Spec

Packets Reference

Packet schema format, reference syntax, and validation in FlowDSL.

A packet is a typed schema for data flowing along an edge. Packets use JSON Schema Draft-07 and can be defined natively or referenced from an AsyncAPI document.

Native packet definition

yaml

components:
  packets:
    EmailPayload:
      type: object
      title: Email Payload
      description: An incoming email from the support inbox
      properties:
        messageId:
          type: string
          description: Unique email identifier (e.g., IMAP UID)
        from:
          type: string
          format: email
        to:
          type: string
          format: email
        subject:
          type: string
          maxLength: 500
        body:
          type: string
        receivedAt:
          type: string
          format: date-time
        headers:
          type: object
          additionalProperties: true
      required: [messageId, from, subject, body, receivedAt]
      additionalProperties: false

Supported JSON Schema Draft-07 keywords

Keyword	Supported	Notes
`type`	Yes	`string`, `number`, `integer`, `boolean`, `object`, `array`, `null`
`properties`	Yes	Object field definitions
`required`	Yes	Array of required field names
`enum`	Yes	Allowed values
`format`	Yes	`email`, `date-time`, `uri`, `uuid`
`minimum` / `maximum`	Yes	Number bounds
`minLength` / `maxLength`	Yes	String length bounds
`pattern`	Yes	Regex pattern
`items`	Yes	Array item schema
`additionalProperties`	Yes	`true`, `false`, or schema
`$ref`	Yes	References within `components.packets`
`oneOf` / `anyOf` / `allOf`	Yes	Schema composition

`$ref` within components

Reference other packets within the same document:

yaml

components:
  packets:
    Address:
      type: object
      properties:
        street: { type: string }
        city: { type: string }
        country: { type: string, minLength: 2, maxLength: 2 }
      required: [street, city, country]

    Order:
      type: object
      properties:
        orderId: { type: string }
        shippingAddress:
          $ref: "#/components/packets/Address"
        billingAddress:
          $ref: "#/components/packets/Address"

AsyncAPI packet reference

Reference a message schema from a linked AsyncAPI document:

yaml

asyncapi: "./events.asyncapi.yaml"

edges:
  - from: OrderReceived
    to: ValidateOrder
    delivery:
      mode: durable
      packet: "asyncapi#/components/messages/OrderPlaced"

The asyncapi#/... syntax is a JSON Pointer path into the AsyncAPI document. The runtime resolves it to the message's payload schema.

Packet reference on a node port

yaml

nodes:
  ValidateOrder:
    inputs:
      in:
        packet: OrderPayload          # Native packet reference
    outputs:
      out:
        packet: "asyncapi#/components/messages/OrderValidated"  # AsyncAPI reference

Naming convention

Element	Convention
Packet names	`PascalCase`
Property names	`camelCase`

Runtime validation

The runtime validates packets:

At startup: Verifies all referenced packet names exist.
At runtime: Validates each packet against its JSON Schema before delivery. Invalid packets are rejected and moved to the dead letter queue with a VALIDATION error code.

Next steps

Components reference — the components section
DeliveryPolicy reference — how packets are referenced on edges
Packets concept — conceptual explanation

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Node Object Reference

Complete field reference for the Node object in FlowDSL.

RetryPolicy Reference

Complete field reference for the RetryPolicy object in FlowDSL.