Listener

List, Inser, Remove, Activate And Deactivate Orakl Network Listeners

The Orakl Network Listener is a microservice that is part of every Orakl Network solution (VRF, Request-Response). The listener configuration includes chain, service, address and eventName property. The Orakl Network Listener listens for an event defined as eventName emitted from smart contract address.

The Orakl Network CLI provides commands to modify both permanent or ephemeral state of Orakl Network Listener. The list of supported actions is shown below:

• List Listeners

• Insert New Listener

• Remove Listener Specified By id

• List Active Listeners

• Activate Listener

• Deactivate Listener

Permanent State

The permanent state of listener is loaded on launch of the Orakl Network Listener service. It is not accessed by other services such as the Orakl Network Worker or the Orakl Network Reporter.

List Listeners

Listeners kept in permanent state can be displayed with listener list command. You can filter the listeners by using optional parameters: --chain or --service .

orakl-cli listener list \
    [--chain ${chain}] \
    [--service ${service}]

• example

orakl-cli listener list --chain baobab --service DATA_FEED

The example output of listener list command is displayed below. It includes three different listeners that should listen on three addresses for three different events: RandomWordsRequested, NewRound and DataRequested.

[
  {
    "id": "1",
    "address": "0x9fE46736679d2D9a65F0992F2272dE9f3c7fa6e0",
    "eventName": "RandomWordsRequested",
    "service": "VRF",
    "chain": "baobab"
  },
  {
    "id": "2",
    "address": "0xa513E6E4b8f2a923D98304ec87F64353C4D5C853",
    "eventName": "NewRound",
    "service": "DATA_FEED",
    "chain": "baobab"
  },
  {
    "id": "3",
    "address": "0x45778c29A34bA00427620b937733490363839d8C",
    "eventName": "DataRequested",
    "service": "REQUEST_RESPONSE",
    "chain": "baobab"
  }
]

To list listeners associated with a specific chain, you can use the --chain parameter.

orakl-cli listener list \
    --chain ${chain}

• example

orakl-cli listener list --chain baobab

To list listeners associated with a specific service, you can use the --service parameter.

orakl-cli listener list \
    --service ${service}

• example

orakl-cli listener list --service VRF

Insert New Listener

To insert a new listener to a permanent listener state, you can use the listener insert command.

orakl-cli listener insert \
    --chain ${chain} \
    --service ${service} \
    --address ${address} \
    --eventName ${eventName}

• example

orakl-cli listener insert --chain baobab --service VRF --address 0x123 --eventName RandomWordsRequested

Remove Listener Specified By id

Listeners can be removed from a permanent listener state by the listener remove command. The listener to remove is specified by its identifier (--id).

orakl-cli listener remove \
    --id ${id}

• example

orakl-cli listener remove --id 72

Ephemeral State

The ephemeral state of listener is created during launch of the Orakl Network Listener service, and is used throughout its lifetime until it terminates. All commands from the Permanent State section will not have affect on the ephemeral state unless you apply the activate or deactivate commands that are described below.

Unlike the permanent listener state, the ephemeral listener state is accessed through a watchman that runs inside of Orakl Network Listener service. For this reason, every command that needs an access to ephemeral state has to specify a --host and a --port parameter that defines the location of the Orakl Network Listener service in the network.

List Active Listeners

All listeners that are part of the permanent state during the launch of the Orakl Network Listener service are automatically made active, and can be listed with listener active command. Listeners that are later activated will be visible through this command as well. If a listener is not in an active state, it does not listen to the event from its configuration.

orakl-cli listener active \
    --host ${host} \
    --port ${port}

• example

orakl-cli listener active --host http://127.0.0.1 --port 3030

Activate Listener

Listeners that are added to the permanent listener state after the launch of the Orakl Network Listener service are inactive by default. Inactive listeners can be activated by the listener activate command with --id parameter. The listener identifier can be found through the listener list command. After a listener becomes active, it starts listening for the events defined in its configuration.

orakl-cli listener activate \
    --id ${id}
    --host ${host} \
    --port ${port}

• example

orakl-cli listener activate --host http://127.0.0.1 --port 3030

Deactivate Listener

Every new active listener requires an extra computation resource, however, in general it operates with low overhead. When a listener spots an event for which it was listening for, it create a new job for the Orakl Network Worker, which then passes new job to the Orakl Network Reporter. The consequence of having an extra listener which we do need is an unnecessarily high load on the overall system.

To deactivate listener, and therefore to lower the load on the system, you can use listener deactivate command.

orakl-cli listener deactivate \
    --id ${id}
    --host ${host} \
    --port ${port}

• example

orakl-cli listener deactivate --host http://127.0.0.1 --port 3030

If you do not want to use listener long-term, you should remove it from the permanent listener state, otherwise it will become active after the Orakl Network Listener restarts.