01.yaml

---
version: 1
interactions:
- request:
    body: ""
    form: {}
    headers: {}
    url: https://httpbin.org/headers
    method: GET
  response:
    body: "{\n  \"headers\": {\n    \"Accept-Encoding\": \"gzip\", \n    \"Host\": \"httpbin.org\", \n    \"User-Agent\": \"Go-http-client/2.0\", \n    \"X-Amzn-Trace-Id\": \"Root=1-5f36b69c-c5b786ff21a06da51a757764\"\n  }\n}\n"
    headers:
      Access-Control-Allow-Credentials:
      - "true"
      Access-Control-Allow-Origin:
      - '*'
      Content-Length:
      - "190"
      Content-Type:
      - application/json
      Date:
      - Fri, 14 Aug 2020 16:06:52 GMT
      Server:
      - gunicorn/19.9.0
    status: 200 OK
    code: 200
    duration: ""

main01.go

package main

import (
	"io"
	"log"
	"net/http"
	"os"
	"time"

	"github.com/dnaeon/go-vcr/cassette"
	"github.com/dnaeon/go-vcr/recorder"
)

func main() {
	if err := run(); err != nil {
		log.Fatalf("!%+v", err)
	}
}

func run() error {
	r, err := recorder.New("fixtures/01")
	if err != nil {
		return err
	}
	defer r.Stop()

	// 此処は省略可能
	{
		r.AddFilter(func(i *cassette.Interaction) error {
			delete(i.Request.Headers, "Authorization")
			return nil
		})
		r.AddPassthrough(func(req *http.Request) bool {
			return req.URL.Path == "/login"
		})
	}

	client := &http.Client{
		Transport: r,
		Timeout:   3 * time.Second,
	}

	url := os.Getenv("URL")
	res, err := client.Get(url)
	if err != nil {
		return err
	}
	if _, err := io.Copy(os.Stdout, res.Body); err != nil {
		return err
	}
	defer res.Body.Close()
	return nil
}

Makefile

export URL ?= https://httpbin.org/headers

01:
	go run main.go