An Output Anyone Can Spend

A contract can read the state of an output only when that output is an input of the same transaction. The oracle output must let anyone spend it, and the spend must return the output with its asset and its state. A script that points to itself does this:

contracts/attestation_beacon.ark @ 9fc10ef

  private function continues(bytes state) {
    require(size(state) == SIZE, "state size");
    require(substr(state, 0, 1) == 0x01, "state version");
    require(tx.outputs[0].scriptPubKey == tx.input.current.scriptPubKey, "script");
    require(tx.outputs[0].assets.lookup(ctrlTxid, ctrlGidx) == 1, "identity asset");
  }

The third require makes the output recursive: output 0 must pay to the script of the input, and the fourth require keeps the identity unit on output 0. The read function has no signature check, so anyone can call it. Each cooperative spend keeps the unit on output 0. Only migrate can change the script. Oracle Output shows the rules of each spend.

Roles

Role	Holds	Action
Signer	A signer key	Signs a price and a time offchain. The output has 1 to 5 signers. `threshold` signers must sign each sample.
Submitter	Nothing	Writes a signed sample into the output. The contract accepts any submitter who has the signatures of the quorum.
Consumer	The asset id	Spends the output in its own transaction to read the price. Pays `readFee`.
Admin	`adminPk`	Replaces the script of the output (`migrate`). Exits the output onchain if the operator is unavailable (`unilateral`). Does not sign prices.

By default, the open-source oracle service uses one key as the signer key and as adminPk.

Understand

Reference

Roles

​Roles

Roles