[core] Allow specifying additional request templates in proxy method

[thchia]

I would like to request for the ability to specify additional content-type mappings for request templates in the ApiGatewayToSqs construct. Internally, this is using the addProxyMethodToApiResource method in the core library. The method hardcodes the AWSIntegration props, allowing just a single request template for application/json.

Use Case

I am using the ApiGatewayToSqs construct, but the caller of the endpoint will be making requests with Content-Type of text/plain. Currently this results in a 415 error response, as it is configured with a body passthrough value of None.

Proposed Solution

The method already accepts a parameter called requestTemplate, but:

• this only lets us change the mapped request, not the content-type for which it applies
• for this reason, it's a bit of a misnomer, since in my understanding the "Request Template" is both the content-type and the mapped request body.

To avoid breaking changes, I can propose adding a new parameter to the addProxyMethodToApiResource method, something like additionalRequestTemplates, which accepts a map of content-type to mapping.

addProxyMethodToApiResource({
  // ...
  additionalRequestTemplates: {
    'text/plain': '...'
  }
})

A similar thing can be done for integrationResponses, so that we can close the request/response loop.

For my specific issue, these changes would be accompanied by a similar change in the ApiGatewayToSqs construct to allow the additional request template to be passed in.

Workaround

I have worked around this by manipulating the low level objects in CDK, but it's unwieldy to say the least.

// This is the method to which we need to add the request template and responses
// It's the method that creates messages in the queue
const createMessageMethod = api.apiGateway.methods.find(
  (method) => method.httpMethod.toUpperCase() === "POST"
);

// Should never be the case
if (!createMessageMethod) return;

// The property we need to change is marked as readonly by TypeScript
// This fudges it so we can change it
type MutableCfnMethodIntegration = {
  -readonly [K in keyof CfnMethod.IntegrationProperty]: CfnMethod.IntegrationProperty[K];
};

const cfnMethod = createMessageMethod.node.defaultChild as CfnMethod;
const integration = cfnMethod.integration as MutableCfnMethodIntegration;

integration.requestTemplates = Object.assign(
  integration.requestTemplates,
  { "text/plain": "..." }
);

Other

• 👋 I may be able to implement this feature request
• ⚠️ This feature might incur a breaking change

---

This is a 🚀 Feature Request

[biffgaut]

Thanks, we'll take a look

[georgebearden]

Hi @thchia - Can you please have a look at #888, which should solve this issue. We still need to implement the optional properties across the other ApiGateway-based constructs, but this would be the pattern.

[georgebearden]

#888 is now merged and will be available in the next release. It also added support for custom integration responses. Cheers!