logging GCS RequestResponse header and body in golang

tracer.go

package main

import (
	"bytes"
	"fmt"
	"io/ioutil"
	"log"
	"mime/multipart"
	"net/http"

	storage "cloud.google.com/go/storage"
	"golang.org/x/net/context"
	"golang.org/x/oauth2/google"
	"google.golang.org/api/option"
)

const (
	bucketName = "your-bucket"
)

var (
	body   *bytes.Buffer
	writer *multipart.Writer
)

type wrapped struct {
	base http.RoundTripper
}

func (w wrapped) RoundTrip(r *http.Request) (*http.Response, error) {

	log.Println("=======================================")
	log.Println("[GCS_REQUEST]")
	log.Printf("%v %v", r.Method, r.URL.String())
	for h, values := range r.Header {
		for _, v := range values {
			log.Printf("%v: %v\n", h, v)
		}
	}

	body, err := ioutil.ReadAll(r.Body)
	if err != nil {
		log.Printf("Error reading body: %v", err)
		return nil, err
	}
	fmt.Printf("%s", string(body))
	r.Body = ioutil.NopCloser(bytes.NewBuffer(body))

	resp, err := w.base.RoundTrip(r)
	log.Printf("[GCS_RESPONSE]\n")
	if err != nil {
		log.Printf("GCS_ERROR: %v", err)
		return resp, err
	}
	for h, values := range resp.Header {
		for _, v := range values {
			log.Printf("%v: %v\n", h, v)
		}
	}
	log.Printf("Response Body: \n")
	body, err = ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Printf("Error reading body: %v", err)
		return resp, err
	}
	fmt.Printf("%s", string(body))
	resp.Body = ioutil.NopCloser(bytes.NewBuffer(body))

	return resp, err
}

func main() {

	ctx := context.Background()

	body = &bytes.Buffer{}
	writer = multipart.NewWriter(body)

	hc, err := google.DefaultClient(ctx)
	if err != nil {
		log.Fatalf("%v", err)
	}
	hc.Transport = wrapped{hc.Transport}

	storageClient, err := storage.NewClient(ctx, option.WithHTTPClient(hc))
	if err != nil {
		fmt.Printf("storage.NewClient: %v", err)
		return
	}
	defer storageClient.Close()

	bkt := storageClient.Bucket(bucketName)

	//https://cloud.google.com/storage/docs/json_api/v1/objects/insert
	names := []string{"foo.txt", "bar.txt"}
	for _, b := range names {
		obj := bkt.Object(b)
		w := obj.NewWriter(ctx)

		if _, err := fmt.Fprintf(w, "foo"); err != nil {
			fmt.Printf("write: %v", err)
			return
		}

		if err := w.Close(); err != nil {
			fmt.Printf("storage. close: %v", err)
			return
		}

		//bkt.Object(b).Delete(ctx)
	}

}