golem-mark-read-only-ts

Marking Agent Methods as Read-Only (TypeScript)

Overview

A read-only agent method is one you promise is a pure read of the agent's already-loaded state: it must not mutate anything and its result must depend only on its inputs and the current state. Golem enforces the most important part of this contract — writes to persistent state, outgoing HTTP, and RPC calls trap at runtime with a ReadOnlyViolation agent error before they run — but it does not detect every source of impurity (in-memory mutation, clocks, randomness, env reads), so keeping the method pure is partly your responsibility (see What Works in a Read-Only Method).

Marking a method read-only also lets the host treat it as a side-effect-free query: it may bypass the invocation queue and agent loading, and read-only methods mapped to GET/HEAD participate in HTTP caching semantics.

Mark a method read-only by setting readOnly: true on the method(...) spec.

Usage

import { z } from 'zod';
import { defineAgent, method } from '@golemcloud/golem-ts-sdk';

export const CounterAgent = defineAgent({
    name: 'CounterAgent',
    id: { name: z.string() },
    methods: {
        // Non-read-only: writes shared state
        increment: method({ input: {}, returns: z.number() }),
        // Read-only: pure read over already-loaded state
        getCount: method({ input: {}, returns: z.number(), readOnly: true }),
    },
});

export const CounterAgentImpl = CounterAgent.implement({
    init: () => ({ count: 0 }),
    methods: {
        increment() {
            this.count += 1;
            return this.count;
        },
        getCount() {
            return this.count;
        },
    },
});

Cache policy. readOnly: true uses the until-write cache policy (the base-SDK default). For finer control, pass an object instead of the boolean: readOnly: { cache: 'no-cache' | 'until-write' | { ttlNanos: <bigint> }, usesPrincipal?: boolean } — no-cache never caches, until-write caches until a mutating (non-read-only) method runs, { ttlNanos } caches for that time-to-live, and usesPrincipal: true keys the cache per caller principal. Reach for a regular (non-read-only) method whenever you need a side effect.

What Works in a Read-Only Method

A read-only method must be a pure function of the agent's already-loaded state and the method inputs. The operations in the middle column go through Golem's durability layer and trap with a ReadOnlyViolation agent error before they run and before anything is persisted. The operations in the right column are not detected — they do not trap, but they still break the contract and must be avoided by you.

Common Pitfalls

• Mutating state, reading a clock, randomness, or env in a read-only method is NOT detected. These do not trap — but they either mutate state that should be immutable here or make the result non-deterministic. The runtime cannot catch them; keeping the method pure is your responsibility. If you need any of them, use a regular (non-read-only) method instead.
• Writes to persistent state, outgoing HTTP (fetch), and RPC do trap. Those go through the durability layer and raise ReadOnlyViolation before running.
• A method that mutates this state must not be readOnly: true — assigning to a state field is a plain in-memory write, not a host call, so it does not trap; keeping the method mutation-free is your responsibility.

Key Points

• readOnly is per-method; an agent can mix read-only and regular methods freely.
• Read-only methods are the natural fit for HTTP GET/HEAD endpoints (load golem-add-http-endpoint-ts).
• A read-only method cannot call another agent via RPC; do read-only RPC fan-out from a regular method instead (see golem-call-another-agent-ts).