Various loading improvements

- Improve responsiveness by downloading the smallest possible chunk
  size when seeking or first loading.

- Improve download time and decrease CPU usage by downloading the
  largest possible chunk size as throughput allows, still allowing
  for reasonable seek responsiveness (~1 second).

- As a result, take refactoring opportunities: simplify prefetching
  logic, download threading, command sending, and some ergonomics.

- Fix disappearing controls in the Spotify mobile UI while loading.

- Fix handling of seek, pause, and play commands while loading.

- Fix download rate calculation (don't use the Mercury rate).

- Fix ping time calculation under lock contention.

audio/src/fetch/mod.rs

@@ -1,14 +1,14 @@
 mod receive;
 
 use std::{
-    cmp::{max, min},
+    cmp::min,
     fs,
     io::{self, Read, Seek, SeekFrom},
     sync::{
         atomic::{AtomicBool, AtomicUsize, Ordering},
         Arc,
     },
-    time::{Duration, Instant},
+    time::Duration,
 };
 
 use futures_util::{future::IntoStream, StreamExt, TryFutureExt};
@@ -16,7 +16,7 @@ use hyper::{client::ResponseFuture, header::CONTENT_RANGE, Body, Response, Statu
 use parking_lot::{Condvar, Mutex};
 use tempfile::NamedTempFile;
 use thiserror::Error;
-use tokio::sync::{mpsc, oneshot};
+use tokio::sync::{mpsc, oneshot, Semaphore};
 
 use librespot_core::{cdn_url::CdnUrl, Error, FileId, Session};
 
@@ -59,17 +59,11 @@ impl From<AudioFileError> for Error {
 /// This is the block size that is typically requested while doing a `seek()` on a file.
 /// The Symphonia decoder requires this to be a power of 2 and > 32 kB.
 /// Note: smaller requests can happen if part of the block is downloaded already.
-pub const MINIMUM_DOWNLOAD_SIZE: usize = 1024 * 128;
+pub const MINIMUM_DOWNLOAD_SIZE: usize = 64 * 1024;
 
 /// The minimum network throughput that we expect. Together with the minimum download size,
 /// this will determine the time we will wait for a response.
-pub const MINIMUM_THROUGHPUT: usize = 8192;
+pub const MINIMUM_THROUGHPUT: usize = 8 * 1024;
-
-/// 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.
-pub const INITIAL_DOWNLOAD_SIZE: usize = 1024 * 8;
 
 /// The ping time that is used for calculations before a ping time was actually measured.
 pub const INITIAL_PING_TIME_ESTIMATE: Duration = Duration::from_millis(500);
@@ -83,45 +77,17 @@ pub const MAXIMUM_ASSUMED_PING_TIME: Duration = Duration::from_millis(1500);
 /// of audio data may be larger or smaller.
 pub const READ_AHEAD_BEFORE_PLAYBACK: Duration = Duration::from_secs(1);
 
-/// Same as `READ_AHEAD_BEFORE_PLAYBACK`, but the time is taken as a factor of the ping
-/// time to the Spotify server. Both `READ_AHEAD_BEFORE_PLAYBACK` and
-/// `READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS` are obeyed.
-/// Note: the calculations are done using the nominal bitrate of the file. The actual amount
-/// of audio data may be larger or smaller.
-pub const READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS: f32 = 2.0;
-
 /// While playing back, this many seconds of data ahead of the current read position are
 /// requested.
 /// Note: the calculations are done using the nominal bitrate of the file. The actual amount
 /// of audio data may be larger or smaller.
 pub const READ_AHEAD_DURING_PLAYBACK: Duration = Duration::from_secs(5);
 
-/// Same as `READ_AHEAD_DURING_PLAYBACK`, but the time is taken as a factor of the ping
-/// time to the Spotify server.
-/// Note: the calculations are done using the nominal bitrate of the file. The actual amount
-/// of audio data may be larger or smaller.
-pub const READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS: f32 = 10.0;
-
 /// 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 calculated as `<pending bytes> < PREFETCH_THRESHOLD_FACTOR * <ping time> * <nominal data rate>`
 pub const PREFETCH_THRESHOLD_FACTOR: f32 = 4.0;
 
-/// 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>`
-/// This mechanism allows for fast downloading of the remainder of the file. The number should be larger
-/// than `1.0` so the download rate ramps up until the bandwidth is saturated. The larger the value, the faster
-/// the download rate ramps up. However, this comes at the cost that it might hurt ping time if a seek is
-/// performed while downloading. Values smaller than `1.0` cause the download rate to collapse and effectively
-/// only `PREFETCH_THRESHOLD_FACTOR` is in effect. Thus, set to `0.0` if bandwidth saturation is not wanted.
-pub const FAST_PREFETCH_THRESHOLD_FACTOR: f32 = 1.5;
-
-/// Limit the number of requests that are pending simultaneously before pre-fetching data. Pending
-/// requests share bandwidth. Thus, having 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.
-pub const MAX_PREFETCH_REQUESTS: usize = 4;
-
 /// The time we will wait to obtain status updates on downloading.
 pub const DOWNLOAD_TIMEOUT: Duration =
     Duration::from_secs((MINIMUM_DOWNLOAD_SIZE / MINIMUM_THROUGHPUT) as u64);
@@ -137,15 +103,12 @@ pub struct StreamingRequest {
     initial_response: Option<Response<Body>>,
     offset: usize,
     length: usize,
-    request_time: Instant,
 }
 
 #[derive(Debug)]
 pub enum StreamLoaderCommand {
-    Fetch(Range),     // signal the stream loader to fetch a range of the file
+    Fetch(Range), // signal the stream loader to fetch a range of the file
-    RandomAccessMode, // optimise download strategy for random access
+    Close,        // terminate and don't load any more data
-    StreamMode,       // optimise download strategy for streaming
-    Close,            // terminate and don't load any more data
 }
 
 #[derive(Clone)]
@@ -182,17 +145,15 @@ impl StreamLoaderController {
     pub fn range_to_end_available(&self) -> bool {
         match self.stream_shared {
             Some(ref shared) => {
-                let read_position = shared.read_position.load(Ordering::Acquire);
+                let read_position = shared.read_position();
                 self.range_available(Range::new(read_position, self.len() - read_position))
             }
             None => true,
         }
     }
 
-    pub fn ping_time(&self) -> Duration {
+    pub fn ping_time(&self) -> Option<Duration> {
-        Duration::from_millis(self.stream_shared.as_ref().map_or(0, |shared| {
+        self.stream_shared.as_ref().map(|shared| shared.ping_time())
-            shared.ping_time_ms.load(Ordering::Relaxed) as u64
-        }))
     }
 
     fn send_stream_loader_command(&self, command: StreamLoaderCommand) {
@@ -252,31 +213,6 @@ impl StreamLoaderController {
         Ok(())
     }
 
-    #[allow(dead_code)]
-    pub fn fetch_next(&self, length: usize) {
-        if let Some(ref shared) = self.stream_shared {
-            let range = Range {
-                start: shared.read_position.load(Ordering::Acquire),
-                length,
-            };
-            self.fetch(range);
-        }
-    }
-
-    #[allow(dead_code)]
-    pub fn fetch_next_blocking(&self, length: usize) -> AudioFileResult {
-        match self.stream_shared {
-            Some(ref shared) => {
-                let range = Range {
-                    start: shared.read_position.load(Ordering::Acquire),
-                    length,
-                };
-                self.fetch_blocking(range)
-            }
-            None => Ok(()),
-        }
-    }
-
     pub fn fetch_next_and_wait(
         &self,
         request_length: usize,
@@ -284,7 +220,7 @@ impl StreamLoaderController {
     ) -> AudioFileResult {
         match self.stream_shared {
             Some(ref shared) => {
-                let start = shared.read_position.load(Ordering::Acquire);
+                let start = shared.read_position();
 
                 let request_range = Range {
                     start,
@@ -304,12 +240,16 @@ impl StreamLoaderController {
 
     pub fn set_random_access_mode(&self) {
         // optimise download strategy for random access
-        self.send_stream_loader_command(StreamLoaderCommand::RandomAccessMode);
+        if let Some(ref shared) = self.stream_shared {
+            shared.set_download_streaming(false)
+        }
     }
 
     pub fn set_stream_mode(&self) {
         // optimise download strategy for streaming
-        self.send_stream_loader_command(StreamLoaderCommand::StreamMode);
+        if let Some(ref shared) = self.stream_shared {
+            shared.set_download_streaming(true)
+        }
     }
 
     pub fn close(&self) {
@@ -337,9 +277,51 @@ struct AudioFileShared {
     cond: Condvar,
     download_status: Mutex<AudioFileDownloadStatus>,
     download_streaming: AtomicBool,
-    number_of_open_requests: AtomicUsize,
+    download_slots: Semaphore,
     ping_time_ms: AtomicUsize,
     read_position: AtomicUsize,
+    throughput: AtomicUsize,
+}
+
+impl AudioFileShared {
+    fn is_download_streaming(&self) -> bool {
+        self.download_streaming.load(Ordering::Acquire)
+    }
+
+    fn set_download_streaming(&self, streaming: bool) {
+        self.download_streaming.store(streaming, Ordering::Release)
+    }
+
+    fn ping_time(&self) -> Duration {
+        let ping_time_ms = self.ping_time_ms.load(Ordering::Acquire);
+        if ping_time_ms > 0 {
+            Duration::from_millis(ping_time_ms as u64)
+        } else {
+            INITIAL_PING_TIME_ESTIMATE
+        }
+    }
+
+    fn set_ping_time(&self, duration: Duration) {
+        self.ping_time_ms
+            .store(duration.as_millis() as usize, Ordering::Release)
+    }
+
+    fn throughput(&self) -> usize {
+        self.throughput.load(Ordering::Acquire)
+    }
+
+    fn set_throughput(&self, throughput: usize) {
+        self.throughput.store(throughput, Ordering::Release)
+    }
+
+    fn read_position(&self) -> usize {
+        self.read_position.load(Ordering::Acquire)
+    }
+
+    fn set_read_position(&self, position: u64) {
+        self.read_position
+            .store(position as usize, Ordering::Release)
+    }
 }
 
 impl AudioFile {
@@ -420,12 +402,11 @@ impl AudioFileStreaming {
         let mut streamer =
             session
                 .spclient()
-                .stream_from_cdn(&cdn_url, 0, INITIAL_DOWNLOAD_SIZE)?;
+                .stream_from_cdn(&cdn_url, 0, MINIMUM_DOWNLOAD_SIZE)?;
 
         // Get the first chunk with the headers to get the file size.
         // The remainder of that chunk with possibly also a response body is then
         // further processed in `audio_file_fetch`.
-        let request_time = Instant::now();
         let response = streamer.next().await.ok_or(AudioFileError::NoData)??;
 
         let code = response.status();
@@ -452,7 +433,6 @@ impl AudioFileStreaming {
             initial_response: Some(response),
             offset: 0,
             length: upper_bound + 1,
-            request_time,
         };
 
         let shared = Arc::new(AudioFileShared {
@@ -464,10 +444,11 @@ impl AudioFileStreaming {
                 requested: RangeSet::new(),
                 downloaded: RangeSet::new(),
             }),
-            download_streaming: AtomicBool::new(true),
+            download_streaming: AtomicBool::new(false),
-            number_of_open_requests: AtomicUsize::new(0),
+            download_slots: Semaphore::new(1),
-            ping_time_ms: AtomicUsize::new(INITIAL_PING_TIME_ESTIMATE.as_millis() as usize),
+            ping_time_ms: AtomicUsize::new(0),
             read_position: AtomicUsize::new(0),
+            throughput: AtomicUsize::new(0),
         });
 
         let write_file = NamedTempFile::new_in(session.config().tmp_dir.clone())?;
@@ -509,20 +490,12 @@ impl Read for AudioFileStreaming {
             return Ok(0);
         }
 
-        let length_to_request = if self.shared.download_streaming.load(Ordering::Acquire) {
+        let length_to_request = if self.shared.is_download_streaming() {
-            // Due to the read-ahead stuff, we potentially request more than the actual request demanded.
-            let ping_time_seconds =
-                Duration::from_millis(self.shared.ping_time_ms.load(Ordering::Relaxed) as u64)
-                    .as_secs_f32();
-
             let length_to_request = length
-                + max(
+                + (READ_AHEAD_DURING_PLAYBACK.as_secs_f32() * self.shared.bytes_per_second as f32)
-                    (READ_AHEAD_DURING_PLAYBACK.as_secs_f32() * self.shared.bytes_per_second as f32)
+                    as usize;
-                        as usize,
+
-                    (READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS
+            // Due to the read-ahead stuff, we potentially request more than the actual request demanded.
-                        * ping_time_seconds
-                        * self.shared.bytes_per_second as f32) as usize,
-                );
             min(length_to_request, self.shared.file_size - offset)
         } else {
             length
@@ -566,9 +539,7 @@ impl Read for AudioFileStreaming {
         let read_len = self.read_file.read(&mut output[..read_len])?;
 
         self.position += read_len as u64;
-        self.shared
+        self.shared.set_read_position(self.position);
-            .read_position
-            .store(self.position as usize, Ordering::Release);
 
         Ok(read_len)
     }
@@ -601,23 +572,17 @@ impl Seek for AudioFileStreaming {
             // Ensure random access mode if we need to download this part.
             // Checking whether we are streaming now is a micro-optimization
             // to save an atomic load.
-            was_streaming = self.shared.download_streaming.load(Ordering::Acquire);
+            was_streaming = self.shared.is_download_streaming();
             if was_streaming {
-                self.shared
+                self.shared.set_download_streaming(false);
-                    .download_streaming
-                    .store(false, Ordering::Release);
             }
         }
 
         self.position = self.read_file.seek(pos)?;
-        self.shared
+        self.shared.set_read_position(self.position);
-            .read_position
-            .store(self.position as usize, Ordering::Release);
 
         if !available && was_streaming {
-            self.shared
+            self.shared.set_download_streaming(true);
-                .download_streaming
-                .store(true, Ordering::Release);
         }
 
         Ok(self.position)

audio/src/fetch/receive.rs

@@ -1,7 +1,7 @@
 use std::{
     cmp::{max, min},
     io::{Seek, SeekFrom, Write},
-    sync::{atomic::Ordering, Arc},
+    sync::Arc,
     time::{Duration, Instant},
 };
 
@@ -17,8 +17,8 @@ use crate::range_set::{Range, RangeSet};
 
 use super::{
     AudioFileError, AudioFileResult, AudioFileShared, StreamLoaderCommand, StreamingRequest,
-    FAST_PREFETCH_THRESHOLD_FACTOR, MAXIMUM_ASSUMED_PING_TIME, MAX_PREFETCH_REQUESTS,
+    MAXIMUM_ASSUMED_PING_TIME, MINIMUM_DOWNLOAD_SIZE, MINIMUM_THROUGHPUT,
-    MINIMUM_DOWNLOAD_SIZE, PREFETCH_THRESHOLD_FACTOR,
+    PREFETCH_THRESHOLD_FACTOR,
 };
 
 struct PartialFileData {
@@ -27,10 +27,13 @@ struct PartialFileData {
 }
 
 enum ReceivedData {
+    Throughput(usize),
     ResponseTime(Duration),
     Data(PartialFileData),
 }
 
+const ONE_SECOND: Duration = Duration::from_secs(1);
+
 async fn receive_data(
     shared: Arc<AudioFileShared>,
     file_data_tx: mpsc::UnboundedSender<ReceivedData>,
@@ -39,15 +42,21 @@ async fn receive_data(
     let mut offset = request.offset;
     let mut actual_length = 0;
 
-    let old_number_of_request = shared
+    let permit = shared.download_slots.acquire().await?;
-        .number_of_open_requests
-        .fetch_add(1, Ordering::SeqCst);
 
-    let mut measure_ping_time = old_number_of_request == 0;
+    let request_time = Instant::now();
+    let mut measure_ping_time = true;
+    let mut measure_throughput = true;
 
     let result: Result<_, Error> = loop {
         let response = match request.initial_response.take() {
-            Some(data) => data,
+            Some(data) => {
+                // the request was already made outside of this function
+                measure_ping_time = false;
+                measure_throughput = false;
+
+                data
+            }
             None => match request.streamer.next().await {
                 Some(Ok(response)) => response,
                 Some(Err(e)) => break Err(e.into()),
@@ -62,6 +71,15 @@ async fn receive_data(
             },
         };
 
+        if measure_ping_time {
+            let duration = Instant::now().duration_since(request_time);
+            // may be zero if we are handling an initial response
+            if duration.as_millis() > 0 {
+                file_data_tx.send(ReceivedData::ResponseTime(duration))?;
+                measure_ping_time = false;
+            }
+        }
+
         let code = response.status();
         if code != StatusCode::PARTIAL_CONTENT {
             if code == StatusCode::TOO_MANY_REQUESTS {
@@ -90,24 +108,18 @@ async fn receive_data(
 
         actual_length += data_size;
         offset += data_size;
-
-        if measure_ping_time {
-            let mut duration = Instant::now() - request.request_time;
-            if duration > MAXIMUM_ASSUMED_PING_TIME {
-                warn!(
-                    "Ping time {} ms exceeds maximum {}, setting to maximum",
-                    duration.as_millis(),
-                    MAXIMUM_ASSUMED_PING_TIME.as_millis()
-                );
-                duration = MAXIMUM_ASSUMED_PING_TIME;
-            }
-            file_data_tx.send(ReceivedData::ResponseTime(duration))?;
-            measure_ping_time = false;
-        }
     };
 
     drop(request.streamer);
 
+    if measure_throughput {
+        let duration = Instant::now().duration_since(request_time).as_millis();
+        if actual_length > 0 && duration > 0 {
+            let throughput = ONE_SECOND.as_millis() as usize * actual_length / duration as usize;
+            file_data_tx.send(ReceivedData::Throughput(throughput))?;
+        }
+    }
+
     let bytes_remaining = request.length - actual_length;
     if bytes_remaining > 0 {
         {
@@ -118,9 +130,7 @@ async fn receive_data(
         }
     }
 
-    shared
+    drop(permit);
-        .number_of_open_requests
-        .fetch_sub(1, Ordering::SeqCst);
 
     if let Err(e) = result {
         error!(
@@ -151,8 +161,8 @@ enum ControlFlow {
 }
 
 impl AudioFileFetch {
-    fn is_download_streaming(&self) -> bool {
+    fn has_download_slots_available(&self) -> bool {
-        self.shared.download_streaming.load(Ordering::Acquire)
+        self.shared.download_slots.available_permits() > 0
     }
 
     fn download_range(&mut self, offset: usize, mut length: usize) -> AudioFileResult {
@@ -160,10 +170,17 @@ impl AudioFileFetch {
             length = MINIMUM_DOWNLOAD_SIZE;
         }
 
+        // If we are in streaming mode (so not seeking) then start downloading as large
+        // of chunks as possible for better throughput and improved CPU usage, while
+        // still being reasonably responsive (~1 second) in case we want to seek.
+        if self.shared.is_download_streaming() {
+            let throughput = self.shared.throughput();
+            length = max(length, throughput);
+        }
+
         if offset + length > self.shared.file_size {
             length = self.shared.file_size - offset;
         }
-
         let mut ranges_to_request = RangeSet::new();
         ranges_to_request.add_range(&Range::new(offset, length));
 
@@ -191,7 +208,6 @@ impl AudioFileFetch {
                 initial_response: None,
                 offset: range.start,
                 length: range.length,
-                request_time: Instant::now(),
             };
 
             self.session.spawn(receive_data(
@@ -204,51 +220,36 @@ impl AudioFileFetch {
         Ok(())
     }
 
-    fn pre_fetch_more_data(
+    fn pre_fetch_more_data(&mut self, bytes: usize) -> AudioFileResult {
-        &mut self,
+        // determine what is still missing
-        bytes: usize,
+        let mut missing_data = RangeSet::new();
-        max_requests_to_send: usize,
+        missing_data.add_range(&Range::new(0, self.shared.file_size));
-    ) -> AudioFileResult {
+        {
-        let mut bytes_to_go = bytes;
+            let download_status = self.shared.download_status.lock();
-        let mut requests_to_go = max_requests_to_send;
+            missing_data.subtract_range_set(&download_status.downloaded);
+            missing_data.subtract_range_set(&download_status.requested);
+        }
 
-        while bytes_to_go > 0 && requests_to_go > 0 {
+        // download data from after the current read position first
-            // determine what is still missing
+        let mut tail_end = RangeSet::new();
-            let mut missing_data = RangeSet::new();
+        let read_position = self.shared.read_position();
-            missing_data.add_range(&Range::new(0, self.shared.file_size));
+        tail_end.add_range(&Range::new(
-            {
+            read_position,
-                let download_status = self.shared.download_status.lock();
+            self.shared.file_size - read_position,
-                missing_data.subtract_range_set(&download_status.downloaded);
+        ));
-                missing_data.subtract_range_set(&download_status.requested);
+        let tail_end = tail_end.intersection(&missing_data);
-            }
 
-            // download data from after the current read position first
+        if !tail_end.is_empty() {
-            let mut tail_end = RangeSet::new();
+            let range = tail_end.get_range(0);
-            let read_position = self.shared.read_position.load(Ordering::Acquire);
+            let offset = range.start;
-            tail_end.add_range(&Range::new(
+            let length = min(range.length, bytes);
-                read_position,
+            self.download_range(offset, length)?;
-                self.shared.file_size - read_position,
+        } else if !missing_data.is_empty() {
-            ));
+            // ok, the tail is downloaded, download something fom the beginning.
-            let tail_end = tail_end.intersection(&missing_data);
+            let range = missing_data.get_range(0);
-
+            let offset = range.start;
-            if !tail_end.is_empty() {
+            let length = min(range.length, bytes);
-                let range = tail_end.get_range(0);
+            self.download_range(offset, length)?;
-                let offset = range.start;
-                let length = min(range.length, bytes_to_go);
-                self.download_range(offset, length)?;
-                requests_to_go -= 1;
-                bytes_to_go -= length;
-            } else if !missing_data.is_empty() {
-                // ok, the tail is downloaded, download something fom the beginning.
-                let range = missing_data.get_range(0);
-                let offset = range.start;
-                let length = min(range.length, bytes_to_go);
-                self.download_range(offset, length)?;
-                requests_to_go -= 1;
-                bytes_to_go -= length;
-            } else {
-                break;
-            }
         }
 
         Ok(())
@@ -256,8 +257,46 @@ impl AudioFileFetch {
 
     fn handle_file_data(&mut self, data: ReceivedData) -> Result<ControlFlow, Error> {
         match data {
-            ReceivedData::ResponseTime(response_time) => {
+            ReceivedData::Throughput(mut throughput) => {
-                let old_ping_time_ms = self.shared.ping_time_ms.load(Ordering::Relaxed);
+                if throughput < MINIMUM_THROUGHPUT {
+                    warn!(
+                        "Throughput {} kbps lower than minimum {}, setting to minimum",
+                        throughput / 1000,
+                        MINIMUM_THROUGHPUT / 1000,
+                    );
+                    throughput = MINIMUM_THROUGHPUT;
+                }
+
+                let old_throughput = self.shared.throughput();
+                let avg_throughput = if old_throughput > 0 {
+                    (old_throughput + throughput) / 2
+                } else {
+                    throughput
+                };
+
+                // print when the new estimate deviates by more than 10% from the last
+                if f32::abs((avg_throughput as f32 - old_throughput as f32) / old_throughput as f32)
+                    > 0.1
+                {
+                    trace!(
+                        "Throughput now estimated as: {} kbps",
+                        avg_throughput / 1000
+                    );
+                }
+
+                self.shared.set_throughput(avg_throughput);
+            }
+            ReceivedData::ResponseTime(mut response_time) => {
+                if response_time > MAXIMUM_ASSUMED_PING_TIME {
+                    warn!(
+                        "Time to first byte {} ms exceeds maximum {}, setting to maximum",
+                        response_time.as_millis(),
+                        MAXIMUM_ASSUMED_PING_TIME.as_millis()
+                    );
+                    response_time = MAXIMUM_ASSUMED_PING_TIME;
+                }
+
+                let old_ping_time_ms = self.shared.ping_time().as_millis();
 
                 // prune old response times. Keep at most two so we can push a third.
                 while self.network_response_times.len() >= 3 {
@@ -268,8 +307,8 @@ impl AudioFileFetch {
                 self.network_response_times.push(response_time);
 
                 // stats::median is experimental. So we calculate the median of up to three ourselves.
-                let ping_time_ms = {
+                let ping_time = {
-                    let response_time = match self.network_response_times.len() {
+                    match self.network_response_times.len() {
                         1 => self.network_response_times[0],
                         2 => (self.network_response_times[0] + self.network_response_times[1]) / 2,
                         3 => {
@@ -278,22 +317,23 @@ impl AudioFileFetch {
                             times[1]
                         }
                         _ => unreachable!(),
-                    };
+                    }
-                    response_time.as_millis() as usize
                 };
 
                 // print when the new estimate deviates by more than 10% from the last
                 if f32::abs(
-                    (ping_time_ms as f32 - old_ping_time_ms as f32) / old_ping_time_ms as f32,
+                    (ping_time.as_millis() as f32 - old_ping_time_ms as f32)
+                        / old_ping_time_ms as f32,
                 ) > 0.1
                 {
-                    debug!("Ping time now estimated as: {} ms", ping_time_ms);
+                    trace!(
+                        "Time to first byte now estimated as: {} ms",
+                        ping_time.as_millis()
+                    );
                 }
 
                 // store our new estimate for everyone to see
-                self.shared
+                self.shared.set_ping_time(ping_time);
-                    .ping_time_ms
-                    .store(ping_time_ms, Ordering::Relaxed);
             }
             ReceivedData::Data(data) => {
                 match self.output.as_mut() {
@@ -333,14 +373,6 @@ impl AudioFileFetch {
             StreamLoaderCommand::Fetch(request) => {
                 self.download_range(request.start, request.length)?
             }
-            StreamLoaderCommand::RandomAccessMode => self
-                .shared
-                .download_streaming
-                .store(false, Ordering::Release),
-            StreamLoaderCommand::StreamMode => self
-                .shared
-                .download_streaming
-                .store(true, Ordering::Release),
             StreamLoaderCommand::Close => return Ok(ControlFlow::Break),
         }
 
@@ -426,40 +458,28 @@ pub(super) async fn audio_file_fetch(
             else => (),
         }
 
-        if fetch.is_download_streaming() {
+        if fetch.shared.is_download_streaming() && fetch.has_download_slots_available() {
-            let number_of_open_requests =
+            let bytes_pending: usize = {
-                fetch.shared.number_of_open_requests.load(Ordering::SeqCst);
+                let download_status = fetch.shared.download_status.lock();
-            if number_of_open_requests < MAX_PREFETCH_REQUESTS {
-                let max_requests_to_send = MAX_PREFETCH_REQUESTS - number_of_open_requests;
 
-                let bytes_pending: usize = {
+                download_status
-                    let download_status = fetch.shared.download_status.lock();
+                    .requested
+                    .minus(&download_status.downloaded)
+                    .len()
+            };
 
-                    download_status
+            let ping_time_seconds = fetch.shared.ping_time().as_secs_f32();
-                        .requested
+            let throughput = fetch.shared.throughput();
-                        .minus(&download_status.downloaded)
-                        .len()
-                };
 
-                let ping_time_seconds =
+            let desired_pending_bytes = max(
-                    Duration::from_millis(fetch.shared.ping_time_ms.load(Ordering::Relaxed) as u64)
+                (PREFETCH_THRESHOLD_FACTOR
-                        .as_secs_f32();
+                    * ping_time_seconds
-                let download_rate = fetch.session.channel().get_download_rate_estimate();
+                    * fetch.shared.bytes_per_second as f32) as usize,
+                (ping_time_seconds * throughput as f32) as usize,
+            );
 
-                let desired_pending_bytes = max(
+            if bytes_pending < desired_pending_bytes {
-                    (PREFETCH_THRESHOLD_FACTOR
+                fetch.pre_fetch_more_data(desired_pending_bytes - bytes_pending)?;
-                        * ping_time_seconds
-                        * fetch.shared.bytes_per_second as f32) as usize,
-                    (FAST_PREFETCH_THRESHOLD_FACTOR * ping_time_seconds * download_rate as f32)
-                        as usize,
-                );
-
-                if bytes_pending < desired_pending_bytes {
-                    fetch.pre_fetch_more_data(
-                        desired_pending_bytes - bytes_pending,
-                        max_requests_to_send,
-                    )?;
-                }
             }
         }
     }

audio/src/lib.rs

@@ -8,7 +8,4 @@ mod range_set;
 
 pub use decrypt::AudioDecrypt;
 pub use fetch::{AudioFile, AudioFileError, StreamLoaderController};
-pub use fetch::{
+pub use fetch::{MINIMUM_DOWNLOAD_SIZE, READ_AHEAD_BEFORE_PLAYBACK, READ_AHEAD_DURING_PLAYBACK};
-    MINIMUM_DOWNLOAD_SIZE, READ_AHEAD_BEFORE_PLAYBACK, READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS,
-    READ_AHEAD_DURING_PLAYBACK, READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS,
-};

connect/src/spirc.rs

@@ -1502,13 +1502,17 @@ impl SpircTask {
     }
 
     fn notify(&mut self, recipient: Option<&str>) -> Result<(), Error> {
-        let status_string = match self.state.get_status() {
+        let status = self.state.get_status();
-            PlayStatus::kPlayStatusLoading => "kPlayStatusLoading",
+
-            PlayStatus::kPlayStatusPause => "kPlayStatusPause",
+        // When in loading state, the Spotify UI is disabled for interaction.
-            PlayStatus::kPlayStatusStop => "kPlayStatusStop",
+        // On desktop this isn't so bad but on mobile it means that the bottom
-            PlayStatus::kPlayStatusPlay => "kPlayStatusPlay",
+        // control disappears entirely. This is very confusing, so don't notify
-        };
+        // in this case.
-        trace!("Sending status to server: [{}]", status_string);
+        if status == PlayStatus::kPlayStatusLoading {
+            return Ok(());
+        }
+
+        trace!("Sending status to server: [{:?}]", status);
         let mut cs = CommandSender::new(self, MessageType::kMessageTypeNotify);
         if let Some(s) = recipient {
             cs = cs.recipient(s);

core/src/channel.rs

@@ -3,7 +3,7 @@ use std::{
     fmt,
     pin::Pin,
     task::{Context, Poll},
-    time::Instant,
+    time::{Duration, Instant},
 };
 
 use byteorder::{BigEndian, ByteOrder};
@@ -27,7 +27,7 @@ component! {
     }
 }
 
-const ONE_SECOND_IN_MS: usize = 1000;
+const ONE_SECOND: Duration = Duration::from_secs(1);
 
 #[derive(Debug, Error, Hash, PartialEq, Eq, Copy, Clone)]
 pub struct ChannelError;
@@ -92,10 +92,8 @@ 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()
+                if (current_time - download_measurement_start) > ONE_SECOND {
-                    > ONE_SECOND_IN_MS as u128
+                    inner.download_rate_estimate = ONE_SECOND.as_millis() as usize
-                {
-                    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);

core/src/error.rs

@@ -14,7 +14,9 @@ use http::{
 };
 use protobuf::ProtobufError;
 use thiserror::Error;
-use tokio::sync::{mpsc::error::SendError, oneshot::error::RecvError};
+use tokio::sync::{
+    mpsc::error::SendError, oneshot::error::RecvError, AcquireError, TryAcquireError,
+};
 use url::ParseError;
 
 #[cfg(feature = "with-dns-sd")]
@@ -451,6 +453,24 @@ impl<T> From<SendError<T>> for Error {
     }
 }
 
+impl From<AcquireError> for Error {
+    fn from(err: AcquireError) -> Self {
+        Self {
+            kind: ErrorKind::ResourceExhausted,
+            error: ErrorMessage(err.to_string()).into(),
+        }
+    }
+}
+
+impl From<TryAcquireError> for Error {
+    fn from(err: TryAcquireError) -> Self {
+        Self {
+            kind: ErrorKind::ResourceExhausted,
+            error: ErrorMessage(err.to_string()).into(),
+        }
+    }
+}
+
 impl From<ToStrError> for Error {
     fn from(err: ToStrError) -> Self {
         Self::new(ErrorKind::FailedPrecondition, err)

playback/src/player.rs

@@ -1,5 +1,4 @@
 use std::{
-    cmp::max,
     collections::HashMap,
     fmt,
     future::Future,
@@ -28,8 +27,7 @@ use tokio::sync::{mpsc, oneshot};
 use crate::{
     audio::{
         AudioDecrypt, AudioFile, StreamLoaderController, READ_AHEAD_BEFORE_PLAYBACK,
-        READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS, READ_AHEAD_DURING_PLAYBACK,
+        READ_AHEAD_DURING_PLAYBACK,
-        READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS,
     },
     audio_backend::Sink,
     config::{Bitrate, NormalisationMethod, NormalisationType, PlayerConfig},
@@ -1096,7 +1094,7 @@ impl PlayerTrackLoader {
             // If the position is invalid just start from
             // the beginning of the track.
             let position_ms = if position_ms > duration_ms {
-                warn!("Invalid start position of {}ms exceeds track's duration of {}ms, starting track from the beginning", position_ms, duration_ms);
+                warn!("Invalid start position of {} ms exceeds track's duration of {} ms, starting track from the beginning", position_ms, duration_ms);
                 0
             } else {
                 position_ms
@@ -1475,22 +1473,28 @@ impl PlayerInternal {
     }
 
     fn handle_play(&mut self) {
-        if let PlayerState::Paused {
+        match self.state {
-            track_id,
+            PlayerState::Paused {
-            play_request_id,
-            stream_position_ms,
-            ..
-        } = self.state
-        {
-            self.state.paused_to_playing();
-            self.send_event(PlayerEvent::Playing {
                 track_id,
                 play_request_id,
-                position_ms: stream_position_ms,
+                stream_position_ms,
-            });
+                ..
-            self.ensure_sink_running();
+            } => {
-        } else {
+                self.state.paused_to_playing();
-            error!("Player::play called from invalid state: {:?}", self.state);
+                self.send_event(PlayerEvent::Playing {
+                    track_id,
+                    play_request_id,
+                    position_ms: stream_position_ms,
+                });
+                self.ensure_sink_running();
+            }
+            PlayerState::Loading {
+                ref mut start_playback,
+                ..
+            } => {
+                *start_playback = true;
+            }
+            _ => error!("Player::play called from invalid state: {:?}", self.state),
         }
     }
 
@@ -1512,6 +1516,12 @@ impl PlayerInternal {
                     position_ms: stream_position_ms,
                 });
             }
+            PlayerState::Loading {
+                ref mut start_playback,
+                ..
+            } => {
+                *start_playback = false;
+            }
             _ => error!("Player::pause called from invalid state: {:?}", self.state),
         }
     }
@@ -1980,6 +1990,25 @@ impl PlayerInternal {
     }
 
     fn handle_command_seek(&mut self, position_ms: u32) -> PlayerResult {
+        // When we are still loading, the user may immediately ask to
+        // seek to another position yet the decoder won't be ready for
+        // that. In this case just restart the loading process but
+        // with the requested position.
+        if let PlayerState::Loading {
+            track_id,
+            play_request_id,
+            start_playback,
+            ..
+        } = self.state
+        {
+            return self.handle_command_load(
+                track_id,
+                play_request_id,
+                start_playback,
+                position_ms,
+            );
+        }
+
         if let Some(decoder) = self.state.decoder() {
             match decoder.seek(position_ms) {
                 Ok(new_position_ms) => {
@@ -2178,21 +2207,14 @@ impl PlayerInternal {
             ..
         } = self.state
         {
-            let ping_time = stream_loader_controller.ping_time().as_secs_f32();
-
             // Request our read ahead range
-            let request_data_length = max(
+            let request_data_length =
-                (READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS * ping_time * bytes_per_second as f32)
+                (READ_AHEAD_DURING_PLAYBACK.as_secs_f32() * bytes_per_second as f32) as usize;
-                    as usize,
-                (READ_AHEAD_DURING_PLAYBACK.as_secs_f32() * bytes_per_second as f32) as usize,
-            );
 
             // Request the part we want to wait for blocking. This effectively means we wait for the previous request to partially complete.
-            let wait_for_data_length = max(
+            let wait_for_data_length =
-                (READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS * ping_time * bytes_per_second as f32)
+                (READ_AHEAD_BEFORE_PLAYBACK.as_secs_f32() * bytes_per_second as f32) as usize;
-                    as usize,
+
-                (READ_AHEAD_BEFORE_PLAYBACK.as_secs_f32() * bytes_per_second as f32) as usize,
-            );
             stream_loader_controller
                 .fetch_next_and_wait(request_data_length, wait_for_data_length)
                 .map_err(Into::into)