Implement Metrics middleware via Prometheus

Metrics is a middleware for logging duration of RPC requests via Prometheus.
It exposes two metrics: appName_rpc_error_requests_count and appName_rpc_responses_duration_seconds.

README.md

@@ -104,14 +104,14 @@ All comments are optional.
 
 # JSON-RPC 2.0 Supported Features
 
-  * [ ] Requests
+  * [x] Requests
     * [x] Single requests
     * [x] Batch requests
     * [x] Notifications
   * [ ] Parameters
     * [x] Named
     * [ ] Position
-    * [ ] Default values
+    * [x] Default values
   * [ ] SMD Schema
     * [ ] Input
     * [ ] Output
@@ -120,15 +120,15 @@ All comments are optional.
 
 # Server Library Features
 
- * [ ] go generate
+ * [x] go generate
  * [ ] Transports
    * [x] HTTP
    * [ ] Websocket
    * [ ] RabbitMQ
- * [ ] Server middleware
-   * [ ] Basic support
-   * [ ] Metrics
-   * [ ] Logging
+ * [x] Server middleware
+   * [x] Basic support
+   * [x] Metrics
+   * [x] Logging
 
 # License
 

middleware.go

@@ -3,7 +3,9 @@ package zenrpc
 import (
 	"context"
 	"encoding/json"
+	"github.com/prometheus/client_golang/prometheus"
 	"log"
+	"strconv"
 	"time"
 )
 
@@ -24,3 +26,48 @@ func Logger(l *log.Logger) MiddlewareFunc {
 		}
 	}
 }
+
+// Metrics is a middleware for logging duration of RPC requests via Prometheus. Default AppName is zenrpc.
+// It exposes two metrics: appName_rpc_error_requests_count and appName_rpc_responses_duration_seconds.
+func Metrics(appName string) MiddlewareFunc {
+	if appName == "" {
+		appName = "zenrpc"
+	}
+
+	rpcErrors := prometheus.NewCounterVec(prometheus.CounterOpts{
+		Namespace: appName,
+		Subsystem: "rpc",
+		Name:      "error_requests_count",
+		Help:      "Error requests count by method and error code.",
+	}, []string{"method", "code"})
+
+	rpcDurations := prometheus.NewSummaryVec(prometheus.SummaryOpts{
+		Namespace: appName,
+		Subsystem: "rpc",
+		Name:      "responses_duration_seconds",
+		Help:      "Response time by method and error code.",
+	}, []string{"method", "code"})
+
+	prometheus.MustRegister(rpcErrors, rpcDurations)
+
+	return func(h InvokeFunc) InvokeFunc {
+		return func(ctx context.Context, method string, params json.RawMessage) Response {
+			start, code := time.Now(), ""
+			r := h(ctx, method, params)
+
+			// log metrics
+			if n := NamespaceFromContext(ctx); n != "" {
+				method = n + "." + method
+			}
+
+			if r.Error != nil {
+				code = strconv.Itoa(r.Error.Code)
+				rpcErrors.WithLabelValues(method, code).Inc()
+			}
+
+			rpcDurations.WithLabelValues(method, code).Observe(time.Since(start).Seconds())
+
+			return r
+		}
+	}
+}

testdata/arithsrv/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"flag"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/sergeyfast/zenrpc"
 	"github.com/sergeyfast/zenrpc/testdata"
 	"log"
@@ -17,9 +18,11 @@ func main() {
 	rpc.Register("arith", testdata.ArithService{})
 	rpc.Register("", testdata.ArithService{}) // public
 	rpc.Use(zenrpc.Logger(log.New(os.Stderr, "", log.LstdFlags)))
+	rpc.Use(zenrpc.Metrics(""))
 
 	http.Handle("/", rpc)
+	http.Handle("/metrics", promhttp.Handler())
 
 	log.Printf("starting arithsrv on %s", *addr)
 	log.Fatal(http.ListenAndServe(*addr, nil))
-}
+}