StepFunctions -> TaskInput cannot select the entire Input

[mrgrain]

Using TaskInput in step functions, it is impossible to select the entire step input.

I would expect to be able to select the entire input using $, however the JSON path validator expects a path to start with $.

Reproduction Steps

In a newly created project, put this as stack:

export class StepfunctionbugStack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const topic = new Topic(this, "topic");

    const definition = new Task(this, "task", {
      task: new PublishToTopic(topic, {
        message: TaskInput.fromDataAt("$")
      })
    });

    new StateMachine(this, "state-machine", {
      stateMachineType: StateMachineType.STANDARD,
      definition
    });
  }
}

Error Log

Data JSON path values must start with '$.'
Subprocess exited with error 1

Environment

• CLI Version : 1.25.0 (build 5ced526)
• Framework Version: 1.25.0
• OS : macOS Mojave 10.14.5
• Language : Typescript 3.7.5

---

This is 🐛 Bug Report

[nija-at]

This seems to be a fundamental limitation of StepFunctions itself, and not necessarily the CDK.

Based on their documentation, they're using JsonPath. I can't seem to find a way in JsonPath to specify a 'select all' operator. The closest that comes is the $..* operator.

Can you try the $..* and see if this satisfies your use case?

[rix0rrr]

Also, in case of the PublishToTopic action, I believe not specifying a TaskInput at all will make it default to the entire message.

[mrgrain]

@nija-at StepFunctions is perfecty happy with a $ to include the entire input. It's also how I would read the JsonPath documentation.

@rix0rrr That's good to know, thanks 👍 I still believe the JsonPath parser isnt't correct though, as $ is a valid JsonPath and meets the extra requirements for StepFunctions. See http://jsonpath.herokuapp.com/?path=$

---

There is another work around as well, but it's not obvious to find:

new PublishToTopic(snsTopic, {
  message: TaskInput.fromText(Data.entirePayload)
})

[nija-at]

@rix0rrr - Message attribute is a mandatory property for the Notification type in the Amazon states language, so what you're suggesting won't work here.

However, I seem to have missed in the documentation that $ is a valid path that refers to selecting everything. (thanks @rix0rrr for pointing this out).

The validations in field.ts will need to updated to support $ and $$.

aws-cdk/packages/@aws-cdk/aws-stepfunctions/lib/fields.ts

Lines 131 to 140 in 983dd40

	function validateDataPath(path: string) {
	if (!path.startsWith('$.')) {
	throw new Error("Data JSON path values must start with '$.'");
	}
	}
	function validateContextPath(path: string) {
	if (!path.startsWith('$$.')) {
	throw new Error("Context JSON path values must start with '$$.'");
	}