Notices

A notice is a verifiable data declaration that attests to off-chain events or conditions and is accompanied by proof.

Notices provide a mechanism to communicate essential off-chain events in the execution layer to the base layer in a verifiable manner.

Consider a scenario within a gaming dApp where players engage in battles. Upon the conclusion of a match, the dApp's backend generates a notice proclaiming the victorious player. This notice contains pertinent off-chain data regarding the match outcome. Once created, the notice is submitted to the rollup server as evidence of the off-chain event.

Crucially, the base layer conducts on-chain validation of these notices through the validateNotice() function of the CartesiDApp contract.

This validation process ensures the integrity and authenticity of the submitted notices, enabling the blockchain to verify and authenticate the declared off-chain events or conditions.

Let's see how a Cartesi dApp's Advance request sends an output to the rollup server as a notice:

JavaScript

async function handle_advance(data) {
  console.log("Received advance request data " + JSON.stringify(data));

  const inputPayload = data["payload"];

  try {
    await fetch(rollup_server + "/notice", {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: JSON.stringify({ payload: inputPayload }),
    });
  } catch (error) {
    //Do something when there is an error
  }

  return "accept";
}

Python

def handle_advance(data):
   logger.info(f"Received advance request data {data}")

   status = "accept"
   try:
       inputPayload = data["payload"]
       ## Send the input payload as a notice
       response = requests.post(
           rollup_server + "/notice", json={"payload": inputPayload}
       )
       logger.info(
           f"Received notice status {response.status_code} body {response.content}"
       )
   except Exception as e:
       #  Emits report with error message here
   return status

querying notices

Frontend clients can query notices using a GraphQL API exposed by the Cartesi Nodes. Refer to the documentation here to query notices from the rollup server.