Define extended teeracle demo cases

[clangenb]

We would like to extend our teeracle demo case to go beyond of trading pairs:

Ideas:

• extra storage field for strings
• extra storage fields for arbitrary data

Then we could:

• Add an extra demo case, which is kind of catchy.
• Expand the documentation on how to change the template to do something besides trading pairs.

[echevrier]

Possible simple use cases

Weather oracle : Temperature, Amount of precipitation at a location

Storage in Teeracle Pallet

• The type of the value to save must be known at compile time (u32, u64, U32F32, …). I don't think it can be arbitrary
• For the exchange_rate, we have a StorageDoubleMap : pub(super) type ExchangeRates = StorageDoubleMap. Similarly, we can add for all use cases a new specific StorageDoubleMap:
  • The name of the storage defines the use case. Ex ExchangeRates, Temperatures,
  • The first key is the key for the value. Ex the trading pair “USD/DOT”, “CHF/TEER”, … or the city where we want to get the Temperature "Zurich", "London",...
  • The second key is the base url of the data source. Ex : https://api.coingecko.com/, https://pro-api.coinmarketcap.com/, ...
• To be more generic and not create a new storage for every specific case, we could use a Triple Storage Map (StorageNMap). The new added key would define the case (ex: exchange_rate, temperature). Ex: for strings value:

/// Any string value from different sources 
#[pallet::storage]
#[pallet::getter(fn some_nmap)]
pub(super) type GeneralStringValues <T: Config> = StorageNMap<
    _,
    (
        NMapKey<Blake2_128Concat, GeneralStringKey>, //Temperature or Precipitation
        NMapKey<Blake2_128Concat, GeneralStringKey >, //Zurich or London
        NMapKey< Blake2_128Concat, DataSourceString >, //https:….
    ),
    GeneralStringValue,
    ValueQuery, //
>;

With:

pub type GeneralStringKey= PalletString;
pub type DataSourceString = PalletString;
pub type GeneralStringValue = PalletString;

In this case we would need an update function:

pub fn update_general_string_value(
            origin: OriginFor<T>,
            data_source: DataSourceString,
            key_1: GeneralStringKey,
            key_2: GeneralStringKey,
            new_value: Option< GeneralStringValue >,
        ) -> DispatchResultWithPostInfo {…}

and new events and errors.

Worker

The worker needs to be reworked, it is not generic enough, but specific to the exchange rate oracle:

• There is no generic OracleSource Trait, the OracleSource Trait has the specific function execute_exchange_rate_request
• The scheduler could be reused or a new scheduler can be easily added: start_interval_market_update
• Specific to the exchange_rate is the call to the enclave : update_market_data_xt

[coax1d]

Discussed with @clangenb

The extended demo will make use of at least one additional oracle such as a weather oracle as stated above by @echevrier. The extended oracle will use a new more generic structure by adapting the app-libs/exchange-oracle as well as the enclave-runtime/Teeracle to be more accommodating to making generic requests untied to exchange rates.

The long tail goal of the Teeracle demo will be to make it far more configurable either via indirect or direct invocation configuration. For now a clear path to adding additional oracles outside the realm of exchanges is what is required for completion.

Requesting to close from @clangenb if this suffices

[clangenb]

Now that I read this again, I suggest that we close it, when we have the demo ready. However, I agree with what has been written. :)

Just a mention, here is the pallet-side PR for this: https://github.com/integritee-network/pallets/pull/109

[coax1d]

Agreed!

[clangenb]

Done!