Json Tranform Lambda

README.md

JsonTransform

Transform Json Input

function input

Use a Pass type Step Function to merge a script under the field name "transformScript into the input JSON.

"Inject Update Status and Updated": {
  "Type": "Pass",
  "Result":"event.doc.status = event.jobStatus.success ? 'finished' : 'failure'; event.doc.updated=new Date()"
  "ResultPath": "$.transformScript",
  "Next": "..."
}

The script can modify the 'event' object containing the parsed input json, which will be returned as the output of the lambda.

In the example above the script adds the following to the input.

"doc": {
    "status": "finished",
    "updated": "2018-03-19T21:20:08.571Z"
  }

index.js

// See README.md for usage
exports.handler = (event, context, callback) => {
    console.log(`${event.trace}: INFO JsonTransform ${JSON.stringify(event)}`)
    try {
        if (event.transformScript) {
            let script = event.transformScript
            delete event.transformScript
            require('vm').runInNewContext(script, {event: event})
        } else {
            console.log(`${event.trace}: WARN JsonTransform missing field 'transformScript'}`)
        }
        callback(null, event)
    } catch (err) {
        console.log(`${event.trace}: ERROR JsonTransform ${JSON.stringify(err)}`)
        callback(err)
    }
}

Note: we use a "trace" value throughout our system's design to track a process across tiers/logs.