handler.go

// Copyright 2023 The PipeCD 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.

// Copyright 2018 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 httpapimetrics

import (
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/prometheus/client_golang/prometheus"
)

const (
	codeLabel   = "code"
	methodLabel = "method"
	pathLabel   = "path"
)

var (
	requestCounter = prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Name: "http_requests_total",
			Help: "Total number of HTTP requests.",
		},
		[]string{codeLabel, methodLabel, pathLabel},
	)

	durationHistgram = prometheus.NewHistogramVec(
		prometheus.HistogramOpts{
			Name:    "http_request_duration_milliseconds",
			Help:    "Histogram of request latencies in milliseconds.",
			Buckets: prometheus.ExponentialBuckets(1, 5, 7),
		},
		[]string{codeLabel, methodLabel, pathLabel},
	)
)

func Register(r prometheus.Registerer) {
	r.MustRegister(
		requestCounter,
		durationHistgram,
	)
}

func Handler(path string, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		d := newDelegator(w, nil)

		next.ServeHTTP(d, r)

		labels := labels(path, r.Method, d.Status())
		durationHistgram.With(labels).Observe(float64(time.Since(start).Milliseconds()))
		requestCounter.With(labels).Inc()
	})
}

func labels(path, reqMethod string, status int) prometheus.Labels {
	labels := prometheus.Labels{}

	labels[pathLabel] = path
	labels[codeLabel] = sanitizeCode(status)
	labels[methodLabel] = sanitizeMethod(reqMethod)

	return labels
}

func sanitizeMethod(m string) string {
	switch m {
	case "GET", "get":
		return "get"
	case "PUT", "put":
		return "put"
	case "HEAD", "head":
		return "head"
	case "POST", "post":
		return "post"
	case "DELETE", "delete":
		return "delete"
	case "CONNECT", "connect":
		return "connect"
	case "OPTIONS", "options":
		return "options"
	case "NOTIFY", "notify":
		return "notify"
	default:
		return strings.ToLower(m)
	}
}

// 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
// the stdlib.
func sanitizeCode(s int) string {
	switch s {
	case 100:
		return "100"
	case 101:
		return "101"

	case 200, 0:
		return "200"
	case 201:
		return "201"
	case 202:
		return "202"
	case 203:
		return "203"
	case 204:
		return "204"
	case 205:
		return "205"
	case 206:
		return "206"

	case 300:
		return "300"
	case 301:
		return "301"
	case 302:
		return "302"
	case 304:
		return "304"
	case 305:
		return "305"
	case 307:
		return "307"

	case 400:
		return "400"
	case 401:
		return "401"
	case 402:
		return "402"
	case 403:
		return "403"
	case 404:
		return "404"
	case 405:
		return "405"
	case 406:
		return "406"
	case 407:
		return "407"
	case 408:
		return "408"
	case 409:
		return "409"
	case 410:
		return "410"
	case 411:
		return "411"
	case 412:
		return "412"
	case 413:
		return "413"
	case 414:
		return "414"
	case 415:
		return "415"
	case 416:
		return "416"
	case 417:
		return "417"
	case 418:
		return "418"

	case 500:
		return "500"
	case 501:
		return "501"
	case 502:
		return "502"
	case 503:
		return "503"
	case 504:
		return "504"
	case 505:
		return "505"

	case 428:
		return "428"
	case 429:
		return "429"
	case 431:
		return "431"
	case 511:
		return "511"

	default:
		return strconv.Itoa(s)
	}
}