    if matches.opt_present("h") {
+    if matches.opt_present(HELP) {
         println!("{}", usage(&args[0], &opts));
         exit(0);
     }
 
-    if matches.opt_present("version") {
+    if matches.opt_present(VERSION) {
         print_version();
         exit(0);
     }
 
-    let verbose = matches.opt_present("verbose");
+    let verbose = matches.opt_present(VERBOSE);
     setup_logging(verbose);
 
     info!(
@@ -395,7 +434,7 @@ fn get_setup(args: &[String]) -> Setup {
         build_id = version::BUILD_ID
     );
 
-    let backend_name = matches.opt_str("backend");
+    let backend_name = matches.opt_str(BACKEND);
     if backend_name == Some("?".into()) {
         list_backends();
         exit(0);
@@ -404,40 +443,41 @@ fn get_setup(args: &[String]) -> Setup {
     let backend = audio_backend::find(backend_name).expect("Invalid backend");
 
     let format = matches
-        .opt_str("format")
+        .opt_str(FORMAT)
-        .as_ref()
+        .as_deref()
-        .map(|format| AudioFormat::try_from(format).expect("Invalid output format"))
+        .map(|format| AudioFormat::from_str(format).expect("Invalid output format"))
         .unwrap_or_default();
 
-    let device = matches.opt_str("device");
+    let device = matches.opt_str(DEVICE);
     if device == Some("?".into()) {
         backend(device, format);
         exit(0);
     }
 
-    let mixer_name = matches.opt_str("mixer");
+    let mixer_name = matches.opt_str(MIXER_NAME);
-    let mixer = mixer::find(mixer_name.as_ref()).expect("Invalid mixer");
+    let mixer = mixer::find(mixer_name.as_deref()).expect("Invalid mixer");
 
     let mixer_config = {
-        let card = matches.opt_str("mixer-card").unwrap_or_else(|| {
+        let card = matches.opt_str(MIXER_CARD).unwrap_or_else(|| {
             if let Some(ref device_name) = device {
                 device_name.to_string()
             } else {
-                String::from("default")
+                MixerConfig::default().card
             }
         });
         let index = matches
-            .opt_str("mixer-index")
+            .opt_str(MIXER_INDEX)
             .map(|index| index.parse::<u32>().unwrap())
             .unwrap_or(0);
         let control = matches
-            .opt_str("mixer-name")
+            .opt_str(MIXER_NAME)
-            .unwrap_or_else(|| String::from("PCM"));
+            .unwrap_or_else(|| MixerConfig::default().control);
         let mut volume_range = matches
-            .opt_str("volume-range")
+            .opt_str(VOLUME_RANGE)
             .map(|range| range.parse::<f64>().unwrap())
-            .unwrap_or_else(|| match mixer_name.as_ref().map(AsRef::as_ref) {
+            .unwrap_or_else(|| match mixer_name.as_deref() {
-                Some("alsa") => 0.0, // let Alsa query the control
+                #[cfg(feature = "alsa-backend")]
+                Some(AlsaMixer::NAME) => 0.0, // let Alsa query the control
                 _ => VolumeCtrl::DEFAULT_DB_RANGE,
             });
         if volume_range < 0.0 {
@@ -449,8 +489,8 @@ fn get_setup(args: &[String]) -> Setup {
             );
         }
         let volume_ctrl = matches
-            .opt_str("volume-ctrl")
+            .opt_str(VOLUME_CTRL)
-            .as_ref()
+            .as_deref()
             .map(|volume_ctrl| {
                 VolumeCtrl::from_str_with_range(volume_ctrl, volume_range)
                     .expect("Invalid volume control type")
@@ -472,26 +512,26 @@ fn get_setup(args: &[String]) -> Setup {
     let cache = {
         let audio_dir;
         let system_dir;
-        if matches.opt_present("disable-audio-cache") {
+        if matches.opt_present(DISABLE_AUDIO_CACHE) {
             audio_dir = None;
             system_dir = matches
-                .opt_str("system-cache")
+                .opt_str(SYSTEM_CACHE)
-                .or_else(|| matches.opt_str("c"))
+                .or_else(|| matches.opt_str(CACHE))
                 .map(|p| p.into());
         } else {
-            let cache_dir = matches.opt_str("c");
+            let cache_dir = matches.opt_str(CACHE);
             audio_dir = cache_dir
                 .as_ref()
                 .map(|p| AsRef::<Path>::as_ref(p).join("files"));
             system_dir = matches
-                .opt_str("system-cache")
+                .opt_str(SYSTEM_CACHE)
                 .or(cache_dir)
                 .map(|p| p.into());
         }
 
         let limit = if audio_dir.is_some() {
             matches
-                .opt_str("cache-size-limit")
+                .opt_str(CACHE_SIZE_LIMIT)
                 .as_deref()
                 .map(parse_file_size)
                 .map(|e| {
@@ -514,7 +554,7 @@ fn get_setup(args: &[String]) -> Setup {
     };
 
     let initial_volume = matches
-        .opt_str("initial-volume")
+        .opt_str(INITIAL_VOLUME)
         .map(|initial_volume| {
             let volume = initial_volume.parse::<u16>().unwrap();
             if volume > 100 {
@@ -523,18 +563,19 @@ fn get_setup(args: &[String]) -> Setup {
             }
             (volume as f32 / 100.0 * VolumeCtrl::MAX_VOLUME as f32) as u16
         })
-        .or_else(|| match mixer_name.as_ref().map(AsRef::as_ref) {
+        .or_else(|| match mixer_name.as_deref() {
-            Some("alsa") => None,
+            #[cfg(feature = "alsa-backend")]
+            Some(AlsaMixer::NAME) => None,
             _ => cache.as_ref().and_then(Cache::volume),
         });
 
     let zeroconf_port = matches
-        .opt_str("zeroconf-port")
+        .opt_str(ZEROCONF_PORT)
         .map(|port| port.parse::<u16>().unwrap())
         .unwrap_or(0);
 
     let name = matches
-        .opt_str("name")
+        .opt_str(NAME)
         .unwrap_or_else(|| "Librespot".to_string());
 
     let credentials = {
@@ -547,8 +588,8 @@ fn get_setup(args: &[String]) -> Setup {
         };
 
         get_credentials(
-            matches.opt_str("username"),
+            matches.opt_str(USERNAME),
-            matches.opt_str("password"),
+            matches.opt_str(PASSWORD),
             cached_credentials,
             password,
         )
@@ -560,7 +601,7 @@ fn get_setup(args: &[String]) -> Setup {
         SessionConfig {
             user_agent: version::VERSION_STRING.to_string(),
             device_id,
-            proxy: matches.opt_str("proxy").or_else(|| std::env::var("http_proxy").ok()).map(
+            proxy: matches.opt_str(PROXY).or_else(|| std::env::var("http_proxy").ok()).map(
                 |s| {
                     match Url::parse(&s) {
                         Ok(url) => {
@@ -578,41 +619,41 @@ fn get_setup(args: &[String]) -> Setup {
                 },
             ),
             ap_port: matches
-                .opt_str("ap-port")
+                .opt_str(AP_PORT)
                 .map(|port| port.parse::<u16>().expect("Invalid port")),
         }
     };
 
     let player_config = {
         let bitrate = matches
-            .opt_str("b")
+            .opt_str(BITRATE)
-            .as_ref()
+            .as_deref()
             .map(|bitrate| Bitrate::from_str(bitrate).expect("Invalid bitrate"))
             .unwrap_or_default();
 
-        let gapless = !matches.opt_present("disable-gapless");
+        let gapless = !matches.opt_present(DISABLE_GAPLESS);
 
-        let normalisation = matches.opt_present("enable-volume-normalisation");
+        let normalisation = matches.opt_present(ENABLE_VOLUME_NORMALISATION);
         let normalisation_method = matches
-            .opt_str("normalisation-method")
+            .opt_str(NORMALISATION_METHOD)
-            .as_ref()
+            .as_deref()
             .map(|method| {
                 NormalisationMethod::from_str(method).expect("Invalid normalisation method")
             })
             .unwrap_or_default();
         let normalisation_type = matches
-            .opt_str("normalisation-gain-type")
+            .opt_str(NORMALISATION_GAIN_TYPE)
-            .as_ref()
+            .as_deref()
             .map(|gain_type| {
                 NormalisationType::from_str(gain_type).expect("Invalid normalisation type")
             })
             .unwrap_or_default();
         let normalisation_pregain = matches
-            .opt_str("normalisation-pregain")
+            .opt_str(NORMALISATION_PREGAIN)
             .map(|pregain| pregain.parse::<f64>().expect("Invalid pregain float value"))
             .unwrap_or(PlayerConfig::default().normalisation_pregain);
         let normalisation_threshold = matches
-            .opt_str("normalisation-threshold")
+            .opt_str(NORMALISATION_THRESHOLD)
             .map(|threshold| {
                 db_to_ratio(
                     threshold
@@ -622,19 +663,23 @@ fn get_setup(args: &[String]) -> Setup {
             })
             .unwrap_or(PlayerConfig::default().normalisation_threshold);
         let normalisation_attack = matches
-            .opt_str("normalisation-attack")
+            .opt_str(NORMALISATION_ATTACK)
-            .map(|attack| attack.parse::<f64>().expect("Invalid attack float value") / MILLIS)
+            .map(|attack| {
+                Duration::from_millis(attack.parse::<u64>().expect("Invalid attack value"))
+            })
             .unwrap_or(PlayerConfig::default().normalisation_attack);
         let normalisation_release = matches
-            .opt_str("normalisation-release")
+            .opt_str(NORMALISATION_RELEASE)
-            .map(|release| release.parse::<f64>().expect("Invalid release float value") / MILLIS)
+            .map(|release| {
+                Duration::from_millis(release.parse::<u64>().expect("Invalid release value"))
+            })
             .unwrap_or(PlayerConfig::default().normalisation_release);
         let normalisation_knee = matches
-            .opt_str("normalisation-knee")
+            .opt_str(NORMALISATION_KNEE)
             .map(|knee| knee.parse::<f64>().expect("Invalid knee float value"))
             .unwrap_or(PlayerConfig::default().normalisation_knee);
 
-        let ditherer_name = matches.opt_str("dither");
+        let ditherer_name = matches.opt_str(DITHER);
         let ditherer = match ditherer_name.as_deref() {
             // explicitly disabled on command line
             Some("none") => None,
@@ -654,7 +699,7 @@ fn get_setup(args: &[String]) -> Setup {
             },
         };
 
-        let passthrough = matches.opt_present("passthrough");
+        let passthrough = matches.opt_present(PASSTHROUGH);
 
         PlayerConfig {
             bitrate,
@@ -674,12 +719,12 @@ fn get_setup(args: &[String]) -> Setup {
 
     let connect_config = {
         let device_type = matches
-            .opt_str("device-type")
+            .opt_str(DEVICE_TYPE)
-            .as_ref()
+            .as_deref()
             .map(|device_type| DeviceType::from_str(device_type).expect("Invalid device type"))
             .unwrap_or_default();
         let has_volume_ctrl = !matches!(mixer_config.volume_ctrl, VolumeCtrl::Fixed);
-        let autoplay = matches.opt_present("autoplay");
+        let autoplay = matches.opt_present(AUTOPLAY);
 
         ConnectConfig {
             name,
@@ -690,9 +735,9 @@ fn get_setup(args: &[String]) -> Setup {
         }
     };
 
-    let enable_discovery = !matches.opt_present("disable-discovery");
+    let enable_discovery = !matches.opt_present(DISABLE_DISCOVERY);
-    let player_event_program = matches.opt_str("onevent");
+    let player_event_program = matches.opt_str(ONEVENT);
-    let emit_sink_events = matches.opt_present("emit-sink-events");
+    let emit_sink_events = matches.opt_present(EMIT_SINK_EVENTS);
 
     Setup {
         format,
@@ -714,8 +759,9 @@ fn get_setup(args: &[String]) -> Setup {
 
 #[tokio::main(flavor = "current_thread")]
 async fn main() {
-    if env::var("RUST_BACKTRACE").is_err() {
+    const RUST_BACKTRACE: &str = "RUST_BACKTRACE";
-        env::set_var("RUST_BACKTRACE", "full")
+    if env::var(RUST_BACKTRACE).is_err() {
+        env::set_var(RUST_BACKTRACE, "full")
     }
 
     let args: Vec<String> = std::env::args().collect();