Auto merge of #9395 - weihanglo:issue-8483, r=alexcrichton

Show transfer rate when fetching/updating registry index

Possibly fixes #8483.

To avoid blinking too frequently, update rate is throttled by one second.

I am not sure how to write tests for it 😂

<img width="896" alt="image" src="https://user-images.githubusercontent.com/14314532/115879831-ac62fb00-a47c-11eb-9b12-735ce8192ebe.png">

# Updated (2020-04-28)

Current looking

```
    Updating crates.io index
       Fetch [==>                      ]  14.50%, 258.45KiB/s

    Updating crates.io index
       Fetch [======>                  ]  40.50%, (1234/282342) resolving deltas
```

Author: bors

src/cargo/sources/git/utils.rs

@@ -3,7 +3,7 @@
 
 use crate::core::GitReference;
 use crate::util::errors::CargoResult;
-use crate::util::{network, Config, IntoUrl, Progress};
+use crate::util::{network, Config, IntoUrl, MetricsCounter, Progress};
 use anyhow::{anyhow, Context as _};
 use cargo_util::{paths, ProcessBuilder};
 use curl::easy::List;
@@ -15,6 +15,7 @@ use std::env;
 use std::fmt;
 use std::path::{Path, PathBuf};
 use std::process::Command;
+use std::time::{Duration, Instant};
 use url::Url;
 
 fn serialize_str<T, S>(t: &T, s: S) -> Result<S::Ok, S::Error>
@@ -677,7 +678,7 @@ fn reset(repo: &git2::Repository, obj: &git2::Object<'_>, config: &Config) -> Ca
     let mut pb = Progress::new("Checkout", config);
     let mut opts = git2::build::CheckoutBuilder::new();
     opts.progress(|_, cur, max| {
-        drop(pb.tick(cur, max));
+        drop(pb.tick(cur, max, ""));
     });
     debug!("doing reset");
     repo.reset(obj, git2::ResetType::Hard, Some(&mut opts))?;
@@ -694,12 +695,49 @@ pub fn with_fetch_options(
     let mut progress = Progress::new("Fetch", config);
     network::with_retry(config, || {
         with_authentication(url, git_config, |f| {
+            let mut last_update = Instant::now();
             let mut rcb = git2::RemoteCallbacks::new();
+            // We choose `N=10` here to make a `300ms * 10slots ~= 3000ms`
+            // sliding window for tracking the data transfer rate (in bytes/s).
+            let mut counter = MetricsCounter::<10>::new(0, last_update);
             rcb.credentials(f);
-
             rcb.transfer_progress(|stats| {
+                let indexed_deltas = stats.indexed_deltas();
+                let msg = if indexed_deltas > 0 {
+                    // Resolving deltas.
+                    format!(
+                        ", ({}/{}) resolving deltas",
+                        indexed_deltas,
+                        stats.total_deltas()
+                    )
+                } else {
+                    // Receiving objects.
+                    //
+                    // # Caveat
+                    //
+                    // Progress bar relies on git2 calling `transfer_progress`
+                    // to update its transfer rate, but we cannot guarantee a
+                    // periodic call of that callback. Thus if we don't receive
+                    // any data for, say, 10 seconds, the rate will get stuck
+                    // and never go down to 0B/s.
+                    // In the future, we need to find away to update the rate
+                    // even when the callback is not called.
+                    let now = Instant::now();
+                    // Scrape a `received_bytes` to the counter every 300ms.
+                    if now - last_update > Duration::from_millis(300) {
+                        counter.add(stats.received_bytes(), now);
+                        last_update = now;
+                    }
+                    fn format_bytes(bytes: f32) -> (&'static str, f32) {
+                        static UNITS: [&str; 5] = ["", "Ki", "Mi", "Gi", "Ti"];
+                        let i = (bytes.log2() / 10.0).min(4.0) as usize;
+                        (UNITS[i], bytes / 1024_f32.powi(i as i32))
+                    }
+                    let (unit, rate) = format_bytes(counter.rate());
+                    format!(", {:.2}{}B/s", rate, unit)
+                };
                 progress
-                    .tick(stats.indexed_objects(), stats.total_objects())
+                    .tick(stats.indexed_objects(), stats.total_objects(), &msg)
                     .is_ok()
             });
 

src/cargo/util/counter.rs

@@ -0,0 +1,67 @@
+use std::time::Instant;
+
+/// A metrics counter storing only latest `N` records.
+pub struct MetricsCounter<const N: usize> {
+    /// Slots to store metrics.
+    slots: [(usize, Instant); N],
+    /// The slot of the oldest record.
+    /// Also the next slot to store the new record.
+    index: usize,
+}
+
+impl<const N: usize> MetricsCounter<N> {
+    /// Creates a new counter with an initial value.
+    pub fn new(init: usize, init_at: Instant) -> Self {
+        debug_assert!(N > 0, "number of slots must be greater than zero");
+        Self {
+            slots: [(init, init_at); N],
+            index: 0,
+        }
+    }
+
+    /// Adds record to the counter.
+    pub fn add(&mut self, data: usize, added_at: Instant) {
+        self.slots[self.index] = (data, added_at);
+        self.index = (self.index + 1) % N;
+    }
+
+    /// Calculates per-second average rate of all slots.
+    pub fn rate(&self) -> f32 {
+        let latest = self.slots[self.index.checked_sub(1).unwrap_or(N - 1)];
+        let oldest = self.slots[self.index];
+        let duration = (latest.1 - oldest.1).as_secs_f32();
+        let avg = (latest.0 - oldest.0) as f32 / duration;
+        if f32::is_nan(avg) {
+            0f32
+        } else {
+            avg
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::MetricsCounter;
+    use std::time::{Duration, Instant};
+
+    #[test]
+    fn counter() {
+        let now = Instant::now();
+        let mut counter = MetricsCounter::<3>::new(0, now);
+        assert_eq!(counter.rate(), 0f32);
+        counter.add(1, now + Duration::from_secs(1));
+        assert_eq!(counter.rate(), 1f32);
+        counter.add(4, now + Duration::from_secs(2));
+        assert_eq!(counter.rate(), 2f32);
+        counter.add(7, now + Duration::from_secs(3));
+        assert_eq!(counter.rate(), 3f32);
+        counter.add(12, now + Duration::from_secs(4));
+        assert_eq!(counter.rate(), 4f32);
+    }
+
+    #[test]
+    #[should_panic(expected = "number of slots must be greater than zero")]
+    fn counter_zero_slot() {
+        let _counter = MetricsCounter::<0>::new(0, Instant::now());
+    }
+}

src/cargo/util/mod.rs

@@ -3,6 +3,7 @@ use std::time::Duration;
 
 pub use self::canonical_url::CanonicalUrl;
 pub use self::config::{homedir, Config, ConfigValue};
+pub(crate) use self::counter::MetricsCounter;
 pub use self::dependency_queue::DependencyQueue;
 pub use self::diagnostic_server::RustfixDiagnosticServer;
 pub use self::errors::{internal, CargoResult, CliResult, Test};
@@ -29,6 +30,7 @@ pub use self::workspace::{
 mod canonical_url;
 pub mod command_prelude;
 pub mod config;
+mod counter;
 pub mod cpu;
 mod dependency_queue;
 pub mod diagnostic_server;

src/cargo/util/progress.rs

@@ -96,7 +96,7 @@ impl<'cfg> Progress<'cfg> {
         Self::with_style(name, ProgressStyle::Percentage, cfg)
     }
 
-    pub fn tick(&mut self, cur: usize, max: usize) -> CargoResult<()> {
+    pub fn tick(&mut self, cur: usize, max: usize, msg: &str) -> CargoResult<()> {
         let s = match &mut self.state {
             Some(s) => s,
             None => return Ok(()),
@@ -118,7 +118,7 @@ impl<'cfg> Progress<'cfg> {
             return Ok(());
         }
 
-        s.tick(cur, max, "")
+        s.tick(cur, max, msg)
     }
 
     pub fn tick_now(&mut self, cur: usize, max: usize, msg: &str) -> CargoResult<()> {