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Coach: An alternative to Rails controllers

Today we're open sourcing Coach, a library that removes the complexity from Rails controllers. Bundle your shared behaviour into highly robust, heavily tested middlewares and rely on Coach to join them together, providing static analysis over the entire chain. Coach ensures you only require a glance to see what's being run on each controller endpoint.

At GoCardless we've replaced all our controller code with Coach middlewares.

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Safely retrying API requests

Today we're announcing support for idempotency keys on our Pro API, which make it safe to retry non-idempotent API requests.

Why are they necessary?

Here's an example that illustrates the purpose of idempotency keys.

You submit a POST request to our /payments endpoint to create a payment. If all goes well, you'll receive a 201 Created response. If the request is invalid, you'll receive a 4xx response, and know that the payment wasn't created. But what if something goes wrong our end and we issue a 500 response? Or what if there's a network issue that means you get no response at all? In these cases you have no way of knowing whether or not the payment was created. This leaves you with two options:

  • Hope the request succeeded, and take no further action.
  • Assume the request failed, and retry it. However, if the request did succeed you'll end up with a duplicate payment.

Not an ideal situation.

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