A system hook that extends a function call by an HTTP call under defined conditions.

Introduction

In order to insert an additional action into the process flow of a functional sequence, the ability for reacting to a function call is required. In yuuvis® Momentum, webhooks are a suitable option for this purpose. They belong to the system hooks and thus are triggered by function calls under specified conditions defined on their predicate attribute.

A webhook extends the function by an HTTP call. Whenever the predicate of a webhook delivers a true result, an optional HTTP call to a web URL defined in the webhook configuration is performed. The process flow is interrupted until the webhook activity is finished. Thus, the webhook can perform additional processing steps before passing the data back to resume the interrupted main process. If the predicate of a webhook delivers a false result, the HTTP call is skipped.

For the additional processing, a custom service has to be implemented. This service must be able to handle the request body and the assigned headers. Please note the maximum header size that should be supported by your custom service.

Import and content update webhooks are called in the Repository service, all others in the API-gateway service.

Any changes to the webhook configuration require a restart of the services that are responsible for the call of the affected functions. 

Webhook Types

Depending on their type, webhooks are triggered in different situations within the data processing chain.

The webhook type dms.response.objects can be triggered in various situations. For some of them there are special webhook types (dms.response.objects.insert, dms.response.objects.update, dms.response.objects.search, dms.response.objects.delete). These sub-webhooks are triggered directly after dms.response.objects.

Predicate

The predicate specifies the condition for the call of individual webhooks. It is declared in the webhook configuration.

If multiple webhooks are registered for the same webhook type, the predicate is applied to the original predicate target for each of them and in the order of definition. Imagine an example scenario with two registered webhooks of the type dms.response.objects.search: 

{
    "enable": true,
    "predicate": "spel:true",
    "type": "dms.response.objects.search",
    "url": <suitable endpoint removing the property 'appEmail:bcc'>,
    "useDiscovery": true
},
{
    "enable": true,
    "predicate": "spel:properties['appEmail:bcc']!=null",
    "type": "dms.response.objects.search",
    "url": <any suitable endpoint>,
    "useDiscovery": true
}

If objects in a search result have the appEmail:bcc property and the first webhook removes this property from the objects, the predicate of the second webhook still matches.

The same behavior holds for the webhook type dms.response.objects and one of its sub-webhook types dms.response.objects.*:

{
    "enable": true,
    "predicate": "spel:true",
    "type": "dms.response.objects",
    "url": <suitable endpoint removing the property 'appEmail:bcc'>,
    "useDiscovery": true
},
{
    "enable": true,
    "predicate": "spel:properties['appEmail:bcc']!=null",
    "type": "dms.response.objects.search",
    "url": <any suitable endpoint>,
    "useDiscovery": true
}

Configuring Webhooks

As a type of system hooks, webhooks are configured in the \service-manager\config\system\systemHookConfiguration.json configuration file within the service manager in JSON format. Any changes to the system hook configuration will not apply until the affected services have been restarted.

>> systemHookConfiguration.json

The timeouts that limit the process time of webhooks in order to avoid system bottlenecks are configured in the application-prod.yml configuration file as shown in the following example:

service:
  connection-timeout-ms: 3000
  socket-timeout-ms: 10000

Loggers for Webhooks

As of version 2022 Spring, the input and output data for each webhook can be monitored via loggers.
>> Logging Configuration

The logging level can be specified

• for all webhooks, e.g., os.dev.webhooks=DEBUG, or
• for individual webhook types, e.g., os.dev.webhooks.dms.request.search=DEBUG.

The logging configuration for each webhook has to be read by the service that calls the webhook. For the individual webhook types, different services are responsible. Thus, please ensure that your webhook logging configuration is defined in a configuration file that is read by its calling service. In order to apply the configuration changes, each calling service has to be refreshed or restarted.

Depending on the logging level, the following details are logged:

Summary

This article gave an overview of the webhook types that are available in yuuvis® Momentum. Check out the "Preprocessing Metadata using Webhooks" tutorial for an example application which shows different webhook types.