Functions & Triggers

Comparable to: Serverless function runtimes, Lambda, Cloud Functions

Key Concepts

Use the concepts below when they fit the task. Not every worker needs all of them.

• A Function is an async handler registered with a unique ID
• A Trigger binds an event source to a function — types include http, durable:subscriber, cron, state, stream, and subscribe
• Functions invoke other functions via trigger() regardless of language or worker location
• The engine handles serialization, routing, and delivery automatically
• HTTP-invoked functions wrap external endpoints as callable function IDs
• Functions can declare request/response formats for documentation and discovery — auto-generated from types in Rust (via schemars::JsonSchema) and Python (via type hints / Pydantic), or manually provided in Node.js

Architecture

registerWorker() connects the worker to the engine, registerFunction defines handlers, registerTrigger binds event sources to those handlers, and the engine routes incoming events to the correct function. Functions can invoke other functions across workers and languages via trigger().

iii Primitives Used

Reference Implementation

• TypeScript: ../references/functions-and-triggers.js
• Python: ../references/functions-and-triggers.py
• Rust: ../references/functions-and-triggers.rs

Each reference shows the same patterns (function registration, trigger binding, cross-function invocation) in its respective language.

Common Patterns

Code using this pattern commonly includes, when relevant:

• registerWorker('ws://localhost:49134', { workerName: 'my-worker' }) — connect to the engine
• registerFunction('namespace::name', async (input) => { ... }) — register a handler
• registerTrigger({ type: 'http', function_id, config: { api_path, http_method, middleware_function_ids? } }) — HTTP trigger (with optional middleware)
• registerTrigger({ type: 'durable:subscriber', function_id, config: { topic } }) — queue trigger
• registerTrigger({ type: 'cron', function_id, config: { expression } }) — cron trigger
• registerTrigger({ type: 'state', function_id, config: { scope, key } }) — state change trigger
• registerTrigger({ type: 'stream', function_id, config: { stream } }) — stream trigger
• registerTrigger({ type: 'subscribe', function_id, config: { topic } }) — pubsub subscriber
• Cross-language invocation: a TypeScript function can trigger a Python or Rust function by ID
• registerTrigger({ ..., metadata: { owner: 'team', priority: 'high' } }) — optional trigger metadata

Request/Response Format (Auto-Registration)

Functions can declare their input/output schemas for documentation and discovery:

• Rust: Derive schemars::JsonSchema on handler input/output types — RegisterFunction::new() auto-generates JSON Schema (Draft 7) from the type
• Python: Use type hints (Pydantic models or primitives) on handler parameters and return types — register_function() auto-extracts JSON Schema (Draft 2020-12)
• Node.js: Pass request_format / response_format manually in the registration message (e.g., via Zod's toJSONSchema())

Adapting This Pattern

Use the adaptations below when they apply to the task.

• Replace placeholder handler logic with real business logic (API calls, DB queries, LLM calls)
• Use namespace::name convention for function IDs to group related functions
• For HTTP endpoints, configure api_path and http_method in the trigger config
• For durable async work, use TriggerAction.Enqueue({ queue }) instead of synchronous trigger
• For fire-and-forget side effects, use TriggerAction.Void()
• Multiple workers in different languages can register functions that invoke each other by ID

Pattern Boundaries

• For HTTP endpoint specifics (request/response format, path params), prefer iii-http-endpoints.
• For queue processing details (retries, concurrency, FIFO), prefer iii-queue-processing.
• For cron scheduling details (expressions, timezones), prefer iii-cron-scheduling.
• For invocation modes (sync vs void vs enqueue), prefer iii-trigger-actions.
• Stay with iii-functions-and-triggers when the primary problem is registering functions, binding triggers, or cross-language invocation.

When to Use

• Use this skill when the task is primarily about iii-functions-and-triggers in the iii engine.
• Triggers when the request directly asks for this pattern or an equivalent implementation.

Boundaries

• Never use this skill as a generic fallback for unrelated tasks.
• You must not apply this skill when a more specific iii skill is a better fit.
• Always verify environment and safety constraints before applying examples from this skill.