func (t *Tracer) Inject(ctx opentracing.SpanContext, format interface{}, carrier interface{}) error {
	c, ok := ctx.(SpanContext)
	if !ok {
		return opentracing.ErrInvalidSpanContext
	}
	if injector, ok := t.injectors[format]; ok {
		return injector.Inject(c, carrier)
	}
	return opentracing.ErrUnsupportedFormat
}
Inject implements Inject() method of opentracing.Tracer
package jaeger
import (
	"fmt"
	"io"
	"os"
	"reflect"
	"strconv"
	"sync"
	"time"
	"github.com/opentracing/opentracing-go"
	"github.com/opentracing/opentracing-go/ext"
	"github.com/uber/jaeger-client-go/internal/baggage"
	"github.com/uber/jaeger-client-go/internal/throttler"
	"github.com/uber/jaeger-client-go/log"
	"github.com/uber/jaeger-client-go/utils"
)
type Tracer struct {
	serviceName string
	hostIPv4    uint32  
	sampler  Sampler
	reporter Reporter
	metrics  Metrics
	logger   log.Logger
	timeNow      func() time.Time
	randomNumber func() uint64
	options struct {
		poolSpans            bool
		gen128Bit            bool  
		zipkinSharedRPCSpan  bool
		highTraceIDGenerator func() uint64  
		maxTagValueLength    int
	}
	spanPool sync.Pool
	injectors  map[interface{}]Injector
	extractors map[interface{}]Extractor
	observer compositeObserver
	tags    []Tag
	process Process
	baggageRestrictionManager baggage.RestrictionManager
	baggageSetter             *baggageSetter
	debugThrottler throttler.Throttler
}
func NewTracer(
	serviceName string,
	sampler Sampler,
	reporter Reporter,
	options ...TracerOption,
) (opentracing.Tracer, io.Closer) {
	t := &Tracer{
		serviceName: serviceName,
		sampler:     sampler,
		reporter:    reporter,
		injectors:   make(map[interface{}]Injector),
		extractors:  make(map[interface{}]Extractor),
		metrics:     *NewNullMetrics(),
		spanPool: sync.Pool{New: func() interface{} {
			return &Span{}
		}},
	}
	for _, option := range options {
		option(t)
	}
	textPropagator := newTextMapPropagator(getDefaultHeadersConfig(), t.metrics)
	t.addCodec(opentracing.TextMap, textPropagator, textPropagator)
	httpHeaderPropagator := newHTTPHeaderPropagator(getDefaultHeadersConfig(), t.metrics)
	t.addCodec(opentracing.HTTPHeaders, httpHeaderPropagator, httpHeaderPropagator)
	binaryPropagator := newBinaryPropagator(t)
	t.addCodec(opentracing.Binary, binaryPropagator, binaryPropagator)
	interopPropagator := &jaegerTraceContextPropagator{tracer: t}
	t.addCodec(SpanContextFormat, interopPropagator, interopPropagator)
	zipkinPropagator := &zipkinPropagator{tracer: t}
	t.addCodec(ZipkinSpanFormat, zipkinPropagator, zipkinPropagator)
	if t.baggageRestrictionManager != nil {
		t.baggageSetter = newBaggageSetter(t.baggageRestrictionManager, &t.metrics)
	} else {
		t.baggageSetter = newBaggageSetter(baggage.NewDefaultRestrictionManager(0), &t.metrics)
	}
	if t.debugThrottler == nil {
		t.debugThrottler = throttler.DefaultThrottler{}
	}
	if t.randomNumber == nil {
		rng := utils.NewRand(time.Now().UnixNano())
		t.randomNumber = func() uint64 {
			return uint64(rng.Int63())
		}
	}
	if t.timeNow == nil {
		t.timeNow = time.Now
	}
	if t.logger == nil {
		t.logger = log.NullLogger
	}
	t.tags = append(t.tags, Tag{key: JaegerClientVersionTagKey, value: JaegerClientVersion})
	if hostname, err := os.Hostname(); err == nil {
		t.tags = append(t.tags, Tag{key: TracerHostnameTagKey, value: hostname})
	}
	if ip, err := utils.HostIP(); err == nil {
		t.tags = append(t.tags, Tag{key: TracerIPTagKey, value: ip.String()})
		t.hostIPv4 = utils.PackIPAsUint32(ip)
	} else {
		t.logger.Error("Unable to determine this host's IP address: " + err.Error())
	}
	if t.options.gen128Bit {
		if t.options.highTraceIDGenerator == nil {
			t.options.highTraceIDGenerator = t.randomNumber
		}
	} else if t.options.highTraceIDGenerator != nil {
		t.logger.Error("Overriding high trace ID generator but not generating " +
			"128 bit trace IDs, consider enabling the \"Gen128Bit\" option")
	}
	if t.options.maxTagValueLength == 0 {
		t.options.maxTagValueLength = DefaultMaxTagValueLength
	}
	t.process = Process{
		Service: serviceName,
		UUID:    strconv.FormatUint(t.randomNumber(), 16),
		Tags:    t.tags,
	}
	if throttler, ok := t.debugThrottler.(ProcessSetter); ok {
		throttler.SetProcess(t.process)
	}
	return t, t
}
func (t *Tracer) addCodec(format interface{}, injector Injector, extractor Extractor) {
	if _, ok := t.injectors[format]; !ok {
		t.injectors[format] = injector
	}
	if _, ok := t.extractors[format]; !ok {
		t.extractors[format] = extractor
	}
}
func (t *Tracer) StartSpan(
	operationName string,
	options ...opentracing.StartSpanOption,
) opentracing.Span {
	sso := opentracing.StartSpanOptions{}
	for _, o := range options {
		o.Apply(&sso)
	}
	return t.startSpanWithOptions(operationName, sso)
}
func (t *Tracer) startSpanWithOptions(
	operationName string,
	options opentracing.StartSpanOptions,
) opentracing.Span {
	if options.StartTime.IsZero() {
		options.StartTime = t.timeNow()
	}
	isValidReference := func(ctx SpanContext) bool {
		return ctx.IsValid() || ctx.isDebugIDContainerOnly() || len(ctx.baggage) != 0
	}
	var references []Reference
	var parent SpanContext
	var hasParent bool  
	for _, ref := range options.References {
		ctx, ok := ref.ReferencedContext.(SpanContext)
		if !ok {
			t.logger.Error(fmt.Sprintf(
				"Reference contains invalid type of SpanReference: %s",
				reflect.ValueOf(ref.ReferencedContext)))
			continue
		}
		if !isValidReference(ctx) {
			continue
		}
		references = append(references, Reference{Type: ref.Type, Context: ctx})
		if !hasParent {
			parent = ctx
			hasParent = ref.Type == opentracing.ChildOfRef
		}
	}
	if !hasParent && isValidReference(parent) {
		hasParent = true
	}
	rpcServer := false
	if v, ok := options.Tags[ext.SpanKindRPCServer.Key]; ok {
		rpcServer = (v == ext.SpanKindRPCServerEnum || v == string(ext.SpanKindRPCServerEnum))
	}
	var samplerTags []Tag
	var ctx SpanContext
	newTrace := false
	if !hasParent || !parent.IsValid() {
		newTrace = true
		ctx.traceID.Low = t.randomID()
		if t.options.gen128Bit {
			ctx.traceID.High = t.options.highTraceIDGenerator()
		}
		ctx.spanID = SpanID(ctx.traceID.Low)
		ctx.parentID = 0
		ctx.flags = byte(0)
		if hasParent && parent.isDebugIDContainerOnly() && t.isDebugAllowed(operationName) {
			ctx.flags |= (flagSampled | flagDebug)
			samplerTags = []Tag{{key: JaegerDebugHeader, value: parent.debugID}}
		} else if sampled, tags := t.sampler.IsSampled(ctx.traceID, operationName); sampled {
			ctx.flags |= flagSampled
			samplerTags = tags
		}
	} else {
		ctx.traceID = parent.traceID
		if rpcServer && t.options.zipkinSharedRPCSpan {
			ctx.spanID = parent.spanID
			ctx.parentID = parent.parentID
		} else {
			ctx.spanID = SpanID(t.randomID())
			ctx.parentID = parent.spanID
		}
		ctx.flags = parent.flags
	}
	if hasParent {
		if l := len(parent.baggage); l > 0 {
			ctx.baggage = make(map[string]string, len(parent.baggage))
			for k, v := range parent.baggage {
				ctx.baggage[k] = v
			}
		}
	}
	sp := t.newSpan()
	sp.context = ctx
	sp.observer = t.observer.OnStartSpan(sp, operationName, options)
	return t.startSpanInternal(
		sp,
		operationName,
		options.StartTime,
		samplerTags,
		options.Tags,
		newTrace,
		rpcServer,
		references,
	)
}