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A recent AWS API Gateway integration forced me to learn something new about service proxy integrations. The situation was an integration between S3 and API Gateway where the Content-Type header of the S3 response was not properly sent through the API Gateway. In short, I needed to create a mapping in the Method Response and then fill in the value in the Integration Response. Here is a CDK example with some of the extra Integration and Method Responses taken out but I am sure the configuration is similar in CloudFormation.
resource.addMethod(
'GET',
new apigateway.AwsIntegration({
service: 's3',
path: '{bucket}/script.js',
integrationHttpMethod: 'GET',
options: {
passthroughBehavior: apigateway.PassthroughBehavior.WHEN_NO_TEMPLATES,
requestParameters: {
'integration.request.header.Content-Type': "'application/x-www-form-urlencoded'",
'integration.request.path.bucket': `'${primaryBucket.bucketName}'`
},
integrationResponses: [
{
statusCode: "200",
responseParameters: {
'method.response.header.Content-Type': 'integration.response.header.Content-Type',
},
},
...
],
},
}),
{
methodResponses: [
{
statusCode: "200",
responseModels: {
'application/json': apigateway.Model.EMPTY_MODEL,
},
responseParameters: {
'method.response.header.Content-Type': true,
},
},
...
],
},
);
The parts to look out for are the integrationResponses.responseParameters and methodResponses.responseParameters.
Simply adding 'method.response.header.Content-Type' to the responseParameters is enough to create the mapping in the Method Response. The value indicates whether or not that header is required, so setting the value to true as I have means that S3 needs to return that header or the response will return an error.
Now that we have a mapping in place in the Method Response, we need to properly create the header in the Integration Response. For this example 'method.response.header.Content-Type': 'integration.response.header.Content-Type' is saying that the Method Response should get it’s Content-Type header from the Integration Responses Content-Type header. What is worth noting is that the key for both the Integration and Method Responses is the same (method.response.header.Content-Type) and that the value in the Integration Response does not necessarily have to come from the integration’s response itself. The Integration Response mapping value can come from a stage variable, static value, or a few other places as can be seen here.