AWS Api Gateway response mapping regex not working

Question

I'm trying to do a mapping from AWS lambda function response using regex. This is my regex: .*statusCode”:406.*

As you can see - I am trying for it to take a specific mapping from the following response:

{
  "statusCode": 406,
  "body": "{\"aerocrs\":{\"success\":false,\"error_type\":\"request\",\"details\":{\"detail\":\"Incorrect reqyest \",\"errorCode\":4}}}",
  "headers": {
    "x-powered-by": "Express",
    "content-type": "application/json; charset=utf-8",
    "content-length": "116",
    "etag": "W/\"74-Zzo6HU1M1kKkLM9KGtX0jJdePQY\"",
    "date": "Thu, 28 Nov 2019 16:03:05 GMT",
    "connection": "close"
  },
  "isBase64Encoded": false
}

However, I always get to the default mapping. When I change the mapping to .*.*, it gets to the correct one, which makes sense, but for some reason this regex isn't working. Do you have any idea? Thanks!

Formatting ruined everything. The regex is .*statusCode”:406.* — Eldad Corem
– Eldad Corem, Commented Nov 28, 2019 at 16:26

Eldad Corem · Accepted Answer · 2019-11-29 12:44:50Z

I managed to find the issue! Thanks to this great person.

Long story short. AWS Api Gateway is SUPER picky and annoying regarding the error regex. This means, that is looking for a specific structure. Something of this sort:

{
  "errorType": "string",
  "errorMessage": "{\"body\":{\"success\":false,\"error_type\":\"request\",\"details\":{\"errorCode\":4}}}",
  "trace": []
}

So the .*.* does work because it is valid for everything, but even a single letter, like .*s.* is causing an issue. What you need to fix is in your lambda function. In my case - I was using nodeJS function, and aws-serverless-express. The aws-serverless-express is super easy as it works perfectly with express. However, I was using:

awsServerlessExpress.proxy(server, event, context);

Which was enough to return the response ok, but not enough to work with the API gateway's annoying regex. Instead, I changed it to this:

awsServerlessExpress.proxy(server, event, context, 'CALLBACK', function(param1, response){
    if (response.statusCode == 200) {
        //Success
        context.done(response.body);
    }
    else {
        //Fail
        context.fail(response.body);
    }
});

And it worked like a charm. Now I took the response body and return it as success / fail. Then it will work with the format that the lambda function knows how to use.

I hope this will help other people not waste 6 hours on this!

ingernet · Accepted Answer · 2019-11-28 23:10:01Z

0

looks like the output has a space before 406. what happens if you add that space to your regex?

--Edited to add: I use this site all the time (with redacted stuff, naturally) - https://regex101.com/

edited Nov 28, 2019 at 23:10

answered Nov 28, 2019 at 23:00

ingernet

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1 Comment

Eldad Corem Over a year ago

Thanks! But it also didn't work, I tried even to just put .*statusCode*. and it still doesn't recognise it. I have also tried in the site you gave - and it's working. It's something in the gateway I think. Here are screen shots: prnt.sc/q3r9l2 and prnt.sc/q3r9zo and prnt.sc/q3rahx

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