Obey crates.io crawler policy: Only make one request per sec (#908)

Fixed https://github.com/taiki-e/install-action/issues/89

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

crates/binstalk/src/ops.rs

@@ -3,6 +3,10 @@
 use std::{path::PathBuf, sync::Arc};
 
 use semver::VersionReq;
+use tokio::{
+    sync::Mutex,
+    time::{interval, Duration, Interval, MissedTickBehavior},
+};
 
 use crate::{
     fetchers::{Data, Fetcher, TargetData},
@@ -37,4 +41,32 @@ pub struct Options {
     pub client: Client,
     pub gh_api_client: GhApiClient,
     pub jobserver_client: LazyJobserverClient,
+    pub crates_io_rate_limit: CratesIoRateLimit,
+}
+
+pub struct CratesIoRateLimit(Mutex<Interval>);
+
+impl Default for CratesIoRateLimit {
+    fn default() -> Self {
+        let mut interval = interval(Duration::from_secs(1));
+        // If somehow one tick is delayed, then next tick should be at least
+        // 1s later than the current tick.
+        //
+        // Other MissedTickBehavior including Burst (default), which will
+        // tick as fast as possible to catch up, and Skip, which will
+        // skip the current tick for the next one.
+        //
+        // Both Burst and Skip is not the expected behavior for rate limit:
+        // ticking as fast as possible would violate crates.io crawler
+        // policy, and skipping the current one will slow down the resolution
+        // process.
+        interval.set_missed_tick_behavior(MissedTickBehavior::Delay);
+        Self(Mutex::new(interval))
+    }
+}
+
+impl CratesIoRateLimit {
+    pub(super) async fn tick(&self) {
+        self.0.lock().await.tick().await;
+    }
 }