AWS APIGateway Integration Response Mapping Templates do not switch correctly based on Content-Type

Question

I am experimenting with an AWS API-Gateway integration with an S3 backend. I have noticed the switch between different mapping-templates in the integration-response does not appear to work.

In integration-response, I have the following mapping templates:

application/json:

{
  type: "JSON",
  body: "$input.body"
}

text/plain:

PlainText:
$input.body

Nothing I can do appears to be able to make the text/plain mapping template to be used - it always uses application/json.

I would expect that the text/plain mapping template to be used based on one of the following being true:

S3 returns content with Content-Type: text/plain.
The initial request to API-Gateway passes an Accept: text/plain header.

As per the example below, S3 returns a Content-Type: text/plain AND I request with Accept: text/plain. API-Gateway correctly responds with Content-Type: text/plain also. However the application/json template is still used to transform the body.

I have even removed application/json as a valid response type from the method-response entirely, but still nothing.

Any thoughts why this is happening?

FYI I am using a classic v1 ApiGateway (Rest).

Execution log for request c24cfce3-2cf3-4693-ad72-4fdf44f4fdcd
Wed May 19 17:13:38 UTC 2021 : Starting execution for request: c24cfce3-2cf3-4693-ad72-4fdf44f4fdcd
Wed May 19 17:13:38 UTC 2021 : HTTP Method: GET, Resource Path: /feeds-poc/test.txt
Wed May 19 17:13:38 UTC 2021 : Method request path: {filename=test.txt}
Wed May 19 17:13:38 UTC 2021 : Method request query string: {}
Wed May 19 17:13:38 UTC 2021 : Method request headers: {Accept=text/plain}
Wed May 19 17:13:38 UTC 2021 : Method request body before transformations: 
Wed May 19 17:13:38 UTC 2021 : Endpoint request URI: https://my-bucket-id.s3.eu-west-1.amazonaws.com/test.txt
Wed May 19 17:13:38 UTC 2021 : Endpoint request headers: {Authorization=****57173a, X-Amz-Date=20210519T171338Z, x-amzn-apigateway-api-id=123456789a, Accept=application/json, User-Agent=AmazonAPIGateway_123456789a, X-Amz-Security-Token=**** [TRUNCATED]
Wed May 19 17:13:38 UTC 2021 : Endpoint request body after transformations: 
Wed May 19 17:13:38 UTC 2021 : Sending request to https://my-bucket-id.s3.eu-west-1.amazonaws.com/test.txt
Wed May 19 17:13:38 UTC 2021 : Received response. Status: 200, Integration latency: 43 ms
Wed May 19 17:13:38 UTC 2021 : Endpoint response headers: {x-amz-id-2=****, x-amz-request-id=****, Date=Wed, 19 May 2021 17:13:39 GMT, Last-Modified=Mon, 17 May 2021 16:45:13 GMT, ETag="420f804aa21220bf0db57bb4b9799c8a", Accept-Ranges=bytes, Content-Type=text/plain, Content-Length=13, Server=AmazonS3}
Wed May 19 17:13:38 UTC 2021 : Endpoint response body before transformations: It's working

Wed May 19 17:13:38 UTC 2021 : Method response body after transformations: {
  type: "JSON",
  body: "It's working
"
}
Wed May 19 17:13:38 UTC 2021 : Method response headers: {X-Amzn-Trace-Id=Root=****, Content-Type=text/plain}
Wed May 19 17:13:38 UTC 2021 : Successfully completed execution
Wed May 19 17:13:38 UTC 2021 : Method completed with status: 200

lintal lintal · Accepted Answer · 2021-05-21T13:21:02

AWS Support confirmed to me that the switch is based on the original request Accept header. Testing this using Postman confirms this functionality.

The test tools built into the AWS console for API-Gateway however do not appear to cater for testing response mapping templates - from AWS support: the purpose of API Gateway test console is only to test the Integration, it doesn't work for end-to-end request.

AWS APIGateway Integration Response Mapping Templates do not switch correctly based on Content-Type

1 Answers