dnaeon/go-vcr

go-vcr simplifies testing by recording your HTTP interactions and replaying them in future runs in order to provide fast, deterministic and accurate testing of your code.

go-vcr was inspired by the VCR library for Ruby.

Install go-vcr by executing the command below:

$ go get -v gopkg.in/dnaeon/go-vcr.v3/recorder

Note, that if you are migrating from a previous version of go-vcr, you need re-create your test cassettes, because as of go-vcr v3 there is a new format of the cassette, which is not backwards-compatible with older releases.

Please check the examples from this repo for example usage of go-vcr.

You can also refer to the test cases for additional examples.

During replay mode, You can customize the way incoming requests are matched against the recorded request/response pairs by defining a MatcherFunc function.

For example, the following matcher will match on method, URL and body:

func customMatcher(r *http.Request, i cassette.Request) bool {
	if r.Body == nil || r.Body == http.NoBody {
		return cassette.DefaultMatcher(r, i)
	}

	var reqBody []byte
	var err error
	reqBody, err = io.ReadAll(r.Body)
	if err != nil {
		log.Fatal("failed to read request body")
	}
	r.Body.Close()
	r.Body = ioutil.NopCloser(bytes.NewBuffer(reqBody))

	return r.Method == i.Method && r.URL.String() == i.URL && string(reqBody) == i.Body
}

func recorderWithCustomMatcher() {
	rec, err := recorder.New("fixtures/matchers")
	if err != nil {
		log.Fatal(err)
	}
	defer rec.Stop() // Make sure recorder is stopped once done with it

	rec.SetReplayableInteractions(true)
	rec.SetMatcher(customMatcher)

	client := rec.GetDefaultClient()
	resp, err := client.Get("https://www.google.com/")
	...
	...
	...
}

Hooks in go-vcr are regular functions which take an HTTP interaction and are invoked in different stages of the playback.

You can use hooks to modify a request/response before it is saved on disk, before it is returned to the client, or anything else that you might want to do with it, e.g. you might want to simply log each captured interaction.

You often provide sensitive data, such as API credentials, when making requests against a service.

By default, this data will be stored in the recorded data but you probably don't want this.

Removing or replacing data before it is stored can be done by adding one or more Hooks to your Recorder.

There are different kinds of hooks, which are invoked in different stages of the playback. The supported hook kinds are AfterCaptureHook, BeforeSaveHook and BeforeResponseReplayHook.

Here is an example that removes the Authorization header from all requests right after capturing a new interaction.

r, err := recorder.New("fixtures/filters")
if err != nil {
	log.Fatal(err)
}
defer r.Stop() // Make sure recorder is stopped once done with it

// Add a hook which removes Authorization headers from all requests
hook := func(i *cassette.Interaction) error {
	delete(i.Request.Headers, "Authorization")
	return nil
}
r.AddHook(hook, recorder.AfterCaptureHook)

Hooks added using recorder.AfterCaptureHook are applied right after an interaction is captured and added to the in-memory cassette. This may not always be what you need. For example if you modify an interaction using this hook kind then subsequent test code will see the edited response.

For instance, if a response body contains an OAuth access token that is needed for subsequent requests, then redacting the access token using a AfterCaptureHook will result in authorization failures in subsequent test code.

In such cases you would want to modify the recorded interactions right before they are saved on disk. For that purpose you should be using a BeforeSaveHook, e.g.

r, err := recorder.New("fixtures/filters")
if err != nil {
	log.Fatal(err)
}
defer r.Stop() // Make sure recorder is stopped once done with it

// Your test code will continue to see the real access token and
// it is redacted before the recorded interactions are saved on disk
hook := func(i *cassette.Interaction) error {
	if strings.Contains(i.Request.URL, "/oauth/token") {
		i.Response.Body = `{"access_token": "[REDACTED]"}`
	}

	return nil
}
r.AddHook(hook, recorder.BeforeSaveHook)

Sometimes you want to allow specific requests to pass through to the remote server without recording anything.

Globally, you can use ModePassthrough for this, but if you want to disable the recorder for individual requests, you can add Passthrough handlers to the recorder.

The function takes a pointer to the original request, and returns a boolean, indicating if the request should pass through to the remote server.

Here's an example to pass through requests to a specific endpoint:

// Passthrough the request to the remote server if the path matches "/login".
r.AddPassthrough(func(req *http.Request) bool {
    return req.URL.Path == "/login"
})

go-vcr is Open Source and licensed under the BSD License