bump github.com/prometheus/client_golang to v1.6.0

vendor/github.com/prometheus/client_golang/prometheus/BUILD

@@ -33,7 +33,9 @@ go_library(
     visibility = ["//build/visible_to:vendor_githubcom_prometheus_CONSUMERS"],
     deps = [
         "//vendor/github.com/beorn7/perks/quantile:go_default_library",
+        "//vendor/github.com/cespare/xxhash/v2:go_default_library",
         "//vendor/github.com/golang/protobuf/proto:go_default_library",
+        "//vendor/github.com/golang/protobuf/ptypes:go_default_library",
         "//vendor/github.com/prometheus/client_golang/prometheus/internal:go_default_library",
         "//vendor/github.com/prometheus/client_model/go:go_default_library",
         "//vendor/github.com/prometheus/common/expfmt:go_default_library",

vendor/github.com/prometheus/client_golang/prometheus/counter.go

@@ -17,6 +17,7 @@ import (
 	"errors"
 	"math"
 	"sync/atomic"
+	"time"
 
 	dto "github.com/prometheus/client_model/go"
 )
@@ -42,11 +43,27 @@ type Counter interface {
 	Add(float64)
 }
 
+// ExemplarAdder is implemented by Counters that offer the option of adding a
+// value to the Counter together with an exemplar. Its AddWithExemplar method
+// works like the Add method of the Counter interface but also replaces the
+// currently saved exemplar (if any) with a new one, created from the provided
+// value, the current time as timestamp, and the provided labels. Empty Labels
+// will lead to a valid (label-less) exemplar. But if Labels is nil, the current
+// exemplar is left in place. AddWithExemplar panics if the value is < 0, if any
+// of the provided labels are invalid, or if the provided labels contain more
+// than 64 runes in total.
+type ExemplarAdder interface {
+	AddWithExemplar(value float64, exemplar Labels)
+}
+
 // CounterOpts is an alias for Opts. See there for doc comments.
 type CounterOpts Opts
 
 // NewCounter creates a new Counter based on the provided CounterOpts.
 //
+// The returned implementation also implements ExemplarAdder. It is safe to
+// perform the corresponding type assertion.
+//
 // The returned implementation tracks the counter value in two separate
 // variables, a float64 and a uint64. The latter is used to track calls of the
 // Inc method and calls of the Add method with a value that can be represented
@@ -61,7 +78,7 @@ func NewCounter(opts CounterOpts) Counter {
 		nil,
 		opts.ConstLabels,
 	)
-	result := &counter{desc: desc, labelPairs: desc.constLabelPairs}
+	result := &counter{desc: desc, labelPairs: desc.constLabelPairs, now: time.Now}
 	result.init(result) // Init self-collection.
 	return result
 }
@@ -78,6 +95,9 @@ type counter struct {
 	desc *Desc
 
 	labelPairs []*dto.LabelPair
+	exemplar   atomic.Value // Containing nil or a *dto.Exemplar.
+
+	now func() time.Time // To mock out time.Now() for testing.
 }
 
 func (c *counter) Desc() *Desc {
@@ -88,6 +108,7 @@ func (c *counter) Add(v float64) {
 	if v < 0 {
 		panic(errors.New("counter cannot decrease in value"))
 	}
+
 	ival := uint64(v)
 	if float64(ival) == v {
 		atomic.AddUint64(&c.valInt, ival)
@@ -103,6 +124,11 @@ func (c *counter) Add(v float64) {
 	}
 }
 
+func (c *counter) AddWithExemplar(v float64, e Labels) {
+	c.Add(v)
+	c.updateExemplar(v, e)
+}
+
 func (c *counter) Inc() {
 	atomic.AddUint64(&c.valInt, 1)
 }
@@ -112,7 +138,23 @@ func (c *counter) Write(out *dto.Metric) error {
 	ival := atomic.LoadUint64(&c.valInt)
 	val := fval + float64(ival)
 
-	return populateMetric(CounterValue, val, c.labelPairs, out)
+	var exemplar *dto.Exemplar
+	if e := c.exemplar.Load(); e != nil {
+		exemplar = e.(*dto.Exemplar)
+	}
+
+	return populateMetric(CounterValue, val, c.labelPairs, exemplar, out)
+}
+
+func (c *counter) updateExemplar(v float64, l Labels) {
+	if l == nil {
+		return
+	}
+	e, err := newExemplar(v, c.now(), l)
+	if err != nil {
+		panic(err)
+	}
+	c.exemplar.Store(e)
 }
 
 // CounterVec is a Collector that bundles a set of Counters that all share the
@@ -138,7 +180,7 @@ func NewCounterVec(opts CounterOpts, labelNames []string) *CounterVec {
 			if len(lvs) != len(desc.variableLabels) {
 				panic(makeInconsistentCardinalityError(desc.fqName, desc.variableLabels, lvs))
 			}
-			result := &counter{desc: desc, labelPairs: makeLabelPairs(desc, lvs)}
+			result := &counter{desc: desc, labelPairs: makeLabelPairs(desc, lvs), now: time.Now}
 			result.init(result) // Init self-collection.
 			return result
 		}),
@@ -267,6 +309,8 @@ type CounterFunc interface {
 // provided function must be concurrency-safe. The function should also honor
 // the contract for a Counter (values only go up, not down), but compliance will
 // not be checked.
+//
+// Check out the ExampleGaugeFunc examples for the similar GaugeFunc.
 func NewCounterFunc(opts CounterOpts, function func() float64) CounterFunc {
 	return newValueFunc(NewDesc(
 		BuildFQName(opts.Namespace, opts.Subsystem, opts.Name),

vendor/github.com/prometheus/client_golang/prometheus/desc.go

@@ -19,6 +19,7 @@ import (
 	"sort"
 	"strings"
 
+	"github.com/cespare/xxhash/v2"
 	"github.com/golang/protobuf/proto"
 	"github.com/prometheus/common/model"
 
@@ -126,24 +127,24 @@ func NewDesc(fqName, help string, variableLabels []string, constLabels Labels) *
 		return d
 	}
 
-	vh := hashNew()
+	xxh := xxhash.New()
 	for _, val := range labelValues {
-		vh = hashAdd(vh, val)
-		vh = hashAddByte(vh, separatorByte)
+		xxh.WriteString(val)
+		xxh.Write(separatorByteSlice)
 	}
-	d.id = vh
+	d.id = xxh.Sum64()
 	// Sort labelNames so that order doesn't matter for the hash.
 	sort.Strings(labelNames)
 	// Now hash together (in this order) the help string and the sorted
 	// label names.
-	lh := hashNew()
-	lh = hashAdd(lh, help)
-	lh = hashAddByte(lh, separatorByte)
+	xxh.Reset()
+	xxh.WriteString(help)
+	xxh.Write(separatorByteSlice)
 	for _, labelName := range labelNames {
-		lh = hashAdd(lh, labelName)
-		lh = hashAddByte(lh, separatorByte)
+		xxh.WriteString(labelName)
+		xxh.Write(separatorByteSlice)
 	}
-	d.dimHash = lh
+	d.dimHash = xxh.Sum64()
 
 	d.constLabelPairs = make([]*dto.LabelPair, 0, len(constLabels))
 	for n, v := range constLabels {

vendor/github.com/prometheus/client_golang/prometheus/doc.go

@@ -84,25 +84,21 @@
 // of those four metric types can be found in the Prometheus docs:
 // https://prometheus.io/docs/concepts/metric_types/
 //
-// A fifth "type" of metric is Untyped. It behaves like a Gauge, but signals the
-// Prometheus server not to assume anything about its type.
-//
-// In addition to the fundamental metric types Gauge, Counter, Summary,
-// Histogram, and Untyped, a very important part of the Prometheus data model is
-// the partitioning of samples along dimensions called labels, which results in
+// In addition to the fundamental metric types Gauge, Counter, Summary, and
+// Histogram, a very important part of the Prometheus data model is the
+// partitioning of samples along dimensions called labels, which results in
 // metric vectors. The fundamental types are GaugeVec, CounterVec, SummaryVec,
-// HistogramVec, and UntypedVec.
+// and HistogramVec.
 //
 // While only the fundamental metric types implement the Metric interface, both
 // the metrics and their vector versions implement the Collector interface. A
 // Collector manages the collection of a number of Metrics, but for convenience,
-// a Metric can also “collect itself”. Note that Gauge, Counter, Summary,
-// Histogram, and Untyped are interfaces themselves while GaugeVec, CounterVec,
-// SummaryVec, HistogramVec, and UntypedVec are not.
+// a Metric can also “collect itself”. Note that Gauge, Counter, Summary, and
+// Histogram are interfaces themselves while GaugeVec, CounterVec, SummaryVec,
+// and HistogramVec are not.
 //
 // To create instances of Metrics and their vector versions, you need a suitable
-// …Opts struct, i.e. GaugeOpts, CounterOpts, SummaryOpts, HistogramOpts, or
-// UntypedOpts.
+// …Opts struct, i.e. GaugeOpts, CounterOpts, SummaryOpts, or HistogramOpts.
 //
 // Custom Collectors and constant Metrics
 //
@@ -118,13 +114,16 @@
 // existing numbers into Prometheus Metrics during collection. An own
 // implementation of the Collector interface is perfect for that. You can create
 // Metric instances “on the fly” using NewConstMetric, NewConstHistogram, and
-// NewConstSummary (and their respective Must… versions). That will happen in
-// the Collect method. The Describe method has to return separate Desc
-// instances, representative of the “throw-away” metrics to be created later.
-// NewDesc comes in handy to create those Desc instances. Alternatively, you
-// could return no Desc at all, which will mark the Collector “unchecked”.  No
-// checks are performed at registration time, but metric consistency will still
-// be ensured at scrape time, i.e. any inconsistencies will lead to scrape
+// NewConstSummary (and their respective Must… versions). NewConstMetric is used
+// for all metric types with just a float64 as their value: Counter, Gauge, and
+// a special “type” called Untyped. Use the latter if you are not sure if the
+// mirrored metric is a Counter or a Gauge. Creation of the Metric instance
+// happens in the Collect method. The Describe method has to return separate
+// Desc instances, representative of the “throw-away” metrics to be created
+// later.  NewDesc comes in handy to create those Desc instances. Alternatively,
+// you could return no Desc at all, which will mark the Collector “unchecked”.
+// No checks are performed at registration time, but metric consistency will
+// still be ensured at scrape time, i.e. any inconsistencies will lead to scrape
 // errors. Thus, with unchecked Collectors, the responsibility to not collect
 // metrics that lead to inconsistencies in the total scrape result lies with the
 // implementer of the Collector. While this is not a desirable state, it is

vendor/github.com/prometheus/client_golang/prometheus/gauge.go

@@ -123,7 +123,7 @@ func (g *gauge) Sub(val float64) {
 
 func (g *gauge) Write(out *dto.Metric) error {
 	val := math.Float64frombits(atomic.LoadUint64(&g.valBits))
-	return populateMetric(GaugeValue, val, g.labelPairs, out)
+	return populateMetric(GaugeValue, val, g.labelPairs, nil, out)
 }
 
 // GaugeVec is a Collector that bundles a set of Gauges that all share the same
@@ -273,9 +273,12 @@ type GaugeFunc interface {
 // NewGaugeFunc creates a new GaugeFunc based on the provided GaugeOpts. The
 // value reported is determined by calling the given function from within the
 // Write method. Take into account that metric collection may happen
-// concurrently. If that results in concurrent calls to Write, like in the case
-// where a GaugeFunc is directly registered with Prometheus, the provided
-// function must be concurrency-safe.
+// concurrently. Therefore, it must be safe to call the provided function
+// concurrently.
+//
+// NewGaugeFunc is a good way to create an “info” style metric with a constant
+// value of 1. Example:
+// https://github.com/prometheus/common/blob/8558a5b7db3c84fa38b4766966059a7bd5bfa2ee/version/info.go#L36-L56
 func NewGaugeFunc(opts GaugeOpts, function func() float64) GaugeFunc {
 	return newValueFunc(NewDesc(
 		BuildFQName(opts.Namespace, opts.Subsystem, opts.Name),

vendor/github.com/prometheus/client_golang/prometheus/go_collector.go

@@ -73,7 +73,7 @@ func NewGoCollector() Collector {
 			nil, nil),
 		gcDesc: NewDesc(
 			"go_gc_duration_seconds",
-			"A summary of the GC invocation durations.",
+			"A summary of the pause duration of garbage collection cycles.",
 			nil, nil),
 		goInfoDesc: NewDesc(
 			"go_info",

vendor/github.com/prometheus/client_golang/prometheus/histogram.go

@@ -20,6 +20,7 @@ import (
 	"sort"
 	"sync"
 	"sync/atomic"
+	"time"
 
 	"github.com/golang/protobuf/proto"
 
@@ -138,7 +139,7 @@ type HistogramOpts struct {
 	// better covered by target labels set by the scraping Prometheus
 	// server, or by one specific metric (e.g. a build_info or a
 	// machine_role metric). See also
-	// https://prometheus.io/docs/instrumenting/writing_exporters/#target-labels,-not-static-scraped-labels
+	// https://prometheus.io/docs/instrumenting/writing_exporters/#target-labels-not-static-scraped-labels
 	ConstLabels Labels
 
 	// Buckets defines the buckets into which observations are counted. Each
@@ -151,6 +152,10 @@ type HistogramOpts struct {
 
 // NewHistogram creates a new Histogram based on the provided HistogramOpts. It
 // panics if the buckets in HistogramOpts are not in strictly increasing order.
+//
+// The returned implementation also implements ExemplarObserver. It is safe to
+// perform the corresponding type assertion. Exemplars are tracked separately
+// for each bucket.
 func NewHistogram(opts HistogramOpts) Histogram {
 	return newHistogram(
 		NewDesc(
@@ -187,7 +192,8 @@ func newHistogram(desc *Desc, opts HistogramOpts, labelValues ...string) Histogr
 		desc:        desc,
 		upperBounds: opts.Buckets,
 		labelPairs:  makeLabelPairs(desc, labelValues),
-		counts:      [2]*histogramCounts{&histogramCounts{}, &histogramCounts{}},
+		counts:      [2]*histogramCounts{{}, {}},
+		now:         time.Now,
 	}
 	for i, upperBound := range h.upperBounds {
 		if i < len(h.upperBounds)-1 {
@@ -205,9 +211,10 @@ func newHistogram(desc *Desc, opts HistogramOpts, labelValues ...string) Histogr
 		}
 	}
 	// Finally we know the final length of h.upperBounds and can make buckets
-	// for both counts:
+	// for both counts as well as exemplars:
 	h.counts[0].buckets = make([]uint64, len(h.upperBounds))
 	h.counts[1].buckets = make([]uint64, len(h.upperBounds))
+	h.exemplars = make([]atomic.Value, len(h.upperBounds)+1)
 
 	h.init(h) // Init self-collection.
 	return h
@@ -254,6 +261,9 @@ type histogram struct {
 
 	upperBounds []float64
 	labelPairs  []*dto.LabelPair
+	exemplars   []atomic.Value // One more than buckets (to include +Inf), each a *dto.Exemplar.
+
+	now func() time.Time // To mock out time.Now() for testing.
 }
 
 func (h *histogram) Desc() *Desc {
@@ -261,36 +271,13 @@ func (h *histogram) Desc() *Desc {
 }
 
 func (h *histogram) Observe(v float64) {
-	// TODO(beorn7): For small numbers of buckets (<30), a linear search is
-	// slightly faster than the binary search. If we really care, we could
-	// switch from one search strategy to the other depending on the number
-	// of buckets.
-	//
-	// Microbenchmarks (BenchmarkHistogramNoLabels):
-	// 11 buckets: 38.3 ns/op linear - binary 48.7 ns/op
-	// 100 buckets: 78.1 ns/op linear - binary 54.9 ns/op
-	// 300 buckets: 154 ns/op linear - binary 61.6 ns/op
-	i := sort.SearchFloat64s(h.upperBounds, v)
+	h.observe(v, h.findBucket(v))
+}
 
-	// We increment h.countAndHotIdx so that the counter in the lower
-	// 63 bits gets incremented. At the same time, we get the new value
-	// back, which we can use to find the currently-hot counts.
-	n := atomic.AddUint64(&h.countAndHotIdx, 1)
-	hotCounts := h.counts[n>>63]
-
-	if i < len(h.upperBounds) {
-		atomic.AddUint64(&hotCounts.buckets[i], 1)
-	}
-	for {
-		oldBits := atomic.LoadUint64(&hotCounts.sumBits)
-		newBits := math.Float64bits(math.Float64frombits(oldBits) + v)
-		if atomic.CompareAndSwapUint64(&hotCounts.sumBits, oldBits, newBits) {
-			break
-		}
-	}
-	// Increment count last as we take it as a signal that the observation
-	// is complete.
-	atomic.AddUint64(&hotCounts.count, 1)
+func (h *histogram) ObserveWithExemplar(v float64, e Labels) {
+	i := h.findBucket(v)
+	h.observe(v, i)
+	h.updateExemplar(v, i, e)
 }
 
 func (h *histogram) Write(out *dto.Metric) error {
@@ -329,6 +316,18 @@ func (h *histogram) Write(out *dto.Metric) error {
 			CumulativeCount: proto.Uint64(cumCount),
 			UpperBound:      proto.Float64(upperBound),
 		}
+		if e := h.exemplars[i].Load(); e != nil {
+			his.Bucket[i].Exemplar = e.(*dto.Exemplar)
+		}
+	}
+	// If there is an exemplar for the +Inf bucket, we have to add that bucket explicitly.
+	if e := h.exemplars[len(h.upperBounds)].Load(); e != nil {
+		b := &dto.Bucket{
+			CumulativeCount: proto.Uint64(count),
+			UpperBound:      proto.Float64(math.Inf(1)),
+			Exemplar:        e.(*dto.Exemplar),
+		}
+		his.Bucket = append(his.Bucket, b)
 	}
 
 	out.Histogram = his
@@ -352,6 +351,57 @@ func (h *histogram) Write(out *dto.Metric) error {
 	return nil
 }
 
+// findBucket returns the index of the bucket for the provided value, or
+// len(h.upperBounds) for the +Inf bucket.
+func (h *histogram) findBucket(v float64) int {
+	// TODO(beorn7): For small numbers of buckets (<30), a linear search is
+	// slightly faster than the binary search. If we really care, we could
+	// switch from one search strategy to the other depending on the number
+	// of buckets.
+	//
+	// Microbenchmarks (BenchmarkHistogramNoLabels):
+	// 11 buckets: 38.3 ns/op linear - binary 48.7 ns/op
+	// 100 buckets: 78.1 ns/op linear - binary 54.9 ns/op
+	// 300 buckets: 154 ns/op linear - binary 61.6 ns/op
+	return sort.SearchFloat64s(h.upperBounds, v)
+}
+
+// observe is the implementation for Observe without the findBucket part.
+func (h *histogram) observe(v float64, bucket int) {
+	// We increment h.countAndHotIdx so that the counter in the lower
+	// 63 bits gets incremented. At the same time, we get the new value
+	// back, which we can use to find the currently-hot counts.
+	n := atomic.AddUint64(&h.countAndHotIdx, 1)
+	hotCounts := h.counts[n>>63]
+
+	if bucket < len(h.upperBounds) {
+		atomic.AddUint64(&hotCounts.buckets[bucket], 1)
+	}
+	for {
+		oldBits := atomic.LoadUint64(&hotCounts.sumBits)
+		newBits := math.Float64bits(math.Float64frombits(oldBits) + v)
+		if atomic.CompareAndSwapUint64(&hotCounts.sumBits, oldBits, newBits) {
+			break
+		}
+	}
+	// Increment count last as we take it as a signal that the observation
+	// is complete.
+	atomic.AddUint64(&hotCounts.count, 1)
+}
+
+// updateExemplar replaces the exemplar for the provided bucket. With empty
+// labels, it's a no-op. It panics if any of the labels is invalid.
+func (h *histogram) updateExemplar(v float64, bucket int, l Labels) {
+	if l == nil {
+		return
+	}
+	e, err := newExemplar(v, h.now(), l)
+	if err != nil {
+		panic(err)
+	}
+	h.exemplars[bucket].Store(e)
+}
+
 // HistogramVec is a Collector that bundles a set of Histograms that all share the
 // same Desc, but have different values for their variable labels. This is used
 // if you want to count the same thing partitioned by various dimensions

vendor/github.com/prometheus/client_golang/prometheus/metric.go

@@ -18,11 +18,12 @@ import (
 	"time"
 
 	"github.com/golang/protobuf/proto"
+	"github.com/prometheus/common/model"
 
 	dto "github.com/prometheus/client_model/go"
 )
 
-const separatorByte byte = 255
+var separatorByteSlice = []byte{model.SeparatorByte} // For convenient use with xxhash.
 
 // A Metric models a single sample value with its meta data being exported to
 // Prometheus. Implementations of Metric in this package are Gauge, Counter,

vendor/github.com/prometheus/client_golang/prometheus/observer.go

@@ -50,3 +50,15 @@ type ObserverVec interface {
 
 	Collector
 }
+
+// ExemplarObserver is implemented by Observers that offer the option of
+// observing a value together with an exemplar. Its ObserveWithExemplar method
+// works like the Observe method of an Observer but also replaces the currently
+// saved exemplar (if any) with a new one, created from the provided value, the
+// current time as timestamp, and the provided Labels. Empty Labels will lead to
+// a valid (label-less) exemplar. But if Labels is nil, the current exemplar is
+// left in place. ObserveWithExemplar panics if any of the provided labels are
+// invalid or if the provided labels contain more than 64 runes in total.
+type ExemplarObserver interface {
+	ObserveWithExemplar(value float64, exemplar Labels)
+}

vendor/github.com/prometheus/client_golang/prometheus/process_collector_windows.go

@@ -33,18 +33,22 @@ var (
 )
 
 type processMemoryCounters struct {
-	// https://docs.microsoft.com/en-us/windows/desktop/api/psapi/ns-psapi-_process_memory_counters_ex
+	// System interface description
+	// https://docs.microsoft.com/en-us/windows/desktop/api/psapi/ns-psapi-process_memory_counters_ex
+
+	// Refer to the Golang internal implementation
+	// https://golang.org/src/internal/syscall/windows/psapi_windows.go
 	_                          uint32
 	PageFaultCount             uint32
-	PeakWorkingSetSize         uint64
-	WorkingSetSize             uint64
-	QuotaPeakPagedPoolUsage    uint64
-	QuotaPagedPoolUsage        uint64
-	QuotaPeakNonPagedPoolUsage uint64
-	QuotaNonPagedPoolUsage     uint64
-	PagefileUsage              uint64
-	PeakPagefileUsage          uint64
-	PrivateUsage               uint64
+	PeakWorkingSetSize         uintptr
+	WorkingSetSize             uintptr
+	QuotaPeakPagedPoolUsage    uintptr
+	QuotaPagedPoolUsage        uintptr
+	QuotaPeakNonPagedPoolUsage uintptr
+	QuotaNonPagedPoolUsage     uintptr
+	PagefileUsage              uintptr
+	PeakPagefileUsage          uintptr
+	PrivateUsage               uintptr
 }
 
 func getProcessMemoryInfo(handle windows.Handle) (processMemoryCounters, error) {

vendor/github.com/prometheus/client_golang/prometheus/promhttp/delegator.go

@@ -53,15 +53,21 @@ func (r *responseWriterDelegator) Written() int64 {
 }
 
 func (r *responseWriterDelegator) WriteHeader(code int) {
+	if r.observeWriteHeader != nil && !r.wroteHeader {
+		// Only call observeWriteHeader for the 1st time. It's a bug if
+		// WriteHeader is called more than once, but we want to protect
+		// against it here. Note that we still delegate the WriteHeader
+		// to the original ResponseWriter to not mask the bug from it.
+		r.observeWriteHeader(code)
+	}
 	r.status = code
 	r.wroteHeader = true
 	r.ResponseWriter.WriteHeader(code)
-	if r.observeWriteHeader != nil {
-		r.observeWriteHeader(code)
-	}
 }
 
 func (r *responseWriterDelegator) Write(b []byte) (int, error) {
+	// If applicable, call WriteHeader here so that observeWriteHeader is
+	// handled appropriately.
 	if !r.wroteHeader {
 		r.WriteHeader(http.StatusOK)
 	}
@@ -82,12 +88,19 @@ func (d closeNotifierDelegator) CloseNotify() <-chan bool {
 	return d.ResponseWriter.(http.CloseNotifier).CloseNotify()
 }
 func (d flusherDelegator) Flush() {
+	// If applicable, call WriteHeader here so that observeWriteHeader is
+	// handled appropriately.
+	if !d.wroteHeader {
+		d.WriteHeader(http.StatusOK)
+	}
 	d.ResponseWriter.(http.Flusher).Flush()
 }
 func (d hijackerDelegator) Hijack() (net.Conn, *bufio.ReadWriter, error) {
 	return d.ResponseWriter.(http.Hijacker).Hijack()
 }
 func (d readerFromDelegator) ReadFrom(re io.Reader) (int64, error) {
+	// If applicable, call WriteHeader here so that observeWriteHeader is
+	// handled appropriately.
 	if !d.wroteHeader {
 		d.WriteHeader(http.StatusOK)
 	}

vendor/github.com/prometheus/client_golang/prometheus/promhttp/http.go

@@ -144,7 +144,12 @@ func HandlerFor(reg prometheus.Gatherer, opts HandlerOpts) http.Handler {
 			}
 		}
 
-		contentType := expfmt.Negotiate(req.Header)
+		var contentType expfmt.Format
+		if opts.EnableOpenMetrics {
+			contentType = expfmt.NegotiateIncludingOpenMetrics(req.Header)
+		} else {
+			contentType = expfmt.Negotiate(req.Header)
+		}
 		header := rsp.Header()
 		header.Set(contentTypeHeader, string(contentType))
 
@@ -162,28 +167,40 @@ func HandlerFor(reg prometheus.Gatherer, opts HandlerOpts) http.Handler {
 
 		enc := expfmt.NewEncoder(w, contentType)
 
-		var lastErr error
-		for _, mf := range mfs {
-			if err := enc.Encode(mf); err != nil {
-				lastErr = err
-				if opts.ErrorLog != nil {
-					opts.ErrorLog.Println("error encoding and sending metric family:", err)
-				}
-				errCnt.WithLabelValues("encoding").Inc()
-				switch opts.ErrorHandling {
-				case PanicOnError:
-					panic(err)
-				case ContinueOnError:
-					// Handled later.
-				case HTTPErrorOnError:
-					httpError(rsp, err)
-					return
-				}
+		// handleError handles the error according to opts.ErrorHandling
+		// and returns true if we have to abort after the handling.
+		handleError := func(err error) bool {
+			if err == nil {
+				return false
 			}
+			if opts.ErrorLog != nil {
+				opts.ErrorLog.Println("error encoding and sending metric family:", err)
+			}
+			errCnt.WithLabelValues("encoding").Inc()
+			switch opts.ErrorHandling {
+			case PanicOnError:
+				panic(err)
+			case HTTPErrorOnError:
+				// We cannot really send an HTTP error at this
+				// point because we most likely have written
+				// something to rsp already. But at least we can
+				// stop sending.
+				return true
+			}
+			// Do nothing in all other cases, including ContinueOnError.
+			return false
 		}
 
-		if lastErr != nil {
-			httpError(rsp, lastErr)
+		for _, mf := range mfs {
+			if handleError(enc.Encode(mf)) {
+				return
+			}
+		}
+		if closer, ok := enc.(expfmt.Closer); ok {
+			// This in particular takes care of the final "# EOF\n" line for OpenMetrics.
+			if handleError(closer.Close()) {
+				return
+			}
 		}
 	})
 
@@ -255,7 +272,12 @@ type HandlerErrorHandling int
 // errors are encountered.
 const (
 	// Serve an HTTP status code 500 upon the first error
-	// encountered. Report the error message in the body.
+	// encountered. Report the error message in the body. Note that HTTP
+	// errors cannot be served anymore once the beginning of a regular
+	// payload has been sent. Thus, in the (unlikely) case that encoding the
+	// payload into the negotiated wire format fails, serving the response
+	// will simply be aborted. Set an ErrorLog in HandlerOpts to detect
+	// those errors.
 	HTTPErrorOnError HandlerErrorHandling = iota
 	// Ignore errors and try to serve as many metrics as possible.  However,
 	// if no metrics can be served, serve an HTTP status code 500 and the
@@ -318,6 +340,16 @@ type HandlerOpts struct {
 	// away). Until the implementation is improved, it is recommended to
 	// implement a separate timeout in potentially slow Collectors.
 	Timeout time.Duration
+	// If true, the experimental OpenMetrics encoding is added to the
+	// possible options during content negotiation. Note that Prometheus
+	// 2.5.0+ will negotiate OpenMetrics as first priority. OpenMetrics is
+	// the only way to transmit exemplars. However, the move to OpenMetrics
+	// is not completely transparent. Most notably, the values of "quantile"
+	// labels of Summaries and "le" labels of Histograms are formatted with
+	// a trailing ".0" if they would otherwise look like integer numbers
+	// (which changes the identity of the resulting series on the Prometheus
+	// server).
+	EnableOpenMetrics bool
 }
 
 // gzipAccepted returns whether the client will accept gzip-encoded content.
@@ -334,11 +366,9 @@ func gzipAccepted(header http.Header) bool {
 }
 
 // httpError removes any content-encoding header and then calls http.Error with
-// the provided error and http.StatusInternalServerErrer. Error contents is
-// supposed to be uncompressed plain text. However, same as with a plain
-// http.Error, any header settings will be void if the header has already been
-// sent. The error message will still be written to the writer, but it will
-// probably be of limited use.
+// the provided error and http.StatusInternalServerError. Error contents is
+// supposed to be uncompressed plain text. Same as with a plain http.Error, this
+// must not be called if the header or any payload has already been sent.
 func httpError(rsp http.ResponseWriter, err error) {
 	rsp.Header().Del(contentEncodingHeader)
 	http.Error(

vendor/github.com/prometheus/client_golang/prometheus/registry.go

@@ -25,6 +25,7 @@ import (
 	"sync"
 	"unicode/utf8"
 
+	"github.com/cespare/xxhash/v2"
 	"github.com/golang/protobuf/proto"
 	"github.com/prometheus/common/expfmt"
 
@@ -74,7 +75,7 @@ func NewRegistry() *Registry {
 // NewPedanticRegistry returns a registry that checks during collection if each
 // collected Metric is consistent with its reported Desc, and if the Desc has
 // actually been registered with the registry. Unchecked Collectors (those whose
-// Describe methed does not yield any descriptors) are excluded from the check.
+// Describe method does not yield any descriptors) are excluded from the check.
 //
 // Usually, a Registry will be happy as long as the union of all collected
 // Metrics is consistent and valid even if some metrics are not consistent with
@@ -266,7 +267,7 @@ func (r *Registry) Register(c Collector) error {
 		descChan           = make(chan *Desc, capDescChan)
 		newDescIDs         = map[uint64]struct{}{}
 		newDimHashesByName = map[string]uint64{}
-		collectorID        uint64 // Just a sum of all desc IDs.
+		collectorID        uint64 // All desc IDs XOR'd together.
 		duplicateDescErr   error
 	)
 	go func() {
@@ -293,12 +294,12 @@ func (r *Registry) Register(c Collector) error {
 		if _, exists := r.descIDs[desc.id]; exists {
 			duplicateDescErr = fmt.Errorf("descriptor %s already exists with the same fully-qualified name and const label values", desc)
 		}
-		// If it is not a duplicate desc in this collector, add it to
+		// If it is not a duplicate desc in this collector, XOR it to
 		// the collectorID.  (We allow duplicate descs within the same
 		// collector, but their existence must be a no-op.)
 		if _, exists := newDescIDs[desc.id]; !exists {
 			newDescIDs[desc.id] = struct{}{}
-			collectorID += desc.id
+			collectorID ^= desc.id
 		}
 
 		// Are all the label names and the help string consistent with
@@ -360,7 +361,7 @@ func (r *Registry) Unregister(c Collector) bool {
 	var (
 		descChan    = make(chan *Desc, capDescChan)
 		descIDs     = map[uint64]struct{}{}
-		collectorID uint64 // Just a sum of the desc IDs.
+		collectorID uint64 // All desc IDs XOR'd together.
 	)
 	go func() {
 		c.Describe(descChan)
@@ -368,7 +369,7 @@ func (r *Registry) Unregister(c Collector) bool {
 	}()
 	for desc := range descChan {
 		if _, exists := descIDs[desc.id]; !exists {
-			collectorID += desc.id
+			collectorID ^= desc.id
 			descIDs[desc.id] = struct{}{}
 		}
 	}
@@ -875,9 +876,9 @@ func checkMetricConsistency(
 	}
 
 	// Is the metric unique (i.e. no other metric with the same name and the same labels)?
-	h := hashNew()
-	h = hashAdd(h, name)
-	h = hashAddByte(h, separatorByte)
+	h := xxhash.New()
+	h.WriteString(name)
+	h.Write(separatorByteSlice)
 	// Make sure label pairs are sorted. We depend on it for the consistency
 	// check.
 	if !sort.IsSorted(labelPairSorter(dtoMetric.Label)) {
@@ -888,18 +889,19 @@ func checkMetricConsistency(
 		dtoMetric.Label = copiedLabels
 	}
 	for _, lp := range dtoMetric.Label {
-		h = hashAdd(h, lp.GetName())
-		h = hashAddByte(h, separatorByte)
-		h = hashAdd(h, lp.GetValue())
-		h = hashAddByte(h, separatorByte)
+		h.WriteString(lp.GetName())
+		h.Write(separatorByteSlice)
+		h.WriteString(lp.GetValue())
+		h.Write(separatorByteSlice)
 	}
-	if _, exists := metricHashes[h]; exists {
+	hSum := h.Sum64()
+	if _, exists := metricHashes[hSum]; exists {
 		return fmt.Errorf(
 			"collected metric %q { %s} was collected before with the same name and label values",
 			name, dtoMetric,
 		)
 	}
-	metricHashes[h] = struct{}{}
+	metricHashes[hSum] = struct{}{}
 	return nil
 }
 

vendor/github.com/prometheus/client_golang/prometheus/summary.go

@@ -208,7 +208,7 @@ func newSummary(desc *Desc, opts SummaryOpts, labelValues ...string) Summary {
 		s := &noObjectivesSummary{
 			desc:       desc,
 			labelPairs: makeLabelPairs(desc, labelValues),
-			counts:     [2]*summaryCounts{&summaryCounts{}, &summaryCounts{}},
+			counts:     [2]*summaryCounts{{}, {}},
 		}
 		s.init(s) // Init self-collection.
 		return s

vendor/github.com/prometheus/client_golang/prometheus/testutil/BUILD

@@ -2,13 +2,17 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
     name = "go_default_library",
-    srcs = ["testutil.go"],
+    srcs = [
+        "lint.go",
+        "testutil.go",
+    ],
     importmap = "k8s.io/kubernetes/vendor/github.com/prometheus/client_golang/prometheus/testutil",
     importpath = "github.com/prometheus/client_golang/prometheus/testutil",
     visibility = ["//build/visible_to:vendor_githubcom_prometheus_CONSUMERS"],
     deps = [
         "//vendor/github.com/prometheus/client_golang/prometheus:go_default_library",
         "//vendor/github.com/prometheus/client_golang/prometheus/internal:go_default_library",
+        "//vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint:go_default_library",
         "//vendor/github.com/prometheus/client_model/go:go_default_library",
         "//vendor/github.com/prometheus/common/expfmt:go_default_library",
     ],
@@ -23,7 +27,10 @@ filegroup(
 
 filegroup(
     name = "all-srcs",
-    srcs = [":package-srcs"],
+    srcs = [
+        ":package-srcs",
+        "//vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint:all-srcs",
+    ],
     tags = ["automanaged"],
     visibility = ["//visibility:public"],
 )

vendor/github.com/prometheus/client_golang/prometheus/testutil/lint.go

@@ -0,0 +1,46 @@
+// Copyright 2020 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 testutil
+
+import (
+	"fmt"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil/promlint"
+)
+
+// CollectAndLint registers the provided Collector with a newly created pedantic
+// Registry. It then calls GatherAndLint with that Registry and with the
+// provided metricNames.
+func CollectAndLint(c prometheus.Collector, metricNames ...string) ([]promlint.Problem, error) {
+	reg := prometheus.NewPedanticRegistry()
+	if err := reg.Register(c); err != nil {
+		return nil, fmt.Errorf("registering collector failed: %s", err)
+	}
+	return GatherAndLint(reg, metricNames...)
+}
+
+// GatherAndLint gathers all metrics from the provided Gatherer and checks them
+// with the linter in the promlint package. If any metricNames are provided,
+// only metrics with those names are checked.
+func GatherAndLint(g prometheus.Gatherer, metricNames ...string) ([]promlint.Problem, error) {
+	got, err := g.Gather()
+	if err != nil {
+		return nil, fmt.Errorf("gathering metrics failed: %s", err)
+	}
+	if metricNames != nil {
+		got = filterMetrics(got, metricNames)
+	}
+	return promlint.NewWithMetricFamilies(got).Lint()
+}

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/BUILD

@@ -0,0 +1,27 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["promlint.go"],
+    importmap = "k8s.io/kubernetes/vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint",
+    importpath = "github.com/prometheus/client_golang/prometheus/testutil/promlint",
+    visibility = ["//build/visible_to:vendor_githubcom_prometheus_CONSUMERS"],
+    deps = [
+        "//vendor/github.com/prometheus/client_model/go:go_default_library",
+        "//vendor/github.com/prometheus/common/expfmt:go_default_library",
+    ],
+)
+
+filegroup(
+    name = "package-srcs",
+    srcs = glob(["**"]),
+    tags = ["automanaged"],
+    visibility = ["//visibility:private"],
+)
+
+filegroup(
+    name = "all-srcs",
+    srcs = [":package-srcs"],
+    tags = ["automanaged"],
+    visibility = ["//visibility:public"],
+)

vendor/github.com/prometheus/client_golang/prometheus/testutil/promlint/promlint.go

@@ -0,0 +1,386 @@
+// Copyright 2020 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 promlint provides a linter for Prometheus metrics.
+package promlint
+
+import (
+	"fmt"
+	"io"
+	"regexp"
+	"sort"
+	"strings"
+
+	"github.com/prometheus/common/expfmt"
+
+	dto "github.com/prometheus/client_model/go"
+)
+
+// A Linter is a Prometheus metrics linter.  It identifies issues with metric
+// names, types, and metadata, and reports them to the caller.
+type Linter struct {
+	// The linter will read metrics in the Prometheus text format from r and
+	// then lint it, _and_ it will lint the metrics provided directly as
+	// MetricFamily proto messages in mfs. Note, however, that the current
+	// constructor functions New and NewWithMetricFamilies only ever set one
+	// of them.
+	r   io.Reader
+	mfs []*dto.MetricFamily
+}
+
+// A Problem is an issue detected by a Linter.
+type Problem struct {
+	// The name of the metric indicated by this Problem.
+	Metric string
+
+	// A description of the issue for this Problem.
+	Text string
+}
+
+// newProblem is helper function to create a Problem.
+func newProblem(mf *dto.MetricFamily, text string) Problem {
+	return Problem{
+		Metric: mf.GetName(),
+		Text:   text,
+	}
+}
+
+// New creates a new Linter that reads an input stream of Prometheus metrics in
+// the Prometheus text exposition format.
+func New(r io.Reader) *Linter {
+	return &Linter{
+		r: r,
+	}
+}
+
+// NewWithMetricFamilies creates a new Linter that reads from a slice of
+// MetricFamily protobuf messages.
+func NewWithMetricFamilies(mfs []*dto.MetricFamily) *Linter {
+	return &Linter{
+		mfs: mfs,
+	}
+}
+
+// Lint performs a linting pass, returning a slice of Problems indicating any
+// issues found in the metrics stream. The slice is sorted by metric name
+// and issue description.
+func (l *Linter) Lint() ([]Problem, error) {
+	var problems []Problem
+
+	if l.r != nil {
+		d := expfmt.NewDecoder(l.r, expfmt.FmtText)
+
+		mf := &dto.MetricFamily{}
+		for {
+			if err := d.Decode(mf); err != nil {
+				if err == io.EOF {
+					break
+				}
+
+				return nil, err
+			}
+
+			problems = append(problems, lint(mf)...)
+		}
+	}
+	for _, mf := range l.mfs {
+		problems = append(problems, lint(mf)...)
+	}
+
+	// Ensure deterministic output.
+	sort.SliceStable(problems, func(i, j int) bool {
+		if problems[i].Metric == problems[j].Metric {
+			return problems[i].Text < problems[j].Text
+		}
+		return problems[i].Metric < problems[j].Metric
+	})
+
+	return problems, nil
+}
+
+// lint is the entry point for linting a single metric.
+func lint(mf *dto.MetricFamily) []Problem {
+	fns := []func(mf *dto.MetricFamily) []Problem{
+		lintHelp,
+		lintMetricUnits,
+		lintCounter,
+		lintHistogramSummaryReserved,
+		lintMetricTypeInName,
+		lintReservedChars,
+		lintCamelCase,
+		lintUnitAbbreviations,
+	}
+
+	var problems []Problem
+	for _, fn := range fns {
+		problems = append(problems, fn(mf)...)
+	}
+
+	// TODO(mdlayher): lint rules for specific metrics types.
+	return problems
+}
+
+// lintHelp detects issues related to the help text for a metric.
+func lintHelp(mf *dto.MetricFamily) []Problem {
+	var problems []Problem
+
+	// Expect all metrics to have help text available.
+	if mf.Help == nil {
+		problems = append(problems, newProblem(mf, "no help text"))
+	}
+
+	return problems
+}
+
+// lintMetricUnits detects issues with metric unit names.
+func lintMetricUnits(mf *dto.MetricFamily) []Problem {
+	var problems []Problem
+
+	unit, base, ok := metricUnits(*mf.Name)
+	if !ok {
+		// No known units detected.
+		return nil
+	}
+
+	// Unit is already a base unit.
+	if unit == base {
+		return nil
+	}
+
+	problems = append(problems, newProblem(mf, fmt.Sprintf("use base unit %q instead of %q", base, unit)))
+
+	return problems
+}
+
+// lintCounter detects issues specific to counters, as well as patterns that should
+// only be used with counters.
+func lintCounter(mf *dto.MetricFamily) []Problem {
+	var problems []Problem
+
+	isCounter := mf.GetType() == dto.MetricType_COUNTER
+	isUntyped := mf.GetType() == dto.MetricType_UNTYPED
+	hasTotalSuffix := strings.HasSuffix(mf.GetName(), "_total")
+
+	switch {
+	case isCounter && !hasTotalSuffix:
+		problems = append(problems, newProblem(mf, `counter metrics should have "_total" suffix`))
+	case !isUntyped && !isCounter && hasTotalSuffix:
+		problems = append(problems, newProblem(mf, `non-counter metrics should not have "_total" suffix`))
+	}
+
+	return problems
+}
+
+// lintHistogramSummaryReserved detects when other types of metrics use names or labels
+// reserved for use by histograms and/or summaries.
+func lintHistogramSummaryReserved(mf *dto.MetricFamily) []Problem {
+	// These rules do not apply to untyped metrics.
+	t := mf.GetType()
+	if t == dto.MetricType_UNTYPED {
+		return nil
+	}
+
+	var problems []Problem
+
+	isHistogram := t == dto.MetricType_HISTOGRAM
+	isSummary := t == dto.MetricType_SUMMARY
+
+	n := mf.GetName()
+
+	if !isHistogram && strings.HasSuffix(n, "_bucket") {
+		problems = append(problems, newProblem(mf, `non-histogram metrics should not have "_bucket" suffix`))
+	}
+	if !isHistogram && !isSummary && strings.HasSuffix(n, "_count") {
+		problems = append(problems, newProblem(mf, `non-histogram and non-summary metrics should not have "_count" suffix`))
+	}
+	if !isHistogram && !isSummary && strings.HasSuffix(n, "_sum") {
+		problems = append(problems, newProblem(mf, `non-histogram and non-summary metrics should not have "_sum" suffix`))
+	}
+
+	for _, m := range mf.GetMetric() {
+		for _, l := range m.GetLabel() {
+			ln := l.GetName()
+
+			if !isHistogram && ln == "le" {
+				problems = append(problems, newProblem(mf, `non-histogram metrics should not have "le" label`))
+			}
+			if !isSummary && ln == "quantile" {
+				problems = append(problems, newProblem(mf, `non-summary metrics should not have "quantile" label`))
+			}
+		}
+	}
+
+	return problems
+}
+
+// lintMetricTypeInName detects when metric types are included in the metric name.
+func lintMetricTypeInName(mf *dto.MetricFamily) []Problem {
+	var problems []Problem
+	n := strings.ToLower(mf.GetName())
+
+	for i, t := range dto.MetricType_name {
+		if i == int32(dto.MetricType_UNTYPED) {
+			continue
+		}
+
+		typename := strings.ToLower(t)
+		if strings.Contains(n, "_"+typename+"_") || strings.HasSuffix(n, "_"+typename) {
+			problems = append(problems, newProblem(mf, fmt.Sprintf(`metric name should not include type '%s'`, typename)))
+		}
+	}
+	return problems
+}
+
+// lintReservedChars detects colons in metric names.
+func lintReservedChars(mf *dto.MetricFamily) []Problem {
+	var problems []Problem
+	if strings.Contains(mf.GetName(), ":") {
+		problems = append(problems, newProblem(mf, "metric names should not contain ':'"))
+	}
+	return problems
+}
+
+var camelCase = regexp.MustCompile(`[a-z][A-Z]`)
+
+// lintCamelCase detects metric names and label names written in camelCase.
+func lintCamelCase(mf *dto.MetricFamily) []Problem {
+	var problems []Problem
+	if camelCase.FindString(mf.GetName()) != "" {
+		problems = append(problems, newProblem(mf, "metric names should be written in 'snake_case' not 'camelCase'"))
+	}
+
+	for _, m := range mf.GetMetric() {
+		for _, l := range m.GetLabel() {
+			if camelCase.FindString(l.GetName()) != "" {
+				problems = append(problems, newProblem(mf, "label names should be written in 'snake_case' not 'camelCase'"))
+			}
+		}
+	}
+	return problems
+}
+
+// lintUnitAbbreviations detects abbreviated units in the metric name.
+func lintUnitAbbreviations(mf *dto.MetricFamily) []Problem {
+	var problems []Problem
+	n := strings.ToLower(mf.GetName())
+	for _, s := range unitAbbreviations {
+		if strings.Contains(n, "_"+s+"_") || strings.HasSuffix(n, "_"+s) {
+			problems = append(problems, newProblem(mf, "metric names should not contain abbreviated units"))
+		}
+	}
+	return problems
+}
+
+// metricUnits attempts to detect known unit types used as part of a metric name,
+// e.g. "foo_bytes_total" or "bar_baz_milligrams".
+func metricUnits(m string) (unit string, base string, ok bool) {
+	ss := strings.Split(m, "_")
+
+	for unit, base := range units {
+		// Also check for "no prefix".
+		for _, p := range append(unitPrefixes, "") {
+			for _, s := range ss {
+				// Attempt to explicitly match a known unit with a known prefix,
+				// as some words may look like "units" when matching suffix.
+				//
+				// As an example, "thermometers" should not match "meters", but
+				// "kilometers" should.
+				if s == p+unit {
+					return p + unit, base, true
+				}
+			}
+		}
+	}
+
+	return "", "", false
+}
+
+// Units and their possible prefixes recognized by this library.  More can be
+// added over time as needed.
+var (
+	// map a unit to the appropriate base unit.
+	units = map[string]string{
+		// Base units.
+		"amperes": "amperes",
+		"bytes":   "bytes",
+		"celsius": "celsius", // Celsius is more common in practice than Kelvin.
+		"grams":   "grams",
+		"joules":  "joules",
+		"meters":  "meters", // Both American and international spelling permitted.
+		"metres":  "metres",
+		"seconds": "seconds",
+		"volts":   "volts",
+
+		// Non base units.
+		// Time.
+		"minutes": "seconds",
+		"hours":   "seconds",
+		"days":    "seconds",
+		"weeks":   "seconds",
+		// Temperature.
+		"kelvin":     "celsius",
+		"kelvins":    "celsius",
+		"fahrenheit": "celsius",
+		"rankine":    "celsius",
+		// Length.
+		"inches": "meters",
+		"yards":  "meters",
+		"miles":  "meters",
+		// Bytes.
+		"bits": "bytes",
+		// Energy.
+		"calories": "joules",
+		// Mass.
+		"pounds": "grams",
+		"ounces": "grams",
+	}
+
+	unitPrefixes = []string{
+		"pico",
+		"nano",
+		"micro",
+		"milli",
+		"centi",
+		"deci",
+		"deca",
+		"hecto",
+		"kilo",
+		"kibi",
+		"mega",
+		"mibi",
+		"giga",
+		"gibi",
+		"tera",
+		"tebi",
+		"peta",
+		"pebi",
+	}
+
+	// Common abbreviations that we'd like to discourage.
+	unitAbbreviations = []string{
+		"s",
+		"ms",
+		"us",
+		"ns",
+		"sec",
+		"b",
+		"kb",
+		"mb",
+		"gb",
+		"tb",
+		"pb",
+		"m",
+		"h",
+		"d",
+	}
+)

vendor/github.com/prometheus/client_golang/prometheus/testutil/testutil.go

@@ -31,6 +31,10 @@
 // testing custom prometheus.Collector implementations and in particular whole
 // exporters, i.e. programs that retrieve telemetry data from a 3rd party source
 // and convert it into Prometheus metrics.
+//
+// In a similar pattern, CollectAndLint and GatherAndLint can be used to detect
+// metrics that have issues with their name, type, or metadata without being
+// necessarily invalid, e.g. a counter with a name missing the “_total” suffix.
 package testutil
 
 import (
@@ -108,9 +112,36 @@ func ToFloat64(c prometheus.Collector) float64 {
 	panic(fmt.Errorf("collected a non-gauge/counter/untyped metric: %s", pb))
 }
 
+// CollectAndCount collects all Metrics from the provided Collector and returns their number.
+//
+// This can be used to assert the number of metrics collected by a given collector after certain operations.
+//
+// This function is only for testing purposes, and even for testing, other approaches
+// are often more appropriate (see this package's documentation).
+func CollectAndCount(c prometheus.Collector) int {
+	var (
+		mCount int
+		mChan  = make(chan prometheus.Metric)
+		done   = make(chan struct{})
+	)
+
+	go func() {
+		for range mChan {
+			mCount++
+		}
+		close(done)
+	}()
+
+	c.Collect(mChan)
+	close(mChan)
+	<-done
+
+	return mCount
+}
+
 // CollectAndCompare registers the provided Collector with a newly created
-// pedantic Registry. It then does the same as GatherAndCompare, gathering the
-// metrics from the pedantic Registry.
+// pedantic Registry. It then calls GatherAndCompare with that Registry and with
+// the provided metricNames.
 func CollectAndCompare(c prometheus.Collector, expected io.Reader, metricNames ...string) error {
 	reg := prometheus.NewPedanticRegistry()
 	if err := reg.Register(c); err != nil {

vendor/github.com/prometheus/client_golang/prometheus/value.go

@@ -16,8 +16,11 @@ package prometheus
 import (
 	"fmt"
 	"sort"
+	"time"
+	"unicode/utf8"
 
 	"github.com/golang/protobuf/proto"
+	"github.com/golang/protobuf/ptypes"
 
 	dto "github.com/prometheus/client_model/go"
 )
@@ -25,7 +28,8 @@ import (
 // ValueType is an enumeration of metric types that represent a simple value.
 type ValueType int
 
-// Possible values for the ValueType enum.
+// Possible values for the ValueType enum. Use UntypedValue to mark a metric
+// with an unknown type.
 const (
 	_ ValueType = iota
 	CounterValue
@@ -69,7 +73,7 @@ func (v *valueFunc) Desc() *Desc {
 }
 
 func (v *valueFunc) Write(out *dto.Metric) error {
-	return populateMetric(v.valType, v.function(), v.labelPairs, out)
+	return populateMetric(v.valType, v.function(), v.labelPairs, nil, out)
 }
 
 // NewConstMetric returns a metric with one fixed value that cannot be
@@ -116,19 +120,20 @@ func (m *constMetric) Desc() *Desc {
 }
 
 func (m *constMetric) Write(out *dto.Metric) error {
-	return populateMetric(m.valType, m.val, m.labelPairs, out)
+	return populateMetric(m.valType, m.val, m.labelPairs, nil, out)
 }
 
 func populateMetric(
 	t ValueType,
 	v float64,
 	labelPairs []*dto.LabelPair,
+	e *dto.Exemplar,
 	m *dto.Metric,
 ) error {
 	m.Label = labelPairs
 	switch t {
 	case CounterValue:
-		m.Counter = &dto.Counter{Value: proto.Float64(v)}
+		m.Counter = &dto.Counter{Value: proto.Float64(v), Exemplar: e}
 	case GaugeValue:
 		m.Gauge = &dto.Gauge{Value: proto.Float64(v)}
 	case UntypedValue:
@@ -160,3 +165,40 @@ func makeLabelPairs(desc *Desc, labelValues []string) []*dto.LabelPair {
 	sort.Sort(labelPairSorter(labelPairs))
 	return labelPairs
 }
+
+// ExemplarMaxRunes is the max total number of runes allowed in exemplar labels.
+const ExemplarMaxRunes = 64
+
+// newExemplar creates a new dto.Exemplar from the provided values. An error is
+// returned if any of the label names or values are invalid or if the total
+// number of runes in the label names and values exceeds ExemplarMaxRunes.
+func newExemplar(value float64, ts time.Time, l Labels) (*dto.Exemplar, error) {
+	e := &dto.Exemplar{}
+	e.Value = proto.Float64(value)
+	tsProto, err := ptypes.TimestampProto(ts)
+	if err != nil {
+		return nil, err
+	}
+	e.Timestamp = tsProto
+	labelPairs := make([]*dto.LabelPair, 0, len(l))
+	var runes int
+	for name, value := range l {
+		if !checkLabelName(name) {
+			return nil, fmt.Errorf("exemplar label name %q is invalid", name)
+		}
+		runes += utf8.RuneCountInString(name)
+		if !utf8.ValidString(value) {
+			return nil, fmt.Errorf("exemplar label value %q is not valid UTF-8", value)
+		}
+		runes += utf8.RuneCountInString(value)
+		labelPairs = append(labelPairs, &dto.LabelPair{
+			Name:  proto.String(name),
+			Value: proto.String(value),
+		})
+	}
+	if runes > ExemplarMaxRunes {
+		return nil, fmt.Errorf("exemplar labels have %d runes, exceeding the limit of %d", runes, ExemplarMaxRunes)
+	}
+	e.Label = labelPairs
+	return e, nil
+}

vendor/github.com/prometheus/client_golang/prometheus/vec.go

@@ -24,7 +24,7 @@ import (
 // their label values. metricVec is not used directly (and therefore
 // unexported). It is used as a building block for implementations of vectors of
 // a given metric type, like GaugeVec, CounterVec, SummaryVec, and HistogramVec.
-// It also handles label currying. It uses basicMetricVec internally.
+// It also handles label currying.
 type metricVec struct {
 	*metricMap
 
@@ -91,6 +91,18 @@ func (m *metricVec) Delete(labels Labels) bool {
 	return m.metricMap.deleteByHashWithLabels(h, labels, m.curry)
 }
 
+// Without explicit forwarding of Describe, Collect, Reset, those methods won't
+// show up in GoDoc.
+
+// Describe implements Collector.
+func (m *metricVec) Describe(ch chan<- *Desc) { m.metricMap.Describe(ch) }
+
+// Collect implements Collector.
+func (m *metricVec) Collect(ch chan<- Metric) { m.metricMap.Collect(ch) }
+
+// Reset deletes all metrics in this vector.
+func (m *metricVec) Reset() { m.metricMap.Reset() }
+
 func (m *metricVec) curryWith(labels Labels) (*metricVec, error) {
 	var (
 		newCurry []curriedLabelValue