Abstract
In some cases, we may need to set the ISI argument from the query resultspropagate the Iroha Special Instruction's result as an argument to the next Iroha Special Instruction building a pipeline from several instructions.
Example
...
In DEX we need to check the conversion amount in the pool for a token to be exchanged. Then we need to send this value to the ISI which will send exchanged funds to the user. Last ISI should send exactly the same amount as defined by the conversion rate query. So query should somehow set this information as an argument to the next ISI.
Introduction
Transaction's processing in Iroha 2.0 is a sequential execution of Iroha Special Instructions on World State View. Current signature looks like this: WorldStateView --execute(ISI_arguments..)→ WorldStateView.
All Iroha Special Instruction's arguments are provided by the incoming transaction and distributed across the ledger as is. The only way to work with current design to cover needs from the Abstract is to set calculation's results on the World State View in form of assets.
Example
We send a composite Iroha Special Instruction to execute the following algorithm:
- Execute Iroha Query to find "conversion amount in the pool" and Add Parameter Asset with this amount to the Account.
- Execute Iroha Query to get this amount and send exchanged funds.
- Execute Iroha Query to get this amount and send them.
- Remove Parameter Asset with this amount from the account.
Because this is one Iroha Special Instruction we will prevent harm from "side" effects of other transactions and instructions. We will also have the same state across all peers with full history of values used for exchange.
Results
Current Iroha Special Instructions model can cover these cases by storing all calculations on the blockchain as assets.