Working with Golem Promises

Golem promises provide a way for Golem agents to wait for an external condition. The agent creates the promise and somehow sends its identifier to the external system responsible for completing the promise. Then the agent can await the promise, being suspended until the external system completes the promise using Golem's REST API.

It is also possible to complete a promise from within a Golem agent using the Golem SDK, which is especially useful when used together with forking.

When a promise is completed, an arbitrary byte array can be attached to it as a payload; this data is returned to the awaiting agent when it continues execution.

Creating a promise

To create a promise simply call the createPromise function:

import {createPromise, PromiseId} from "@golemcloud/golem-ts-sdk"
 
function createPromiseId(): PromiseId {
    const promiseId: PromiseId = createPromise()
    return promiseId
}

The returned value has the type PromiseId, and defined as the following (including the nested types):

export type OplogIndex = bigint
 
export type Uuid = {
    highBits: bigint
    lowBits: bigint
}
 
// Represents a Golem component
export type ComponentId = {
    uuid: Uuid
}
 
// Represents a Golem agent
export type AgentId = {
    componentId: ComponentId
    agentId: string
}
 
// A promise ID is a value that can be passed to an external Golem API to complete that promise
// from an arbitrary external source, while Golem agents can await for this completion.
export type PromiseId = {
    agentId: AgentId
    oplogIdx: OplogIndex
}

Awaiting a promise

To await a promise, use the async awaitPromise function, which returns the promise result as a byte array payload. Here's an example that awaits a promise, then decodes the payload from JSON format:

import { awaitPromise, PromiseId } from "@golemcloud/golem-ts-sdk"
 
type MyPayload = {
  id: string
}
 
async function waitForPayload(promiseId: PromiseId): Promise<MyPayload> {
  const byteArrayPayload: Uint8Array = await awaitPromise(promiseId)
  return JSON.parse(new TextDecoder().decode(byteArrayPayload)) as MyPayload
}

Note that if an agent is only awaiting Golem promises (one or more), the agent gets suspended and is not going to consume any resources while waiting.

Completing a promise from within an agent

To complete a promise from within an agent, use the completePromise function. The following example completes a promise with a value encoded as JSON:

import { completePromise, PromiseId } from "@golemcloud/golem-ts-sdk"
 
function completeFromAgent(promiseId: PromiseId): boolean {
  const payload = {
    id: "value",
    meta: "data",
  }
  const byteArrayPayload: Uint8Array = new TextEncoder().encode(JSON.stringify(payload))
  return completePromise(promiseId, byteArrayPayload)
}

Completing a promise from an external source

To see how to use the promise ID to complete a promise through the external REST API, check the REST API documentation.

Webhooks

Golem Webhooks are built on top of promises. They provide a higher-level API for creating public callback URLs that complete a promise when an external system POSTs to them. See the Webhooks documentation for details.

Transactions Updating Agents