promhttp: Check validity of method and code label values (#962) (#987)

* Check validity of method and code label values

Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>

* Use more flexibly functional option pattern for configuration

Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>

* Update documentation

Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>

* Simplify

Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>

* Fix inconsistent method naming

Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>

Co-authored-by: Kemal Akkoyun <kakkoyun@users.noreply.github.com>

prometheus/promhttp/instrument_client.go

@@ -49,7 +49,10 @@ func InstrumentRoundTripperInFlight(gauge prometheus.Gauge, next http.RoundTripp
 // http.RoundTripper to observe the request result with the provided CounterVec.
 // The CounterVec must have zero, one, or two non-const non-curried labels. For
 // those, the only allowed label names are "code" and "method". The function
-// panics otherwise. Partitioning of the CounterVec happens by HTTP status code
+// panics otherwise. For the "method" label a predefined default label value set
+// is used to filter given values. Values besides predefined values will count
+// as `unknown` method.`WithExtraMethods` can be used to add more
+// methods to the set. Partitioning of the CounterVec happens by HTTP status code
 // and/or HTTP method if the respective instance label names are present in the
 // CounterVec. For unpartitioned counting, use a CounterVec with zero labels.
 //
@@ -57,13 +60,18 @@ func InstrumentRoundTripperInFlight(gauge prometheus.Gauge, next http.RoundTripp
 // is not incremented.
 //
 // See the example for ExampleInstrumentRoundTripperDuration for example usage.
-func InstrumentRoundTripperCounter(counter *prometheus.CounterVec, next http.RoundTripper) RoundTripperFunc {
+func InstrumentRoundTripperCounter(counter *prometheus.CounterVec, next http.RoundTripper, opts ...Option) RoundTripperFunc {
+	rtOpts := &option{}
+	for _, o := range opts {
+		o(rtOpts)
+	}
+
 	code, method := checkLabels(counter)
 
 	return RoundTripperFunc(func(r *http.Request) (*http.Response, error) {
 		resp, err := next.RoundTrip(r)
 		if err == nil {
-			counter.With(labels(code, method, r.Method, resp.StatusCode)).Inc()
+			counter.With(labels(code, method, r.Method, resp.StatusCode, rtOpts.extraMethods...)).Inc()
 		}
 		return resp, err
 	})
@@ -73,7 +81,10 @@ func InstrumentRoundTripperCounter(counter *prometheus.CounterVec, next http.Rou
 // http.RoundTripper to observe the request duration with the provided
 // ObserverVec.  The ObserverVec must have zero, one, or two non-const
 // non-curried labels. For those, the only allowed label names are "code" and
-// "method". The function panics otherwise. The Observe method of the Observer
+// "method". The function panics otherwise. For the "method" label a predefined
+// default label value set is used to filter given values. Values besides
+// predefined values will count as `unknown` method. `WithExtraMethods`
+// can be used to add more methods to the set. The Observe method of the Observer
 // in the ObserverVec is called with the request duration in
 // seconds. Partitioning happens by HTTP status code and/or HTTP method if the
 // respective instance label names are present in the ObserverVec. For
@@ -85,14 +96,19 @@ func InstrumentRoundTripperCounter(counter *prometheus.CounterVec, next http.Rou
 //
 // Note that this method is only guaranteed to never observe negative durations
 // if used with Go1.9+.
-func InstrumentRoundTripperDuration(obs prometheus.ObserverVec, next http.RoundTripper) RoundTripperFunc {
+func InstrumentRoundTripperDuration(obs prometheus.ObserverVec, next http.RoundTripper, opts ...Option) RoundTripperFunc {
+	rtOpts := &option{}
+	for _, o := range opts {
+		o(rtOpts)
+	}
+
 	code, method := checkLabels(obs)
 
 	return RoundTripperFunc(func(r *http.Request) (*http.Response, error) {
 		start := time.Now()
 		resp, err := next.RoundTrip(r)
 		if err == nil {
-			obs.With(labels(code, method, r.Method, resp.StatusCode)).Observe(time.Since(start).Seconds())
+			obs.With(labels(code, method, r.Method, resp.StatusCode, rtOpts.extraMethods...)).Observe(time.Since(start).Seconds())
 		}
 		return resp, err
 	})

prometheus/promhttp/instrument_server.go

@@ -45,7 +45,10 @@ func InstrumentHandlerInFlight(g prometheus.Gauge, next http.Handler) http.Handl
 // http.Handler to observe the request duration with the provided ObserverVec.
 // The ObserverVec must have valid metric and label names and must have zero,
 // one, or two non-const non-curried labels. For those, the only allowed label
-// names are "code" and "method". The function panics otherwise. The Observe
+// names are "code" and "method". The function panics otherwise. For the "method"
+// label a predefined default label value set is used to filter given values.
+// Values besides predefined values will count as `unknown` method.
+//`WithExtraMethods` can be used to add more methods to the set. The Observe
 // method of the Observer in the ObserverVec is called with the request duration
 // in seconds. Partitioning happens by HTTP status code and/or HTTP method if
 // the respective instance label names are present in the ObserverVec. For
@@ -58,7 +61,12 @@ func InstrumentHandlerInFlight(g prometheus.Gauge, next http.Handler) http.Handl
 //
 // Note that this method is only guaranteed to never observe negative durations
 // if used with Go1.9+.
-func InstrumentHandlerDuration(obs prometheus.ObserverVec, next http.Handler) http.HandlerFunc {
+func InstrumentHandlerDuration(obs prometheus.ObserverVec, next http.Handler, opts ...Option) http.HandlerFunc {
+	mwOpts := &option{}
+	for _, o := range opts {
+		o(mwOpts)
+	}
+
 	code, method := checkLabels(obs)
 
 	if code {
@@ -67,14 +75,14 @@ func InstrumentHandlerDuration(obs prometheus.ObserverVec, next http.Handler) ht
 			d := newDelegator(w, nil)
 			next.ServeHTTP(d, r)
 
-			obs.With(labels(code, method, r.Method, d.Status())).Observe(time.Since(now).Seconds())
+			obs.With(labels(code, method, r.Method, d.Status(), mwOpts.extraMethods...)).Observe(time.Since(now).Seconds())
 		})
 	}
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		now := time.Now()
 		next.ServeHTTP(w, r)
-		obs.With(labels(code, method, r.Method, 0)).Observe(time.Since(now).Seconds())
+		obs.With(labels(code, method, r.Method, 0, mwOpts.extraMethods...)).Observe(time.Since(now).Seconds())
 	})
 }
 
@@ -82,7 +90,10 @@ func InstrumentHandlerDuration(obs prometheus.ObserverVec, next http.Handler) ht
 // to observe the request result with the provided CounterVec. The CounterVec
 // must have valid metric and label names and must have zero, one, or two
 // non-const non-curried labels. For those, the only allowed label names are
-// "code" and "method". The function panics otherwise. Partitioning of the
+// "code" and "method". The function panics otherwise. For the "method"
+// label a predefined default label value set is used to filter given values.
+// Values besides predefined values will count as `unknown` method.
+// `WithExtraMethods` can be used to add more methods to the set. Partitioning of the
 // CounterVec happens by HTTP status code and/or HTTP method if the respective
 // instance label names are present in the CounterVec. For unpartitioned
 // counting, use a CounterVec with zero labels.
@@ -92,20 +103,25 @@ func InstrumentHandlerDuration(obs prometheus.ObserverVec, next http.Handler) ht
 // If the wrapped Handler panics, the Counter is not incremented.
 //
 // See the example for InstrumentHandlerDuration for example usage.
-func InstrumentHandlerCounter(counter *prometheus.CounterVec, next http.Handler) http.HandlerFunc {
+func InstrumentHandlerCounter(counter *prometheus.CounterVec, next http.Handler, opts ...Option) http.HandlerFunc {
+	mwOpts := &option{}
+	for _, o := range opts {
+		o(mwOpts)
+	}
+
 	code, method := checkLabels(counter)
 
 	if code {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			d := newDelegator(w, nil)
 			next.ServeHTTP(d, r)
-			counter.With(labels(code, method, r.Method, d.Status())).Inc()
+			counter.With(labels(code, method, r.Method, d.Status(), mwOpts.extraMethods...)).Inc()
 		})
 	}
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		next.ServeHTTP(w, r)
-		counter.With(labels(code, method, r.Method, 0)).Inc()
+		counter.With(labels(code, method, r.Method, 0, mwOpts.extraMethods...)).Inc()
 	})
 }
 
@@ -114,7 +130,10 @@ func InstrumentHandlerCounter(counter *prometheus.CounterVec, next http.Handler)
 // until the response headers are written. The ObserverVec must have valid
 // metric and label names and must have zero, one, or two non-const non-curried
 // labels. For those, the only allowed label names are "code" and "method". The
-// function panics otherwise. The Observe method of the Observer in the
+// function panics otherwise. For the "method" label a predefined default label
+// value set is used to filter given values. Values besides predefined values
+// will count as `unknown` method.`WithExtraMethods` can be used to add more
+// methods to the set. The Observe method of the Observer in the
 // ObserverVec is called with the request duration in seconds. Partitioning
 // happens by HTTP status code and/or HTTP method if the respective instance
 // label names are present in the ObserverVec. For unpartitioned observations,
@@ -128,13 +147,18 @@ func InstrumentHandlerCounter(counter *prometheus.CounterVec, next http.Handler)
 // if used with Go1.9+.
 //
 // See the example for InstrumentHandlerDuration for example usage.
-func InstrumentHandlerTimeToWriteHeader(obs prometheus.ObserverVec, next http.Handler) http.HandlerFunc {
+func InstrumentHandlerTimeToWriteHeader(obs prometheus.ObserverVec, next http.Handler, opts ...Option) http.HandlerFunc {
+	mwOpts := &option{}
+	for _, o := range opts {
+		o(mwOpts)
+	}
+
 	code, method := checkLabels(obs)
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		now := time.Now()
 		d := newDelegator(w, func(status int) {
-			obs.With(labels(code, method, r.Method, status)).Observe(time.Since(now).Seconds())
+			obs.With(labels(code, method, r.Method, status, mwOpts.extraMethods...)).Observe(time.Since(now).Seconds())
 		})
 		next.ServeHTTP(d, r)
 	})
@@ -144,8 +168,11 @@ func InstrumentHandlerTimeToWriteHeader(obs prometheus.ObserverVec, next http.Ha
 // http.Handler to observe the request size with the provided ObserverVec. The
 // ObserverVec must have valid metric and label names and must have zero, one,
 // or two non-const non-curried labels. For those, the only allowed label names
-// are "code" and "method". The function panics otherwise. The Observe method of
+// are "code" and "method". The function panics otherwise. For the "method"
-// the Observer in the ObserverVec is called with the request size in
+// label a predefined default label value set is used to filter given values.
+// Values besides predefined values will count as `unknown` method.
+// `WithExtraMethods` can be used to add more methods to the set. The Observe
+// method of the Observer in the ObserverVec is called with the request size in
 // bytes. Partitioning happens by HTTP status code and/or HTTP method if the
 // respective instance label names are present in the ObserverVec. For
 // unpartitioned observations, use an ObserverVec with zero labels. Note that
@@ -156,7 +183,12 @@ func InstrumentHandlerTimeToWriteHeader(obs prometheus.ObserverVec, next http.Ha
 // If the wrapped Handler panics, no values are reported.
 //
 // See the example for InstrumentHandlerDuration for example usage.
-func InstrumentHandlerRequestSize(obs prometheus.ObserverVec, next http.Handler) http.HandlerFunc {
+func InstrumentHandlerRequestSize(obs prometheus.ObserverVec, next http.Handler, opts ...Option) http.HandlerFunc {
+	mwOpts := &option{}
+	for _, o := range opts {
+		o(mwOpts)
+	}
+
 	code, method := checkLabels(obs)
 
 	if code {
@@ -164,14 +196,14 @@ func InstrumentHandlerRequestSize(obs prometheus.ObserverVec, next http.Handler)
 			d := newDelegator(w, nil)
 			next.ServeHTTP(d, r)
 			size := computeApproximateRequestSize(r)
-			obs.With(labels(code, method, r.Method, d.Status())).Observe(float64(size))
+			obs.With(labels(code, method, r.Method, d.Status(), mwOpts.extraMethods...)).Observe(float64(size))
 		})
 	}
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		next.ServeHTTP(w, r)
 		size := computeApproximateRequestSize(r)
-		obs.With(labels(code, method, r.Method, 0)).Observe(float64(size))
+		obs.With(labels(code, method, r.Method, 0, mwOpts.extraMethods...)).Observe(float64(size))
 	})
 }
 
@@ -179,8 +211,11 @@ func InstrumentHandlerRequestSize(obs prometheus.ObserverVec, next http.Handler)
 // http.Handler to observe the response size with the provided ObserverVec. The
 // ObserverVec must have valid metric and label names and must have zero, one,
 // or two non-const non-curried labels. For those, the only allowed label names
-// are "code" and "method". The function panics otherwise. The Observe method of
+// are "code" and "method". The function panics otherwise. For the "method"
-// the Observer in the ObserverVec is called with the response size in
+// label a predefined default label value set is used to filter given values.
+// Values besides predefined values will count as `unknown` method.
+// `WithExtraMethods` can be used to add more methods to the set. The Observe
+// method of the Observer in the ObserverVec is called with the response size in
 // bytes. Partitioning happens by HTTP status code and/or HTTP method if the
 // respective instance label names are present in the ObserverVec. For
 // unpartitioned observations, use an ObserverVec with zero labels. Note that
@@ -191,12 +226,18 @@ func InstrumentHandlerRequestSize(obs prometheus.ObserverVec, next http.Handler)
 // If the wrapped Handler panics, no values are reported.
 //
 // See the example for InstrumentHandlerDuration for example usage.
-func InstrumentHandlerResponseSize(obs prometheus.ObserverVec, next http.Handler) http.Handler {
+func InstrumentHandlerResponseSize(obs prometheus.ObserverVec, next http.Handler, opts ...Option) http.Handler {
+	mwOpts := &option{}
+	for _, o := range opts {
+		o(mwOpts)
+	}
+
 	code, method := checkLabels(obs)
+
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		d := newDelegator(w, nil)
 		next.ServeHTTP(d, r)
-		obs.With(labels(code, method, r.Method, d.Status())).Observe(float64(d.Written()))
+		obs.With(labels(code, method, r.Method, d.Status(), mwOpts.extraMethods...)).Observe(float64(d.Written()))
 	})
 }
 
@@ -290,7 +331,7 @@ func isLabelCurried(c prometheus.Collector, label string) bool {
 // unnecessary allocations on each request.
 var emptyLabels = prometheus.Labels{}
 
-func labels(code, method bool, reqMethod string, status int) prometheus.Labels {
+func labels(code, method bool, reqMethod string, status int, extraMethods ...string) prometheus.Labels {
 	if !(code || method) {
 		return emptyLabels
 	}
@@ -300,7 +341,7 @@ func labels(code, method bool, reqMethod string, status int) prometheus.Labels {
 		labels["code"] = sanitizeCode(status)
 	}
 	if method {
-		labels["method"] = sanitizeMethod(reqMethod)
+		labels["method"] = sanitizeMethod(reqMethod, extraMethods...)
 	}
 
 	return labels
@@ -330,7 +371,12 @@ func computeApproximateRequestSize(r *http.Request) int {
 	return s
 }
 
-func sanitizeMethod(m string) string {
+// If the wrapped http.Handler has a known method, it will be sanitized and returned.
+// Otherwise, "unknown" will be returned. The known method list can be extended
+// as needed by using extraMethods parameter.
+func sanitizeMethod(m string, extraMethods ...string) string {
+	// See https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods for
+	// the methods chosen as default.
 	switch m {
 	case "GET", "get":
 		return "get"
@@ -348,15 +394,25 @@ func sanitizeMethod(m string) string {
 		return "options"
 	case "NOTIFY", "notify":
 		return "notify"
+	case "TRACE", "trace":
+		return "trace"
+	case "PATCH", "patch":
+		return "patch"
 	default:
-		return strings.ToLower(m)
+		for _, method := range extraMethods {
+			if strings.EqualFold(m, method) {
+				return strings.ToLower(m)
+			}
+		}
+		return "unknown"
 	}
 }
 
 // If the wrapped http.Handler has not set a status code, i.e. the value is
-// currently 0, santizeCode will return 200, for consistency with behavior in
+// currently 0, sanitizeCode will return 200, for consistency with behavior in
 // the stdlib.
 func sanitizeCode(s int) string {
+	// See for accepted codes https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml
 	switch s {
 	case 100:
 		return "100"
@@ -453,6 +509,9 @@ func sanitizeCode(s int) string {
 		return "511"
 
 	default:
-		return strconv.Itoa(s)
+		if s >= 100 && s <= 599 {
+			return strconv.Itoa(s)
+		}
+		return "unknown"
 	}
 }

prometheus/promhttp/instrument_server_test.go

@@ -204,6 +204,122 @@ func TestLabelCheck(t *testing.T) {
 	}
 }
 
+func TestLabels(t *testing.T) {
+	scenarios := map[string]struct {
+		varLabels    []string
+		reqMethod    string
+		respStatus   int
+		extraMethods []string
+		wantLabels   prometheus.Labels
+		ok           bool
+	}{
+		"empty": {
+			varLabels:  []string{},
+			wantLabels: emptyLabels,
+			reqMethod:  "GET",
+			respStatus: 200,
+			ok:         true,
+		},
+		"code as single var label": {
+			varLabels:  []string{"code"},
+			reqMethod:  "GET",
+			respStatus: 200,
+			wantLabels: prometheus.Labels{"code": "200"},
+			ok:         true,
+		},
+		"code as single var label and out-of-range code": {
+			varLabels:  []string{"code"},
+			reqMethod:  "GET",
+			respStatus: 99,
+			wantLabels: prometheus.Labels{"code": "unknown"},
+			ok:         true,
+		},
+		"code as single var label and in-range but unrecognized code": {
+			varLabels:  []string{"code"},
+			reqMethod:  "GET",
+			respStatus: 308,
+			wantLabels: prometheus.Labels{"code": "308"},
+			ok:         true,
+		},
+		"method as single var label": {
+			varLabels:  []string{"method"},
+			reqMethod:  "GET",
+			respStatus: 200,
+			wantLabels: prometheus.Labels{"method": "get"},
+			ok:         true,
+		},
+		"method as single var label and unknown method": {
+			varLabels:  []string{"method"},
+			reqMethod:  "CUSTOM_METHOD",
+			respStatus: 200,
+			wantLabels: prometheus.Labels{"method": "unknown"},
+			ok:         true,
+		},
+		"code and method as var labels": {
+			varLabels:  []string{"method", "code"},
+			reqMethod:  "GET",
+			respStatus: 200,
+			wantLabels: prometheus.Labels{"method": "get", "code": "200"},
+			ok:         true,
+		},
+		"method as single var label with extra methods specified": {
+			varLabels:    []string{"method"},
+			reqMethod:    "CUSTOM_METHOD",
+			respStatus:   200,
+			extraMethods: []string{"CUSTOM_METHOD", "CUSTOM_METHOD_1"},
+			wantLabels:   prometheus.Labels{"method": "custom_method"},
+			ok:           true,
+		},
+		"all labels used with an unknown method and out-of-range code": {
+			varLabels:  []string{"code", "method"},
+			reqMethod:  "CUSTOM_METHOD",
+			respStatus: 99,
+			wantLabels: prometheus.Labels{"method": "unknown", "code": "unknown"},
+			ok:         false,
+		},
+	}
+	checkLabels := func(labels []string) (gotCode bool, gotMethod bool) {
+		for _, label := range labels {
+			switch label {
+			case "code":
+				gotCode = true
+			case "method":
+				gotMethod = true
+			default:
+				panic("metric partitioned with non-supported labels for this test")
+			}
+		}
+		return
+	}
+	equalLabels := func(gotLabels, wantLabels prometheus.Labels) bool {
+		if len(gotLabels) != len(wantLabels) {
+			return false
+		}
+		for ln, lv := range gotLabels {
+			olv, ok := wantLabels[ln]
+			if !ok {
+				return false
+			}
+			if olv != lv {
+				return false
+			}
+		}
+		return true
+	}
+
+	for name, sc := range scenarios {
+		t.Run(name, func(t *testing.T) {
+			if sc.ok {
+				gotCode, gotMethod := checkLabels(sc.varLabels)
+				gotLabels := labels(gotCode, gotMethod, sc.reqMethod, sc.respStatus, sc.extraMethods...)
+				if !equalLabels(gotLabels, sc.wantLabels) {
+					t.Errorf("wanted labels=%v for counter, got code=%v", sc.wantLabels, gotLabels)
+				}
+			}
+		})
+	}
+}
+
 func TestMiddlewareAPI(t *testing.T) {
 	reg := prometheus.NewRegistry()
 

prometheus/promhttp/option.go

@@ -0,0 +1,31 @@
+// Copyright 2022 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package promhttp
+
+// Option are used to configure a middleware or round tripper..
+type Option func(*option)
+
+type option struct {
+	extraMethods []string
+}
+
+// WithExtraMethods adds additional HTTP methods to the list of allowed methods.
+// See https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods for the default list.
+//
+// See the example for ExampleInstrumentHandlerWithExtraMethods for example usage.
+func WithExtraMethods(methods ...string) Option {
+	return func(o *option) {
+		o.extraMethods = methods
+	}
+}

prometheus/promhttp/option_test.go

@@ -0,0 +1,65 @@
+// Copyright 2022 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package promhttp
+
+import (
+	"log"
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+func ExampleInstrumentHandlerWithExtraMethods() {
+	counter := prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "api_requests_total",
+			Help: "A counter for requests to the wrapped handler.",
+		},
+		[]string{"code", "method"},
+	)
+
+	// duration is partitioned by the HTTP method and handler. It uses custom
+	// buckets based on the expected request duration.
+	duration := prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "request_duration_seconds",
+			Help:    "A histogram of latencies for requests.",
+			Buckets: []float64{.25, .5, 1, 2.5, 5, 10},
+		},
+		[]string{"handler", "method"},
+	)
+
+	// Create the handlers that will be wrapped by the middleware.
+	pullHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte("Pull"))
+	})
+
+	// Specify additional HTTP methods to be added to the label allow list.
+	opts := WithExtraMethods("CUSTOM_METHOD")
+
+	// Instrument the handlers with all the metrics, injecting the "handler"
+	// label by currying.
+	pullChain :=
+		InstrumentHandlerDuration(duration.MustCurryWith(prometheus.Labels{"handler": "pull"}),
+			InstrumentHandlerCounter(counter, pullHandler, opts),
+			opts,
+		)
+
+	http.Handle("/metrics", Handler())
+	http.Handle("/pull", pullChain)
+
+	if err := http.ListenAndServe(":3000", nil); err != nil {
+		log.Fatal(err)
+	}
+}