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middleware.go
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middleware.go
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package ginprometheus
import (
"bytes"
"errors"
"io/ioutil"
"log"
"net/http"
"os"
"strconv"
"time"
"github.com/gin-gonic/gin"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promhttp"
"strings"
dto "github.com/prometheus/client_model/go"
)
const magicString = "zZgWfBxLqvG8kc8IMv3POi2Bb0tZI3vAnBx+gBaFi9FyPzB/CzKUer1yufDa"
var (
defaultMetricPath = "/metrics"
)
/*
URLLabelMappingFn is a function which can be supplied to the middleware to control
the cardinality of the request counter's "url" label, which might be required in some contexts.
For instance, if for a "/customer/:name" route you don't want to generate a time series for every
possible customer name, you could use this function:
func(c *gin.Context) string {
url := c.Request.URL.String()
for _, p := range c.Params {
if p.Key == "name" {
url = strings.Replace(url, p.Value, ":name", 1)
break
}
}
return url
}
which would map "/customer/alice" and "/customer/bob" to their template "/customer/:name".
*/
type URLLabelMappingFn func(c *gin.Context) string
func NewBuilder() *Prometheus {
p := &Prometheus{
MetricsPath: defaultMetricPath,
urlLabelMappingFn: func(c *gin.Context) string {
return c.Request.URL.String() // i.e. by default do nothing, i.e. return URL as is
},
}
return p
}
type PrometheusMiddlerwareBuilder interface {
Auth(accounts gin.Accounts) PrometheusMiddlerwareBuilder
UrlMapping(function URLLabelMappingFn) PrometheusMiddlerwareBuilder
Counter(counter *prometheus.CounterVec) PrometheusMiddlerwareBuilder
Duration(observer prometheus.ObserverVec) PrometheusMiddlerwareBuilder
RequestSize(observer prometheus.ObserverVec) PrometheusMiddlerwareBuilder
ResponseSize(observer prometheus.ObserverVec) PrometheusMiddlerwareBuilder
PushGateway(pushGatewayURL, metricsURL string, pushIntervalSeconds time.Duration) PrometheusPushGatewayMiddlewareBuilder
Use(e *gin.Engine)
}
func (p *Prometheus) Auth(accounts gin.Accounts) PrometheusMiddlerwareBuilder {
p.accounts = accounts
return p
}
func (p *Prometheus) UrlMapping(function URLLabelMappingFn) PrometheusMiddlerwareBuilder {
p.urlLabelMappingFn = function
return p
}
type metricInfo struct {
code, method, url string
duration, requestSize, responseSize float64
}
type metricFunc func(metricInfo *metricInfo)
func (p *Prometheus) Counter(counter *prometheus.CounterVec) PrometheusMiddlerwareBuilder {
code, method, url := checkLabels(counter)
p.reqCnt = metricFunc(func(i *metricInfo) {
counter.With(labels(code, method, url, i.code, i.method, i.url)).Inc()
})
return p
}
func (p *Prometheus) Duration(observer prometheus.ObserverVec) PrometheusMiddlerwareBuilder {
code, method, url := checkLabels(observer)
p.reqDur = metricFunc(func(i *metricInfo) {
observer.With(labels(code, method, url, i.code, i.method, i.url)).Observe(i.duration)
})
return p
}
func (p *Prometheus) RequestSize(observer prometheus.ObserverVec) PrometheusMiddlerwareBuilder {
code, method, url := checkLabels(observer)
p.reqSz = metricFunc(func(i *metricInfo) {
observer.With(labels(code, method, url, i.code, i.method, i.url)).Observe(i.requestSize)
})
return p
}
func (p *Prometheus) ResponseSize(observer prometheus.ObserverVec) PrometheusMiddlerwareBuilder {
code, method, url := checkLabels(observer)
p.resSz = metricFunc(func(i *metricInfo) {
observer.With(labels(code, method, url, i.code, i.method, i.url)).Observe(i.responseSize)
})
return p
}
// PushGateway sends metrics to a remote pushgateway exposed on pushGatewayURL
// every pushIntervalSeconds. Metrics are fetched from metricsURL
func (p *Prometheus) PushGateway(pushGatewayURL, metricsURL string, pushIntervalSeconds time.Duration) PrometheusPushGatewayMiddlewareBuilder {
p.ppg.pushGatewayURL = pushGatewayURL
p.ppg.metricsURL = metricsURL
p.ppg.pushIntervalSeconds = pushIntervalSeconds
p.startPushTicker()
return p
}
// Use adds the middleware to a gin engine.
func (p *Prometheus) Use(e *gin.Engine) {
e.Use(p.handlerFunc())
if p.accounts != nil {
p.setMetricsPathWithAuth(e, p.accounts)
} else {
p.setMetricsPath(e)
}
}
type PrometheusPushGatewayMiddlewareBuilder interface {
Job(job string)
ListenAddress(address string)
Use(e *gin.Engine)
}
// Job job name, defaults to "gin"
func (p *Prometheus) Job(j string) {
p.ppg.job = j
}
// ListenAddress for exposing metrics on address. If not set, it will be exposed at the
// same address of the gin engine that is being used
func (p *Prometheus) ListenAddress(address string) {
p.listenAddress = address
if p.listenAddress != "" {
p.router = gin.Default()
}
}
// Prometheus contains the metrics gathered by the instance and its path
type Prometheus struct {
reqCnt, reqDur, reqSz, resSz metricFunc
router *gin.Engine
listenAddress string
ppg PrometheusPushGateway
accounts gin.Accounts
MetricsPath string
urlLabelMappingFn URLLabelMappingFn
}
// PrometheusPushGateway contains the configuration for pushing to a Prometheus pushgateway (optional)
type PrometheusPushGateway struct {
// Push interval in seconds
pushIntervalSeconds time.Duration
// Push Gateway URL in format http://domain:port
// where JOBNAME can be any string of your choice
pushGatewayURL string
// Local metrics URL where metrics are fetched from, this could be ommited in the future
// if implemented using prometheus common/expfmt instead
metricsURL string
// pushgateway job name, defaults to "gin"
job string
}
func (p *Prometheus) setMetricsPath(e *gin.Engine) {
if p.listenAddress != "" {
p.router.GET(p.MetricsPath, prometheusHandler())
p.runServer()
} else {
e.GET(p.MetricsPath, prometheusHandler())
}
}
func (p *Prometheus) setMetricsPathWithAuth(e *gin.Engine, accounts gin.Accounts) {
if p.listenAddress != "" {
p.router.GET(p.MetricsPath, gin.BasicAuth(accounts), prometheusHandler())
p.runServer()
} else {
e.GET(p.MetricsPath, gin.BasicAuth(accounts), prometheusHandler())
}
}
func (p *Prometheus) runServer() {
if p.listenAddress != "" {
go p.router.Run(p.listenAddress)
}
}
func (p *Prometheus) getMetrics() []byte {
response, _ := http.Get(p.ppg.metricsURL)
defer response.Body.Close()
body, _ := ioutil.ReadAll(response.Body)
return body
}
func (p *Prometheus) getPushGatewayURL() string {
h, _ := os.Hostname()
if p.ppg.job == "" {
p.ppg.job = "gin"
}
return p.ppg.pushGatewayURL + "/metrics/job/" + p.ppg.job + "/instance/" + h
}
func (p *Prometheus) sendMetricsToPushGateway(metrics []byte) {
req, err := http.NewRequest("POST", p.getPushGatewayURL(), bytes.NewBuffer(metrics))
client := &http.Client{}
_, err = client.Do(req)
if err != nil {
log.Printf("Error sending to push gatway: %s\n", err.Error())
}
}
func (p *Prometheus) startPushTicker() {
ticker := time.NewTicker(time.Second * p.ppg.pushIntervalSeconds)
go func() {
for range ticker.C {
p.sendMetricsToPushGateway(p.getMetrics())
}
}()
}
func (p *Prometheus) handlerFunc() gin.HandlerFunc {
return func(c *gin.Context) {
if c.Request.URL.String() == p.MetricsPath {
c.Next()
return
}
start := time.Now()
reqSz := computeApproximateRequestSize(c.Request)
c.Next()
info := metricInfo{
method: sanitizeMethod(c.Request.Method),
code: sanitizeCode(c.Writer.Status()),
url: p.urlLabelMappingFn(c),
duration: float64(time.Since(start)) / float64(time.Second),
requestSize: float64(reqSz),
responseSize: float64(c.Writer.Size()),
}
if p.reqCnt != nil {
p.reqCnt(&info)
}
if p.reqDur != nil {
p.reqDur(&info)
}
if p.reqSz != nil {
p.reqSz(&info)
}
if p.resSz != nil {
p.resSz(&info)
}
}
}
func prometheusHandler() gin.HandlerFunc {
h := promhttp.Handler()
return func(c *gin.Context) {
h.ServeHTTP(c.Writer, c.Request)
}
}
// From https://github.com/DanielHeckrath/gin-prometheus/blob/master/gin_prometheus.go
func computeApproximateRequestSize(r *http.Request) int {
s := 0
if r.URL != nil {
s = len(r.URL.String())
}
s += len(r.Method)
s += len(r.Proto)
for name, values := range r.Header {
s += len(name)
for _, value := range values {
s += len(value)
}
}
s += len(r.Host)
// N.B. r.Form and r.MultipartForm are assumed to be included in r.URL.
if r.ContentLength != -1 {
s += int(r.ContentLength)
}
return s
}
var emptyLabels = prometheus.Labels{}
func labels(codeExists, methodExists, urlExists bool, method, code, url string) prometheus.Labels {
if !(codeExists || methodExists || urlExists) {
return emptyLabels
}
labels := prometheus.Labels{}
if codeExists {
labels["code"] = code
}
if methodExists {
labels["method"] = method
}
if urlExists {
labels["url"] = url
}
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:
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)
}
}
func checkLabels(c prometheus.Collector) (code bool, method bool, url bool) {
// TODO(beorn7): Remove this hacky way to check for instance labels
// once Descriptors can have their dimensionality queried.
var (
desc *prometheus.Desc
m prometheus.Metric
pm dto.Metric
lvs []string
)
// Get the Desc from the Collector.
descc := make(chan *prometheus.Desc, 1)
c.Describe(descc)
select {
case desc = <-descc:
default:
panic("no description provided by collector")
}
select {
case <-descc:
panic("more than one description provided by collector")
default:
}
close(descc)
// Create a ConstMetric with the Desc. Since we don't know how many
// variable labels there are, try for as long as it needs.
for err := errors.New("dummy"); err != nil; lvs = append(lvs, magicString) {
m, err = prometheus.NewConstMetric(desc, prometheus.UntypedValue, 0, lvs...)
}
// Write out the metric into a proto message and look at the labels.
// If the value is not the magicString, it is a constLabel, which doesn't interest us.
// If the label is curried, it doesn't interest us.
// In all other cases, only "code" or "method" is allowed.
if err := m.Write(&pm); err != nil {
panic("error checking metric for labels")
}
for _, label := range pm.Label {
name, value := label.GetName(), label.GetValue()
if value != magicString || isLabelCurried(c, name) {
continue
}
switch name {
case "code":
code = true
case "method":
method = true
case "url":
url = true
default:
panic("metric partitioned with non-supported labels")
}
}
return
}
func isLabelCurried(c prometheus.Collector, label string) bool {
// This is even hackier than the label test above.
// We essentially try to curry again and see if it works.
// But for that, we need to type-convert to the two
// types we use here, ObserverVec or *CounterVec.
switch v := c.(type) {
case *prometheus.CounterVec:
if _, err := v.CurryWith(prometheus.Labels{label: "dummy"}); err == nil {
return false
}
case prometheus.ObserverVec:
if _, err := v.CurryWith(prometheus.Labels{label: "dummy"}); err == nil {
return false
}
default:
panic("unsupported metric vec type")
}
return true
}