Add time to write header handler middleware (#304)
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42552c195d
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@ -20,8 +20,11 @@ import (
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"net/http"
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)
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func newDelegator(w http.ResponseWriter) delegator {
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d := &responseWriterDelegator{ResponseWriter: w}
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func newDelegator(w http.ResponseWriter, observeWriteHeaderFunc func(int)) delegator {
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d := &responseWriterDelegator{
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ResponseWriter: w,
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observeWriteHeader: observeWriteHeaderFunc,
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}
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_, cn := w.(http.CloseNotifier)
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_, fl := w.(http.Flusher)
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@ -22,8 +22,11 @@ import (
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// newDelegator handles the four different methods of upgrading a
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// http.ResponseWriter to delegator.
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func newDelegator(w http.ResponseWriter) delegator {
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d := &responseWriterDelegator{ResponseWriter: w}
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func newDelegator(w http.ResponseWriter, observeWriteHeaderFunc func(int)) delegator {
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d := &responseWriterDelegator{
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ResponseWriter: w,
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observeWriteHeader: observeWriteHeaderFunc,
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}
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_, cn := w.(http.CloseNotifier)
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_, fl := w.(http.Flusher)
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@ -63,7 +63,7 @@ func InstrumentHandlerDuration(obs prometheus.ObserverVec, next http.Handler) ht
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if code {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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now := time.Now()
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d := newDelegator(w)
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d := newDelegator(w, nil)
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next.ServeHTTP(d, r)
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obs.With(labels(code, method, r.Method, d.Status())).Observe(time.Since(now).Seconds())
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@ -96,7 +96,7 @@ func InstrumentHandlerCounter(counter *prometheus.CounterVec, next http.Handler)
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if code {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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d := newDelegator(w)
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d := newDelegator(w, nil)
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next.ServeHTTP(d, r)
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counter.With(labels(code, method, r.Method, d.Status())).Inc()
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})
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@ -108,6 +108,34 @@ func InstrumentHandlerCounter(counter *prometheus.CounterVec, next http.Handler)
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})
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}
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// InstrumentHandlerTimeToWriteHeader is a middleware that wraps the provided
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// http.Handler to observe with the provided ObserverVec the request duration
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// until the response headers are written. The ObserverVec must have zero, one,
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// or two labels. The only allowed label names are "code" and "method". The
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// function panics if any other instance labels are provided. The Observe
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// method of the Observer in the ObserverVec is called with the request
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// duration in seconds. Partitioning happens by HTTP status code and/or HTTP
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// method if the respective instance label names are present in the
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// ObserverVec. For unpartitioned observations, use an ObserverVec with zero
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// labels. Note that partitioning of Histograms is expensive and should be used
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// judiciously.
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//
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// If the wrapped Handler panics before calling WriteHeader, no value is
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// reported.
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//
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// See the example for InstrumentHandlerDuration for example usage.
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func InstrumentHandlerTimeToWriteHeader(obs prometheus.ObserverVec, next http.Handler) http.HandlerFunc {
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code, method := checkLabels(obs)
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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now := time.Now()
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d := newDelegator(w, func(status int) {
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obs.With(labels(code, method, r.Method, status)).Observe(time.Since(now).Seconds())
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})
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next.ServeHTTP(d, r)
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})
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}
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// InstrumentHandlerRequestSize is a middleware that wraps the provided
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// http.Handler to observe the request size with the provided ObserverVec.
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// The ObserverVec must have zero, one, or two labels. The only allowed label
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@ -129,7 +157,7 @@ func InstrumentHandlerRequestSize(obs prometheus.ObserverVec, next http.Handler)
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if code {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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d := newDelegator(w)
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d := newDelegator(w, nil)
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next.ServeHTTP(d, r)
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size := computeApproximateRequestSize(r)
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obs.With(labels(code, method, r.Method, d.Status())).Observe(float64(size))
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@ -162,7 +190,7 @@ func InstrumentHandlerRequestSize(obs prometheus.ObserverVec, next http.Handler)
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func InstrumentHandlerResponseSize(obs prometheus.ObserverVec, next http.Handler) http.Handler {
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code, method := checkLabels(obs)
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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d := newDelegator(w)
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d := newDelegator(w, nil)
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next.ServeHTTP(d, r)
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obs.With(labels(code, method, r.Method, d.Status())).Observe(float64(d.Written()))
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})
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@ -418,10 +446,11 @@ type delegator interface {
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type responseWriterDelegator struct {
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http.ResponseWriter
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handler, method string
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status int
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written int64
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wroteHeader bool
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handler, method string
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status int
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written int64
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wroteHeader bool
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observeWriteHeader func(int)
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}
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func (r *responseWriterDelegator) Status() int {
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@ -436,6 +465,9 @@ func (r *responseWriterDelegator) WriteHeader(code int) {
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r.status = code
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r.wroteHeader = true
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r.ResponseWriter.WriteHeader(code)
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if r.observeWriteHeader != nil {
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r.observeWriteHeader(code)
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}
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}
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func (r *responseWriterDelegator) Write(b []byte) (int, error) {
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@ -48,6 +48,16 @@ func TestMiddlewareAPI(t *testing.T) {
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[]string{"method"},
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)
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writeHeaderVec := prometheus.NewHistogramVec(
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prometheus.HistogramOpts{
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Name: "write_header_duration_seconds",
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Help: "A histogram of time to first write latencies.",
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Buckets: prometheus.DefBuckets,
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ConstLabels: prometheus.Labels{"handler": "api"},
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},
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[]string{},
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)
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responseSize := prometheus.NewHistogramVec(
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prometheus.HistogramOpts{
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Name: "push_request_size_bytes",
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@ -61,12 +71,14 @@ func TestMiddlewareAPI(t *testing.T) {
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w.Write([]byte("OK"))
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})
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reg.MustRegister(inFlightGauge, counter, histVec, responseSize)
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reg.MustRegister(inFlightGauge, counter, histVec, responseSize, writeHeaderVec)
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chain := InstrumentHandlerInFlight(inFlightGauge,
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InstrumentHandlerCounter(counter,
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InstrumentHandlerDuration(histVec,
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InstrumentHandlerResponseSize(responseSize, handler),
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InstrumentHandlerTimeToWriteHeader(writeHeaderVec,
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InstrumentHandlerResponseSize(responseSize, handler),
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),
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),
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),
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)
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@ -76,6 +88,23 @@ func TestMiddlewareAPI(t *testing.T) {
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chain.ServeHTTP(w, r)
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}
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func TestInstrumentTimeToFirstWrite(t *testing.T) {
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var i int
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dobs := &responseWriterDelegator{
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ResponseWriter: httptest.NewRecorder(),
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observeWriteHeader: func(status int) {
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i = status
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},
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}
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d := newDelegator(dobs, nil)
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d.WriteHeader(http.StatusOK)
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if i != http.StatusOK {
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t.Fatalf("failed to execute observeWriteHeader")
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}
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}
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func ExampleInstrumentHandlerDuration() {
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inFlightGauge := prometheus.NewGauge(prometheus.GaugeOpts{
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Name: "in_flight_requests",
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