signalk-server

<!DOCTYPE html><html class="default" lang="en" data-base="../../../"><head><meta charset="utf-8"/><meta http-equiv="x-ua-compatible" content="IE=edge"/><title>AssemblyScript Plugins | Signal K</title><meta name="description" content="Documentation for Signal K"/><meta name="viewport" content="width=device-width, initial-scale=1"/><link rel="stylesheet" href="../../../assets/style.css?cache=1783009712609"/><link rel="stylesheet" href="../../../assets/highlight.css?cache=1783009712609"/><script defer src="../../../assets/main.js?cache=1783009712609"></script><script async src="../../../assets/icons.js?cache=1783009712609" id="tsd-icons-script"></script><script async src="../../../assets/search.js?cache=1783009712609" id="tsd-search-script"></script><script async src="../../../assets/navigation.js?cache=1783009712609" id="tsd-nav-script"></script><script async src="../../../assets/hierarchy.js?cache=1783009712609" id="tsd-hierarchy-script"></script><link rel="stylesheet" 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352.9c-1.3 1-1 3.3 .7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1zm-10.8-8.1c-.7 1.3 .3 2.9 2.3 3.9 1.6 1 3.6 .7 4.3-.7 .7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3 .7zm32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3 .7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1zm-11.4-14.7c-1.6 1-1.6 3.6 0 5.9 1.6 2.3 4.3 3.3 5.6 2.3 1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2z"></path></svg></a><a href="#" class="tsd-widget menu" id="tsd-toolbar-menu-trigger" data-toggle="menu" aria-label="Menu"><svg width="16" height="16" viewBox="0 0 16 16" fill="none" aria-hidden="true"><use href="../../../assets/icons.svg#icon-menu"></use></svg></a></div></div></header><div class="container container-main"><div class="col-content"><div class="tsd-page-title"><ul class="tsd-breadcrumb" aria-label="Breadcrumb"><li><a href="../../../Developing.html">Developing</a></li><li><a href="../../Plugins.html">Plugins</a></li><li><a href="../WASM_Plugins.html">WASM Plugins</a></li><li><a href="" aria-current="page">AssemblyScript Plugins</a></li></ul></div><div class="tsd-panel tsd-typography"><h1 id="creating-assemblyscript-plugins" class="tsd-anchor-link">Creating AssemblyScript Plugins<a href="#creating-assemblyscript-plugins" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h1> AssemblyScript is the recommended language for developers familiar with TypeScript. It produces the smallest binaries (3-10 KB) and has the fastest development cycle. <h2 id="step-1-install-sdk" class="tsd-anchor-link">Step 1: Install SDK<a href="#step-1-install-sdk" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h2> <pre><code class="bash">npm install @signalk/assemblyscript-plugin-sdk npm install --save-dev assemblyscript </code><button type="button">Copy</button></pre> <h2 id="step-2-create-plugin-file" class="tsd-anchor-link">Step 2: Create Plugin File<a href="#step-2-create-plugin-file" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h2> Create <code>assembly/index.ts</code>: <pre><code class="typescript">import { Plugin, Delta, Update, PathValue, emit, setStatus } from '@signalk/assemblyscript-plugin-sdk/assembly' class MyPlugin extends Plugin { name(): string { return 'My AssemblyScript Plugin' } schema(): string { return `{ "type": "object", "properties": { "updateRate": { "type": "number", "default": 1000 } } }` } start(config: string): i32 { setStatus('Started') // Emit a test delta const pathValue = new PathValue('test.value', '"hello"') const update = new Update([pathValue]) const delta = new Delta('vessels.self', [update]) emit(delta) return 0 // Success } stop(): i32 { setStatus('Stopped') return 0 } } // Export for Signal K const plugin = new MyPlugin() export function plugin_name(): string { return plugin.name() } export function plugin_schema(): string { return plugin.schema() } export function plugin_start(configPtr: usize, configLen: usize): i32 { const configBytes = new Uint8Array(configLen) for (let i = 0; i < configLen; i++) { configBytes[i] = load<u8>(configPtr + i) } const configJson = String.UTF8.decode(configBytes.buffer) return plugin.start(configJson) } export function plugin_stop(): i32 { return plugin.stop() } </code><button type="button">Copy</button></pre> Note on Plugin IDs: The plugin ID is automatically derived from your <code>package.json</code> name. For example: <ul> <li><code>@signalk/example-weather-plugin</code> → <code>_signalk_example-weather-plugin</code></li> <li><code>my-simple-plugin</code> → <code>my-simple-plugin</code></li> </ul> This ensures unique plugin IDs (npm guarantees package name uniqueness) and eliminates discrepancies between package name and plugin ID. <h2 id="step-3-configure-build" class="tsd-anchor-link">Step 3: Configure Build<a href="#step-3-configure-build" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h2> Create <code>asconfig.json</code>: <pre><code class="json">{ "targets": { "release": { "outFile": "plugin.wasm", "optimize": true, "shrinkLevel": 2, "converge": true, "noAssert": true, "runtime": "incremental", "exportRuntime": true }, "debug": { "outFile": "build/plugin.debug.wasm", "sourceMap": true, "debug": true, "runtime": "incremental", "exportRuntime": true } }, "options": { "bindings": "esm" } } </code><button type="button">Copy</button></pre> Important: <code>exportRuntime: true</code> is required for the AssemblyScript loader to work. This exports runtime helper functions like <code>__newString</code> and <code>__getString</code> that the server uses for automatic string conversions. <h2 id="step-4-build" class="tsd-anchor-link">Step 4: Build<a href="#step-4-build" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h2> <pre><code class="bash">npx asc assembly/index.ts --target release </code><button type="button">Copy</button></pre> <h2 id="step-5-create-packagejson" class="tsd-anchor-link">Step 5: Create package.json<a href="#step-5-create-packagejson" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h2> <pre><code class="json">{ "name": "my-wasm-plugin", "version": "0.1.0", "keywords": ["signalk-wasm-plugin"], "wasmManifest": "plugin.wasm", "wasmCapabilities": { "dataRead": true, "dataWrite": true, "storage": "vfs-only" } } </code><button type="button">Copy</button></pre> <blockquote> Important: What makes a WASM plugin? The <code>wasmManifest</code> field is the key identifier that tells Signal K this is a WASM plugin (not a Node.js plugin). It must point to your compiled <code>.wasm</code> file. The package name can be anything - scoped (<code>@myorg/my-plugin</code>) or unscoped (<code>my-wasm-plugin</code>). Choose a name that makes sense for your plugin and avoids conflicts on npm. </blockquote> <h2 id="step-6-test-install" class="tsd-anchor-link">Step 6: Test Install<a href="#step-6-test-install" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h2> Option 1: Symlink (Recommended for Development) Symlinking your plugin directory allows you to make changes and rebuild without copying files: <pre><code class="bash"># From your Signal K node_modules directory cd ~/.signalk/node_modules ln -s /path/to/your/my-wasm-plugin my-wasm-plugin # Now any changes you make and rebuild will be picked up on server restart </code><button type="button">Copy</button></pre> Option 2: Direct Copy <pre><code class="bash">mkdir -p ~/.signalk/node_modules/my-wasm-plugin cp plugin.wasm package.json ~/.signalk/node_modules/my-wasm-plugin/ # If your plugin has a public/ folder with web UI: cp -r public ~/.signalk/node_modules/my-wasm-plugin/ </code><button type="button">Copy</button></pre> Option 3: NPM Package Install <pre><code class="bash"># If you've packaged with `npm pack` npm install -g ./my-wasm-plugin-1.0.0.tgz # Or install from npm registry (if published) npm install -g my-wasm-plugin </code><button type="button">Copy</button></pre> Note: Symlinking is the most efficient method for development - changes are picked up on server restart without copying files. Use npm install for production deployments or when distributing plugins. Important: If your plugin includes static files (like a web UI in the <code>public/</code> folder), make sure to copy that folder as well. Static files are automatically served at <code>/plugins/your-plugin-id/</code> when the plugin is loaded. <h2 id="step-7-verify-plugin-configuration-in-admin-ui" class="tsd-anchor-link">Step 7: Verify Plugin Configuration in Admin UI<a href="#step-7-verify-plugin-configuration-in-admin-ui" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h2> After installing your plugin, verify it appears in the Admin UI: <ol> <li> Navigate to Plugin Configuration: Open the Admin UI at <code>http://your-server:3000/admin/</code> and go to Server → Plugin Config </li> <li> Check Plugin List: Your WASM plugin should appear in the list with: <ul> <li>Plugin name (from <code>name()</code> export)</li> <li>Version (from <code>package.json</code>)</li> <li>Enable/Disable toggle</li> <li>Configuration form (based on <code>schema()</code> export)</li> </ul> </li> <li> Verify Configuration Persistence: <ul> <li>Configuration is saved to <code>~/.signalk/plugin-config-data/your-plugin-id.json</code></li> <li>Changes are applied immediately (plugin restarts automatically)</li> <li>The file structure is:<pre><code class="json">{ "enabled": true, "enableDebug": false, "configuration": { "updateRate": 1000 } } </code><button type="button">Copy</button></pre> </li> </ul> </li> <li> Troubleshooting: <ul> <li>If plugin doesn't appear: Check <code>package.json</code> has the <code>signalk-wasm-plugin</code> keyword and <code>wasmManifest</code> field</li> <li>If configuration form is empty: Verify <code>schema()</code> export returns valid JSON Schema</li> <li>If settings don't persist: Check file permissions on <code>~/.signalk/plugin-config-data/</code></li> </ul> </li> </ol> Important: The Admin UI shows all plugins (both Node.js and WASM) in a unified list. WASM plugins integrate seamlessly with the existing plugin configuration system. <h2 id="api-reference" class="tsd-anchor-link">API Reference<a href="#api-reference" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h2> <h3 id="base-classes" class="tsd-anchor-link">Base Classes<a href="#base-classes" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h3> <h4 id="_" class="tsd-anchor-link"><code>Plugin</code><a href="#_" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Abstract base class for all plugins. Methods to implement: <ul> <li><code>id(): string</code> - Unique plugin identifier</li> <li><code>name(): string</code> - Human-readable name</li> <li><code>schema(): string</code> - JSON schema for configuration</li> <li><code>start(config: string): i32</code> - Initialize plugin</li> <li><code>stop(): i32</code> - Clean shutdown</li> </ul> <h3 id="signal-k-types" class="tsd-anchor-link">Signal K Types<a href="#signal-k-types" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h3> <h4 id="_-1" class="tsd-anchor-link"><code>Delta</code><a href="#_-1" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Represents a Signal K delta message. <pre><code class="typescript">const delta = new Delta('vessels.self', [update]) </code><button type="button">Copy</button></pre> <h4 id="_-2" class="tsd-anchor-link"><code>Update</code><a href="#_-2" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Represents an update within a delta. The server automatically adds <code>$source</code> and <code>timestamp</code>. <pre><code class="typescript">const update = new Update([pathValue]) </code><button type="button">Copy</button></pre> <h4 id="_-3" class="tsd-anchor-link"><code>PathValue</code><a href="#_-3" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Represents a path-value pair. <pre><code class="typescript">const pathValue = new PathValue('navigation.position', positionJson) </code><button type="button">Copy</button></pre> <h4 id="_-4" class="tsd-anchor-link"><code>Position</code><a href="#_-4" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> GPS position with latitude/longitude. <pre><code class="typescript">const pos = new Position(60.1, 24.9) const posJson = pos.toJSON() </code><button type="button">Copy</button></pre> <h4 id="_-5" class="tsd-anchor-link"><code>Notification</code><a href="#_-5" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Signal K notification. <pre><code class="typescript">const notif = new Notification(NotificationState.normal, 'Hello!') const notifJson = notif.toJSON() </code><button type="button">Copy</button></pre> <h3 id="api-functions" class="tsd-anchor-link">API Functions<a href="#api-functions" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h3> <h4 id="_-6" class="tsd-anchor-link"><code>emit(delta: Delta): void</code><a href="#_-6" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Emit a delta message to Signal K server. <pre><code class="typescript">emit(delta) </code><button type="button">Copy</button></pre> Requires capability: <code>dataWrite: true</code> <h4 id="_-7" class="tsd-anchor-link"><code>setStatus(message: string): void</code><a href="#_-7" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Set plugin status (shown in admin UI). <pre><code class="typescript">setStatus('Running normally') </code><button type="button">Copy</button></pre> <h4 id="_-8" class="tsd-anchor-link"><code>setError(message: string): void</code><a href="#_-8" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Report an error (shown in admin UI). <pre><code class="typescript">setError('Sensor connection failed') </code><button type="button">Copy</button></pre> <h4 id="_-9" class="tsd-anchor-link"><code>debug(message: string): void</code><a href="#_-9" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Log debug message to server logs. <pre><code class="typescript">debug('Processing data: ' + value.toString()) </code><button type="button">Copy</button></pre> <h4 id="_-10" class="tsd-anchor-link"><code>getSelfPath(path: string): string | null</code><a href="#_-10" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Read data from vessel.self. <pre><code class="typescript">const speedJson = getSelfPath('navigation.speedOverGround') if (speedJson !== null) { const speed = parseFloat(speedJson) } </code><button type="button">Copy</button></pre> Requires capability: <code>dataRead: true</code> <h4 id="_-11" class="tsd-anchor-link"><code>getPath(path: string): string | null</code><a href="#_-11" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Read data from any context. <pre><code class="typescript">const posJson = getPath('vessels.self.navigation.position') </code><button type="button">Copy</button></pre> Requires capability: <code>dataRead: true</code> <h4 id="_-12" class="tsd-anchor-link"><code>readConfig(): string</code><a href="#_-12" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Read plugin configuration. <pre><code class="typescript">const configJson = readConfig() </code><button type="button">Copy</button></pre> <h4 id="_-13" class="tsd-anchor-link"><code>saveConfig(configJson: string): i32</code><a href="#_-13" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h4> Save plugin configuration. <pre><code class="typescript">const result = saveConfig(JSON.stringify(config)) if (result !== 0) { setError('Failed to save config') } </code><button type="button">Copy</button></pre> <h3 id="helper-functions" class="tsd-anchor-link">Helper Functions<a href="#helper-functions" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h3> <pre><code class="typescript">import { createSimpleDelta, getCurrentTimestamp } from '@signalk/assemblyscript-plugin-sdk' // Quick delta creation const delta = createSimpleDelta('my-plugin', 'test.value', '"hello"') emit(delta) </code><button type="button">Copy</button></pre> <h3 id="json-parsing" class="tsd-anchor-link">JSON Parsing<a href="#json-parsing" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h3> The SDK includes <a href="https://github.com/near/assemblyscript-json">assemblyscript-json</a> for parsing JSON data. This is useful when working with configuration, API responses, or resource provider requests. <pre><code class="typescript">import { JSON } from '@signalk/assemblyscript-plugin-sdk/assembly' // Parse a JSON string const jsonStr = '{"name": "My Boat", "speed": 5.2}' const parsed = JSON.parse(jsonStr) if (parsed.isObj) { const obj = parsed as JSON.Obj // Get string values const nameValue = obj.getString('name') if (nameValue !== null) { const name = nameValue.valueOf() // "My Boat" } // Get number values const speedValue = obj.getNum('speed') if (speedValue !== null) { const speed = speedValue.valueOf() // 5.2 (as f64) } } </code><button type="button">Copy</button></pre> Available methods on <code>JSON.Obj</code>: <ul> <li><code>getString(key)</code> - Returns <code>JSON.Str | null</code></li> <li><code>getNum(key)</code> - Returns <code>JSON.Num | null</code></li> <li><code>getBool(key)</code> - Returns <code>JSON.Bool | null</code></li> <li><code>getObj(key)</code> - Returns <code>JSON.Obj | null</code></li> <li><code>getArr(key)</code> - Returns <code>JSON.Arr | null</code></li> <li><code>getValue(key)</code> - Returns <code>JSON.Value | null</code></li> </ul> Note: Plugins using resource providers or parsing complex JSON should add <code>assemblyscript-json</code> to their dependencies: <pre><code class="bash">npm install assemblyscript-json </code><button type="button">Copy</button></pre> <h3 id="json-value-encoding" class="tsd-anchor-link">JSON Value Encoding<a href="#json-value-encoding" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h3> Values must be JSON-encoded strings: <pre><code class="typescript">// Numbers const pathValue = new PathValue('temperature', '25.5') // Strings (note the quotes) const pathValue = new PathValue('name', '"My Boat"') // Objects const pathValue = new PathValue( 'position', '{"latitude":60.1,"longitude":24.9}' ) // Use helper classes const pos = new Position(60.1, 24.9) const pathValue = new PathValue('position', pos.toJSON()) </code><button type="button">Copy</button></pre> <h2 id="resource-providers" class="tsd-anchor-link">Resource Providers<a href="#resource-providers" aria-label="Permalink" class="tsd-anchor-icon"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="../../../assets/icons.svg#icon-anchor"></use></svg></a></h2> WASM plugins can register as resource provi