You can use webhook subscriptions to receive notifications about particular events that occur in an account. These event notifications are sent as a HTTP POST to the callback URL that you specify in the subscription.

​

Subscribing to events

​

Event types

Webhook subscriptions can be managed using the /webhooks endpoint. To see a list of available events make a GET request to /webhooks/types which will return a list of strings representing the events:

{
    "value": [
        "activitycode.created",
        "activitycode.deleted",
        "activitycode.updated",
        "archive.updated",
        "billingconfiguration.updated",
        "contact.created",
        "contact.deleted",
        "contact.restored",
        "contact.updated",
        "expense.created",
        "expense.deleted",
        "expense.updated",
        "event.updated",
        "files.updated",
        "fee.created",
        "fee.deleted",
        "fee.updated",
        "firm.created",
        "firm.updated",
        "firmuser.updated",
        "invoice.finalized",
        "layoutdesign.updated",
        "layoutmatter.created",
        "layoutmatter.updated",
        "mattertype.created",
        "mattertype.deleted",
        "mattertype.restored",
        "mattertype.updated",
        "matter.created",
        "matter.updated",
        "matteritems.updated",
        "matterstage.updated",
        "memo.created",
        "memo.updated",
        "memo.deleted",
        "memo.restored",
        "roles.updated",
        "staff.created",
        "staff.updated",
        "stageset.created",
        "stageset.updated",
        "task.created",
        "task.updated",
        "task.deleted",
        "user.registered",
        "user.unregistered",
        "error"
    ]
}

The /webhooks endpoint will also allow you to list, edit and delete any subscriptions that you have created.

​

Creating a subscription

To create a subscription, make a POST request to the /webhooks endpoint:

curl --request POST 'https://api.smokeball.com/webhooks' \
  --header 'Content-Type: application/json' \
  --data-raw '{  \r\n  \"name\": \"MyContactsWebhook\",\r\n  \"eventTypes\": [\r\n    \"contact.created\",\r\n    \"contact.updated\",\r\n    \"contact.deleted\",\r\n    \"contact.restored\"\r\n  ],    \r\n  \"eventNotificationUrl\": \"https:\/\/mydomain.com\/webhooks\/contacts\",  \r\n}'

• Response *

HTTP/1.1 200 OK
Content-Type: application/json

{
  "id": "82336fc0-8208-406f-b11c-f2b520d081a3",
  "key": "i7641529ue420n8b9",
  "name": "MyContactsWebhook",
  "eventTypes": [
    "contact.created",
    "contact.updated",
    "contact.deleted",
    "contact.restored"
  ],
  "eventNotificationUrl": "https://mydomain.com/webhooks/contacts",
  "createdDateUtc": "2021-05-05T01:36:43.0503643Z",
  "updatedDateUtc": "2021-05-05T01:36:43.0503944Z"
}

​

Event handling

​

Notification schema

Webhook notifications contain event-specific data in their payload field. The structure varies by event type - refer to the relevant API documentation for payload details.

Below is a sample notification for a matter.updated event:

{    
    "accountId": "1e53979d-9269-4159-b104-2e603670f59d",
    "subscriptionId": "6543c46b-d1d5-4a00-8732-36a63a20c3b4",
    "type": "matter.updated",
    "source": "API",
    "payload": {
        "id": "68df1d38-b9a3-4855-b32f-6af1aae2f258",
        "externalSystemId": null,
        "number": "10001",
        "title": "John Smith | Sale",
        "matterType": {
            "id": "602b31b2-da47-4b17-9ff5-f84f3f3efeec",
            "rel": "MatterTypes"
        },
        "clients": [
            {
                "id": "6aeee3fb-7587-4b33-8570-9d34dbde5d8f",
                "rel": "Contacts"
            }
        ],
        "description": "Sale of Franchise",
        "status": "Open"
    },
    "timestamp": 637981232724209300
}

​

Handling duplicate events

Webhook endpoints may occasionally receive the same event more than once. We advise that you guard against this by making your event processing idempotent.

​

Order of events

Smokeball does not guarantee delivery of events in the order in which they are generated. It is rare but possible that you may receive a contact.updated event before a contact.created event.

​

Preventing infinite update loops

If you initiate a change to a resource via the API you will more than likely receive one or more webhook events caused by that change. If you are not careful you might find yourself in an update loop like the following scenario:

1. A change is made to a resource in your system
2. This triggers your code to call the Smokeball API to update the corresponding resource in Smokeball
3. You receive a webhook event from Smokeball for the resource you updated
4. You update the resource in your system
5. This triggers you to call the Smokabll API to update the corresponding resource
6. and so on…

To avoid this scenario it is recommended that you set the RequestId header with all of you API requests. If supplied, this header will always be returned in your API responses as well as all webhook events that were triggered from your original request. This allows you to filter or ignore webhook events that were initiaited by your changes.

​

Error Handling

Because our API request handling is an eventually consistent operation, we supply a error webhook event so you can be notified when processing your API request has failed. We provide the name and id of the failed resource and a description of the problem.

A sample of the error payload is as follows:

{
   "accountId": "1e53979d-9269-4159-b104-2e603670f59d",
    "subscriptionId": "6543c46b-d1d5-4a00-8732-36a63a20c3b4",
    "type": "error",
    "source": "API",
    "payload": {
      "message": "Contact does not belong to account 1e53979d-9269-4159-b104-2e603670f59d.",
      "resourceName": "contact",
      "resourceId": "fbd61c97-ee92-49b7-ba8e-84e0ed857078"
    },
    "timestamp": 637981232724209300
}

​

Verifying webhooks

If you supplied a key when you created a subscription, a header called Signature will be included when Smokeball calls your callback URL. The signature is a HMAC SHA256 hash that was created with the key that you provided. You can perform the same hashing process on your event processing side to verify that the request came from Smokeball.

​

Computing the HMAC

The Signature hash is calculated using these three bits of information:

1. The Timestamp header which is the ticks representation of the UTC datetime (.Net format) the webhook was sent
2. The RequestId header
3. Your ClientId that you use to authenticate with the API

These three parameters need to be concatenated into a single string, seperated by a | and can then be used to create the hash. For example:

// Your key you provided in the subscription
var key = "ei7641529ue420n8b9aa";

var timestamp = "637558795239278688";
var requestId = "38583489-09c4-49ef-b58c-ef1b34208cca";
var clientId = "lou1qnn0llav95f";

var payload = "637558795239278688|38583489-09c4-49ef-b58c-ef1b34208cca|lou1qnn0llav95";

var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(key));
var hash = hmac.ComputeHash(Encoding.UTF8.GetBytes(payload));
return BitConverter.ToString(hash).Replace("-", "").ToLower();

This produces the hash string feb4b838a272884f6d2c2580b2c7ebb0b2f725b90e8baa6f9b5e1a17a9faec2d

​

Guarding against replay attacks

A replay attack is when an attacker intercepts a valid payload and its signature, then re-transmits them. To mitigate such attacks Smokeball provides a Timestamp header which is the ticks representation (.Net format) of when the webhook event was sent. It is also part of the verification signature so an attacker can not change the timestamp without invalidating the signature.

If the signature is valid but the timestamp is too old, you may choose to reject the message.