How to implement VerneMQ plugins using a HTTP interface
The VerneMQ Webhooks plugin provides an easy and flexible way to build powerful plugins for VerneMQ using web hooks. With VerneMQ Webhooks you are free to select the implementation language to match your technical requirements or the language in which you feel comfortable and productive in. You can use any modern language such as Python, Go, C#/.Net and indeed any language in which you can build something that can handle HTTP requests.
The idea of VerneMQ Webhooks very simple: you can register an HTTP endpoint with a VerneMQ plugin hook and whenever the hook (such as auth_on_register
) is called, the VerneMQ Webhooks plugin dispatches a HTTP post request to the registered endpoint. The HTTP post request contains a HTTP header like vernemq-hook: auth_on_register
and a JSON encoded payload. The endpoint then responds with code 200 on success and with a JSON encoded payload informing the VerneMQ Webhooks plugin which action to take (if any).
To enable webhooks make sure to set:
And then each webhook can be configured like this:
It is also possible to dynamically register webhooks at run-time:
See which endpoints are registered:
And finally deregistering an endpoint:
We recommend placing the endpoint implementation locally on each VerneMQ node such that each request can go over localhost without being subject to network issues. Also note that currently VerneMQ Webhooks does not encrypt requests in any way or use HTTPS, so care should be taken if the endpoints are made reachable over the network.
Each registered hook uses by default a connection pool containing maximally 100 connections. This can be changed by setting vmq_webhooks.pool_max_connections
to a different value. Similarly the vmq_webhooks.pool_timeout
configuration (value is in milliseconds) can be set to control how long an unused connection should stay in the connection pool before being closed and removed. The default value is 60000 (60 seconds).
These options are available in VerneMQ 1.4.0.
VerneMQ webhooks support caching of the auth_on_register
, auth_on_publish
and auth_on_subscribe
hooks.
This can be used to speed up authentication and authorization tremendously. All data passed to these hooks is used to look if the call is in the cache, except in the case of the auth_on_publish
where the payload is omitted.
To enable caching for an endpoint simply return the cache-control: max-age=AgeInSeconds
in the response headers to one of the mentioned hooks. If the call was successful (authentication granted), the request will be cached together with any modifiers, except for the payload
modifier in the auth_on_publish
hook.
Whenever a non-expired entry is looked up in the cache the endpoint will not be called and the modifiers of the cached entry will be returned, if any.
It is possible to inspect the cache using:
Cache entries are currently not actively disposed after expiry and will remain in memory.
All webhooks are called with method POST
. All hooks need to be answered with the HTTP code 200
to be considered successful. Any hook called that does not return the 200
code will be logged as an error as will any hook with an unparseable payload.
All hooks are called with the header vernemq-hook
which contains the name of the hook in question.
For detailed information about the hooks and when they are called, see the sections Session Lifecycle, Subscribe Flow and Publish Flow.
Note, when overriding a mountpoint or a client-id both have to be returned by the webhook implementation for it to have an effect.
Header: vernemq-hook: auth_on_register
Webhook example payload:
A minimal response indicating the authentication was successful looks like:
It is also possible to override various client specific settings by returning an array of modifiers:
Note, the retry_interval
is in milli-seconds. It is possible to override many more settings, see the Session Lifecycle for more information.
Other possible responses:
Header: vernemq-hook: auth_on_subscribe
Webhook example payload:
A minimal response indicating the subscription authorization was successful looks like:
Another example where where the topics to subscribe have been rewritten looks like:
Note, you can also pass a qos
with value 128
which means it was either not possible or the client was not allowed to subscribe to that specific question.
Other possible responses:
Header: vernemq-hook: auth_on_publish
Note, in the example below the payload is not base64 encoded which is not the default.
Webhook example payload:
A minimal response indicating the publish was authorized looks like:
A more complex example where the publish topic, qos, payload and retain flag is rewritten looks like:
Other possible responses:
Header: vernemq-hook: on_register
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_publish
Note, in the example below the payload is not base64 encoded which is not the default.
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_subscribe
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_unsubscribe
Webhook example payload:
Example response: