Make httpmetris work better with OTEL (#198)

## Rationale

Here we add a option to improve HTTP metrics reporting with OTEL.

## Changes
* Add `NewV2` function to `httpmetrics` which uses attributes over metric names

## Meta
[W-13781478](https://gus.lightning.force.com/a07EE00001WSFXiYAP)

hmiddleware/httpmetrics/httpmetrics.go

@@ -81,7 +81,7 @@ var dashRe = regexp.MustCompile(`[_]+`)
 // request context. For example, a chi.Router that mounts a sub-router on / to
 // handle a set of paths might have a set of patterns like:
 //
-//    []string{"/*", "/kpi/v1/apps/:id"}
+//	[]string{"/*", "/kpi/v1/apps/:id"}
 //
 // which would be transformed into a metric called "kpi.v1.apps.id".
 func nameRoutePatterns(patterns []string) string {

hmiddleware/httpmetrics/httpmetrics_v2.go

@@ -0,0 +1,72 @@
+package httpmetrics
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/heroku/x/go-kit/metrics"
+	"github.com/heroku/x/go-kit/metricsregistry"
+
+	"github.com/go-chi/chi"
+	"github.com/go-chi/chi/middleware"
+)
+
+const (
+	// metric names
+	requestDuration = "http.server.duration" // duration in milliseconds
+
+	// metric attribute keys
+	routeKey         = "http.route"
+	methodKey        = "http.request.method"
+	statusKey        = "http.response.status_code"
+	serverAddressKey = "server.address"
+	urlSchemeKey     = "url.scheme"
+)
+
+// NewOTEL returns an HTTP middleware which captures HTTP request counts and latency
+// annotated with attributes for method, route, status.
+//
+// See https://opentelemetry.io/docs/specs/otel/metrics/semantic_conventions/http-metrics/
+func NewOTEL(p metrics.Provider) func(http.Handler) http.Handler {
+	reg := metricsregistry.New(p)
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			ww := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
+
+			start := time.Now()
+			next.ServeHTTP(ww, r)
+			dur := time.Since(start)
+
+			labels := []string{
+				methodKey, r.Method,
+			}
+
+			if status := ww.Status(); status != 0 {
+				kv := []string{statusKey, strconv.Itoa(status)}
+				labels = append(labels, kv...)
+			}
+
+			ctx := r.Context()
+			if ctx.Value(chi.RouteCtxKey) != nil {
+				rtCtx := chi.RouteContext(ctx)
+				if len(rtCtx.RoutePatterns) > 0 {
+					// pick last route pattern as it is the one chi used
+					route := rtCtx.RoutePatterns[len(rtCtx.RoutePatterns)-1]
+					kv := []string{routeKey, route}
+					labels = append(labels, kv...)
+				}
+			}
+
+			if r.URL != nil {
+				kv := []string{
+					urlSchemeKey, r.URL.Scheme,
+					serverAddressKey, r.URL.Host,
+				}
+				labels = append(labels, kv...)
+			}
+
+			reg.GetOrRegisterExplicitHistogram(requestDuration, metrics.ThirtySecondDistribution).With(labels...).Observe(ms(dur))
+		})
+	}
+}

hmiddleware/httpmetrics/httpmetrics_v2_test.go

@@ -0,0 +1,89 @@
+package httpmetrics
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/go-chi/chi"
+
+	"github.com/heroku/x/go-kit/metrics/testmetrics"
+)
+
+func TestOTELMiddleware(t *testing.T) {
+	p := testmetrics.NewProvider(t)
+
+	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	})
+
+	r := httptest.NewRequest("GET", "http://example.org/foo/bar", nil)
+	w := httptest.NewRecorder()
+
+	hand := NewOTEL(p)(next)
+	hand.ServeHTTP(w, r)
+
+	p.CheckObservationCount("http.server.duration.http.request.method:GET:url.scheme:http:server.address:example.org", 1)
+}
+
+func TestOTELResponseStatus(t *testing.T) {
+	p := testmetrics.NewProvider(t)
+
+	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(502)
+	})
+
+	r := httptest.NewRequest("GET", "http://example.org/foo/bar", nil)
+	w := httptest.NewRecorder()
+
+	hand := NewOTEL(p)(next)
+	hand.ServeHTTP(w, r)
+
+	p.CheckObservationCount("http.server.duration.http.request.method:GET:http.response.status_code:502:url.scheme:http:server.address:example.org", 1)
+}
+
+func TestOTELChi(t *testing.T) {
+	p := testmetrics.NewProvider(t)
+
+	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	})
+
+	r := httptest.NewRequest("GET", "http://example.org/foo/bar", nil)
+
+	rctx := chi.NewRouteContext()
+	rctx.RoutePatterns = []string{"/*", "/apps/{foo_id}/bars/{bar_id}"}
+	r = r.WithContext(context.WithValue(r.Context(), chi.RouteCtxKey, rctx))
+
+	w := httptest.NewRecorder()
+
+	hand := NewOTEL(p)(next)
+	hand.ServeHTTP(w, r)
+
+	p.CheckObservationCount("http.server.duration.http.request.method:GET:http.route:/apps/{foo_id}/bars/{bar_id}:url.scheme:http:server.address:example.org", 1)
+
+}
+
+func TestOTELNestedChiRouters(t *testing.T) {
+	p := testmetrics.NewProvider(t)
+
+	inner := chi.NewRouter()
+	inner.Get("/hello/{name}", func(w http.ResponseWriter, r *http.Request) {
+		name := chi.URLParam(r, "id")
+		if _, err := io.WriteString(w, fmt.Sprintf("Hello %s!", name)); err != nil {
+			t.Fatal("unexpected error", err)
+		}
+	})
+
+	outer := chi.NewRouter()
+	outer.Use(NewOTEL(p))
+	outer.Mount("/", inner)
+
+	r := httptest.NewRequest("GET", "http://example.org/hello/world", nil)
+	w := httptest.NewRecorder()
+	outer.ServeHTTP(w, r)
+
+	p.CheckObservationCount("http.server.duration.http.request.method:GET:http.response.status_code:200:http.route:/hello/{name}:url.scheme:http:server.address:example.org", 1)
+
+}