func (p *textMapPropagator) addBaggageKeyPrefix(key string) string {
	return fmt.Sprintf("%v%v", p.headerKeys.TraceBaggageHeaderPrefix, key)
}
Converts a baggage item key into an http header format,
by prepending TraceBaggageHeaderPrefix and encoding the key string
package jaeger
import (
	"bytes"
	"encoding/binary"
	"fmt"
	"io"
	"log"
	"net/url"
	"strings"
	"sync"
	opentracing "github.com/opentracing/opentracing-go"
)
type Injector interface {
	Inject(ctx SpanContext, carrier interface{}) error
}
type Extractor interface {
	Extract(carrier interface{}) (SpanContext, error)
}
type textMapPropagator struct {
	headerKeys  *HeadersConfig
	metrics     Metrics
	encodeValue func(string) string
	decodeValue func(string) string
}
func newTextMapPropagator(headerKeys *HeadersConfig, metrics Metrics) *textMapPropagator {
	return &textMapPropagator{
		headerKeys: headerKeys,
		metrics:    metrics,
		encodeValue: func(val string) string {
			return val
		},
		decodeValue: func(val string) string {
			return val
		},
	}
}
func newHTTPHeaderPropagator(headerKeys *HeadersConfig, metrics Metrics) *textMapPropagator {
	return &textMapPropagator{
		headerKeys: headerKeys,
		metrics:    metrics,
		encodeValue: func(val string) string {
			return url.QueryEscape(val)
		},
		decodeValue: func(val string) string {
			if v, err := url.QueryUnescape(val); err == nil {
				return v
			}
			return val
		},
	}
}
type binaryPropagator struct {
	tracer  *Tracer
	buffers sync.Pool
}
func newBinaryPropagator(tracer *Tracer) *binaryPropagator {
	return &binaryPropagator{
		tracer:  tracer,
		buffers: sync.Pool{New: func() interface{} { return &bytes.Buffer{} }},
	}
}
func (p *textMapPropagator) Inject(
	sc SpanContext,
	abstractCarrier interface{},
) error {
	textMapWriter, ok := abstractCarrier.(opentracing.TextMapWriter)
	if !ok {
		return opentracing.ErrInvalidCarrier
	}
	textMapWriter.Set(p.headerKeys.TraceContextHeaderName, sc.String())
	for k, v := range sc.baggage {
		safeKey := p.addBaggageKeyPrefix(k)
		safeVal := p.encodeValue(v)
		textMapWriter.Set(safeKey, safeVal)
	}
	return nil
}
func (p *textMapPropagator) Extract(abstractCarrier interface{}) (SpanContext, error) {
	textMapReader, ok := abstractCarrier.(opentracing.TextMapReader)
	if !ok {
		return emptyContext, opentracing.ErrInvalidCarrier
	}
	var ctx SpanContext
	var baggage map[string]string
	err := textMapReader.ForeachKey(func(rawKey, value string) error {
		key := strings.ToLower(rawKey)  
		if key == p.headerKeys.TraceContextHeaderName {
			var err error
			safeVal := p.decodeValue(value)
			if ctx, err = ContextFromString(safeVal); err != nil {
				return err
			}
		} else if key == p.headerKeys.JaegerDebugHeader {
			ctx.debugID = p.decodeValue(value)
		} else if key == p.headerKeys.JaegerBaggageHeader {
			if baggage == nil {
				baggage = make(map[string]string)
			}
			for k, v := range p.parseCommaSeparatedMap(value) {
				baggage[k] = v
			}
		} else if strings.HasPrefix(key, p.headerKeys.TraceBaggageHeaderPrefix) {
			if baggage == nil {
				baggage = make(map[string]string)
			}
			safeKey := p.removeBaggageKeyPrefix(key)
			safeVal := p.decodeValue(value)
			baggage[safeKey] = safeVal
		}
		return nil
	})
	if err != nil {
		p.metrics.DecodingErrors.Inc(1)
		return emptyContext, err
	}
	if !ctx.traceID.IsValid() && ctx.debugID == "" && len(baggage) == 0 {
		return emptyContext, opentracing.ErrSpanContextNotFound
	}
	ctx.baggage = baggage
	return ctx, nil
}
func (p *binaryPropagator) Inject(
	sc SpanContext,
	abstractCarrier interface{},
) error {
	carrier, ok := abstractCarrier.(io.Writer)
	if !ok {
		return opentracing.ErrInvalidCarrier
	}
	if err := binary.Write(carrier, binary.BigEndian, sc.traceID); err != nil {
		return err
	}
	if err := binary.Write(carrier, binary.BigEndian, sc.spanID); err != nil {
		return err
	}
	if err := binary.Write(carrier, binary.BigEndian, sc.parentID); err != nil {
		return err
	}
	if err := binary.Write(carrier, binary.BigEndian, sc.flags); err != nil {
		return err
	}
	if err := binary.Write(carrier, binary.BigEndian, int32(len(sc.baggage))); err != nil {
		return err
	}
	for k, v := range sc.baggage {
		if err := binary.Write(carrier, binary.BigEndian, int32(len(k))); err != nil {
			return err
		}
		io.WriteString(carrier, k)
		if err := binary.Write(carrier, binary.BigEndian, int32(len(v))); err != nil {
			return err
		}
		io.WriteString(carrier, v)
	}
	return nil
}
func (p *binaryPropagator) Extract(abstractCarrier interface{}) (SpanContext, error) {
	carrier, ok := abstractCarrier.(io.Reader)
	if !ok {
		return emptyContext, opentracing.ErrInvalidCarrier
	}
	var ctx SpanContext
	if err := binary.Read(carrier, binary.BigEndian, &ctx.traceID); err != nil {
		return emptyContext, opentracing.ErrSpanContextCorrupted
	}
	if err := binary.Read(carrier, binary.BigEndian, &ctx.spanID); err != nil {
		return emptyContext, opentracing.ErrSpanContextCorrupted
	}
	if err := binary.Read(carrier, binary.BigEndian, &ctx.parentID); err != nil {
		return emptyContext, opentracing.ErrSpanContextCorrupted
	}
	if err := binary.Read(carrier, binary.BigEndian, &ctx.flags); err != nil {
		return emptyContext, opentracing.ErrSpanContextCorrupted
	}
	var numBaggage int32
	if err := binary.Read(carrier, binary.BigEndian, &numBaggage); err != nil {
		return emptyContext, opentracing.ErrSpanContextCorrupted
	}
	if iNumBaggage := int(numBaggage); iNumBaggage > 0 {
		ctx.baggage = make(map[string]string, iNumBaggage)
		buf := p.buffers.Get().(*bytes.Buffer)
		defer p.buffers.Put(buf)
		var keyLen, valLen int32
		for i := 0; i < iNumBaggage; i++ {
			if err := binary.Read(carrier, binary.BigEndian, &keyLen); err != nil {
				return emptyContext, opentracing.ErrSpanContextCorrupted
			}
			buf.Reset()
			buf.Grow(int(keyLen))
			if n, err := io.CopyN(buf, carrier, int64(keyLen)); err != nil || int32(n) != keyLen {
				return emptyContext, opentracing.ErrSpanContextCorrupted
			}
			key := buf.String()
			if err := binary.Read(carrier, binary.BigEndian, &valLen); err != nil {
				return emptyContext, opentracing.ErrSpanContextCorrupted
			}
			buf.Reset()
			buf.Grow(int(valLen))
			if n, err := io.CopyN(buf, carrier, int64(valLen)); err != nil || int32(n) != valLen {
				return emptyContext, opentracing.ErrSpanContextCorrupted
			}
			ctx.baggage[key] = buf.String()
		}
	}
	return ctx, nil
}
func (p *textMapPropagator) parseCommaSeparatedMap(value string) map[string]string {
	baggage := make(map[string]string)
	value, err := url.QueryUnescape(value)
	if err != nil {
		log.Printf("Unable to unescape %s, %v", value, err)
		return baggage
	}
	for _, kvpair := range strings.Split(value, ",") {
		kv := strings.Split(strings.TrimSpace(kvpair), "=")
		if len(kv) == 2 {
			baggage[kv[0]] = kv[1]
		} else {
			log.Printf("Malformed value passed in for %s", p.headerKeys.JaegerBaggageHeader)
		}
	}
	return baggage
}