[aws-events] API Destination Input Transformer missing quotes

[sethgeoghegan]

Problem Summary

I have an EventBridge event that I want to send to an API Destination target. The Input Transformer generated by CDK is not quoting strings, which is resulting in invalid JSON in the API request made by the API Destination.

I am assuming this is not a bug, but a misunderstanding on my behalf on how the CDK constructs are meant to be used.

Details

The EventBridge payload looks like this

{
  "version": "0",
  "id": "89d1a02d-5ec7-412e-82f5-13505f849b41",
  "detail-type": "Scheduled Event",
  "source": "aws.events",
  "account": "123456789012",
  "time": "2016-12-30T18:44:49Z",
  "region": "us-east-1",
  "resources": ["arn:aws:events:us-east-1:123456789012:rule/SampleRule"],
  "detail": {
    "ended_at":"2024-08-29T04:51:12.778Z",
  }
}

I want to transform this event into an API request to https://someapi.com/ with the detail.ended_at field passed in the body of the API request. In pseudocode:

POST https://someapi.com/
Content-Type: application/json

{
  "timestamp": "2024-08-29T04:51:12.778Z"
}

I'm creating an API Destination and Input Transformer as follows:

import * as targets from "aws-cdk-lib/aws-events-targets";
import * as events from "aws-cdk-lib/aws-events";

const myApiDest = new events.ApiDestination(stack, "myApiDest", {
    connection: myConnection,
    endpoint: "https://someapi.com/",
  })
  
const myTarget = new targets.ApiDestination(myApiDest, {
     event: events.RuleTargetInput.fromObject({
         timestamp: events.EventField.fromPath('$.detail.ended_at')
     })
})

This creates an Input Transformer that does not escape the ended_at field with quotes, which results in invalid JSON.

I can manually update the Template in the AWS Console, which results in the valid JSON output I'm looking for:

However, I cannot figure out how to use CDK to generate a template that includes quotes around the value of $.detail.ended_at. However, I've gotten rather close with this attempt:

const myTarget = new targets.ApiDestination(myApiDest, {
     event: events.RuleTargetInput.fromObject({
         timestamp: `${events.EventField.fromPath('$.detail.ended_at')}`,
         timestamp2: `TEST${events.EventField.fromPath('$.detail.ended_at')}`,
     })
})

Which output the following. The timestamp field lacks any quotes and is invalid JSON. timestamp2 has a TEST prefix, which is also not what I want.

{
  "timestamp": 2024 - 08 - 29 T04: 51: 12.778 Z,
  "timestamp2": "TEST2024-08-29T04:51:12.778Z"
}