Oracle standard module

[dpc]

For UX purposes it's useful if the user can know e.g. fiat prices.

To keep it federated, it would be great if Fedimind could run it.

We could add a new core module where the whole purpose is agreeing on certain facts (e.g. BTC/USD price).

Design

Voting

Voting would happen exactly like it happens for block fee rate and block height in wallet module already. Each peer, when they change their vote, sends a ConsensusItem::Vote:

struct Vote {
  id: u64,
  value: u64,
}

As you can see index allows voting on arbitrary number of things.

For each id and peer in the Federation, the values would be tracked and the final value would be the median.

To prevent unconstrained blowing up disk & memory use space, each id needs to be enabled first with a ConsensItem::Enable(u64), until threshold is reached. Before then OracleVotes for it are illegal. A ConsensusItem::Disable seems useful to have as well.

Fedimint the Open Source Project would track id to "underlying meaning" allocation (e.g. national currencies), with a range dedicated to custom usage.

Source configuration

For each id, each guardian should be able to configure one or more multiple sources:

• idx - index of the source
• SourceType - from a list of implemented source typs (eg. json call; jsonrpc call)
• SourceUrl - URL specific for the type (eg.
• SourceSelector - eg. jq-like syntax to pick the value from the source
• decimalShift - before rounding down an integer, multiply by 10 ^ {decimalShift}
• SuccessPeriod - time to query the source again after a success
• FailurePeriod - time to query the source again after a failure

Fedimint should come with the defaults (probably randomly chosen from at least 3) for each standard id

Note: this is a peer-local configuration, so each guardian is free to change it anytime.

Source Modes

How to query multiple sources for same id with different indexes:

• failover - from lowest to hightest, use first success
• median - query all, calculculate a median

Overrides

For each id guardian should be able to specify a manual override:

• id : u64 - which id to override
• value : u64 - value to override with
• until: Option<u64>- unix timestamp till which the override should apply; forever if None

This should be possible for the fedimint-cli and Admin UI.

APIs

Global, public

• get_value(id: u64) -> Option<u64>

Admin-Private:

• enableId(id: u64)
• disableId(id: u64)
• setOverride(id: u64, value: u64, until: Option<u64>)
• setSource(idx: u32, type: String, url: String, selector: String, decimalShift: s8, sPeriod: u32, fPeriod: u32);
• getVote(idx: u64) -> u64;
• setSourceMode(mode: String);

[elsirion]

I wonder if it would be useful to have two kinds of modules: oracles and the current modules. Then e.g. the block height could be an oracle module that both the LN and Wallet module depend on.

[dpc]

Then e.g. the block height could be an oracle module that both the LN and Wallet module depend on.

Crossed my mind to make this module responsible for block height and fee rate as well.