func FromHTTPRequest(tracer opentracing.Tracer, operationName string, logger log.Logger) kithttp.RequestFunc {
	return func(ctx context.Context, req *http.Request) context.Context {
		var span opentracing.Span
		wireContext, err := tracer.Extract(
			opentracing.TextMap,
			opentracing.HTTPHeadersCarrier(req.Header),
		)
		if err != nil && err != opentracing.ErrSpanContextNotFound {
			logger.Log("err", err)
		}
		span = tracer.StartSpan(operationName, ext.RPCServerOption(wireContext))
		ext.HTTPMethod.Set(span, req.Method)
		ext.HTTPUrl.Set(span, req.URL.String())
		return opentracing.ContextWithSpan(ctx, span)
	}
}
FromHTTPRequest returns an http RequestFunc that tries to join with an
OpenTracing trace found in `req` and starts a new Span called
`operationName` accordingly. If no trace could be found in `req`, the Span
will be a trace root. The Span is incorporated in the returned Context and
can be retrieved with opentracing.SpanFromContext(ctx).
package opentracing
import (
	"context"
	"net"
	"net/http"
	"strconv"
	"github.com/opentracing/opentracing-go"
	"github.com/opentracing/opentracing-go/ext"
	"github.com/go-kit/kit/log"
	kithttp "github.com/go-kit/kit/transport/http"
)
func ToHTTPRequest(tracer opentracing.Tracer, logger log.Logger) kithttp.RequestFunc {
	return func(ctx context.Context, req *http.Request) context.Context {
		if span := opentracing.SpanFromContext(ctx); span != nil {
			ext.HTTPMethod.Set(span, req.Method)
			ext.HTTPUrl.Set(span, req.URL.String())
			host, portString, err := net.SplitHostPort(req.URL.Host)
			if err == nil {
				ext.PeerHostname.Set(span, host)
				if port, err := strconv.Atoi(portString); err != nil {
					ext.PeerPort.Set(span, uint16(port))
				}
			} else {
				ext.PeerHostname.Set(span, req.URL.Host)
			}
			if err = tracer.Inject(
				span.Context(),
				opentracing.TextMap,
				opentracing.HTTPHeadersCarrier(req.Header),
			); err != nil {
				logger.Log("err", err)
			}
		}
		return ctx
	}
}