@ternion/opc-link-client

A lightweight TypeScript client library for interacting with the QNetLinks OPC REST API. This library provides a type-safe interface for reading and writing OPC UA node values through a RESTful API.

Features

• Fully type-safe API client with comprehensive TypeScript support and proper return types
• Class-based API with TernionOpcLinkClient for easy instantiation
• Read operations: Query cached values, read specific nodes, and retrieve aliases with typed responses
• Write operations: Write Boolean, Int16, and Float values to OPC nodes
• Alias support: Convenient access to predefined alias channels (bool, int16, float)
• Convenience methods: Helper methods for reading channels and vectors with proper typing
• Error handling: Comprehensive error handling with descriptive messages
• ESM modules: Modern ES module syntax with native Node.js support
• Zero dependencies: Uses native fetch API (Node.js 18+)

Prerequisites

• Node.js 18+ (required for native fetch API)
• QNetLinks OPC REST API running at http://localhost:9990 (default, configurable)

Installation

npm install @ternion/opc-link-client

Quick Start

import { TernionOpcLinkClient } from '@ternion/opc-link-client';

// Create a client instance (uses default URL: http://localhost:9990/opc/api/v1)
const client = new TernionOpcLinkClient();

// Or specify a custom API URL
const client = new TernionOpcLinkClient('http://your-api-host:port/opc/api/v1');

// Get API information
const info = await client.getApiInfo();
console.log(info);

// Check API health
const health = await client.getHealth();
console.log(health);

Usage

Basic Example

import { TernionOpcLinkClient } from '@ternion/opc-link-client';

const client = new TernionOpcLinkClient();

// Get all cached values
const values = await client.getValues();
console.log(values);

Reading Values

import { TernionOpcLinkClient } from '@ternion/opc-link-client';

const client = new TernionOpcLinkClient();

// Read a specific node by ID
const value = await client.getValue('ns=1;s=Boolean.0');

// Read by alias (channel 0 of bool type)
const aliasValue = await client.getAlias('bool', 0);

// Get all aliases of a type
const allBools = await client.getAllAliases('bool');

// Force a fresh read (bypass cache)
const freshValue = await client.readNode({ 
  nodeId: 'ns=1;s=Boolean.0', 
  forceRefresh: true 
});

Writing Values

import { TernionOpcLinkClient } from '@ternion/opc-link-client';

const client = new TernionOpcLinkClient();

// Write using convenience helpers
await client.writeBoolean(0, true);        // Write to Boolean.0
await client.writeInt16(1, 42);            // Write to Int16.1
await client.writeFloat(2, 3.14159);       // Write to Float.2

// Write using generic writeNode method
await client.writeNode({
  nodeId: 'ns=1;s=CustomNode',
  dataType: 'Boolean',
  value: true,
  refreshCache: true
});

Error Handling

All methods throw errors on failure. Always wrap calls in try-catch:

try {
  await client.writeBoolean(0, true);
} catch (error) {
  console.error('Write failed:', error);
  // Handle error appropriately
}

API Reference

TernionOpcLinkClient Class

Constructor

new TernionOpcLinkClient(apiBaseUrl?: string)

Creates a new client instance. The apiBaseUrl parameter is optional and defaults to "http://localhost:9990/opc/api/v1".

Methods

Information & Health

• getApiInfo(): Promise<ApiInfo> - Get API metadata and available endpoints
• getHealth(): Promise<HealthStatus> - Get current health status of the bridge

Reading Values

• getValues(): Promise<NodeValue[]> - Get all cached node values
• getValue(nodeId: string): Promise<NodeValue> - Get cached value for a specific node
• getAlias(type: AliasType, channel: number): Promise<NodeValue> - Get value by alias and channel
• getAllAliases(type: AliasType): Promise<AliasCollection> - Get all channels for an alias type
• readNode(request: ReadRequest): Promise<NodeValue> - Read a node (optionally force refresh)
• readBoolean(channel: number, forceRefresh?: boolean): Promise<NodeValue> - Read Boolean channel
• readInt16(channel: number, forceRefresh?: boolean): Promise<NodeValue> - Read Int16 channel
• readFloat(channel: number, forceRefresh?: boolean): Promise<NodeValue> - Read Float channel
• readBooleanVector(forceRefresh?: boolean): Promise<NodeValue> - Read BooleanVector node
• readInt16Vector(forceRefresh?: boolean): Promise<NodeValue> - Read Int16Vector node
• readFloatVector(forceRefresh?: boolean): Promise<NodeValue> - Read FloatVector node

Writing Values

• writeNode(request: WriteRequest): Promise<WriteResponse> - Generic write function
• writeBoolean(channel: number, data: boolean): Promise<WriteResponse> - Write boolean value
• writeInt16(channel: number, data: number): Promise<WriteResponse> - Write 16-bit integer (-32768 to 32767)
• writeFloat(channel: number, data: number): Promise<WriteResponse> - Write floating-point value

Static Validation Methods

• TernionOpcLinkClient.validateChannel(channel: number): void - Validate channel index
• TernionOpcLinkClient.validateAliasType(type: string): asserts type is AliasType - Validate alias type

Types

AliasType

type AliasType = 'bool' | 'int16' | 'float';

ReadRequest

interface ReadRequest {
  nodeId: string;
  forceRefresh?: boolean;
}

WriteRequest

interface WriteRequest {
  nodeId: string;
  dataType: 'Boolean' | 'Int16' | 'Float' | string | number;
  value: unknown;
  arrayType?: string | number;
  refreshCache?: boolean;
}

WriteResponse

interface WriteResponse {
  status: string;
  nodeId: string;
  result: NodeValue;
}

NodeValue

interface NodeValue {
  nodeId: string;
  value: unknown;
  dataType: string;
  arrayType: string;
  statusCode: string;
  sourceTimestamp: string;
  serverTimestamp: string;
  updatedAt: string;
}

ApiInfo

interface ApiInfo {
  [key: string]: unknown;
}

API metadata information returned by the root endpoint.

HealthStatus

interface HealthStatus {
  [key: string]: unknown;
}

Health status information returned by the health endpoint.

AliasCollection

type AliasCollection = NodeValue[];

Collection of alias values returned by getAllAliases().

Examples

See the examples/ directory for complete usage examples.

Run the demo example:

npm start

Or directly:

npx tsx examples/demo.ts

Development

Building

npm run build

This compiles TypeScript to the dist/ directory.

Type Checking

npx tsc --noEmit

Cleaning

npm run clean

Removes the dist/ directory.

Project Structure

@ternion/opc-link-client/
├── src/
│   ├── index.ts                  # Main entry point
│   └── ternion-opc-link-client/
│       └── ternion-opc-link-client.ts  # Client implementation
├── dist/                         # Compiled output (generated)
├── examples/                     # Example code
│   └── demo.ts
├── package.json
├── tsconfig.json
└── README.md

License

MIT

Changelog

[Unreleased]

Improved

• Type Safety: Replaced all Promise<unknown> return types with proper TypeScript interfaces
  • getApiInfo() now returns Promise<ApiInfo>
  • getHealth() now returns Promise<HealthStatus>
  • getValues() now returns Promise<NodeValue[]>
  • getValue(), getAlias(), readNode(), and all convenience read methods now return Promise<NodeValue>
  • getAllAliases() now returns Promise<AliasCollection>
• Added new exported types: ApiInfo, HealthStatus, and AliasCollection
• Enhanced type safety throughout the library for better IDE autocomplete and compile-time error checking