Port

Ports are the input and output endpoints of a node. Input ports receive packets, output ports send them. In a node definition, ports are declared under ports.input and ports.output:

title: My Console Log Node
ns: console
name: log
ports:
  input:
    msg:
      type: string
  output:
    out:
      type: string
fn: |
  output = () => {
    console.log($.msg)
    cb({ out: $.get('msg') })
  }  

Port schema

Each port follows the JSON Schema-based Port model. Common properties:

Property	Description
type	Data type: string, number, boolean, array, object, any, function (required)
required	Whether the port must be filled (false makes it optional)
default	Default value used when no data arrives
context	Initial value stored in the node
persist	Keep the last value so read() can be called again
title	Display name
description	Port description
enum	Allowed values

Any standard JSON Schema constraint (minimum, maximum, pattern, minLength, items, properties, …) can also be used for validation.

InputPort

Created for each port in ports.input. Packets arriving over connected links are queued on the port.

port.fill(packet)     // push a packet onto the queue
port.read()           // shift and return the first packet (increments reads)
port.peek()           // look at the first packet without consuming it
port.isFilled()       // whether data is available

read() returns a Packet; it throws when the queue is empty and the port has no context, default, or persist to fall back on. isFilled() returns one of the port states (EMPTY, FILLED, PERSIST, DIRECT, CONTEXT, DEFAULT, NOT_REQUIRED).

Context, default and persist:

port.setContext(value)   // set the initial/context value
port.clearContext()
port.setDefault(value)
port.clearDefault()
port.persist = true      // keep the last value
port.setPersist(value)

Properties:

Property	Description
data	Queue of received packets
fills	Number of packets received
reads	Number of packets read
required	Whether the port is required
type	Port data type
context	The context packet, if set

OutputPort

Created for each port in ports.output. Packets written to an output port are forwarded to every connected link.

port.write(packet)   // send a packet to all connected links

write() accepts a Packet or a plain value (which is wrapped). Each connected link receives a clone of the packet. fills counts the writes.

Events

  /**
   * Fill event
   *
   * @event Port#fill
   * @type {object}
   */
  public static readonly FILL = 'fill'

  /**
   * Data event
   *
   * @event Port#data
   * @type {Packet}
   */
  public static readonly DATA = 'data'

Input ports emit fill when a packet is queued. Output ports emit data when a packet is written.