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On Demand Jobs

On demand jobs are special kind of jobs that can be used to access a processor on demand from a dapp. This is achieved by having the job open a websocket connection to the acurast websocket service and setup handlers to process incoming messages.

On Demand job script​

The snippet below shows a very simple on demand job script that setups a websocket connection to the acurast websocket service and registers a payload handler that just sends back the message it receives.

_STD_.ws.open( // open a websocket connection to the provided server
    [
       "wss://ws-1.ws-server-1.acurast.com",
       "wss://ws-1.ws-server-2.acurast.com ",
    ],
    () => {
        print("open: success")
        _STD_.ws.registerPayloadHandler((payload) => { // register a handler for incoming messages
            _STD_.ws.send(payload.sender, payload.payload) // just send back the received message
        })
    },
    (err) => {
        print("open: error " + err)
    }
);

An on demand job should be scheduled with a long duration since the job needs to continuously run in order to be able to process incoming messages.

dApp integration​

A dApp can start interacting with a running on demand job by integrating the Acurast typescript SDK. See the example dapp for on how a simple integration works.

Acurast websocket service​

The Acurast websocket service is a P2P service that allows to simply send messages to clients connected to it. Clients are authenticated during the initial connection setup by signing a challenge with their private key (in case of a processor, that would be the private key specifically generated for the job creator).

The initial connection setup and authentication flow is as follows:

  • Client sends an init message to the websocket service.
  • Websocket service responds with a challenge message, providing the bytes to be signed.
  • Client creates the payload to sign by concatenating the challenge bytes, the client public key and a 16 bytes nonce.
  • Client signs the payload and responds to the challenge by sending beck the signature alongside the originally received challenge bytes, client public key and nonce.
  • Websocket service verifies the signature and if it is valid accepts the connection.

After a client is authenticated, it can be addressed by specifying its public key as the recipient.