Introducing yakbak: Record and playback HTTP interactions in NodeJS

Did you know that the new Front End of is one big Flickr API client? Writing a client for an existing API or service can be a lot of fun, but decoupling and testing that client can be quite tricky. There are many different approaches to taking the backing service out of the equation when it comes to writing tests for client code. Today we’ll discuss the pros and cons of some of these approaches, describe how the Flickr Front End team tests service-dependent libraries, and introduce you to our new NodeJS HTTP playback module: yakbak!

Scenario: Testing a Flickr API Client

Let’s jump into some code, shall we? Suppose we’re testing a (very, very simple) photo search API client:

Currently, this code will make an HTTP request to the Flickr API on every test run. This is less than desirable for several reasons:

  • UGC is unpredictable. In this test, we’re asserting that the response code is an HTTP 200, but obviously our client code needs to provide the response data to be useful. It’s impossible to write a meaningful and predictable test against live content.
  • Traffic is unpredictable. This photos search API call usually takes ~150ms for simple queries, but a more complex query or a call during peak traffic may take longer.
  • Downtime is unpredictable. Every service has downtime (the term is “four nines,” not “one hundred percent” for a reason), and if your service is down, your client tests will fail.
  • Networks are unpredictable. Have you ever tried coding on a plane? Enough said.

We want our test suite to be consistent, predictable, and fast. We’re also only trying to test our client code, not the API. Let’s take a look at some ways to replace the API with a control, allowing us to predictably test the client code.

Approach 1: Stub the HTTP client methods

We’re using superagent as our HTTP client, so we could use a mocking library like sinon to stub out superagent’s Request methods:

With these changes, we never actually make an HTTP request to the API during a test run. Now our test is predictable, controlled, and it runs crazy fast. However, this approach has some major drawbacks:

  • Tightly coupled with superagent. We’re all up in the client’s implementation details here, so if superagent ever changes their API, we’ll need to correct our tests to match. Likewise, if we ever want to use a different HTTP client, we’ll need to correct our tests as well.
  • Difficult to specify the full HTTP response. Here we’re only specifying the statusCode; what about when we need to specify the body or the headers? Talk about verbose.
  • Not necessarily accurate. We’re trusting the test author to provide a fake response that matches what the actual server would send back. What happens if the API changes the response schema? Some unhappy developer will have to manually update the tests to match reality (probably an intern, let’s be honest).

We’ve at least managed to replace the service with a control in our tests, but we can do (slightly) better.

Approach 2: Mock the NodeJS HTTP module

Every NodeJS HTTP client will eventually delegate to the standard NodeJS http module to perform the network request. This means we can intercept the request at a low level by using a tool like nock:

Great! We’re no longer stubbing out superagent and we can still control the HTTP response. This avoids the HTTP client coupling from the previous step, but still has many similar drawbacks:

  • We’re still completely implementation-dependent. If we want to pass a new query string parameter to our service, for example, we’ll also need to add it to the test so that nock will match the request.
  • It’s still laborious to specify the response headers, body, etc.
  • It’s still difficult to make sure the response body always matches reality.

At this point, it’s worth noting that none of these bullet points were an issue back when we were actually making the HTTP request. So, let’s do exactly that (once!).

Approach 3: Record and playback the HTTP interaction

The Ruby community created the excellent VCR gem for recording and replaying HTTP interactions during tests. Recorded HTTP requests exist as “tapes”, which are just files with some sort of format describing the interaction. The basic workflow goes like this:

  1. The client makes an actual HTTP request.
  2. VCR sits in front of the system’s HTTP library and intercepts the request.
  3. If VCR has a tape matching the request, it simply replays the response to the client.
  4. Otherwise, VCR lets the HTTP request through to the service, records the interaction to a new tape on disk and plays it back to the client.

Introducing yakbak

Today we’re open-sourcing yakbak, our take on recording and playing back HTTP interactions in NodeJS. Here’s what our tests look like with a yakbak proxy:

Here we’ve created a standard NodeJS http.Server with our proxy middleware. We’ve also configured our client to point to the proxy server instead of the origin service. Look, no implementation details!

yakbak tries to do things The Node Way™ wherever possible. For example, each yakbak “tape” is actually its own module that simply exports an http.Server handler, which allows us to do some really cool things. For example, it’s trivial to create a server that always responds a certain way. Since the tape’s hash is based solely on the incoming request, we can easily edit the response however we like. We’re also kicking around a handful of enhancements that should make yakbak an even more powerful development tool.

Thanks to yakbak, we’ve been writing fast, consistent, and reliable tests for our HTTP clients and applications. Want to give it a spin? Check it out today:

P.S. We’re hiring!

Do you love development tooling and helping keep teams on the latest and greatest technology? Or maybe you just want to help build the best home for your photos on the entire internet? We’re hiring Front End Ops and tons of other great positions. We’d love to hear from you!

Flickr API Going SSL-Only on June 27th, 2014

If you read my recent post, you know that the Flickr API fully supports SSL. We’ve already updated our web and mobile apps to use HTTPS, and you no longer need to use “” to access the Flickr API via SSL. Simply update your code to call:

We want communication with Flickr to be secure, all the time. So, we are tightening things up. Effective this week, all new API keys will work via HTTPS only. On June 27th, we will deprecate non-SSL access to the API. If you haven’t already made the change to HTTPS, now is the time!

Blackout Tests

In preparation for the June 27th cut-off date, we will run two “blackout” tests, each for 2 hours, so that you can ensure that API calls in your app no longer use HTTP. If you have changed your code to use HTTPS, your app should function normally during the blackout window. If you have not changed your code to use HTTPS, then during the 2-hr blackout window all API calls from your application will fail. The API will return a 403 status code for non-SSL requests.

Important Dates and Times

  • Change in new API keys:  6 May 2014 (If you request a new API key after 6 May, it will be issued for HTTPS only)
  • First blackout window: 3 June 2014, 10:00-12:00 Pacific Daylight Time (PDT) / 17:00-19:00 GMT
  • Second blackout window: 17 June 2014, 18:00-20:00 (PDT) / 18 June 2014, 01:00-03:00 GMT
  • Non-SSL calls deprecated: 27 June 2014, 10:00 (PDT) / 17:00 GMT

More About the Flickr API Endpoints

In the API documentation, all of the endpoints have been updated to HTTPS. While OAuth adds security by removing the need to authenticate by username and password, sending all traffic over SSL further protects our users’ data while in transit.

The SSL endpoints for the Flickr API are:

And for uploads:

For applications that use well-established HTTP client libraries, this switch should only require updating the protocol and (maybe) some updated configuration.

We realize that this change might be more difficult for some. We will follow the Developer Support Group closely, so please let us hear your questions. We will respond to them there, and will collect questions of general interest in the below FAQ.

FAQs About the Transition to SSL-Only for the Flickr API

Question:  I only have a Flickr API key because I use an application or plugin that calls the Flickr API.  Will that application or plugin continue to work after June 27th?  Do I need to do something?
Answer:  An application or plugin that calls the Flickr API will stop working on June 27th if its owner does not make the changes we’ve described above.  There are many, many providers of such services and plugins.  We have notified them about this transition via email, blog post, developer lists, and on Twitter.  As a user of such a service or plugin, you have no action to do for the transition unless the application or plugin owner asks you to upgrade to a new version.  You also have the option to reach out to the application or plugin owner to assure yourself of their plans to handle this transition.

Question: Are all urls going to be HTTPS from now on?
Answer: Yes, all urls returned by the API are now HTTPS, and all requests to HTTP in the browser are redirected to HTTPS.

Question: Should I switch my code to HTTPS right away or should I wait a bit?
Answer: Switch now. The important thing is for your app to be changed to HTTPS before the first blackout on 3 June 2014. In fact, if your app is a mobile app, the earlier the better, so that your users will be more likely to upgrade before the first blackout.

Question:  Do I need a new API key to replace my old one for this transition?
Answer:  No, you don’t need a new API key for this transition.  You keep your existing key, and you change the code where you call the Flickr API, so that you call it with the HTTPS protocol, instead of HTTP. Change it to this:

Question:  What do I do with the new API key that is being issued by Flickr as of May 6?
Answer:  We are not automatically issuing a new key to you.  What happened on 6 May was a change to how we handle new API keys.  From now on, if you submit a request for a new key, that new key will only support calls to the Flickr API over HTTPS; it will not support calls to the API over HTTP.  You do not need to request a new API key for this transition.

Question:  I received your email about the API going SSL-only on June 27th.  Do I need to do something?
Answer:  Maybe not.  If you already call the API over HTTPS, then you’re good.  No action needed.  But if your code currently calls the API over HTTP, then, YES, you do need to do something.  In your code you need to change the protocol to HTTPS.  Like this:

Question: If I use a protocol-less call to the API or match the protocol of the page that is making the call, do I need to change anything?  
Yes, you should change your calls to specifically use HTTPS. During the blackout period and starting on June 27th, protocol-less calls to the Flickr API from non-SSL pages will fail.

Question:  Will the old endpoints continue to be supported in addition to the new endpoints, or will only the latter be supported?
Answer:  Yes, endpoints will still be supported.  If you use that today, your application will continue to work during the blackout windows and after 27 June.

Posted in API

New SSL Endpoints for the Flickr API

Sometime in the last few months, we went and updated our API SSL endpoints. Shame on us for not making a bigger deal about it!

In the past, to access the Flickr API via SSL you needed to use the “” subdomain… Not anymore!

Now calling the API via SSL is as easy as updating your code to call:

In fact, it’s so easy that we want everyone to use it.

You’ll notice in the API documentation that all of the endpoints have been updated to https. While OAuth adds security by removing the need to authenticate by username and password, sending all traffic over SSL will further protect our users’ data while in transit.

The SSL endpoints for the Flickr API are:

And for uploads:

Later this year we will be migrating the Flickr API to SSL access only. We’ll let you know the exact date in advance, and will run a blackout test before the big day. For applications that use well established HTTP client libraries, this should only require updating the protocol and (maybe) some updated configuration. We’ll also be working with API kit developers, so updating many apps will be a git pull away.

Of course we realize that this change might be more difficult for some. We’ll be following the Developer Support Group closely, so please let us hear your questions, comments, and concerns.

This is the first step of many improvements that we’ll be making to the API and our developer tools this year, and we’ll post additional details and timelines as we go. Want to help? We’re hiring!