p2.7: prometheus /metrics

Default GET /metrics is Prometheus text; JSON stays at /metrics.json and ?format=json. :8443 needs the metrics caller bearer; loopback stays open. Restricted callers have no per-caller series and no tavily:restricted gauge.
2026-09-23 21:49:38 -07:00
parent c19a58d1e3
commit 4372673184
339 changed files with 73851 additions and 145 deletions
@@ -0,0 +1,471 @@
+// Copyright 2015 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 expfmt
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"math"
+	"mime"
+	"net/http"
+
+	dto "github.com/prometheus/client_model/go"
+	"google.golang.org/protobuf/encoding/protodelim"
+
+	"github.com/prometheus/common/model"
+)
+
+// Decoder types decode an input stream into metric families.
+type Decoder interface {
+	Decode(*dto.MetricFamily) error
+}
+
+// DecodeOptions contains options used by the Decoder and in sample extraction.
+type DecodeOptions struct {
+	// Timestamp is added to each value from the stream that has no explicit timestamp set.
+	Timestamp model.Time
+}
+
+// ResponseFormat extracts the correct format from a HTTP response header.
+// If no matching format can be found FormatUnknown is returned.
+func ResponseFormat(h http.Header) Format {
+	ct := h.Get(hdrContentType)
+
+	mediatype, params, err := mime.ParseMediaType(ct)
+	if err != nil {
+		return FmtUnknown
+	}
+
+	const textType = "text/plain"
+
+	switch mediatype {
+	case ProtoType:
+		if p, ok := params["proto"]; ok && p != ProtoProtocol {
+			return FmtUnknown
+		}
+		if e, ok := params["encoding"]; ok && e != "delimited" {
+			return FmtUnknown
+		}
+		return FmtProtoDelim
+
+	case textType:
+		if v, ok := params["version"]; ok && v != TextVersion {
+			return FmtUnknown
+		}
+		return FmtText
+	}
+
+	return FmtUnknown
+}
+
+// NewDecoder returns a new decoder based on the given input format. Metric
+// names are validated based on the provided Format -- if the format requires
+// escaping, traditional Prometheus validity checking is used. Otherwise, names
+// are checked for UTF-8 validity. Supported formats include delimited protobuf
+// and Prometheus text format. For historical reasons, this decoder falls back
+// to classic text decoding for other legacy formats, but returns an error for
+// unsupported formats such as OpenMetrics 2.0. This decoder does not fully
+// support OpenMetrics although it may often succeed for OpenMetrics 1.0 due to
+// the similarities between the formats. This decoder may not support the latest
+// features of Prometheus text format and is not intended for high-performance
+// applications.
+// See: https://github.com/prometheus/common/issues/812
+func NewDecoder(r io.Reader, format Format) Decoder {
+	scheme := model.LegacyValidation
+	if format.ToEscapingScheme() == model.NoEscaping {
+		scheme = model.UTF8Validation
+	}
+	switch format.FormatType() {
+	case TypeProtoDelim:
+		return &protoDecoder{r: bufio.NewReader(r), s: scheme}
+	case TypeProtoText, TypeProtoCompact:
+		return &errDecoder{err: fmt.Errorf("format %s not supported for decoding", format)}
+	case TypeOpenMetrics:
+		_, params, err := mime.ParseMediaType(string(format))
+		if err == nil && params["version"] == OpenMetricsVersion_2_0_0 {
+			return &errDecoder{err: fmt.Errorf("format %s not supported for decoding", format)}
+		}
+	}
+	return &textDecoder{r: r, s: scheme}
+}
+
+// protoDecoder implements the Decoder interface for protocol buffers.
+type protoDecoder struct {
+	r protodelim.Reader
+	s model.ValidationScheme
+}
+
+// Decode implements the Decoder interface.
+func (d *protoDecoder) Decode(v *dto.MetricFamily) error {
+	opts := protodelim.UnmarshalOptions{
+		MaxSize: -1,
+	}
+	if err := opts.UnmarshalFrom(d.r, v); err != nil {
+		return err
+	}
+	if !d.s.IsValidMetricName(v.GetName()) {
+		return fmt.Errorf("invalid metric name %q", v.GetName())
+	}
+	for _, m := range v.GetMetric() {
+		if m == nil {
+			continue
+		}
+		for _, l := range m.GetLabel() {
+			if l == nil {
+				continue
+			}
+			if !model.LabelValue(l.GetValue()).IsValid() {
+				return fmt.Errorf("invalid label value %q", l.GetValue())
+			}
+			if !d.s.IsValidLabelName(l.GetName()) {
+				return fmt.Errorf("invalid label name %q", l.GetName())
+			}
+		}
+	}
+	return nil
+}
+
+// errDecoder is an error-state decoder that always returns the same error.
+type errDecoder struct {
+	err error
+}
+
+func (d *errDecoder) Decode(*dto.MetricFamily) error {
+	return d.err
+}
+
+// textDecoder implements the Decoder interface for the text protocol.
+type textDecoder struct {
+	r    io.Reader
+	fams map[string]*dto.MetricFamily
+	s    model.ValidationScheme
+	err  error
+}
+
+// Decode implements the Decoder interface.
+func (d *textDecoder) Decode(v *dto.MetricFamily) error {
+	if d.err == nil {
+		// Read all metrics in one shot.
+		p := NewTextParser(d.s)
+		d.fams, d.err = p.TextToMetricFamilies(d.r)
+		// If we don't get an error, store io.EOF for the end.
+		if d.err == nil {
+			d.err = io.EOF
+		}
+	}
+	// Pick off one MetricFamily per Decode until there's nothing left.
+	for key, fam := range d.fams {
+		v.Name = fam.Name
+		v.Help = fam.Help
+		v.Type = fam.Type
+		v.Metric = fam.Metric
+		delete(d.fams, key)
+		return nil
+	}
+	return d.err
+}
+
+// SampleDecoder wraps a Decoder to extract samples from the metric families
+// decoded by the wrapped Decoder.
+type SampleDecoder struct {
+	Dec  Decoder
+	Opts *DecodeOptions
+
+	f dto.MetricFamily
+}
+
+// Decode calls the Decode method of the wrapped Decoder and then extracts the
+// samples from the decoded MetricFamily into the provided model.Vector.
+func (sd *SampleDecoder) Decode(s *model.Vector) error {
+	err := sd.Dec.Decode(&sd.f)
+	if err != nil {
+		return err
+	}
+	*s, err = extractSamples(&sd.f, sd.Opts)
+	return err
+}
+
+// ExtractSamples builds a slice of samples from the provided metric
+// families. If an error occurs during sample extraction, it continues to
+// extract from the remaining metric families. The returned error is the last
+// error that has occurred.
+func ExtractSamples(o *DecodeOptions, fams ...*dto.MetricFamily) (model.Vector, error) {
+	var (
+		all     model.Vector
+		lastErr error
+	)
+	for _, f := range fams {
+		some, err := extractSamples(f, o)
+		if err != nil {
+			lastErr = err
+			continue
+		}
+		all = append(all, some...)
+	}
+	return all, lastErr
+}
+
+func extractSamples(f *dto.MetricFamily, o *DecodeOptions) (model.Vector, error) {
+	switch f.GetType() {
+	case dto.MetricType_COUNTER:
+		return extractCounter(o, f), nil
+	case dto.MetricType_GAUGE:
+		return extractGauge(o, f), nil
+	case dto.MetricType_SUMMARY:
+		return extractSummary(o, f), nil
+	case dto.MetricType_UNTYPED:
+		return extractUntyped(o, f), nil
+	case dto.MetricType_HISTOGRAM, dto.MetricType_GAUGE_HISTOGRAM:
+		return extractHistogram(o, f), nil
+	}
+	return nil, fmt.Errorf("expfmt.extractSamples: unknown metric family type %v", f.GetType())
+}
+
+func extractCounter(o *DecodeOptions, f *dto.MetricFamily) model.Vector {
+	samples := make(model.Vector, 0, len(f.Metric))
+
+	for _, m := range f.Metric {
+		if m.Counter == nil {
+			continue
+		}
+
+		lset := make(model.LabelSet, len(m.Label)+1)
+		for _, p := range m.Label {
+			lset[model.LabelName(p.GetName())] = model.LabelValue(p.GetValue())
+		}
+		lset[model.MetricNameLabel] = model.LabelValue(f.GetName())
+
+		smpl := &model.Sample{
+			Metric: model.Metric(lset),
+			Value:  model.SampleValue(m.Counter.GetValue()),
+		}
+
+		if m.TimestampMs != nil {
+			smpl.Timestamp = model.TimeFromUnixNano(*m.TimestampMs * 1000000)
+		} else {
+			smpl.Timestamp = o.Timestamp
+		}
+
+		samples = append(samples, smpl)
+	}
+
+	return samples
+}
+
+func extractGauge(o *DecodeOptions, f *dto.MetricFamily) model.Vector {
+	samples := make(model.Vector, 0, len(f.Metric))
+
+	for _, m := range f.Metric {
+		if m.Gauge == nil {
+			continue
+		}
+
+		lset := make(model.LabelSet, len(m.Label)+1)
+		for _, p := range m.Label {
+			lset[model.LabelName(p.GetName())] = model.LabelValue(p.GetValue())
+		}
+		lset[model.MetricNameLabel] = model.LabelValue(f.GetName())
+
+		smpl := &model.Sample{
+			Metric: model.Metric(lset),
+			Value:  model.SampleValue(m.Gauge.GetValue()),
+		}
+
+		if m.TimestampMs != nil {
+			smpl.Timestamp = model.TimeFromUnixNano(*m.TimestampMs * 1000000)
+		} else {
+			smpl.Timestamp = o.Timestamp
+		}
+
+		samples = append(samples, smpl)
+	}
+
+	return samples
+}
+
+func extractUntyped(o *DecodeOptions, f *dto.MetricFamily) model.Vector {
+	samples := make(model.Vector, 0, len(f.Metric))
+
+	for _, m := range f.Metric {
+		if m.Untyped == nil {
+			continue
+		}
+
+		lset := make(model.LabelSet, len(m.Label)+1)
+		for _, p := range m.Label {
+			lset[model.LabelName(p.GetName())] = model.LabelValue(p.GetValue())
+		}
+		lset[model.MetricNameLabel] = model.LabelValue(f.GetName())
+
+		smpl := &model.Sample{
+			Metric: model.Metric(lset),
+			Value:  model.SampleValue(m.Untyped.GetValue()),
+		}
+
+		if m.TimestampMs != nil {
+			smpl.Timestamp = model.TimeFromUnixNano(*m.TimestampMs * 1000000)
+		} else {
+			smpl.Timestamp = o.Timestamp
+		}
+
+		samples = append(samples, smpl)
+	}
+
+	return samples
+}
+
+func extractSummary(o *DecodeOptions, f *dto.MetricFamily) model.Vector {
+	samples := make(model.Vector, 0, len(f.Metric))
+
+	for _, m := range f.Metric {
+		if m.Summary == nil {
+			continue
+		}
+
+		timestamp := o.Timestamp
+		if m.TimestampMs != nil {
+			timestamp = model.TimeFromUnixNano(*m.TimestampMs * 1000000)
+		}
+
+		for _, q := range m.Summary.Quantile {
+			lset := make(model.LabelSet, len(m.Label)+2)
+			for _, p := range m.Label {
+				lset[model.LabelName(p.GetName())] = model.LabelValue(p.GetValue())
+			}
+			// BUG(matt): Update other names to "quantile".
+			lset[model.LabelName(model.QuantileLabel)] = model.LabelValue(fmt.Sprint(q.GetQuantile()))
+			lset[model.MetricNameLabel] = model.LabelValue(f.GetName())
+
+			samples = append(samples, &model.Sample{
+				Metric:    model.Metric(lset),
+				Value:     model.SampleValue(q.GetValue()),
+				Timestamp: timestamp,
+			})
+		}
+
+		lset := make(model.LabelSet, len(m.Label)+1)
+		for _, p := range m.Label {
+			lset[model.LabelName(p.GetName())] = model.LabelValue(p.GetValue())
+		}
+		lset[model.MetricNameLabel] = model.LabelValue(f.GetName() + "_sum")
+
+		samples = append(samples, &model.Sample{
+			Metric:    model.Metric(lset),
+			Value:     model.SampleValue(m.Summary.GetSampleSum()),
+			Timestamp: timestamp,
+		})
+
+		lset = make(model.LabelSet, len(m.Label)+1)
+		for _, p := range m.Label {
+			lset[model.LabelName(p.GetName())] = model.LabelValue(p.GetValue())
+		}
+		lset[model.MetricNameLabel] = model.LabelValue(f.GetName() + "_count")
+
+		samples = append(samples, &model.Sample{
+			Metric:    model.Metric(lset),
+			Value:     model.SampleValue(m.Summary.GetSampleCount()),
+			Timestamp: timestamp,
+		})
+	}
+
+	return samples
+}
+
+func extractHistogram(o *DecodeOptions, f *dto.MetricFamily) model.Vector {
+	samples := make(model.Vector, 0, len(f.Metric))
+
+	for _, m := range f.Metric {
+		if m.Histogram == nil {
+			continue
+		}
+
+		timestamp := o.Timestamp
+		if m.TimestampMs != nil {
+			timestamp = model.TimeFromUnixNano(*m.TimestampMs * 1000000)
+		}
+
+		infSeen := false
+
+		for _, q := range m.Histogram.Bucket {
+			lset := make(model.LabelSet, len(m.Label)+2)
+			for _, p := range m.Label {
+				lset[model.LabelName(p.GetName())] = model.LabelValue(p.GetValue())
+			}
+			lset[model.LabelName(model.BucketLabel)] = model.LabelValue(fmt.Sprint(q.GetUpperBound()))
+			lset[model.MetricNameLabel] = model.LabelValue(f.GetName() + "_bucket")
+
+			if math.IsInf(q.GetUpperBound(), +1) {
+				infSeen = true
+			}
+
+			v := q.GetCumulativeCountFloat()
+			if v <= 0 {
+				v = float64(q.GetCumulativeCount())
+			}
+			samples = append(samples, &model.Sample{
+				Metric:    model.Metric(lset),
+				Value:     model.SampleValue(v),
+				Timestamp: timestamp,
+			})
+		}
+
+		lset := make(model.LabelSet, len(m.Label)+1)
+		for _, p := range m.Label {
+			lset[model.LabelName(p.GetName())] = model.LabelValue(p.GetValue())
+		}
+		lset[model.MetricNameLabel] = model.LabelValue(f.GetName() + "_sum")
+
+		samples = append(samples, &model.Sample{
+			Metric:    model.Metric(lset),
+			Value:     model.SampleValue(m.Histogram.GetSampleSum()),
+			Timestamp: timestamp,
+		})
+
+		lset = make(model.LabelSet, len(m.Label)+1)
+		for _, p := range m.Label {
+			lset[model.LabelName(p.GetName())] = model.LabelValue(p.GetValue())
+		}
+		lset[model.MetricNameLabel] = model.LabelValue(f.GetName() + "_count")
+
+		v := m.Histogram.GetSampleCountFloat()
+		if v <= 0 {
+			v = float64(m.Histogram.GetSampleCount())
+		}
+		count := &model.Sample{
+			Metric:    model.Metric(lset),
+			Value:     model.SampleValue(v),
+			Timestamp: timestamp,
+		}
+		samples = append(samples, count)
+
+		if !infSeen {
+			// Append an infinity bucket sample.
+			lset := make(model.LabelSet, len(m.Label)+2)
+			for _, p := range m.Label {
+				lset[model.LabelName(p.GetName())] = model.LabelValue(p.GetValue())
+			}
+			lset[model.LabelName(model.BucketLabel)] = model.LabelValue("+Inf")
+			lset[model.MetricNameLabel] = model.LabelValue(f.GetName() + "_bucket")
+
+			samples = append(samples, &model.Sample{
+				Metric:    model.Metric(lset),
+				Value:     count.Value,
+				Timestamp: timestamp,
+			})
+		}
+	}
+
+	return samples
+}
@@ -0,0 +1,250 @@
+// Copyright 2015 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 expfmt
+
+import (
+	"fmt"
+	"io"
+	"mime"
+	"net/http"
+
+	"github.com/munnerz/goautoneg"
+	dto "github.com/prometheus/client_model/go"
+	"google.golang.org/protobuf/encoding/protodelim"
+	"google.golang.org/protobuf/encoding/prototext"
+
+	"github.com/prometheus/common/model"
+)
+
+var formatToAccept = map[Format]goautoneg.Accept{}
+
+func init() {
+	for _, f := range []Format{
+		FmtText,
+		FmtProtoDelim,
+		FmtProtoText,
+		FmtProtoCompact,
+		FmtOpenMetrics_1_0_0,
+		fmtOpenMetrics_2_0_0,
+		FmtOpenMetrics_0_0_1,
+	} {
+		if parsed := goautoneg.ParseAccept(string(f)); len(parsed) > 0 {
+			formatToAccept[f] = parsed[0]
+		}
+	}
+}
+
+// Encoder types encode metric families into an underlying wire protocol.
+type Encoder interface {
+	Encode(*dto.MetricFamily) error
+}
+
+// Closer is implemented by Encoders that need to be closed to finalize
+// encoding. (For example, OpenMetrics needs a final `# EOF` line.)
+//
+// Note that all Encoder implementations returned from this package implement
+// Closer, too, even if the Close call is a no-op. This happens in preparation
+// for adding a Close method to the Encoder interface directly in a (mildly
+// breaking) release in the future.
+type Closer interface {
+	Close() error
+}
+
+type encoderCloser struct {
+	encode func(*dto.MetricFamily) error
+	close  func() error
+}
+
+func (ec encoderCloser) Encode(v *dto.MetricFamily) error {
+	return ec.encode(v)
+}
+
+func (ec encoderCloser) Close() error {
+	return ec.close()
+}
+
+// Negotiate returns the Content-Type based on the given Accept header. If no
+// appropriate accepted type is found, FmtText is returned (which is the
+// Prometheus text format).
+//
+// Deprecated: Use NegotiateAccept(h, FmtProtoDelim, FmtProtoText, FmtProtoCompact, FmtText)
+// or specify only the formats supported by your server.
+func Negotiate(h http.Header) Format {
+	return NegotiateAccept(h, FmtProtoDelim, FmtProtoText, FmtProtoCompact, FmtText)
+}
+
+// NegotiateIncludingOpenMetrics works like Negotiate but includes
+// FmtOpenMetrics as an option for the result.
+//
+// Deprecated: Use NegotiateAccept(h, FmtOpenMetrics_1_0_0, FmtOpenMetrics_0_0_1, FmtProtoDelim, FmtProtoText, FmtProtoCompact, FmtText)
+// or specify only the formats supported by your server.
+func NegotiateIncludingOpenMetrics(h http.Header) Format {
+	return NegotiateAccept(h, FmtOpenMetrics_1_0_0, FmtOpenMetrics_0_0_1, FmtProtoDelim, FmtProtoText, FmtProtoCompact, FmtText)
+}
+
+// NegotiateAccept returns the Content-Type based on the given Accept header
+// and the list of accepted Formats provided by the caller, in order of preference.
+// If no accepted format matches the Accept header, it falls back to the text
+// format if present in the accepted list, or the first accepted format (or FmtText
+// if accepted is empty).
+func NegotiateAccept(h http.Header, accepted ...Format) Format {
+	escapingScheme := Format("; escaping=" + model.NameEscapingScheme.String())
+	for _, ac := range goautoneg.ParseAccept(h.Get(hdrAccept)) {
+		if escapeParam := ac.Params[model.EscapingKey]; escapeParam != "" {
+			switch Format(escapeParam) {
+			case model.AllowUTF8, model.EscapeUnderscores, model.EscapeDots, model.EscapeValues:
+				escapingScheme = Format("; escaping=" + escapeParam)
+			default:
+				// If the escaping parameter is unknown, ignore it.
+			}
+		}
+
+		for _, f := range accepted {
+			if matchFormat(ac, f) {
+				return f + escapingScheme
+			}
+		}
+	}
+	for _, f := range accepted {
+		if f.FormatType() == TypeTextPlain {
+			return f + escapingScheme
+		}
+	}
+	if len(accepted) > 0 {
+		return accepted[0] + escapingScheme
+	}
+	return FmtText + escapingScheme
+}
+
+// matchFormat checks if a parsed accept clause matches a given Format.
+func matchFormat(ac goautoneg.Accept, f Format) bool {
+	target, ok := formatToAccept[f]
+	if !ok {
+		parsed := goautoneg.ParseAccept(string(f))
+		if len(parsed) == 0 {
+			return false
+		}
+		target = parsed[0]
+	}
+
+	if ac.Type != "*" && ac.Type != target.Type {
+		return false
+	}
+	if ac.SubType != "*" && ac.SubType != target.SubType {
+		return false
+	}
+
+	// Default OpenMetrics version to OpenMetricsVersion_0_0_1.
+	acVersion := ac.Params["version"]
+	if acVersion == "" && ac.Type+"/"+ac.SubType == OpenMetricsType {
+		acVersion = OpenMetricsVersion_0_0_1
+	}
+	if acVersion == "" && ac.Type == "text" && ac.SubType == "plain" {
+		acVersion = TextVersion
+	}
+
+	// General param matching.
+	for k, v := range target.Params {
+		if k == "charset" {
+			continue
+		}
+		acVal := ac.Params[k]
+		if k == "version" {
+			acVal = acVersion
+		}
+		if acVal != v {
+			return false
+		}
+	}
+
+	return true
+}
+
+// NewEncoder returns a new encoder based on content type negotiation. All
+// Encoder implementations returned by NewEncoder also implement Closer, and
+// callers should always call the Close method. It is currently only required
+// for FmtOpenMetrics, but a future (breaking) release will add the Close method
+// to the Encoder interface directly. The current version of the Encoder
+// interface is kept for backwards compatibility.
+// In cases where the Format does not allow for UTF-8 names, the global
+// NameEscapingScheme will be applied.
+//
+// NewEncoder can be called with additional options to customize the OpenMetrics text output.
+// For example:
+// NewEncoder(w, FmtOpenMetrics_1_0_0, WithCreatedLines())
+//
+// Extra options are ignored for all other formats.
+func NewEncoder(w io.Writer, format Format, options ...EncoderOption) Encoder {
+	escapingScheme := format.ToEscapingScheme()
+
+	switch format.FormatType() {
+	case TypeProtoDelim:
+		return encoderCloser{
+			encode: func(v *dto.MetricFamily) error {
+				_, err := protodelim.MarshalTo(w, model.EscapeMetricFamily(v, escapingScheme))
+				return err
+			},
+			close: func() error { return nil },
+		}
+	case TypeProtoCompact:
+		return encoderCloser{
+			encode: func(v *dto.MetricFamily) error {
+				_, err := fmt.Fprintln(w, model.EscapeMetricFamily(v, escapingScheme).String())
+				return err
+			},
+			close: func() error { return nil },
+		}
+	case TypeProtoText:
+		return encoderCloser{
+			encode: func(v *dto.MetricFamily) error {
+				_, err := fmt.Fprintln(w, prototext.Format(model.EscapeMetricFamily(v, escapingScheme)))
+				return err
+			},
+			close: func() error { return nil },
+		}
+	case TypeTextPlain:
+		return encoderCloser{
+			encode: func(v *dto.MetricFamily) error {
+				_, err := MetricFamilyToText(w, model.EscapeMetricFamily(v, escapingScheme))
+				return err
+			},
+			close: func() error { return nil },
+		}
+	case TypeOpenMetrics:
+		_, params, err := mime.ParseMediaType(string(format))
+		if err == nil && params["version"] == OpenMetricsVersion_2_0_0 {
+			return encoderCloser{
+				encode: func(v *dto.MetricFamily) error {
+					_, err := MetricFamilyToOpenMetrics20(w, model.EscapeMetricFamily(v, escapingScheme), options...)
+					return err
+				},
+				close: func() error {
+					_, err := FinalizeOpenMetrics(w)
+					return err
+				},
+			}
+		}
+		return encoderCloser{
+			encode: func(v *dto.MetricFamily) error {
+				_, err := MetricFamilyToOpenMetrics(w, model.EscapeMetricFamily(v, escapingScheme), options...)
+				return err
+			},
+			close: func() error {
+				_, err := FinalizeOpenMetrics(w)
+				return err
+			},
+		}
+	}
+	panic(fmt.Errorf("expfmt.NewEncoder: unknown format %q", format))
+}
@@ -0,0 +1,223 @@
+// Copyright 2015 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 expfmt contains tools for reading and writing Prometheus metrics.
+package expfmt
+
+import (
+	"errors"
+	"strings"
+
+	"github.com/prometheus/common/model"
+)
+
+// Format specifies the HTTP content type of the different wire protocols.
+type Format string
+
+// Constants to assemble the Content-Type values for the different wire
+// protocols. The Content-Type strings here are all for the legacy exposition
+// formats, where valid characters for metric names and label names are limited.
+// Support for arbitrary UTF-8 characters in those names is already partially
+// implemented in this module (see model.ValidationScheme), but to actually use
+// it on the wire, new content-type strings will have to be agreed upon and
+// added here.
+const (
+	TextVersion   = "0.0.4"
+	ProtoType     = `application/vnd.google.protobuf`
+	ProtoProtocol = `io.prometheus.client.MetricFamily`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeProtoCompact) instead.
+	ProtoFmt        = ProtoType + "; proto=" + ProtoProtocol + ";"
+	OpenMetricsType = `application/openmetrics-text`
+	//nolint:revive // Allow for underscores.
+	OpenMetricsVersion_0_0_1 = "0.0.1"
+	//nolint:revive // Allow for underscores.
+	OpenMetricsVersion_1_0_0 = "1.0.0"
+	//nolint:revive // Allow for underscores.
+	OpenMetricsVersion_2_0_0 = "2.0.0"
+
+	// The Content-Type values for the different wire protocols. Do not do direct
+	// comparisons to these constants, instead use the comparison functions.
+	//
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeUnknown) instead.
+	FmtUnknown Format = `<unknown>`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeTextPlain) instead.
+	FmtText Format = `text/plain; version=` + TextVersion + `; charset=utf-8`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeProtoDelim) instead.
+	FmtProtoDelim Format = ProtoFmt + ` encoding=delimited`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeProtoText) instead.
+	FmtProtoText Format = ProtoFmt + ` encoding=text`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeProtoCompact) instead.
+	FmtProtoCompact Format = ProtoFmt + ` encoding=compact-text`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeOpenMetrics) instead.
+	//nolint:revive // Allow for underscores.
+	FmtOpenMetrics_1_0_0 Format = OpenMetricsType + `; version=` + OpenMetricsVersion_1_0_0 + `; charset=utf-8`
+	//nolint:revive // Allow for underscores.
+	fmtOpenMetrics_2_0_0 Format = OpenMetricsType + `; version=` + OpenMetricsVersion_2_0_0 + `; charset=utf-8`
+	// Deprecated: Use expfmt.NewFormat(expfmt.TypeOpenMetrics) instead.
+	//nolint:revive // Allow for underscores.
+	FmtOpenMetrics_0_0_1 Format = OpenMetricsType + `; version=` + OpenMetricsVersion_0_0_1 + `; charset=utf-8`
+)
+
+const (
+	hdrContentType = "Content-Type"
+	hdrAccept      = "Accept"
+)
+
+// FormatType is a Go enum representing the overall category for the given
+// Format. As the number of Format permutations increases, doing basic string
+// comparisons are not feasible, so this enum captures the most useful
+// high-level attribute of the Format string.
+type FormatType int
+
+const (
+	TypeUnknown FormatType = iota
+	TypeProtoCompact
+	TypeProtoDelim
+	TypeProtoText
+	TypeTextPlain
+	TypeOpenMetrics
+)
+
+// NewFormat generates a new Format from the type provided. Mostly used for
+// tests, most Formats should be generated as part of content negotiation in
+// encode.go. If a type has more than one version, the latest version will be
+// returned.
+func NewFormat(t FormatType) Format {
+	switch t {
+	case TypeProtoCompact:
+		return FmtProtoCompact
+	case TypeProtoDelim:
+		return FmtProtoDelim
+	case TypeProtoText:
+		return FmtProtoText
+	case TypeTextPlain:
+		return FmtText
+	case TypeOpenMetrics:
+		return FmtOpenMetrics_1_0_0
+	default:
+		return FmtUnknown
+	}
+}
+
+// NewOpenMetricsFormat generates a new OpenMetrics format matching the
+// specified version number.
+//
+// Note: OpenMetrics version 2.0.0 is experimental and encode-only (currently
+// supporting counter, gauge, and untyped metric types).
+func NewOpenMetricsFormat(version string) (Format, error) {
+	if version == OpenMetricsVersion_0_0_1 {
+		return FmtOpenMetrics_0_0_1, nil
+	}
+	if version == OpenMetricsVersion_1_0_0 {
+		return FmtOpenMetrics_1_0_0, nil
+	}
+	if version == OpenMetricsVersion_2_0_0 {
+		// OpenMetrics 2.0.0 is experimental and encode-only (counter/gauge/untyped).
+		return fmtOpenMetrics_2_0_0, nil
+	}
+	return FmtUnknown, errors.New("unknown open metrics version string")
+}
+
+// WithEscapingScheme returns a copy of Format with the specified escaping
+// scheme appended to the end. If an escaping scheme already exists it is
+// removed.
+func (f Format) WithEscapingScheme(s model.EscapingScheme) Format {
+	var terms []string
+	for p := range strings.SplitSeq(string(f), ";") {
+		toks := strings.Split(p, "=")
+		if len(toks) != 2 {
+			trimmed := strings.TrimSpace(p)
+			if len(trimmed) > 0 {
+				terms = append(terms, trimmed)
+			}
+			continue
+		}
+		key := strings.TrimSpace(toks[0])
+		if key != model.EscapingKey {
+			terms = append(terms, strings.TrimSpace(p))
+		}
+	}
+	terms = append(terms, model.EscapingKey+"="+s.String())
+	return Format(strings.Join(terms, "; "))
+}
+
+// FormatType deduces an overall FormatType for the given format.
+func (f Format) FormatType() FormatType {
+	toks := strings.Split(string(f), ";")
+	params := make(map[string]string)
+	for i, t := range toks {
+		if i == 0 {
+			continue
+		}
+		args := strings.Split(t, "=")
+		if len(args) != 2 {
+			continue
+		}
+		params[strings.TrimSpace(args[0])] = strings.TrimSpace(args[1])
+	}
+
+	switch strings.TrimSpace(toks[0]) {
+	case ProtoType:
+		if params["proto"] != ProtoProtocol {
+			return TypeUnknown
+		}
+		switch params["encoding"] {
+		case "delimited":
+			return TypeProtoDelim
+		case "text":
+			return TypeProtoText
+		case "compact-text":
+			return TypeProtoCompact
+		default:
+			return TypeUnknown
+		}
+	case OpenMetricsType:
+		if params["charset"] != "utf-8" {
+			return TypeUnknown
+		}
+		return TypeOpenMetrics
+	case "text/plain":
+		v, ok := params["version"]
+		if !ok {
+			return TypeTextPlain
+		}
+		if v == TextVersion {
+			return TypeTextPlain
+		}
+		return TypeUnknown
+	default:
+		return TypeUnknown
+	}
+}
+
+// ToEscapingScheme returns an EscapingScheme depending on the Format. Iff the
+// Format contains a escaping=allow-utf-8 term, it will select NoEscaping. If a valid
+// "escaping" term exists, that will be used. Otherwise, the global default will
+// be returned.
+func (f Format) ToEscapingScheme() model.EscapingScheme {
+	for p := range strings.SplitSeq(string(f), ";") {
+		toks := strings.Split(p, "=")
+		if len(toks) != 2 {
+			continue
+		}
+		key, value := strings.TrimSpace(toks[0]), strings.TrimSpace(toks[1])
+		if key == model.EscapingKey {
+			scheme, err := model.ToEscapingScheme(value)
+			if err != nil {
+				return model.NameEscapingScheme
+			}
+			return scheme
+		}
+	}
+	return model.NameEscapingScheme
+}
@@ -0,0 +1,39 @@
+// Copyright 2014 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.
+
+// Build only when actually fuzzing
+//go:build gofuzz
+
+package expfmt
+
+import (
+	"bytes"
+
+	"github.com/prometheus/common/model"
+)
+
+// Fuzz text metric parser with with github.com/dvyukov/go-fuzz:
+//
+//	go-fuzz-build github.com/prometheus/common/expfmt
+//	go-fuzz -bin expfmt-fuzz.zip -workdir fuzz
+//
+// Further input samples should go in the folder fuzz/corpus.
+func Fuzz(in []byte) int {
+	parser := NewTextParser(model.UTF8Validation)
+	_, err := parser.TextToMetricFamilies(bytes.NewReader(in))
+	if err != nil {
+		return 0
+	}
+
+	return 1
+}
@@ -0,0 +1,425 @@
+// Copyright 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 expfmt
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"math"
+	"strconv"
+	"strings"
+
+	dto "github.com/prometheus/client_model/go"
+	"google.golang.org/protobuf/types/known/timestamppb"
+)
+
+// MetricFamilyToOpenMetrics20 converts a MetricFamily proto message into the
+// OpenMetrics text format version 2.0.0 and writes the resulting lines to 'out'.
+// It returns the number of bytes written and any error encountered.
+//
+// NOTE: This method targets OpenMetrics 2.0.0 (currently aligned with 2.0-rc.0) which is experimental and
+// encode-only (currently supporting counter, gauge, and untyped metric types).
+// Breaking changes might happen in the future. This implementation is still a
+// work-in-progress, and does not yet support all features of the format.
+// EncoderOptions are accepted for signature compatibility with
+// MetricFamilyToOpenMetrics and are currently ignored.
+func MetricFamilyToOpenMetrics20(out io.Writer, in *dto.MetricFamily, options ...EncoderOption) (written int, err error) {
+	// Options are accepted for signature compatibility and ignored.
+	_ = options
+	name := in.GetName()
+	if name == "" {
+		return 0, fmt.Errorf("MetricFamily has no name: %s", in)
+	}
+	if containsRawNewline(name) {
+		return 0, fmt.Errorf("MetricFamily name %q contains raw newlines", name)
+	}
+	if in.Unit != nil && containsRawNewline(*in.Unit) {
+		return 0, fmt.Errorf("MetricFamily unit %q contains raw newlines", *in.Unit)
+	}
+
+	// Try the interface upgrade. If it doesn't work, we'll use a
+	// bufio.Writer from the sync.Pool.
+	w, ok := out.(enhancedWriter)
+	if !ok {
+		b := bufPool.Get().(*bufio.Writer)
+		b.Reset(out)
+		w = b
+		defer func() {
+			bErr := b.Flush()
+			if err == nil {
+				err = bErr
+			}
+			bufPool.Put(b)
+		}()
+	}
+
+	var (
+		n          int
+		metricType = in.GetType()
+	)
+
+	// Comments, first HELP, then TYPE.
+	if in.Help != nil {
+		n, err = w.WriteString("# HELP ")
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = writeName(w, name)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte(' ')
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err = writeEscapedString(w, *in.Help, true)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte('\n')
+		written++
+		if err != nil {
+			return written, err
+		}
+	}
+	n, err = w.WriteString("# TYPE ")
+	written += n
+	if err != nil {
+		return written, err
+	}
+	n, err = writeName(w, name)
+	written += n
+	if err != nil {
+		return written, err
+	}
+	switch metricType {
+	case dto.MetricType_COUNTER:
+		n, err = w.WriteString(" counter\n")
+	case dto.MetricType_GAUGE:
+		n, err = w.WriteString(" gauge\n")
+	case dto.MetricType_SUMMARY:
+		n, err = w.WriteString(" summary\n")
+	case dto.MetricType_UNTYPED:
+		n, err = w.WriteString(" unknown\n")
+	case dto.MetricType_HISTOGRAM:
+		n, err = w.WriteString(" histogram\n")
+	case dto.MetricType_GAUGE_HISTOGRAM:
+		n, err = w.WriteString(" gaugehistogram\n")
+	default:
+		// TODO: Support Info and StateSet once they are supported in the
+		// Prometheus protobuf format.
+		return written, fmt.Errorf("unknown metric type %s", metricType.String())
+	}
+	written += n
+	if err != nil {
+		return written, err
+	}
+	if in.Unit != nil {
+		n, err = w.WriteString("# UNIT ")
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = writeName(w, name)
+		written += n
+		if err != nil {
+			return written, err
+		}
+
+		err = w.WriteByte(' ')
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err = writeEscapedString(w, *in.Unit, true)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte('\n')
+		written++
+		if err != nil {
+			return written, err
+		}
+	}
+
+	// Finally the samples, one line for each.
+	for _, metric := range in.Metric {
+		if metric == nil {
+			return written, fmt.Errorf("expected non-nil metric in MetricFamily %s", name)
+		}
+		switch metricType {
+		case dto.MetricType_COUNTER:
+			if metric.Counter == nil {
+				return written, fmt.Errorf("expected counter in metric %s %s", name, metric)
+			}
+			val := metric.Counter.GetValue()
+			if math.IsNaN(val) {
+				return written, fmt.Errorf("counter value cannot be NaN in metric %s", name)
+			}
+			if val < 0 {
+				return written, fmt.Errorf("counter value cannot be negative (%g) in metric %s", val, name)
+			}
+			n, err = writeOpenMetrics20Sample(w, name, metric, val, 0, false, metric.Counter.CreatedTimestamp, metric.Counter.Exemplar)
+		case dto.MetricType_GAUGE:
+			if metric.Gauge == nil {
+				return written, fmt.Errorf("expected gauge in metric %s %s", name, metric)
+			}
+			n, err = writeOpenMetrics20Sample(w, name, metric, metric.Gauge.GetValue(), 0, false, nil, nil)
+		case dto.MetricType_UNTYPED:
+			if metric.Untyped == nil {
+				return written, fmt.Errorf("expected untyped in metric %s %s", name, metric)
+			}
+			n, err = writeOpenMetrics20Sample(w, name, metric, metric.Untyped.GetValue(), 0, false, nil, nil)
+		case dto.MetricType_SUMMARY:
+			if metric.Summary == nil {
+				return written, fmt.Errorf("expected summary in metric %s %s", name, metric)
+			}
+			n, err = writeCompositeSummary(w, name, metric)
+		case dto.MetricType_HISTOGRAM, dto.MetricType_GAUGE_HISTOGRAM:
+			if metric.Histogram == nil {
+				return written, fmt.Errorf("expected histogram in metric %s %s", name, metric)
+			}
+			n, err = writeCompositeHistogram(w, name, metric, metricType == dto.MetricType_GAUGE_HISTOGRAM)
+		default:
+			return written, fmt.Errorf("unexpected type in metric %s %s", name, metric)
+		}
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+	return written, nil
+}
+
+// writeOpenMetrics20Sample writes a single sample for simple types (Counter, Gauge, Untyped).
+func writeOpenMetrics20Sample(w enhancedWriter, name string, metric *dto.Metric, floatValue float64, intValue uint64, useIntValue bool, startTimestamp *timestamppb.Timestamp, exemplar *dto.Exemplar) (int, error) {
+	if err := validateLabels20(metric.Label); err != nil {
+		return 0, err
+	}
+	written := 0
+	n, err := writeOpenMetricsNameAndLabelPairs(w, name, metric.Label, "", 0)
+	written += n
+	if err != nil {
+		return written, err
+	}
+	err = w.WriteByte(' ')
+	written++
+	if err != nil {
+		return written, err
+	}
+
+	if useIntValue {
+		n, err = writeUint(w, intValue)
+	} else {
+		n, err = writeOpenMetricsFloat(w, floatValue)
+	}
+	written += n
+	if err != nil {
+		return written, err
+	}
+
+	if metric.TimestampMs != nil {
+		err = w.WriteByte(' ')
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err = writeOpenMetrics20Timestamp(w, float64(*metric.TimestampMs)/1000)
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+
+	// Start Timestamp
+	if startTimestamp != nil {
+		if err := startTimestamp.CheckValid(); err != nil {
+			return written, fmt.Errorf("invalid created timestamp in metric %s: %w", name, err)
+		}
+		n, err = w.WriteString(" st@")
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = writeProtoTimestamp(w, startTimestamp)
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+
+	if exemplar != nil {
+		n, err = writeExemplar20(w, exemplar)
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+
+	err = w.WriteByte('\n')
+	written++
+	if err != nil {
+		return written, err
+	}
+	return written, nil
+}
+
+// writeExemplar20 writes the provided exemplar in OpenMetrics 2.0 format to w.
+// In OpenMetrics 2.0, invalid exemplars or exemplars without a timestamp are dropped.
+func writeExemplar20(w enhancedWriter, e *dto.Exemplar) (int, error) {
+	if e == nil {
+		return 0, nil
+	}
+	// In OpenMetrics 2.0, invalid exemplars are dropped rather than failing the entire exposition.
+	if err := validateExemplar20(e); err != nil {
+		return 0, nil
+	}
+	written := 0
+	n, err := w.WriteString(" # ")
+	written += n
+	if err != nil {
+		return written, err
+	}
+	if len(e.Label) == 0 {
+		n, err = w.WriteString("{}")
+	} else {
+		n, err = writeOpenMetricsNameAndLabelPairs(w, "", e.Label, "", 0)
+	}
+	written += n
+	if err != nil {
+		return written, err
+	}
+	err = w.WriteByte(' ')
+	written++
+	if err != nil {
+		return written, err
+	}
+	n, err = writeOpenMetricsFloat(w, e.GetValue())
+	written += n
+	if err != nil {
+		return written, err
+	}
+	err = w.WriteByte(' ')
+	written++
+	if err != nil {
+		return written, err
+	}
+	ts := e.Timestamp
+	n, err = writeProtoTimestamp(w, ts)
+	written += n
+	if err != nil {
+		return written, err
+	}
+	return written, nil
+}
+
+// writeOpenMetrics20Timestamp writes a float64 as a timestamp without scientific notation.
+func writeOpenMetrics20Timestamp(w enhancedWriter, f float64) (int, error) {
+	bp := numBufPool.Get().(*[]byte)
+	*bp = strconv.AppendFloat((*bp)[:0], f, 'f', -1, 64)
+	written, err := w.Write(*bp)
+	numBufPool.Put(bp)
+	return written, err
+}
+
+// Stubs for Summary and Histogram
+
+func writeCompositeSummary(w enhancedWriter, name string, metric *dto.Metric) (int, error) {
+	_ = w
+	_ = name
+	_ = metric
+	return 0, errors.New("summary not implemented yet")
+}
+
+func writeCompositeHistogram(w enhancedWriter, name string, metric *dto.Metric, isGauge bool) (int, error) {
+	_ = w
+	_ = name
+	_ = metric
+	_ = isGauge
+	return 0, errors.New("histogram not implemented yet")
+}
+
+func validateLabels20(labels []*dto.LabelPair) error {
+	for _, lp := range labels {
+		if lp == nil {
+			return errors.New("expected non-nil label pair")
+		}
+		lname := lp.GetName()
+		if lname == "" {
+			return errors.New("label name cannot be empty")
+		}
+		if containsRawNewline(lname) {
+			return fmt.Errorf("label name %q contains raw newlines", lname)
+		}
+	}
+	return nil
+}
+
+func containsRawNewline(s string) bool {
+	return strings.IndexByte(s, '\n') >= 0 || strings.IndexByte(s, '\r') >= 0
+}
+
+func validateExemplar20(e *dto.Exemplar) error {
+	if e.Timestamp == nil {
+		return errors.New("exemplar timestamp is required")
+	}
+	if err := e.Timestamp.CheckValid(); err != nil {
+		return err
+	}
+	return validateLabels20(e.Label)
+}
+
+func writeProtoTimestamp(w enhancedWriter, ts *timestamppb.Timestamp) (int, error) {
+	if err := ts.CheckValid(); err != nil {
+		return 0, err
+	}
+	n, err := writeInt(w, ts.Seconds)
+	if err != nil {
+		return n, err
+	}
+	if ts.Nanos == 0 {
+		return n, nil
+	}
+	err = w.WriteByte('.')
+	written := n + 1
+	if err != nil {
+		return written, err
+	}
+	bp := numBufPool.Get().(*[]byte)
+	*bp = strconv.AppendInt((*bp)[:0], int64(ts.Nanos), 10)
+	pad := 9 - len(*bp)
+	for range pad {
+		err = w.WriteByte('0')
+		written++
+		if err != nil {
+			numBufPool.Put(bp)
+			return written, err
+		}
+	}
+	val := *bp
+	for len(val) > 0 && val[len(val)-1] == '0' {
+		val = val[:len(val)-1]
+	}
+	n2, err := w.Write(val)
+	written += n2
+	numBufPool.Put(bp)
+	return written, err
+}
@@ -0,0 +1,688 @@
+// 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 expfmt
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"math"
+	"strconv"
+	"strings"
+
+	dto "github.com/prometheus/client_model/go"
+	"google.golang.org/protobuf/types/known/timestamppb"
+
+	"github.com/prometheus/common/model"
+)
+
+type encoderOption struct {
+	withCreatedLines bool
+}
+
+type EncoderOption func(*encoderOption)
+
+// WithCreatedLines is an EncoderOption that configures the OpenMetrics encoder
+// to include _created lines (See
+// https://github.com/prometheus/OpenMetrics/blob/v1.0.0/specification/OpenMetrics.md#counter-1).
+// Created timestamps can improve the accuracy of series reset detection, but
+// come with a bandwidth cost.
+//
+// At the time of writing, created timestamp ingestion is still experimental in
+// Prometheus and need to be enabled with the feature-flag
+// `--feature-flag=created-timestamp-zero-ingestion`, and breaking changes are
+// still possible. Therefore, it is recommended to use this feature with caution.
+func WithCreatedLines() EncoderOption {
+	return func(t *encoderOption) {
+		t.withCreatedLines = true
+	}
+}
+
+// MetricFamilyToOpenMetrics converts a MetricFamily proto message into the
+// OpenMetrics text format and writes the resulting lines to 'out'. It returns
+// the number of bytes written and any error encountered. The output will have
+// the same order as the input, no further sorting is performed. Furthermore,
+// this function assumes the input is already sanitized and does not perform any
+// sanity checks. If the input contains duplicate metrics or invalid metric or
+// label names, the conversion will result in invalid text format output.
+//
+// If metric names conform to the legacy validation pattern, they will be placed
+// outside the brackets in the traditional way, like `foo{}`. If the metric name
+// fails the legacy validation check, it will be placed quoted inside the
+// brackets: `{"foo"}`. As stated above, the input is assumed to be santized and
+// no error will be thrown in this case.
+//
+// Similar to metric names, if label names conform to the legacy validation
+// pattern, they will be unquoted as normal, like `foo{bar="baz"}`. If the label
+// name fails the legacy validation check, it will be quoted:
+// `foo{"bar"="baz"}`. As stated above, the input is assumed to be santized and
+// no error will be thrown in this case.
+//
+// This function fulfills the type 'expfmt.encoder'.
+//
+// Note that OpenMetrics requires a final `# EOF` line. Since this function acts
+// on individual metric families, it is the responsibility of the caller to
+// append this line to 'out' once all metric families have been written.
+// Conveniently, this can be done by calling FinalizeOpenMetrics.
+//
+// The output should be fully OpenMetrics compliant. However, there are a few
+// missing features and peculiarities to avoid complications when switching from
+// Prometheus to OpenMetrics or vice versa:
+//
+//   - Counters are expected to have the `_total` suffix in their metric name. In
+//     the output, the suffix will be truncated from the `# TYPE`, `# HELP` and `# UNIT`
+//     lines. A counter with a missing `_total` suffix is not an error. However,
+//     its type will be set to `unknown` in that case to avoid invalid OpenMetrics
+//     output.
+//
+//   - No support for the following (optional) features: info type,
+//     stateset type, gaugehistogram type.
+//
+//   - The size of exemplar labels is not checked (i.e. it's possible to create
+//     exemplars that are larger than allowed by the OpenMetrics specification).
+//
+//   - The value of Counters is not checked. (OpenMetrics doesn't allow counters
+//     with a `NaN` value.)
+func MetricFamilyToOpenMetrics(out io.Writer, in *dto.MetricFamily, options ...EncoderOption) (written int, err error) {
+	toOM := encoderOption{}
+	for _, option := range options {
+		option(&toOM)
+	}
+
+	name := in.GetName()
+	if name == "" {
+		return 0, fmt.Errorf("MetricFamily has no name: %s", in)
+	}
+
+	// Try the interface upgrade. If it doesn't work, we'll use a
+	// bufio.Writer from the sync.Pool.
+	w, ok := out.(enhancedWriter)
+	if !ok {
+		b := bufPool.Get().(*bufio.Writer)
+		b.Reset(out)
+		w = b
+		defer func() {
+			bErr := b.Flush()
+			if err == nil {
+				err = bErr
+			}
+			bufPool.Put(b)
+		}()
+	}
+
+	var (
+		n             int
+		metricType    = in.GetType()
+		compliantName = name
+	)
+	if metricType == dto.MetricType_COUNTER && strings.HasSuffix(compliantName, "_total") {
+		compliantName = name[:len(name)-6]
+	}
+
+	// Comments, first HELP, then TYPE.
+	if in.Help != nil {
+		n, err = w.WriteString("# HELP ")
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = writeName(w, compliantName)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte(' ')
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err = writeEscapedString(w, *in.Help, true)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte('\n')
+		written++
+		if err != nil {
+			return written, err
+		}
+	}
+	n, err = w.WriteString("# TYPE ")
+	written += n
+	if err != nil {
+		return written, err
+	}
+	n, err = writeName(w, compliantName)
+	written += n
+	if err != nil {
+		return written, err
+	}
+	switch metricType {
+	case dto.MetricType_COUNTER:
+		if strings.HasSuffix(name, "_total") {
+			n, err = w.WriteString(" counter\n")
+		} else {
+			n, err = w.WriteString(" unknown\n")
+		}
+	case dto.MetricType_GAUGE:
+		n, err = w.WriteString(" gauge\n")
+	case dto.MetricType_SUMMARY:
+		n, err = w.WriteString(" summary\n")
+	case dto.MetricType_UNTYPED:
+		n, err = w.WriteString(" unknown\n")
+	case dto.MetricType_HISTOGRAM:
+		n, err = w.WriteString(" histogram\n")
+	case dto.MetricType_GAUGE_HISTOGRAM:
+		n, err = w.WriteString(" gaugehistogram\n")
+	default:
+		return written, fmt.Errorf("unknown metric type %s", metricType.String())
+	}
+	written += n
+	if err != nil {
+		return written, err
+	}
+	if in.Unit != nil {
+		n, err = w.WriteString("# UNIT ")
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = writeName(w, compliantName)
+		written += n
+		if err != nil {
+			return written, err
+		}
+
+		err = w.WriteByte(' ')
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err = writeEscapedString(w, *in.Unit, true)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte('\n')
+		written++
+		if err != nil {
+			return written, err
+		}
+	}
+
+	var createdTsBytesWritten int
+
+	// Finally the samples, one line for each.
+	if metricType == dto.MetricType_COUNTER && strings.HasSuffix(name, "_total") {
+		compliantName += "_total"
+	}
+	for _, metric := range in.Metric {
+		switch metricType {
+		case dto.MetricType_COUNTER:
+			if metric.Counter == nil {
+				return written, fmt.Errorf(
+					"expected counter in metric %s %s", compliantName, metric,
+				)
+			}
+			n, err = writeOpenMetricsSample(
+				w, compliantName, "", metric, "", 0,
+				metric.Counter.GetValue(), 0, false,
+				metric.Counter.Exemplar,
+			)
+			if toOM.withCreatedLines && metric.Counter.CreatedTimestamp != nil {
+				createdTsBytesWritten, err = writeOpenMetricsCreated(w, compliantName, "_total", metric, "", 0, metric.Counter.GetCreatedTimestamp())
+				n += createdTsBytesWritten
+			}
+		case dto.MetricType_GAUGE:
+			if metric.Gauge == nil {
+				return written, fmt.Errorf(
+					"expected gauge in metric %s %s", compliantName, metric,
+				)
+			}
+			n, err = writeOpenMetricsSample(
+				w, compliantName, "", metric, "", 0,
+				metric.Gauge.GetValue(), 0, false,
+				nil,
+			)
+		case dto.MetricType_UNTYPED:
+			if metric.Untyped == nil {
+				return written, fmt.Errorf(
+					"expected untyped in metric %s %s", compliantName, metric,
+				)
+			}
+			n, err = writeOpenMetricsSample(
+				w, compliantName, "", metric, "", 0,
+				metric.Untyped.GetValue(), 0, false,
+				nil,
+			)
+		case dto.MetricType_SUMMARY:
+			if metric.Summary == nil {
+				return written, fmt.Errorf(
+					"expected summary in metric %s %s", compliantName, metric,
+				)
+			}
+			for _, q := range metric.Summary.Quantile {
+				n, err = writeOpenMetricsSample(
+					w, compliantName, "", metric,
+					model.QuantileLabel, q.GetQuantile(),
+					q.GetValue(), 0, false,
+					nil,
+				)
+				written += n
+				if err != nil {
+					return written, err
+				}
+			}
+			n, err = writeOpenMetricsSample(
+				w, compliantName, "_sum", metric, "", 0,
+				metric.Summary.GetSampleSum(), 0, false,
+				nil,
+			)
+			written += n
+			if err != nil {
+				return written, err
+			}
+			n, err = writeOpenMetricsSample(
+				w, compliantName, "_count", metric, "", 0,
+				0, metric.Summary.GetSampleCount(), true,
+				nil,
+			)
+			if toOM.withCreatedLines && metric.Summary.CreatedTimestamp != nil {
+				createdTsBytesWritten, err = writeOpenMetricsCreated(w, compliantName, "", metric, "", 0, metric.Summary.GetCreatedTimestamp())
+				n += createdTsBytesWritten
+			}
+		case dto.MetricType_HISTOGRAM, dto.MetricType_GAUGE_HISTOGRAM:
+			if metric.Histogram == nil {
+				return written, fmt.Errorf(
+					"expected histogram in metric %s %s", compliantName, metric,
+				)
+			}
+			infSeen := false
+			for _, b := range metric.Histogram.Bucket {
+				if b.GetCumulativeCountFloat() > 0 {
+					return written, fmt.Errorf(
+						"OpenMetrics v1.0 does not support float histogram %s %s",
+						compliantName, metric,
+					)
+				}
+				n, err = writeOpenMetricsSample(
+					w, compliantName, "_bucket", metric,
+					model.BucketLabel, b.GetUpperBound(),
+					0, b.GetCumulativeCount(), true,
+					b.Exemplar,
+				)
+				written += n
+				if err != nil {
+					return written, err
+				}
+				if math.IsInf(b.GetUpperBound(), +1) {
+					infSeen = true
+				}
+			}
+			if !infSeen {
+				n, err = writeOpenMetricsSample(
+					w, compliantName, "_bucket", metric,
+					model.BucketLabel, math.Inf(+1),
+					0, metric.Histogram.GetSampleCount(), true,
+					nil,
+				)
+				// We do not check for a float sample count here
+				// because we will check for it below (and error
+				// out if needed).
+				written += n
+				if err != nil {
+					return written, err
+				}
+			}
+			n, err = writeOpenMetricsSample(
+				w, compliantName, "_sum", metric, "", 0,
+				metric.Histogram.GetSampleSum(), 0, false,
+				nil,
+			)
+			written += n
+			if err != nil {
+				return written, err
+			}
+			if metric.Histogram.GetSampleCountFloat() > 0 {
+				return written, fmt.Errorf(
+					"OpenMetrics v1.0 does not support float histogram %s %s",
+					compliantName, metric,
+				)
+			}
+			n, err = writeOpenMetricsSample(
+				w, compliantName, "_count", metric, "", 0,
+				0, metric.Histogram.GetSampleCount(), true,
+				nil,
+			)
+			if toOM.withCreatedLines && metric.Histogram.CreatedTimestamp != nil {
+				createdTsBytesWritten, err = writeOpenMetricsCreated(w, compliantName, "", metric, "", 0, metric.Histogram.GetCreatedTimestamp())
+				n += createdTsBytesWritten
+			}
+		default:
+			return written, fmt.Errorf(
+				"unexpected type in metric %s %s", compliantName, metric,
+			)
+		}
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+	return written, err
+}
+
+// FinalizeOpenMetrics writes the final `# EOF\n` line required by OpenMetrics.
+func FinalizeOpenMetrics(w io.Writer) (written int, err error) {
+	return w.Write([]byte("# EOF\n"))
+}
+
+// writeOpenMetricsSample writes a single sample in OpenMetrics text format to
+// w, given the metric name, the metric proto message itself, optionally an
+// additional label name with a float64 value (use empty string as label name if
+// not required), the value (optionally as float64 or uint64, determined by
+// useIntValue), and optionally an exemplar (use nil if not required). The
+// function returns the number of bytes written and any error encountered.
+func writeOpenMetricsSample(
+	w enhancedWriter,
+	name, suffix string,
+	metric *dto.Metric,
+	additionalLabelName string, additionalLabelValue float64,
+	floatValue float64, intValue uint64, useIntValue bool,
+	exemplar *dto.Exemplar,
+) (int, error) {
+	written := 0
+	n, err := writeOpenMetricsNameAndLabelPairs(
+		w, name+suffix, metric.Label, additionalLabelName, additionalLabelValue,
+	)
+	written += n
+	if err != nil {
+		return written, err
+	}
+	err = w.WriteByte(' ')
+	written++
+	if err != nil {
+		return written, err
+	}
+	if useIntValue {
+		n, err = writeUint(w, intValue)
+	} else {
+		n, err = writeOpenMetricsFloat(w, floatValue)
+	}
+	written += n
+	if err != nil {
+		return written, err
+	}
+	if metric.TimestampMs != nil {
+		err = w.WriteByte(' ')
+		written++
+		if err != nil {
+			return written, err
+		}
+		// TODO(beorn7): Format this directly without converting to a float first.
+		n, err = writeOpenMetricsFloat(w, float64(*metric.TimestampMs)/1000)
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+	if exemplar != nil && len(exemplar.Label) > 0 {
+		n, err = writeExemplar(w, exemplar)
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+	err = w.WriteByte('\n')
+	written++
+	if err != nil {
+		return written, err
+	}
+	return written, nil
+}
+
+// writeOpenMetricsNameAndLabelPairs works like writeOpenMetricsSample but
+// formats the float in OpenMetrics style.
+func writeOpenMetricsNameAndLabelPairs(
+	w enhancedWriter,
+	name string,
+	in []*dto.LabelPair,
+	additionalLabelName string, additionalLabelValue float64,
+) (int, error) {
+	var (
+		written            int
+		separator          byte = '{'
+		metricInsideBraces      = false
+	)
+
+	if name != "" {
+		// If the name does not pass the legacy validity check, we must put the
+		// metric name inside the braces, quoted.
+		if !model.LegacyValidation.IsValidMetricName(name) {
+			metricInsideBraces = true
+			err := w.WriteByte(separator)
+			written++
+			if err != nil {
+				return written, err
+			}
+			separator = ','
+		}
+
+		n, err := writeName(w, name)
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+
+	if len(in) == 0 && additionalLabelName == "" {
+		if metricInsideBraces {
+			err := w.WriteByte('}')
+			written++
+			if err != nil {
+				return written, err
+			}
+		}
+		return written, nil
+	}
+
+	for _, lp := range in {
+		err := w.WriteByte(separator)
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err := writeName(w, lp.GetName())
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = w.WriteString(`="`)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = writeEscapedString(w, lp.GetValue(), true)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte('"')
+		written++
+		if err != nil {
+			return written, err
+		}
+		separator = ','
+	}
+	if additionalLabelName != "" {
+		err := w.WriteByte(separator)
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err := w.WriteString(additionalLabelName)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = w.WriteString(`="`)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = writeOpenMetricsFloat(w, additionalLabelValue)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte('"')
+		written++
+		if err != nil {
+			return written, err
+		}
+	}
+	err := w.WriteByte('}')
+	written++
+	if err != nil {
+		return written, err
+	}
+	return written, nil
+}
+
+// writeOpenMetricsCreated writes the created timestamp for a single time series
+// following OpenMetrics text format to w, given the metric name, the metric proto
+// message itself, optionally a suffix to be removed, e.g. '_total' for counters,
+// an additional label name with a float64 value (use empty string as label name if
+// not required) and the timestamp that represents the created timestamp.
+// The function returns the number of bytes written and any error encountered.
+func writeOpenMetricsCreated(w enhancedWriter,
+	name, suffixToTrim string, metric *dto.Metric,
+	additionalLabelName string, additionalLabelValue float64,
+	createdTimestamp *timestamppb.Timestamp,
+) (int, error) {
+	written := 0
+	n, err := writeOpenMetricsNameAndLabelPairs(
+		w, strings.TrimSuffix(name, suffixToTrim)+"_created", metric.Label, additionalLabelName, additionalLabelValue,
+	)
+	written += n
+	if err != nil {
+		return written, err
+	}
+
+	err = w.WriteByte(' ')
+	written++
+	if err != nil {
+		return written, err
+	}
+
+	// TODO(beorn7): Format this directly from components of ts to
+	// avoid overflow/underflow and precision issues of the float
+	// conversion.
+	n, err = writeOpenMetricsFloat(w, float64(createdTimestamp.AsTime().UnixNano())/1e9)
+	written += n
+	if err != nil {
+		return written, err
+	}
+
+	err = w.WriteByte('\n')
+	written++
+	if err != nil {
+		return written, err
+	}
+	return written, nil
+}
+
+// writeExemplar writes the provided exemplar in OpenMetrics format to w. The
+// function returns the number of bytes written and any error encountered.
+func writeExemplar(w enhancedWriter, e *dto.Exemplar) (int, error) {
+	written := 0
+	n, err := w.WriteString(" # ")
+	written += n
+	if err != nil {
+		return written, err
+	}
+	n, err = writeOpenMetricsNameAndLabelPairs(w, "", e.Label, "", 0)
+	written += n
+	if err != nil {
+		return written, err
+	}
+	err = w.WriteByte(' ')
+	written++
+	if err != nil {
+		return written, err
+	}
+	n, err = writeOpenMetricsFloat(w, e.GetValue())
+	written += n
+	if err != nil {
+		return written, err
+	}
+	if e.Timestamp != nil {
+		err = w.WriteByte(' ')
+		written++
+		if err != nil {
+			return written, err
+		}
+		err = e.Timestamp.CheckValid()
+		if err != nil {
+			return written, err
+		}
+		ts := e.Timestamp.AsTime()
+		// TODO(beorn7): Format this directly from components of ts to
+		// avoid overflow/underflow and precision issues of the float
+		// conversion.
+		n, err = writeOpenMetricsFloat(w, float64(ts.UnixNano())/1e9)
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+	return written, nil
+}
+
+// writeOpenMetricsFloat works like writeFloat but appends ".0" if the resulting
+// number would otherwise contain neither a "." nor an "e".
+func writeOpenMetricsFloat(w enhancedWriter, f float64) (int, error) {
+	switch {
+	case f == 1:
+		return w.WriteString("1.0")
+	case f == 0:
+		return w.WriteString("0.0")
+	case f == -1:
+		return w.WriteString("-1.0")
+	case math.IsNaN(f):
+		return w.WriteString("NaN")
+	case math.IsInf(f, +1):
+		return w.WriteString("+Inf")
+	case math.IsInf(f, -1):
+		return w.WriteString("-Inf")
+	default:
+		bp := numBufPool.Get().(*[]byte)
+		*bp = strconv.AppendFloat((*bp)[:0], f, 'g', -1, 64)
+		if !bytes.ContainsAny(*bp, "e.") {
+			*bp = append(*bp, '.', '0')
+		}
+		written, err := w.Write(*bp)
+		numBufPool.Put(bp)
+		return written, err
+	}
+}
+
+// writeUint is like writeInt just for uint64.
+func writeUint(w enhancedWriter, u uint64) (int, error) {
+	bp := numBufPool.Get().(*[]byte)
+	*bp = strconv.AppendUint((*bp)[:0], u, 10)
+	written, err := w.Write(*bp)
+	numBufPool.Put(bp)
+	return written, err
+}
@@ -0,0 +1,532 @@
+// Copyright 2014 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 expfmt
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"math"
+	"strconv"
+	"strings"
+	"sync"
+
+	dto "github.com/prometheus/client_model/go"
+
+	"github.com/prometheus/common/model"
+)
+
+// enhancedWriter has all the enhanced write functions needed here. bufio.Writer
+// implements it.
+type enhancedWriter interface {
+	io.Writer
+	WriteRune(r rune) (n int, err error)
+	WriteString(s string) (n int, err error)
+	WriteByte(c byte) error
+}
+
+const (
+	initialNumBufSize = 24
+)
+
+var (
+	bufPool = sync.Pool{
+		New: func() any {
+			return bufio.NewWriter(io.Discard)
+		},
+	}
+	numBufPool = sync.Pool{
+		New: func() any {
+			b := make([]byte, 0, initialNumBufSize)
+			return &b
+		},
+	}
+)
+
+// MetricFamilyToText converts a MetricFamily proto message into text format and
+// writes the resulting lines to 'out'. It returns the number of bytes written
+// and any error encountered. The output will have the same order as the input,
+// no further sorting is performed. Furthermore, this function assumes the input
+// is already sanitized and does not perform any sanity checks. If the input
+// contains duplicate metrics or invalid metric or label names, the conversion
+// will result in invalid text format output.
+//
+// If metric names conform to the legacy validation pattern, they will be placed
+// outside the brackets in the traditional way, like `foo{}`. If the metric name
+// fails the legacy validation check, it will be placed quoted inside the
+// brackets: `{"foo"}`. As stated above, the input is assumed to be santized and
+// no error will be thrown in this case.
+//
+// Similar to metric names, if label names conform to the legacy validation
+// pattern, they will be unquoted as normal, like `foo{bar="baz"}`. If the label
+// name fails the legacy validation check, it will be quoted:
+// `foo{"bar"="baz"}`. As stated above, the input is assumed to be santized and
+// no error will be thrown in this case.
+//
+// This method fulfills the type 'prometheus.encoder'.
+func MetricFamilyToText(out io.Writer, in *dto.MetricFamily) (written int, err error) {
+	// Fail-fast checks.
+	if len(in.Metric) == 0 {
+		return 0, fmt.Errorf("MetricFamily has no metrics: %s", in)
+	}
+	name := in.GetName()
+	if name == "" {
+		return 0, fmt.Errorf("MetricFamily has no name: %s", in)
+	}
+
+	// Try the interface upgrade. If it doesn't work, we'll use a
+	// bufio.Writer from the sync.Pool.
+	w, ok := out.(enhancedWriter)
+	if !ok {
+		b := bufPool.Get().(*bufio.Writer)
+		b.Reset(out)
+		w = b
+		defer func() {
+			bErr := b.Flush()
+			if err == nil {
+				err = bErr
+			}
+			bufPool.Put(b)
+		}()
+	}
+
+	var n int
+
+	// Comments, first HELP, then TYPE.
+	if in.Help != nil {
+		n, err = w.WriteString("# HELP ")
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = writeName(w, name)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte(' ')
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err = writeEscapedString(w, *in.Help, false)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte('\n')
+		written++
+		if err != nil {
+			return written, err
+		}
+	}
+	n, err = w.WriteString("# TYPE ")
+	written += n
+	if err != nil {
+		return written, err
+	}
+	n, err = writeName(w, name)
+	written += n
+	if err != nil {
+		return written, err
+	}
+	metricType := in.GetType()
+	switch metricType {
+	case dto.MetricType_COUNTER:
+		n, err = w.WriteString(" counter\n")
+	case dto.MetricType_GAUGE:
+		n, err = w.WriteString(" gauge\n")
+	case dto.MetricType_SUMMARY:
+		n, err = w.WriteString(" summary\n")
+	case dto.MetricType_UNTYPED:
+		n, err = w.WriteString(" untyped\n")
+	case dto.MetricType_HISTOGRAM, dto.MetricType_GAUGE_HISTOGRAM:
+		// The classic Prometheus text format has no notion of a gauge
+		// histogram. We render a gauge histogram in the same way as a
+		// regular histogram.
+		n, err = w.WriteString(" histogram\n")
+	default:
+		return written, fmt.Errorf("unknown metric type %s", metricType.String())
+	}
+	written += n
+	if err != nil {
+		return written, err
+	}
+
+	// Finally the samples, one line for each.
+	for _, metric := range in.Metric {
+		switch metricType {
+		case dto.MetricType_COUNTER:
+			if metric.Counter == nil {
+				return written, fmt.Errorf(
+					"expected counter in metric %s %s", name, metric,
+				)
+			}
+			n, err = writeSample(
+				w, name, "", metric, "", 0,
+				metric.Counter.GetValue(),
+			)
+		case dto.MetricType_GAUGE:
+			if metric.Gauge == nil {
+				return written, fmt.Errorf(
+					"expected gauge in metric %s %s", name, metric,
+				)
+			}
+			n, err = writeSample(
+				w, name, "", metric, "", 0,
+				metric.Gauge.GetValue(),
+			)
+		case dto.MetricType_UNTYPED:
+			if metric.Untyped == nil {
+				return written, fmt.Errorf(
+					"expected untyped in metric %s %s", name, metric,
+				)
+			}
+			n, err = writeSample(
+				w, name, "", metric, "", 0,
+				metric.Untyped.GetValue(),
+			)
+		case dto.MetricType_SUMMARY:
+			if metric.Summary == nil {
+				return written, fmt.Errorf(
+					"expected summary in metric %s %s", name, metric,
+				)
+			}
+			for _, q := range metric.Summary.Quantile {
+				n, err = writeSample(
+					w, name, "", metric,
+					model.QuantileLabel, q.GetQuantile(),
+					q.GetValue(),
+				)
+				written += n
+				if err != nil {
+					return written, err
+				}
+			}
+			n, err = writeSample(
+				w, name, "_sum", metric, "", 0,
+				metric.Summary.GetSampleSum(),
+			)
+			written += n
+			if err != nil {
+				return written, err
+			}
+			n, err = writeSample(
+				w, name, "_count", metric, "", 0,
+				float64(metric.Summary.GetSampleCount()),
+			)
+		case dto.MetricType_HISTOGRAM, dto.MetricType_GAUGE_HISTOGRAM:
+			if metric.Histogram == nil {
+				return written, fmt.Errorf(
+					"expected histogram in metric %s %s", name, metric,
+				)
+			}
+			infSeen := false
+			for _, b := range metric.Histogram.Bucket {
+				v := b.GetCumulativeCountFloat()
+				if v == 0 {
+					v = float64(b.GetCumulativeCount())
+				}
+				n, err = writeSample(
+					w, name, "_bucket", metric,
+					model.BucketLabel, b.GetUpperBound(),
+					v,
+				)
+				written += n
+				if err != nil {
+					return written, err
+				}
+				if math.IsInf(b.GetUpperBound(), +1) {
+					infSeen = true
+				}
+			}
+			if !infSeen {
+				v := metric.Histogram.GetSampleCountFloat()
+				if v == 0 {
+					v = float64(metric.Histogram.GetSampleCount())
+				}
+				n, err = writeSample(
+					w, name, "_bucket", metric,
+					model.BucketLabel, math.Inf(+1),
+					v,
+				)
+				written += n
+				if err != nil {
+					return written, err
+				}
+			}
+			n, err = writeSample(
+				w, name, "_sum", metric, "", 0,
+				metric.Histogram.GetSampleSum(),
+			)
+			written += n
+			if err != nil {
+				return written, err
+			}
+			v := metric.Histogram.GetSampleCountFloat()
+			if v == 0 {
+				v = float64(metric.Histogram.GetSampleCount())
+			}
+			n, err = writeSample(w, name, "_count", metric, "", 0, v)
+		default:
+			return written, fmt.Errorf(
+				"unexpected type in metric %s %s", name, metric,
+			)
+		}
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+	return written, err
+}
+
+// writeSample writes a single sample in text format to w, given the metric
+// name, the metric proto message itself, optionally an additional label name
+// with a float64 value (use empty string as label name if not required), and
+// the value. The function returns the number of bytes written and any error
+// encountered.
+func writeSample(
+	w enhancedWriter,
+	name, suffix string,
+	metric *dto.Metric,
+	additionalLabelName string, additionalLabelValue float64,
+	value float64,
+) (int, error) {
+	written := 0
+	n, err := writeNameAndLabelPairs(
+		w, name+suffix, metric.Label, additionalLabelName, additionalLabelValue,
+	)
+	written += n
+	if err != nil {
+		return written, err
+	}
+	err = w.WriteByte(' ')
+	written++
+	if err != nil {
+		return written, err
+	}
+	n, err = writeFloat(w, value)
+	written += n
+	if err != nil {
+		return written, err
+	}
+	if metric.TimestampMs != nil {
+		err = w.WriteByte(' ')
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err = writeInt(w, *metric.TimestampMs)
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+	err = w.WriteByte('\n')
+	written++
+	if err != nil {
+		return written, err
+	}
+	return written, nil
+}
+
+// writeNameAndLabelPairs converts a slice of LabelPair proto messages plus the
+// explicitly given metric name and additional label pair into text formatted as
+// required by the text format and writes it to 'w'. An empty slice in
+// combination with an empty string 'additionalLabelName' results in nothing
+// being written. Otherwise, the label pairs are written, escaped as required by
+// the text format, and enclosed in '{...}'. The function returns the number of
+// bytes written and any error encountered. If the metric name is not
+// legacy-valid, it will be put inside the brackets as well. Legacy-invalid
+// label names will also be quoted.
+func writeNameAndLabelPairs(
+	w enhancedWriter,
+	name string,
+	in []*dto.LabelPair,
+	additionalLabelName string, additionalLabelValue float64,
+) (int, error) {
+	var (
+		written            int
+		separator          byte = '{'
+		metricInsideBraces      = false
+	)
+
+	if name != "" {
+		// If the name does not pass the legacy validity check, we must put the
+		// metric name inside the braces.
+		if !model.LegacyValidation.IsValidMetricName(name) {
+			metricInsideBraces = true
+			err := w.WriteByte(separator)
+			written++
+			if err != nil {
+				return written, err
+			}
+			separator = ','
+		}
+		n, err := writeName(w, name)
+		written += n
+		if err != nil {
+			return written, err
+		}
+	}
+
+	if len(in) == 0 && additionalLabelName == "" {
+		if metricInsideBraces {
+			err := w.WriteByte('}')
+			written++
+			if err != nil {
+				return written, err
+			}
+		}
+		return written, nil
+	}
+
+	for _, lp := range in {
+		err := w.WriteByte(separator)
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err := writeName(w, lp.GetName())
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = w.WriteString(`="`)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = writeEscapedString(w, lp.GetValue(), true)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte('"')
+		written++
+		if err != nil {
+			return written, err
+		}
+		separator = ','
+	}
+	if additionalLabelName != "" {
+		err := w.WriteByte(separator)
+		written++
+		if err != nil {
+			return written, err
+		}
+		n, err := w.WriteString(additionalLabelName)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = w.WriteString(`="`)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		n, err = writeFloat(w, additionalLabelValue)
+		written += n
+		if err != nil {
+			return written, err
+		}
+		err = w.WriteByte('"')
+		written++
+		if err != nil {
+			return written, err
+		}
+	}
+	err := w.WriteByte('}')
+	written++
+	if err != nil {
+		return written, err
+	}
+	return written, nil
+}
+
+// writeEscapedString replaces '\' by '\\', new line character by '\n', and - if
+// includeDoubleQuote is true - '"' by '\"'.
+var (
+	escaper       = strings.NewReplacer("\\", `\\`, "\n", `\n`)
+	quotedEscaper = strings.NewReplacer("\\", `\\`, "\n", `\n`, "\"", `\"`)
+)
+
+func writeEscapedString(w enhancedWriter, v string, includeDoubleQuote bool) (int, error) {
+	if includeDoubleQuote {
+		return quotedEscaper.WriteString(w, v)
+	}
+	return escaper.WriteString(w, v)
+}
+
+// writeFloat is equivalent to fmt.Fprint with a float64 argument but hardcodes
+// a few common cases for increased efficiency. For non-hardcoded cases, it uses
+// strconv.AppendFloat to avoid allocations, similar to writeInt.
+func writeFloat(w enhancedWriter, f float64) (int, error) {
+	switch {
+	case f == 1:
+		return 1, w.WriteByte('1')
+	case f == 0:
+		return 1, w.WriteByte('0')
+	case f == -1:
+		return w.WriteString("-1")
+	case math.IsNaN(f):
+		return w.WriteString("NaN")
+	case math.IsInf(f, +1):
+		return w.WriteString("+Inf")
+	case math.IsInf(f, -1):
+		return w.WriteString("-Inf")
+	default:
+		bp := numBufPool.Get().(*[]byte)
+		*bp = strconv.AppendFloat((*bp)[:0], f, 'g', -1, 64)
+		written, err := w.Write(*bp)
+		numBufPool.Put(bp)
+		return written, err
+	}
+}
+
+// writeInt is equivalent to fmt.Fprint with an int64 argument but uses
+// strconv.AppendInt with a byte slice taken from a sync.Pool to avoid
+// allocations.
+func writeInt(w enhancedWriter, i int64) (int, error) {
+	bp := numBufPool.Get().(*[]byte)
+	*bp = strconv.AppendInt((*bp)[:0], i, 10)
+	written, err := w.Write(*bp)
+	numBufPool.Put(bp)
+	return written, err
+}
+
+// writeName writes a string as-is if it complies with the legacy naming
+// scheme, or escapes it in double quotes if not.
+func writeName(w enhancedWriter, name string) (int, error) {
+	if model.LegacyValidation.IsValidMetricName(name) {
+		return w.WriteString(name)
+	}
+	var written int
+	var err error
+	err = w.WriteByte('"')
+	written++
+	if err != nil {
+		return written, err
+	}
+	var n int
+	n, err = writeEscapedString(w, name, true)
+	written += n
+	if err != nil {
+		return written, err
+	}
+	err = w.WriteByte('"')
+	written++
+	return written, err
+}