Returning binary body and http headers from an AWS lambda through API gateway

Question

I have a lambda that needs to return a binary object and some http headers (e.g. content-type) through an api gateway (using lambda integration) OR redirect to another URL. In the binary support examples (e.g. https://aws.amazon.com/blogs/compute/binary-support-for-api-integrations-with-amazon-api-gateway/) the lambda only returns the (base64 of the) binary object (the image). In my case, I also need to return a status code and http headers (or something equivalent). I struggle with how I can make this work with binary support in api gateway.

The lambda returns a json on this form:

{
  "statusCode": 200,
  "headers": {
    "content-type": "image/jpeg"
  },
  "body": "/9j/4AAQS...gLDAoKCAwZK",
  "isBase64Encoded": true
}

In the integration response I add body mappings for image/jpeg (etc) of the form:

$input.json('$.body')

And header mapping for 'content-type' like so:

integration.response.body.headers['content-type']

I've tried many variations of the above, but the result is consistently

Execution failed due to configuration error: Unable to transform response

How do I transform the json from the lambda into a form that can be converted to binary by the api gateway, with http headers and all? Can I get more debug logging out of the api gateway to show more specific what it is unhappy with?

Is there perhaps a way to get more debug logging out of the api gateway?

No. Sorry. Instead I returned a redirect to another lambda that only returned binary objects. So, several lambdas. Clumsy, but works- — simon
I did get this working. Works great in fact. As long as you configure the resource as a proxy resource and ensure that your accept mime type matches the Binary Media Types setting in Settings for your API (in api gateway). — Michael Wiles

movermeyer movermeyer · Accepted Answer · 2018-03-20T20:26:20

I recently got this working after facing a similar problem.

In my case, I was missing two things:

First, I needed to change the list of types AWS will send to the upstream in the "Accept" header"

"x-amazon-apigateway-binary-media-types" : [
  "image/jpeg"
]

Secondly, I needed to set the Integration Response to "Convert to binary (if needed)":

"contentHandling": "CONVERT_TO_BINARY"

See this answer for the details, and sample config.

I also found that I wasn't being patient enough. Whenever I deployed the API, I was checking immediately, instead of waiting a few minutes for the changes to propagate.

Returning binary body and http headers from an AWS lambda through API gateway

3 Answers