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Abstract

Iroha Special Instructions processing requires to have a permissions based security model + a way to store some "triggers" on the block chain.

Whitepaper and Iroha v1 documentation were researched. The proposal is to use already existing Iroha Special Instructions + Assets mechanisms for Permissions implementation. 

Introduction

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https://github.com/hyperledger/iroha/blob/iroha2-dev/iroha_2_whitepaper.md#211-data-permissions require protection of data from read and write cases.

...

The same can be done with custom permissions, storing them in assets components of the account.This whole concept can be used for event listeners, `Instruction::Listener` can be executed for their configuration, but additionally to storing them in assets components of the account we need to find a way to store global Listeners (Domain level, Peer level) and define cases where we need time based listeners.

"Listeners" store

Current design assumes that we provide instructions with a mutable reference to `WorldStateView` after their validation and store on the block chain. So the only way to trigger Listeners of Conditions (changes in World State View) and Blocks and, possibly, Time is to store them in `WorldStateView`:

  6 /// Current state of the blockchain alligned with `Iroha` module.
  7 #[derive(Debug, Clone)]
  8 pub struct WorldStateView {
  9     peer: Peer,
        listeners: Vec<ListenerInstruction>,
 10 }
 11 
 12 impl WorldStateView {
 13     /// Default `WorldStateView` constructor.
 14 +---  3 lines: pub fn new(peer: Peer) -> Self {··························································································································
 17 
 18     /// Put `ValidBlock` of information with changes in form of **Iroha Special Instructions**
 19     /// into the world.
 20     pub async fn put(&mut self, block: &CommittedBlock) {
 21         for transaction in &block.transactions {
 22             if let Err(e) = &transaction.proceed(self) {
 23                 eprintln!("Failed to procced transaction on WSV: {}", e);
 24             }
 25         }
 26     }

As you can see - `put` method may invoke (trigger) listeners execution (because they are just a set of out of the box instructions). The question is - should we execute them here or send a new transaction to the ledger?

ASAP execution

Let's imagine as soon as possible execution and consequences:

 12 impl WorldStateView {
 13     /// Default `WorldStateView` constructor.
 14 +---  3 lines: pub fn new(peer: Peer) -> Self {··························································································································
 17 
 18     /// Put `ValidBlock` of information with changes in form of **Iroha Special Instructions**
 19     /// into the world.
 20     pub async fn put(&mut self, block: &CommittedBlock) {
 21         for transaction in &block.transactions {
 22             if let Err(e) = &transaction.proceed(self) {
 23                 eprintln!("Failed to procced transaction on WSV: {}", e);
 24             }
                for listener in self.listeners {
                  listener.execute(self);
                }
 25         }
 26     }

First question - how should listener understand was it triggered or not? It has only current state, not the delta of changes.

Second one - how should we spread results of it's execution between peers and synchronize I/O actions like notifications, etc.?

Third one - how should we check that listener execution will not break next transactions?

This questions gave us following requirements:

• Listeners should be executed only once in the ledger
• Listeners should be able to track changes (in time, blockchain and world_state_view)
• Listeners should be not executed during validation phase (to prevent unexpected I/O)
• Listeners should be executed after all block's transactions execution

Follow-up execution

What if instead of asap execution we will only form a new transaction with a set of instructions to execute?

 18     /// Put `ValidBlock` of information with changes in form of **Iroha Special Instructions**
 19     /// into the world.
 20     pub async fn put(&mut self, block: &CommittedBlock) {
 21         for transaction in &block.transactions {
 22             if let Err(e) = &transaction.proceed(self) {
 23                 eprintln!("Failed to procced transaction on WSV: {}", e);
 24             }
 25         }
            client.submit_all(
                listeners.execute(self, block)
            );
 26     }

But almost all requirements stay open with this solution.

The problematic

The main problem is how Iroha Special Instructions with only World State View as input can be triggered by World State View changes and where to store such Iroha Special Instructions.

World State View by itself held all information needed for the triggering but the current ISI model doesn't provide a way to use them instead of "hardcoded" entities.

If we will be able to make new Out of the Box set of ISI - `ListenerInstruction` with possible variants like `On{trigger: Box<Instruction>, generators: Box<Fn(?)→[Instruction]}` we will be able to store them on the Peer and execute on every `WorldStateView:put` which will result in a new set of generated instructions. This brings us to the next question - what this triggered instructions should know about their triggers - if nothing than we are good with current `ISI::execute` signature. But if we need to pass some information, we should store this info. And to do not change good (in my humble opinion) signature of `ISI::execute` we should store this trigger-related information in generated Instructions. Which means that for cases where we need this information we need special Iroha Special Instructions =)

Let's try to simplify these thoughts:

BLOCK --> WorldStateView
WorldStateView --check triggers & generate [ISI]--> WorldStateView::Vec<ListenerInstruction>
WorldStateView --execute instructions--> BLOCK
WorldStateView --send new transaction--> Iroha

This approach fits almost all our requirements, the problem is to not send new transactions on validation stage and prevent execution of I\O related instructions multiple times.

The second one should be moved into separate RFC because it also implied to regular ISI.

The first one should be addressed here.

Results