Using Webhooks in a Rust Golem Agent

Overview

Golem webhooks let an agent generate a temporary public URL that, when POSTed to by an external system, delivers the request body to the agent. Under the hood, a webhook is backed by a Golem promise — the agent is durably suspended while waiting for the callback, consuming no resources.

This is useful for:

Integrating with webhook-driven APIs (payment gateways, CI/CD, GitHub, Stripe, etc.)
Receiving asynchronous callbacks from external services
Building event-driven workflows where an external system notifies the agent

Prerequisites

The agent type must be deployed via an HTTP API mount (mount = "/..." on #[agent_definition] and an httpApi deployment in golem.yaml). Without a mount, webhooks cannot be created.

Guide	Description
`golem-add-http-endpoint-rust`	Setting up the HTTP mount and endpoint annotations required before using webhooks
`golem-configure-api-domain`	Configuring `httpApi` in `golem.yaml`
`golem-wait-for-external-input-rust`	Lower-level promise API if you need more control than webhooks provide

API

All functions are in the golem_rust crate:

Function / Type	Description
`create_webhook()`	Creates a webhook (promise + public URL) and returns a `WebhookHandler`
`WebhookHandler::url()`	Returns the public URL to share with external systems
`WebhookHandler` (await)	Implements `IntoFuture` — use `.await` to get the `WebhookRequestPayload`
`WebhookRequestPayload::json::<T>()`	Decodes the POST body as JSON (`T: DeserializeOwned`)
`WebhookRequestPayload::raw_data()`	Returns the raw POST body as `Vec<u8>`

Imports


use golem_rust::create_webhook;

Webhook URL Structure

Webhook URLs have the form:


https://<domain>/<prefix>/<suffix>/<id>

<domain> — the domain where the HTTP API is deployed

<prefix> — defaults to /webhooks, customizable via webhookUrl in the httpApi deployment section of golem.yaml:


httpApi:
  deployments:
    local:
    - domain: my-app.localhost:9006
      webhookUrl: "/my-custom-webhooks/"
      agents:
        OrderAgent: {}

<suffix> — defaults to the agent type name in kebab-case (e.g., OrderAgent → order-agent), customizable via webhook_suffix
<id> — a unique identifier for the specific webhook instance

Webhook Suffix

You can configure a webhook_suffix on the #[agent_definition] to override the default kebab-case agent name in the webhook URL:


#[agent_definition(mount = "/api/orders/{id}", webhook_suffix = "/workflow-hooks")]
pub trait OrderAgent {
    fn new(id: String) -> Self;
    // ...
}

Path variables in {braces} are also supported in webhook_suffix:


#[agent_definition(mount = "/api/events/{name}", webhook_suffix = "/{agent-type}/callbacks/{name}")]

Usage Pattern


let webhook = create_webhook();
let url = webhook.url().to_string();
 
// Share `url` with an external service (e.g., register it as a callback URL)
// The agent is durably suspended here until the external service POSTs to the URL
 
let payload = webhook.await;

2. Decode the Payload as JSON


use serde::Deserialize;
 
#[derive(Deserialize)]
struct PaymentEvent {
    status: String,
    amount: u64,
}
 
let webhook = create_webhook();
// ... share webhook.url() ...
let payload = webhook.await;
let event: PaymentEvent = payload.json().expect("Invalid payload");

3. Use Raw Bytes


let webhook = create_webhook();
// ... share webhook.url() ...
let payload = webhook.await;
let raw: Vec<u8> = payload.raw_data();

Complete Example


use golem_rust::{agent_definition, agent_implementation, endpoint, Schema, create_webhook};
use serde::Deserialize;
 
#[derive(Deserialize)]
struct WebhookEvent {
    event_type: String,
    data: String,
}
 
#[agent_definition(mount = "/integrations/{name}")]
pub trait IntegrationAgent {
    fn new(name: String) -> Self;
 
    async fn register_and_wait(&mut self) -> String;
 
    fn get_last_event(&self) -> String;
}
 
struct IntegrationAgentImpl {
    name: String,
    last_event: String,
}
 
#[agent_implementation]
impl IntegrationAgent for IntegrationAgentImpl {
    fn new(name: String) -> Self {
        Self {
            name,
            last_event: String::new(),
        }
    }
 
    #[endpoint(post = "/register")]
    async fn register_and_wait(&mut self) -> String {
        // 1. Create a webhook
        let webhook = create_webhook();
        let url = webhook.url().to_string();
 
        // 2. In a real scenario, you would register `url` with an external service here.
        //    For this example, the URL is returned so the caller can POST to it.
        //    The agent is durably suspended while awaiting.
 
        // 3. Wait for the external POST
        let payload = webhook.await;
        let event: WebhookEvent = payload.json().expect("Invalid webhook payload");
 
        self.last_event = format!("{}: {}", event.event_type, event.data);
        self.last_event.clone()
    }
 
    #[endpoint(get = "/last-event")]
    fn get_last_event(&self) -> String {
        self.last_event.clone()
    }
}

Key Constraints

The agent must have an HTTP mount (mount = "..." on #[agent_definition]) and be deployed via httpApi in golem.yaml
The webhook URL is a one-time-use URL — once POSTed to, the promise is completed and the URL becomes invalid
Only POST requests to the webhook URL will complete the promise
WebhookHandler implements IntoFuture, so use .await to wait for the callback
The agent is durably suspended while waiting — it survives failures, restarts, and updates