Application-events module

The Application Events Module is a standalone service that bridges Guardian's internal NATS event bus and external HTTP-based systems. It removes the need for external integrators to operate their own NATS client by providing:

A webhook registry — register HTTP endpoints that receive event payloads via POST.
A streaming endpoint — consume all events as a chunked JSON stream over HTTP.
A REST API — manage webhook subscriptions and enumerate available event subjects.

The service runs on port 3012 by default. Interactive Swagger documentation is available at http://localhost:3012/api-docs.

Architecture

Guardian Services
      │
      │ publishes events to
      ▼
   NATS Broker
      │
      │ subscribed by
      ▼
Application Events Module (port 3012)
      │
      ├──► Registered Webhooks (HTTP POST to your URLs)
      │
      └──► GET /api/events/subscribe (chunked JSON stream)

On startup the module:

Connects to MongoDB to load persisted webhook registrations.
Connects to the NATS broker and subscribes to all exposed event subjects.
For each received message, delivers the payload to all matching registered webhooks.

The simplest way to consume events is the streaming endpoint. It returns a chunked JSON array that stays open as long as the connection is alive. Each element is a JSON object with the event subject and payload.

curl -N http://localhost:3012/api/events/subscribe

Example stream output:

[
{"subject":"external-events.token_minted","payload":{"tokenId":"0.0.1554488","tokenValue":10}},
{"subject":"external-events.ipfs_added_file","payload":{"cid":"QmPs2ufs5VQPYGGX1ewEjKSR8zuEmeuWK4GBKFHZjXTCAQ","url":"ipfs://QmPs2ufs5VQPYGGX1ewEjKSR8zuEmeuWK4GBKFHZjXTCAQ"}},

The stream remains open. When the NATS connection closes, the array is terminated with {"connection":"closed"}].

Quickstart: Register a Webhook

Step 1 — Retrieve the list of available event subjects:

curl http://localhost:3012/api/events

Returns a JSON array of all event subject strings the module is currently forwarding, for example:

[
  "external-events.token_minted",
  "external-events.token_mint_complete",
  "external-events.error_logs",
  "external-events.block_event",
  "external-events.ipfs_added_file",
  "policy-event-policy-ready",
  "policy-engine-event-publish-policies",
  ...
]

Step 2 — Register a webhook for one or more event subjects:

curl -X POST http://localhost:3012/api/webhooks \
  -H "Content-Type: application/json" \
  -d '{
    "url": "https://your-system.example.com/guardian-events",
    "events": [
      "external-events.token_minted",
      "external-events.block_event"
    ]
  }'

Response 201 Created:

{
  "id": "63e3e5e8a01b3c001234abcd"
}

Step 3 — Receive events at your endpoint:

When Guardian mints a token, your endpoint will receive an HTTP POST:

{
  "tokenId": "0.0.1554488",
  "tokenValue": 10,
  "memo": "policy-mint"
}

REST API Reference

List Available Event Subjects

GET /api/events

Returns the complete list of NATS event subjects the module is currently subscribed to and will forward to webhooks or the streaming endpoint.

Status: 200 OK

[
  "external-events.token_minted",
  "external-events.token_mint_complete",
  "external-events.error_logs",
  "external-events.block_event",
  "external-events.ipfs_added_file",
  "policy-event-generate-policy",
  "policy-event-policy-ready",
  "..."
]

GET /api/events/subscribe

Opens a persistent chunked HTTP response. Each chunk is a JSON object:

{"subject": "<event-subject>", "payload": <event-payload>}

The response uses Transfer-Encoding: chunked and Content-Type: application/json. The stream starts with [ and each element is separated by ,\n. The array is closed when the NATS connection terminates.

Status: 200 OK (streaming)

Register a Webhook

POST /api/webhooks

Persists a new webhook registration. The module will HTTP POST the event payload to url whenever an event matching one of the registered events subjects is received.

Request Body:

{
  "url": "https://your-system.example.com/events",
  "events": [
    "external-events.token_minted",
    "external-events.block_event"
  ]
}

Field

Type

Required

Description

url

string

Yes

Publicly reachable HTTPS URL that accepts POST requests

events

string[]

List of event subjects to subscribe to; omit or pass [] to receive all events

Status: 201 Created

{
  "id": "63e3e5e8a01b3c001234abcd"
}

Field

Description

id

MongoDB ObjectId of the created webhook registration

Error Responses:

Status

Description

400 Bad Request

Request body failed schema validation

500 Internal Server Error

Database write failed

List Registered Webhooks

GET /api/webhooks

Returns all persisted webhook registrations.

Status: 200 OK

[
  {
    "_id": "63e3e5e8a01b3c001234abcd",
    "url": "https://your-system.example.com/events",
    "events": ["external-events.token_minted"],
    "createdAt": "2026-04-06T08:00:00.000Z"
  }
]

Retrieve a Webhook

GET /api/webhooks/{id}

Returns a single webhook registration by its MongoDB ObjectId.

Path Parameters:

Parameter

Type

Required

Description

id

string

Yes

MongoDB ObjectId of the webhook

Status: 200 OK

{
  "_id": "63e3e5e8a01b3c001234abcd",
  "url": "https://your-system.example.com/events",
  "events": ["external-events.token_minted"],
  "createdAt": "2026-04-06T08:00:00.000Z"
}

Error Responses:

Status

Description

404 Not Found

No webhook exists with the given id

Update a Webhook

PUT /api/webhooks/{id}

Replaces the url and events fields of an existing webhook registration.

Path Parameters:

Parameter

Type

Required

Description

id

string

Yes

MongoDB ObjectId of the webhook

Request Body:

{
  "url": "https://your-system.example.com/new-endpoint",
  "events": [
    "external-events.token_minted",
    "external-events.token_mint_complete"
  ]
}

Field

Type

Required

Description

url

string

Yes

Updated destination URL

events

string[]

Yes

Updated list of event subjects

Status: 204 No Content

Error Responses:

Status

Description

400 Bad Request

Request body failed schema validation

404 Not Found

No webhook exists with the given id

Delete a Webhook

DELETE /api/webhooks/{id}

Removes a webhook registration. The module will immediately stop forwarding events to the associated URL.

Path Parameters:

Parameter

Type

Required

Description

id

string

Yes

MongoDB ObjectId of the webhook to delete

Status: 204 No Content

Available Event Subjects

The module exposes all events from three sources, minus internal request/reply hooks that are not suitable for HTTP delivery. Use GET /api/events to retrieve the live list. The categories are:

Core External Events

Subject

Description

external-events.token_minted

Token successfully minted

external-events.token_mint_complete

Mint batch complete

external-events.error_logs

Error written to Guardian logger

external-events.block_event

Policy block execution event

external-events.ipfs_added_file

File pinned to IPFS

The following subjects are excluded from webhook/stream delivery because they are request/reply hooks requiring a synchronous NATS response: external-events.ipfs_before_upload_content, external-events.ipfs_after_read_content, external-events.ipfs_loaded_file

Policy Coordination Events (selected)

Subject

Description

policy-event-generate-policy

Policy instance generation started

policy-event-policy-ready

Policy instance is ready to serve requests

policy-event-policy-start-error

Policy failed to start

policy-event-delete-policy

Policy instance deleted

policy-event-block-update-broadcast

A block's state changed and UI should refresh

policy-event-mrv-data

MRV (measurement, reporting, verification) data received

policy-event-record-update-broadcast

Recording state changed

Policy Engine Events (selected)

Subject

Description

policy-engine-event-create-policies

New policy created

policy-engine-event-publish-policies

Policy published to Hedera

policy-engine-event-dry-run-policies

Policy entered dry-run mode

policy-engine-event-draft-policies

Policy reverted to draft

policy-engine-event-delete-policy-async

Async policy deletion started

policy-engine-event-migrate-data

Policy data migration started

policy-engine-event-receive-external-data

External data submitted to a running policy

The full enumeration of all policy coordination and engine event subjects is defined in:

Webhook Delivery

When an event is received on a subscribed NATS subject, the module iterates over all registered webhooks whose events array includes that subject and performs an HTTP POST to each registered URL.

Method: POST
Content-Type: application/json
Body: The raw event payload (the object published on NATS)

Delivery is best-effort. If a webhook URL returns an error or times out, the failure is logged and the module moves on. There is no built-in retry mechanism — design your endpoint to be idempotent and implement your own retry handling if required.

Configuration

The module is configured via environment variables. The key variables are:

Variable

Default

Description

PORT

3012

HTTP port the service binds to

MONGODB_URI

—

MongoDB connection string for webhook persistence

MQ_ADDRESS

—

NATS broker address (e.g., nats://localhost:4222)

Refer to the application-events/.env.example file in the repository for the complete list.

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Architecture

Quickstart: Subscribe via Streaming Endpoint

Quickstart: Register a Webhook

REST API Reference

List Available Event Subjects

Subscribe to Event Stream

Register a Webhook

List Registered Webhooks

Retrieve a Webhook

Update a Webhook

Delete a Webhook

Available Event Subjects

Core External Events

Policy Coordination Events (selected)

Policy Engine Events (selected)

Webhook Delivery

Configuration