@farar/nodes

Nodes

Nodes provides a framework for building type-safe data transformation graphs using Node.js streams.

Introduction

Nodes provides an intuitive framework for constructing data transformation graphs using native Node.js streams. You can use the built-in library of commonly used data transformation Node classes or implement your own.

Features

• A type-safe graph-like API pattern for building data transformation graphs based on Node.js streams.
• Consume any native Node.js Readable, Writable, Duplex, or Transform stream and add it to your graph.
• Error handling and selective termination of inoperable graph components.
• Automatic message queueing in order to assist with handling of backpressure.

Table of Contents

• Installation
• Concepts
• Examples
  • A Graph-API-Pattern Logger Implementation
• API
• How-Tos
  • How to Implement a Data Transformation Node
  • How to Consume a Readable, Writable, Duplex, or Transform Node.js Stream
• Backpressure
• Best Practices
• Error Handling
• Test

Installation

npm install @farar/nodes

Concepts

Node

A Node is a component of a graph-like data transformation pipeline. Each Node is responsible for transforming its input into an output that can be consumed by its connected Node instances. By connecting Node instances into a network, sophisticated graph-like data transformation pipelines can be constructed.

Examples

A Graph API Pattern Logger Implementation ^</example>

Please see the Streams Logger implementation.

API

The Node class.

new nodes.Node<InT, OutT>(stream, options)

• <IntT> The input into the stream.
• <OutT> The output from the stream.
• stream <stream.Writable | stream.Readable> An instance of a Writable, Readable, Duplex, or Transform Node.js stream.
• options <NodeOptions>
  • errorHandler <(err: Error, ...params: Array<unknown>) => void> An optional error handler that will be used in the event of an internal Error. Default: console.error

public node.connect(...nodes)

• nodes <Array<T>> An array of Node<OutT, unknown> to be connected to this Node.

Returns: <Node<InT, OutT>>

public node.disconnect(...nodes)

• nodes <Array<T>> An array of Node<OutT, unknown> to be disconnected from this Node.

Returns: <Node<InT, OutT>>

protected node._write(data, encoding)

• data <InT> Data to write to the writable side of the stream.
• encoding <NodeJS.BufferEncoding> An optional Node.js encoding Default: utf-8. Returns: <Promise<void>>

The Nodes Config Settings Object

Config.errorHandler <ErrorHandler> An optional error handler. Default: console.error

Config.debug <boolean> Announce internal activities e.g., connectiing and disconnecting from Node instances. Default: false

How-Tos

How to Implement a Data Transformation Node

In order to implement a data transformation Node, extend the Node class and pass a Node.js stream.Writable implementation to the super's constructor.

For example, the following StringToNumber implementation will convert a numeric string to a number.

NB In this example, writableObjectMode and readableObjectMode are both set to true; hence, the Node.js stream implementation will handle the input and output as objects. It's important that writableObjectMode and readableObjectMode accurately reflect the input and output types of your Node.

import * as stream from 'node:stream';
import { Config, Node } from '@farar/nodes';

export class StringToNumber extends Node<string, number> {

    constructor(options: stream.TransformOptions) {
        super(new stream.Transform({
            ...options, ...{
                writableObjectMode: true,
                readableObjectMode: true,
                transform: (chunk: string, encoding: BufferEncoding, callback: stream.TransformCallback) => {
                    try {
                        const result = parseFloat(chunk.toString());
                        callback(null, result);
                    }
                    catch (err) {
                        if (err instanceof Error) {
                            callback(err);
                            Config.errorHandler(err);
                        }
                    }
                }
            }
        }));
    }
}

How to Consume a Readable, Writable, Duplex, or Transform Node.js Stream

In this hypothetical example a type-safe Node is constructed from a net.Socket. The resulting Node instance can be used in a data transformation graph.

import * as net from "node:net";
import { once } from "node:events";

net.createServer((socket: net.Socket) => socket.pipe(socket)).listen(3000);
const socket = net.createConnection({ port: 3000 });
await once(socket, "connect");
const socketHandler = new Node<Buffer, Buffer>(socket);

Backpressure

The Node class has a _write method that respects backpressue; when a stream is draining it will queue messages until a drain event is emitted by the Node's stream. Your application can optionally monitor the size of the queue and respond appropriately.

If you have a stream that is backpressuring, you can increase the high water mark on the stream in order to mitigate drain events.

Best Practices

Avoid reuse of Node instances (unless you know what you are doing!).

Reusing the same Node instance can result in unexpected phenomena. If the same Node instance is used in different locations in your graph, you need to think carefully about the resulting edges that are connected to both the input and the output of the Node instance. Most of the time if you need to use the same class of Node more than once, it's advisable to create a new instance for each use.

Error Handling

Nodes may be used in diverse contexts, each with unique requirements. Nodes should never throw if the API is used in accordance with the documentation. However, "phenomena happens"; hence, you may choose to handle errors accordingly!

Nodes defaults to logging its errors to process.stderr. If your application requires that errors throw, you may set an errorHandler on the Config object that does that. Alternatively, your handler may consume the Error and handle it otherwise.

Optionally configure all internal Node errors to be thrown.

import { Config } from "@farar/nodes";
Config.errorHandler = (err: Error) => {
    throw err;
};

Test

git clone https://github.com/faranalytics/nodes.git
cd nodes
npm install && npm update
npm test