add metrics middleware

Signed-off-by: Augustin Husson <husson.augustin@gmail.com>

Author: Nexucis

rest/api.go

@@ -22,6 +22,8 @@ import (
 	"github.com/prometheus-community/promql-langserver/internal/vendored/go-tools/lsp/protocol"
 	"github.com/prometheus-community/promql-langserver/langserver"
 	promClient "github.com/prometheus-community/promql-langserver/prometheus"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/prometheus/common/route"
 )
 
@@ -73,6 +75,7 @@ func (d *lspData) returnPosition() (protocol.Position, error) {
 
 type API struct {
 	langServer    langserver.HeadlessServer
+	mdws          []middlewareFunc
 	enableMetrics bool
 }
 
@@ -81,8 +84,15 @@ func NewLangServerAPI(ctx context.Context, metadataService promClient.MetadataSe
 	if err != nil {
 		return nil, err
 	}
+	mdws := []middlewareFunc{manageDocumentMiddleware(lgs)}
+	if enableMetrics {
+		apiMetric := newAPIMetrics()
+		prometheus.MustRegister(apiMetric)
+		mdws = append(mdws, apiMetric.instrumentHTTPRequest)
+	}
 	return &API{
 		langServer:    lgs,
+		mdws:          mdws,
 		enableMetrics: enableMetrics,
 	}, nil
 }
@@ -93,10 +103,16 @@ func (a *API) Register(r *route.Router, prefix string) {
 	r.Post(prefix+"/completion", a.handle(a.completion))
 	r.Post(prefix+"/hover", a.handle(a.hover))
 	r.Post(prefix+"/signatureHelp", a.handle(a.signature))
+	if a.enableMetrics {
+		r.Get("/metrics", promhttp.Handler().ServeHTTP)
+	}
 }
 
 func (a *API) handle(h http.HandlerFunc) http.HandlerFunc {
-	endpoint := manageDocumentMiddleware(a.langServer)(h)
+	endpoint := h
+	for _, mdw := range a.mdws {
+		endpoint = mdw(endpoint)
+	}
 	return endpoint
 }
 

rest/middleware.go

@@ -17,11 +17,13 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"time"
 
 	"github.com/google/uuid"
 	"github.com/pkg/errors"
 	"github.com/prometheus-community/promql-langserver/internal/vendored/go-tools/lsp/protocol"
 	"github.com/prometheus-community/promql-langserver/langserver"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 type key int
@@ -129,3 +131,60 @@ func manageDocumentMiddleware(langServer langserver.HeadlessServer) middlewareFu
 		}
 	}
 }
+
+const (
+	defaultMetricNamespace = "langserver"
+	labelHandler           = "handler"
+)
+
+type apiMetrics struct {
+	totalHTTPRequest    *prometheus.CounterVec
+	durationHTTPRequest *prometheus.SummaryVec
+}
+
+func newAPIMetrics() *apiMetrics {
+	return &apiMetrics{
+		totalHTTPRequest: prometheus.NewCounterVec(prometheus.CounterOpts{
+			Namespace: defaultMetricNamespace,
+			Name:      "http_request_total",
+			Help:      "Total of HTTP requests received by the API",
+		}, []string{labelHandler}),
+		durationHTTPRequest: prometheus.NewSummaryVec(prometheus.SummaryOpts{
+			Namespace: defaultMetricNamespace,
+			Name:      "http_request_duration_second",
+			Help:      "HTTP request latencies in second",
+		}, []string{labelHandler}),
+	}
+}
+
+func (m *apiMetrics) Collect(ch chan<- prometheus.Metric) {
+	m.totalHTTPRequest.Collect(ch)
+	m.durationHTTPRequest.Collect(ch)
+}
+
+func (m *apiMetrics) Describe(ch chan<- *prometheus.Desc) {
+	m.totalHTTPRequest.Describe(ch)
+	m.durationHTTPRequest.Describe(ch)
+}
+
+func (m *apiMetrics) instrumentHTTPRequest(next http.HandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now()
+		// Call the next middleware.
+		// This middleware should be executed in the first in the chain of the middleware in order to have an accurate execution time.
+		next(w, r)
+
+		elaspsed := time.Since(start).Seconds()
+
+		counter, err := m.totalHTTPRequest.GetMetricWith(prometheus.Labels{labelHandler: r.URL.Path})
+		if err != nil {
+			return
+		}
+		counter.Inc()
+		sum, err := m.durationHTTPRequest.GetMetricWith(prometheus.Labels{labelHandler: r.URL.Path})
+		if err != nil {
+			return
+		}
+		sum.Observe(elaspsed)
+	}
+}