add metrics middleware (#711)

* add metrics middleware

middleware/metrics/metrics.go

@@ -0,0 +1,107 @@
+package metrics
+
+import (
+	"context"
+	"strconv"
+	"time"
+
+	"github.com/go-kratos/kratos/v2/errors"
+	"github.com/go-kratos/kratos/v2/metrics"
+	"github.com/go-kratos/kratos/v2/middleware"
+	"github.com/go-kratos/kratos/v2/transport/grpc"
+	"github.com/go-kratos/kratos/v2/transport/http"
+	"github.com/gorilla/mux"
+)
+
+// Option is metrics option.
+type Option func(*options)
+
+type options struct {
+	// counter: <kind>_<client/server>_requests_code_total{method, path, code}
+	requests metrics.Counter
+	// histogram: <kind>_<client/server>_requests_seconds_bucket{method, path}
+	seconds metrics.Observer
+}
+
+// Server is middleware server-side metrics.
+func Server(opts ...Option) middleware.Middleware {
+	options := options{}
+	for _, o := range opts {
+		o(&options)
+	}
+	return func(handler middleware.Handler) middleware.Handler {
+		return func(ctx context.Context, req interface{}) (interface{}, error) {
+			var (
+				method string
+				path   string
+				code   int32
+			)
+			if info, ok := grpc.FromServerContext(ctx); ok {
+				method = "POST"
+				path = info.FullMethod
+			} else if info, ok := http.FromServerContext(ctx); ok {
+				method = info.Request.Method
+				if route := mux.CurrentRoute(info.Request); route != nil {
+					// /path/123 -> /path/{id}
+					path, _ = route.GetPathTemplate()
+				} else {
+					path = info.Request.RequestURI
+				}
+			}
+			startTime := time.Now()
+			reply, err := handler(ctx, req)
+			if err != nil {
+				code = errors.Code(err)
+			}
+			if options.requests != nil {
+				options.requests.With(method, path, strconv.Itoa(int(code))).Inc()
+			}
+			if options.seconds != nil {
+				options.seconds.With(method, path).Observe(time.Since(startTime).Seconds())
+			}
+			return reply, err
+
+		}
+	}
+}
+
+// Client is middleware client-side metrics.
+func Client(opts ...Option) middleware.Middleware {
+	options := options{}
+	for _, o := range opts {
+		o(&options)
+	}
+	return func(handler middleware.Handler) middleware.Handler {
+		return func(ctx context.Context, req interface{}) (interface{}, error) {
+			var (
+				method string
+				path   string
+				code   int32
+			)
+			if info, ok := grpc.FromServerContext(ctx); ok {
+				method = "POST"
+				path = info.FullMethod
+			} else if info, ok := http.FromServerContext(ctx); ok {
+				method = info.Request.Method
+				if route := mux.CurrentRoute(info.Request); route != nil {
+					// /path/123 -> /path/{id}
+					path, _ = route.GetPathTemplate()
+				} else {
+					path = info.Request.RequestURI
+				}
+			}
+			startTime := time.Now()
+			reply, err := handler(ctx, req)
+			if err != nil {
+				code = errors.Code(err)
+			}
+			if options.requests != nil {
+				options.requests.With(method, path, strconv.Itoa(int(code))).Inc()
+			}
+			if options.seconds != nil {
+				options.seconds.With(method, path).Observe(time.Since(startTime).Seconds())
+			}
+			return reply, err
+		}
+	}
+}