func ServerTags(tags map[string]string) ServerOption {
	return func(h *handler) {
		h.defaultTags = tags
	}
}
ServerTags adds default Tags to inject into server spans.
package http
import (
	"io"
	"net/http"
	"strconv"
	"sync/atomic"
	zipkin "github.com/openzipkin/zipkin-go"
	"github.com/openzipkin/zipkin-go/model"
	"github.com/openzipkin/zipkin-go/propagation/b3"
)
type handler struct {
	tracer          *zipkin.Tracer
	name            string
	next            http.Handler
	tagResponseSize bool
	defaultTags     map[string]string
	requestSampler  RequestSamplerFunc
	errHandler      ErrHandler
}
type ServerOption func(*handler)