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// 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 (
"context"
"log"
"net/http"
"github.com/prometheus/client_golang/prometheus"
)
type key int
const (
CtxResolverKey key = iota
)
func ExampleWithExtraMethods() {
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)
}
}
func ExampleWithLabelFromCtx() {
counter := prometheus.NewCounterVec(
prometheus.CounterOpts{
Name: "api_requests_total",
Help: "A counter for requests to the wrapped handler.",
},
[]string{"code", "method", "myheader"},
)
// duration is partitioned by the HTTP method, handler and request header
// value. It uses custom buckets based on the expected request duration.
// Beware to not have too high cardinality on the values of header. You
// always should sanitize external inputs.
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", "myheader"},
)
// 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 := WithLabelFromCtx("myheader",
func(ctx context.Context) string {
return ctx.Value(CtxResolverKey).(string)
},
)
// 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,
)
middleware := func(next http.HandlerFunc) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
ctx := context.WithValue(r.Context(), CtxResolverKey, r.Header.Get("x-my-header"))
next(w, r.WithContext(ctx))
}
}
http.Handle("/metrics", Handler())
http.Handle("/pull", middleware(pullChain))
if err := http.ListenAndServe(":3000", nil); err != nil {
log.Fatal(err)
}
}
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