asl-path-validator

What is in this library:

This library provides a parser to validate Path, Reference Path, and Payload Template expressions for the Amazon States Language

The parser produces an Abstract Syntax Tree (AST) for the expression if it's valid. Additional checks are performed if necessary to limit the operators or presence of functions based on the context.

Samples from the spec

The expressions resemble JSONPath.

$.store.book
$.store\.book
$.\stor\e.boo\k
$.store.book.title
$.foo.\.bar
$.foo\@bar.baz\[\[.\?pretty
$.&Ж中.\uD800\uDF46
$.ledgers.branch[0].pending.count
$.ledgers.branch[0]
$.ledgers[0][22][315].foo
$['store']['book']
$['store'][0]['book']

validate a single expression

expect(validatePath("$.library.movies", AslPathContext.REFERENCE_PATH)).toStrictEqual({
  isValid: true,
});

register validators as AJV formats

Provides adapters to register as custom format validators for AJV.

The AJV schemas for the Step Functions are not provided here. See asl-validator for schemas. See the provided unit tests for integrating. An example schema is defined to illustrate how to leverage AJV to invoke our custom validation.

beforeAll(() => {
  ajv = new Ajv({
    schemas: [example, payloadTemplateSchema],
    allowUnionTypes: true,
  });
  registerAll(ajv);
});
it("should accept valid input", () => {
  expect.hasAssertions();
  const input = loadDefinition("valid.json");
  const result = ajv.validate(
    "https://asl-path-validator.cloud/example.json#",
    input
  );
  expect(result).toBe(true);
});

How this is done

1. leverage AJV to do schema validation (see asl-validator for the schemas)
2. custom formatter validates the Path and Reference Path fields
3. Payload Templates leverage patternProperties to validate fields ending in ".$"
4. Generated parser from a PEG grammar provides the actual validation logic

Formal Definitions

The spec references a Java library for the syntax of the expressions.
The documentation for the referenced library has more functionality than is supported by the AWS Step Function runtimes.

Context Expressions

When a Path begins with "$$", two dollar signs, this signals that it is intended to identify content within the Context Object. The first dollar sign is stripped, and the remaining text, which begins with a dollar sign, is interpreted as the JSONPath applying to the Context Object.

Intrinsic Functions

These functions are available within the context of a Payload Template only.

The relevant fields to examine are Parameters and ResultSelector.

Filter Expressions and Operators

Filters are logical expressions used to filter arrays. A typical filter would be [?(@.age > 18)] where @ represents the current item being processed.

Note that the comparison operators only work with numeric values in the AWS Data flow simulator

What fields should be validated

The table below includes all the fields within a Step Function that are validated.

See asl-validator 3.x branch or higher for schemas modeling ASL.

The schema provided here illustrate how to integrate and includes a recursive definition for the Payload Template context.