feat(layer): add throttle layer (#2444)

* chore(core): add throttle layer module

* feat(core): add throttle layer

* feat(core): change throttle strategy based on PR review

* feat(core): refine docs and naming in ThrottleLayer

core/Cargo.toml

@@ -75,6 +75,7 @@ layers-all = [
   "layers-prometheus",
   "layers-tracing",
   "layers-minitrace",
+  "layers-throttle",
 ]
 # Enable layers chaos support
 layers-chaos = ["dep:rand"]
@@ -90,6 +91,8 @@ layers-minitrace = ["dep:minitrace"]
 layers-tracing = ["dep:tracing"]
 # Enable layers oteltrace support.
 layers-otel-trace = ["dep:opentelemetry"]
+# Enable layers throttle support.
+layers-throttle = ["dep:governor"]
 
 services-azblob = [
   "dep:sha2",
@@ -175,6 +178,7 @@ dashmap = { version = "5.4", optional = true }
 dirs = { version = "5.0.1", optional = true }
 flagset = "0.4"
 futures = { version = "0.3", default-features = false, features = ["std"] }
+governor = { version = "0.5", optional = true, features = ["std"] }
 hdrs = { version = "0.2", optional = true, features = ["async_file"] }
 http = "0.2.5"
 hyper = "0.14"

core/src/layers/mod.rs

@@ -76,5 +76,11 @@ pub use self::madsim::MadsimServer;
 
 #[cfg(feature = "layers-otel-trace")]
 mod oteltrace;
+
+#[cfg(feature = "layers-throttle")]
+mod throttle;
+#[cfg(feature = "layers-throttle")]
+pub use self::throttle::ThrottleLayer;
+
 #[cfg(feature = "layers-otel-trace")]
 pub use self::oteltrace::OtelTraceLayer;