Your API sucks : Error handling

Exceptional validation

So many places I’ve seen throw an exception for the first validation error they encounter:

HTTP 500 - Credit Card number invalid

When I see that, I need to make multiple calls before I can see what’s wrong. If you’re going to validate, try and validate everything beyond authentication in one shot, like this:

HTTP 400

{
    validationErrors: [
        {"CreditCardNumber" : "Must be 16 characters"}
        {"ExpiryDate" : "Must be in the future"}
        {"CCV" : "Is required"}
    ]
}

Success : ERROR

If something went wrong, make it obvious. On the web, use a 4xx or 5xx status code, instead of a 200 OK. In code, throw an exception. This isn’t C, we don’t need to rely on errno any more. If I see success, I want valid data. Parsing your error messages isn’t part of the deal. Especially if they have spelling mistakes.

Illegal characters

If I see that your API won’t let me have O’Malley as a name, or Flat 1/2 as an address, I will immediately start thinking of Bobby Tables, and I will assume you have a poor encoding excuse at your backend. If you can’t handle that, you shouldn’t be writing an API. As the security sucks said, you should not be my weakest link.

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