refactor(http/prom): rename generic duration infrastructure (#4419)

* refactor(http/prom): rename RecordResponse to RecordDuration

this type is not itself a service in all cases. it *is* a service, and
is accordingly aliased to both RecordRequestDuration and
RecordResponseDuration, depending on which metrics structure it is
provided.

to help clarify this code, this renames this generic tower service
infrastructure to RecordDuration.

Signed-off-by: katelyn martin <kate@buoyant.io>

* refactor(http/prom): rename NewRecordResponse to NewRecordDuration

as in the previous commit, which applied this change to the tower service
middleware, this commit applies a change to the duration "new service"
middleware.

this type is generic over a metrics structure and emits services that
either record request or response duration, depending on the metics
provided.

Signed-off-by: katelyn martin <kate@buoyant.io>

* nit(http/prom): fix impl banner comments

Signed-off-by: katelyn martin <kate@buoyant.io>

* nit(app/inbound): rename layer variable bindings

'body' was a sensible name when there was only one layer instrumenting
body streams. now that there are request and response telemetry layers,
we should use more specific terminology.

Signed-off-by: katelyn martin <kate@buoyant.io>

---------

Signed-off-by: katelyn martin <kate@buoyant.io>

Author: cratelyn

linkerd/app/inbound/src/http/router/metrics.rs

@@ -25,12 +25,12 @@ pub(super) fn layer<N>(
         count_reqs::NewCountRequests::layer_via(extract)
     };
 
-    let body = {
+    let response_body = {
         let extract = ExtractResponseBodyDataMetrics::new(response_body_data.clone());
         NewRecordResponseBodyData::layer_via(extract)
     };
 
-    let request = {
+    let request_body = {
         let extract = ExtractRequestBodyDataParams::new(request_body_data.clone());
         NewRecordRequestBodyData::layer_via(extract)
     };
@@ -40,7 +40,9 @@ pub(super) fn layer<N>(
         NewRecordStatusCode::layer_via(extract)
     };
 
-    svc::layer::mk(move |inner| count.layer(body.layer(request.layer(status.layer(inner)))))
+    svc::layer::mk(move |inner| {
+        count.layer(response_body.layer(request_body.layer(status.layer(inner))))
+    })
 }
 
 /// An `N`-typed service instrumented with metrics middleware.

linkerd/app/outbound/src/http/logical/policy/route/metrics.rs

@@ -70,7 +70,7 @@ pub type LabelHttpRouteBackendRsp = LabelHttpRsp<labels::RouteBackend>;
 pub type LabelGrpcRouteBackendRsp = LabelGrpcRsp<labels::RouteBackend>;
 
 pub type NewRecordDuration<T, M, N> =
-    record_response::NewRecordResponse<T, ExtractRecordDurationParams<M>, M, N>;
+    record_response::NewRecordDuration<T, ExtractRecordDurationParams<M>, M, N>;
 
 #[derive(Clone, Debug)]
 pub struct ExtractRecordDurationParams<M>(pub M);

linkerd/http/prom/src/record_response.rs

@@ -23,7 +23,7 @@ pub use self::{
     response::{NewResponseDuration, RecordResponseDuration, ResponseMetrics},
 };
 
-/// A set of parameters that can be used to construct a `RecordResponse` layer.
+/// A set of parameters that can be used to construct a [`RecordDuration`] layer.
 pub struct Params<L: MkStreamLabel, M> {
     pub labeler: L,
     pub metric: M,
@@ -35,22 +35,22 @@ pub struct RequestCancelled;
 
 /// Instruments an `N`-typed [`svc::NewService<T>`] with metrics.
 ///
-/// Builds [`RecordResponse<L, M, S>`] instances by extracting `L`- and `M`-typed [`Params<L, M>`]
+/// Builds [`RecordDuration<L, M, S>`] instances by extracting `L`- and `M`-typed [`Params<L, M>`]
 /// parameters from `T`-typed stack targets using an `X`-typed [`svc::ExtractParam<P, T>`]
 /// implementation.
 ///
 /// The `L`-typed [`MkStreamLabel`] inspects requests and emits a [`StreamLabel`], which is
 /// intended to be used to generate labels for the `M`-typed metrics.
 #[derive(Clone, Debug)]
-pub struct NewRecordResponse<L, X, M, N> {
+pub struct NewRecordDuration<L, X, M, N> {
     inner: N,
     extract: X,
     _marker: std::marker::PhantomData<fn() -> (L, M)>,
 }
 
 /// A Service that can record a request/response durations.
 #[derive(Clone, Debug)]
-pub struct RecordResponse<L, M, S> {
+pub struct RecordDuration<L, M, S> {
     inner: S,
     labeler: L,
     metric: M,
@@ -97,9 +97,9 @@ impl MetricConstructor<Histogram> for MkDurationHistogram {
     }
 }
 
-// === impl NewRecordResponse ===
+// === impl NewRecordDuration ===
 
-impl<L, X, M, N> NewRecordResponse<L, X, M, N>
+impl<L, X, M, N> NewRecordDuration<L, X, M, N>
 where
     L: MkStreamLabel,
 {
@@ -119,7 +119,7 @@ where
     }
 }
 
-impl<L, M, N> NewRecordResponse<L, (), M, N>
+impl<L, M, N> NewRecordDuration<L, (), M, N>
 where
     L: MkStreamLabel,
 {
@@ -128,24 +128,24 @@ where
     }
 }
 
-impl<T, L, X, M, N> svc::NewService<T> for NewRecordResponse<L, X, M, N>
+impl<T, L, X, M, N> svc::NewService<T> for NewRecordDuration<L, X, M, N>
 where
     L: MkStreamLabel,
     X: svc::ExtractParam<Params<L, M>, T>,
     N: svc::NewService<T>,
 {
-    type Service = RecordResponse<L, M, N::Service>;
+    type Service = RecordDuration<L, M, N::Service>;
 
     fn new_service(&self, target: T) -> Self::Service {
         let Params { labeler, metric } = self.extract.extract_param(&target);
         let inner = self.inner.new_service(target);
-        RecordResponse::new(labeler, metric, inner)
+        RecordDuration::new(labeler, metric, inner)
     }
 }
 
-// === impl RecordResponse ===
+// === impl RecordDuration ===
 
-impl<L, M, S> RecordResponse<L, M, S>
+impl<L, M, S> RecordDuration<L, M, S>
 where
     L: MkStreamLabel,
 {

linkerd/http/prom/src/record_response/request.rs

@@ -17,10 +17,10 @@ pub struct RequestMetrics<L> {
 }
 
 pub type NewRequestDuration<L, X, N> =
-    super::NewRecordResponse<L, X, RequestMetrics<<L as MkStreamLabel>::DurationLabels>, N>;
+    super::NewRecordDuration<L, X, RequestMetrics<<L as MkStreamLabel>::DurationLabels>, N>;
 
 pub type RecordRequestDuration<L, S> =
-    super::RecordResponse<L, RequestMetrics<<L as MkStreamLabel>::DurationLabels>, S>;
+    super::RecordDuration<L, RequestMetrics<<L as MkStreamLabel>::DurationLabels>, S>;
 
 // === impl RequestMetrics ===
 
@@ -61,6 +61,8 @@ impl<L> Clone for RequestMetrics<L> {
     }
 }
 
+// === impl RecordRequestDuration ===
+
 impl<ReqB, L, S> svc::Service<http::Request<ReqB>> for RecordRequestDuration<L, S>
 where
     L: MkStreamLabel,

linkerd/http/prom/src/record_response/response.rs

@@ -18,10 +18,10 @@ pub struct ResponseMetrics<L> {
 }
 
 pub type NewResponseDuration<L, X, N> =
-    super::NewRecordResponse<L, X, ResponseMetrics<<L as MkStreamLabel>::DurationLabels>, N>;
+    super::NewRecordDuration<L, X, ResponseMetrics<<L as MkStreamLabel>::DurationLabels>, N>;
 
 pub type RecordResponseDuration<L, S> =
-    super::RecordResponse<L, ResponseMetrics<<L as MkStreamLabel>::DurationLabels>, S>;
+    super::RecordDuration<L, ResponseMetrics<<L as MkStreamLabel>::DurationLabels>, S>;
 
 /// Notifies the response body when the request body is flushed.
 #[pin_project::pin_project(PinnedDrop)]
@@ -64,6 +64,8 @@ impl<L> Clone for ResponseMetrics<L> {
     }
 }
 
+// === impl RecordResponseDuration ===
+
 impl<M, S> svc::Service<http::Request<BoxBody>> for RecordResponseDuration<M, S>
 where
     M: MkStreamLabel,
@@ -105,7 +107,7 @@ where
     }
 }
 
-// === impl ResponseBody ===
+// === impl RequestBody ===
 
 impl<B> http_body::Body for RequestBody<B>
 where