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Introduction

As an example of a dapp that runs on Griffin, we present a simple Order Book.

dApp Overview

Each time a user starts an order, a new script UTxO is created. This UTxO contains, in its datum, information specific to that instance: payment details along with the sender addresses. To ensure the initial conditions of the orders, a special control Token is minted at the start. This strategy follows the ideas described in this article from Well-Typed, where the minted NFT is called the state token.

The script is the same for every order available. Anyone can see all the orders that were opened by other users and resolve them, or cancel their own. The control Token Minting Policy remains constant for every order, and the asset class must be included in the datum for subsequent validations on cancel or resolve operations.

When an order is canceled or resolved, the corresponding UTxO is spent, and funds go to the corresponding wallet addresses. The control Token is then burned.

Script UTxO

Datum

  • Sender’s address
  • The amount and asset class of the receiver’s payment
  • Asset Class of the Control Token

Value

  • Control Token
  • The sender’s tokens to exchange
  • Minimum amount of coins per output

Transactions

Start

In this transaction, a user locks the tokens they want to exchange and specifies the tokens they want to receive. The control Token is then minted.

startOrder diagram

Cancel

The user can cancel the order and receive the locked tokens back. The control Token is then burned.

cancelOrder diagram

Resolve

The other user pays k2 Token B, closing the script and burning the control token. Each user gets the corresponding tokens.

resolveOrder diagram

Validator Scripts

Script Validator

Validates the transactions that involve spending the script UTxO: Cancel and Resolve.

In the Cancel operation, the validator ensures:

  • The address that is trying to cancel the order is the same as the Sender’s address.
  • The control token is burned after the transaction.

In the Resolve operation, the validator ensures:

  • The sender’s address receives the tokens specified in the datum.
  • The control token is burned after the transaction.

Control Token minting policy

Minting:

  • A single token is minted.
  • The minted token is the correct control token.
  • The token is paid to the script address.
  • The volume of tokens the resolving address (receiver) will transfer surpasses 0.
  • The sender’s address is signing the transaction.

Burning:

  • A single token is burned.
  • The burned token is the correct control token.