You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: decode.go
    path of file: ./repos/streamdal/apps/server/vendor/github.com/prometheus/common/expfmt
    
    the code of the file until where you have to start completion: // 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.
// If the input format does not imply otherwise, a text format decoder is returned.
func NewDecoder(r io.Reader, format Format) Decoder {
	switch format {
	case FmtProtoDelim:
		return &protoDecoder{r: r}
	}
	return &textDecoder{r: 
    
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
			}

			samples = append(samples, &model.Sample{
				Metric:    model.Metric(lset),
				Value:     model.SampleValue(q.GetCumulativeCount()),
				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")

		count := &model.Sample{
			Metric:    model.Metric(lset),
			Value:     model.SampleValue(m.Histogram.GetSampleCount()),
			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
}