Add price feed pallet

pallets/price-feed/Cargo.toml

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+[package]
+authors = ['ChainSafe Systems']
+description = 'FRAME pallet to implement PINT price feeds.'
+edition = '2018'
+license = 'LGPL-3.0-only'
+name = 'pallet-price-feed'
+readme = 'README.md'
+repository = 'https://github.com/ChainSafe/PINT/'
+version = '0.0.1'
+
+[features]
+default = ['std']
+std = [
+    'serde',
+    'codec/std',
+    'frame-support/std',
+    'frame-system/std',
+    'pallet-balances/std',
+    'pallet-chainlink-feed/std',
+]
+[dependencies.codec]
+default-features = false
+features = ['derive']
+package = 'parity-scale-codec'
+version = '2.0.0'
+
+[dependencies.frame-support]
+default-features = false
+git = 'https://github.com/paritytech/substrate.git'
+branch = 'rococo-v1'
+version = '3.0.0'
+
+[dependencies.frame-system]
+default-features = false
+git = 'https://github.com/paritytech/substrate.git'
+branch = 'rococo-v1'
+version = '3.0.0'
+
+[dependencies.pallet-chainlink-feed]
+default_features = false
+package = 'pallet-chainlink-feed'
+git = "https://github.com/mattsse/chainlink-polkadot"
+# this is substrate v3 branch that is upstreamed with rococo-v1
+# and requires https://github.com/ChainSafe/PINT/issues/37
+# see also https://github.com/ChainSafe/PINT/pull/39
+branch = "substrate-v3"
+
+[dependencies]
+serde = { version = "1.0.101", optional = true }
+
+[dev-dependencies.pallet-balances]
+default-features = false
+git = 'https://github.com/paritytech/substrate.git'
+branch = 'rococo-v1'
+version = '3.0.0'
+
+[dev-dependencies.sp-core]
+default-features = false
+git = 'https://github.com/paritytech/substrate.git'
+branch = 'rococo-v1'
+version = '3.0.0'
+
+[dev-dependencies.sp-io]
+default-features = false
+git = 'https://github.com/paritytech/substrate.git'
+branch = 'rococo-v1'
+version = '3.0.0'
+
+[dev-dependencies.sp-runtime]
+default-features = false
+git = 'https://github.com/paritytech/substrate.git'
+branch = 'rococo-v1'
+version = '3.0.0'
+
+[package.metadata.docs.rs]
+targets = ['x86_64-unknown-linux-gnu']

pallets/price-feed/README.md

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+License: LGPL-3.0-only

pallets/price-feed/src/lib.rs

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+// Copyright 2021 ChainSafe Systems
+// SPDX-License-Identifier: LGPL-3.0-only
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+pub use pallet::*;
+
+#[cfg(test)]
+mod mock;
+#[cfg(test)]
+pub use mock::FeedBuilder;
+
+#[cfg(test)]
+mod tests;
+
+/// Additional type used in this pallet
+mod traits;
+/// Additional structures used in this pallet
+mod types;
+
+#[frame_support::pallet]
+// this is requires as the #[pallet::event] proc macro generates code that violates this lint
+#[allow(clippy::unused_unit)]
+pub mod pallet {
+    pub use crate::traits::PriceFeed;
+    use crate::types::{AssetPricePair, Price};
+    use frame_support::sp_runtime::FixedPointNumber;
+    use frame_support::sp_std::convert::TryInto;
+    #[cfg(feature = "std")]
+    use frame_support::traits::GenesisBuild;
+    use frame_support::{pallet_prelude::*, traits::Get};
+    use frame_system::pallet_prelude::*;
+    use pallet_chainlink_feed::{FeedInterface, FeedOracle};
+    use std::cmp::Ordering;
+
+    type FeedIdFor<T> = <<T as Config>::Oracle as FeedOracle<T>>::FeedId;
+
+    type FeedValueFor<T> =
+        <<<T as Config>::Oracle as FeedOracle<T>>::Feed as FeedInterface<T>>::Value;
+
+    /// Provides access to all the price feeds
+    /// This is used to determine the equivalent amount of PINT for assets
+    #[pallet::config]
+    pub trait Config: frame_system::Config {
+        /// The origin that is allowed to insert asset -> feed mappings
+        type AdminOrigin: EnsureOrigin<Self::Origin>;
+
+        /// The asset identifier for the native asset (PINT).
+        #[pallet::constant]
+        type SelfAssetId: Get<Self::AssetId>;
+
+        /// Type used to identify the assets.
+        type AssetId: Parameter + Member + MaybeSerializeDeserialize;
+
+        /// The internal oracle that gives access to the asset's price feeds.
+        ///
+        /// NOTE: this assumes all the feeds provide data in the same base currency.
+        /// When querying the price of an asset (`quote`/`asset`) from the oracle,
+        /// its price is given by means of the asset pair `(base / quote)`. (e.g. DOT/PINT)
+        type Oracle: FeedOracle<Self>;
+
+        type Event: From<Event<Self>> + IsType<<Self as frame_system::Config>::Event>;
+    }
+
+    #[pallet::pallet]
+    #[pallet::generate_store(pub(super) trait Store)]
+    pub struct Pallet<T>(_);
+
+    #[pallet::storage]
+    /// Store a mapping (AssetId) -> FeedId for all active assets
+    pub type AssetFeeds<T: Config> =
+        StorageMap<_, Blake2_128Concat, T::AssetId, FeedIdFor<T>, OptionQuery>;
+
+    #[pallet::genesis_config]
+    pub struct GenesisConfig<T: Config>
+    where
+        <<T as Config>::Oracle as FeedOracle<T>>::FeedId: MaybeSerializeDeserialize,
+    {
+        /// The mappings to insert at genesis
+        pub asset_feeds: Vec<(T::AssetId, FeedIdFor<T>)>,
+    }
+
+    #[cfg(feature = "std")]
+    impl<T: Config> Default for GenesisConfig<T>
+    where
+        <<T as Config>::Oracle as FeedOracle<T>>::FeedId: MaybeSerializeDeserialize,
+    {
+        fn default() -> Self {
+            Self {
+                asset_feeds: Default::default(),
+            }
+        }
+    }
+
+    #[pallet::genesis_build]
+    impl<T: Config> GenesisBuild<T> for GenesisConfig<T>
+    where
+        <<T as Config>::Oracle as FeedOracle<T>>::FeedId: MaybeSerializeDeserialize,
+    {
+        fn build(&self) {
+            for (asset, feed) in &self.asset_feeds {
+                AssetFeeds::<T>::insert(asset.clone(), feed.clone())
+            }
+        }
+    }
+
+    #[cfg(feature = "std")]
+    impl<T: Config> GenesisConfig<T>
+    where
+        <<T as Config>::Oracle as FeedOracle<T>>::FeedId: MaybeSerializeDeserialize,
+    {
+        /// Direct implementation of `GenesisBuild::build_storage`.
+        ///
+        /// Kept in order not to break dependency.
+        pub fn build_storage(&self) -> Result<frame_support::sp_runtime::Storage, String> {
+            <Self as GenesisBuild<T>>::build_storage(self)
+        }
+
+        /// Direct implementation of `GenesisBuild::assimilate_storage`.
+        ///
+        /// Kept in order not to break dependency.
+        pub fn assimilate_storage(
+            &self,
+            storage: &mut frame_support::sp_runtime::Storage,
+        ) -> Result<(), String> {
+            <Self as GenesisBuild<T>>::assimilate_storage(self, storage)
+        }
+    }
+
+    #[pallet::event]
+    #[pallet::generate_deposit(pub(super) fn deposit_event)]
+    pub enum Event<T: Config> {
+        /// A new assetId -> feedId mapping was inserted
+        /// \[AssetId, NewFeedId, OldFeedId\]
+        UpdateAssetPriceFeed(T::AssetId, FeedIdFor<T>, Option<FeedIdFor<T>>),
+        /// An assetId -> feedId was removed
+        /// \[AssetId, FeedId\]
+        RemoveAssetPriceFeed(T::AssetId, Option<FeedIdFor<T>>),
+    }
+
+    #[pallet::call]
+    impl<T: Config> Pallet<T> {
+        /// Callable by an admin to track a price feed identifier for the asset
+        #[pallet::weight(10_000)] // TODO: Set weights
+        pub fn track_asset_price_feed(
+            origin: OriginFor<T>,
+            asset_id: T::AssetId,
+            feed_id: FeedIdFor<T>,
+        ) -> DispatchResultWithPostInfo {
+            T::AdminOrigin::ensure_origin(origin)?;
+            let old_feed_id = AssetFeeds::<T>::mutate(&asset_id, |maybe_feed_id| {
+                maybe_feed_id.replace(feed_id.clone())
+            });
+            Self::deposit_event(Event::UpdateAssetPriceFeed(asset_id, feed_id, old_feed_id));
+            Ok(().into())
+        }
+
+        /// Callable by an admin to untrack the asset's price feed.
+        #[pallet::weight(10_000)] // TODO: Set weights
+        pub fn untrack_asset_price_feed(
+            origin: OriginFor<T>,
+            asset_id: T::AssetId,
+        ) -> DispatchResultWithPostInfo {
+            T::AdminOrigin::ensure_origin(origin)?;
+            let feed_id = AssetFeeds::<T>::take(&asset_id);
+            Self::deposit_event(Event::RemoveAssetPriceFeed(asset_id, feed_id));
+            Ok(().into())
+        }
+    }
+
+    #[pallet::error]
+    pub enum Error<T> {
+        /// Thrown if no price feed was found for an asset
+        AssetPriceFeedNotFound,
+        /// Thrown when the underlying price feed does not yet contain a valid round.
+        InvalidFeedValue,
+        /// Thrown if the calculation of the price ratio fails due to exceeding the
+        /// accuracy of the configured price.
+        ExceededAccuracy,
+    }
+
+    #[pallet::hooks]
+    impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {}
+
+    impl<T: Config> Pallet<T> {
+        /// Returns the corresponding identifier for the asset's price feed
+        pub fn get_asset_feed_id(asset_id: &T::AssetId) -> Option<FeedIdFor<T>> {
+            AssetFeeds::<T>::get(asset_id)
+        }
+
+        /// Returns the latest value in the feed together with the feed's decimals
+        /// or an error if no feed was found for the given
+        /// or the feed doesn't contain any valid round yet.
+        fn get_latest_valid_value(
+            feed_id: FeedIdFor<T>,
+        ) -> Result<(FeedValueFor<T>, u8), DispatchError> {
+            let feed = T::Oracle::feed(feed_id).ok_or(Error::<T>::AssetPriceFeedNotFound)?;
+            ensure!(
+                feed.first_valid_round().is_some(),
+                Error::<T>::InvalidFeedValue
+            );
+            Ok((feed.latest_data().answer, feed.decimals()))
+        }
+    }
+    impl<T: Config> Pallet<T>
+    where
+        FeedValueFor<T>: TryInto<u128>,
+    {
+        fn adjust_with_multiplier(value: u128, exp: u8) -> Result<u128, DispatchError> {
+            let multiplier = 10u128
+                .checked_pow(exp.into())
+                .ok_or(Error::<T>::ExceededAccuracy)?;
+            Ok(value
+                .checked_mul(multiplier)
+                .ok_or(Error::<T>::ExceededAccuracy)?)
+        }
+    }
+
+    impl<T: Config> PriceFeed<T::AssetId> for Pallet<T>
+    where
+        FeedValueFor<T>: TryInto<u128>,
+    {
+        /// Returns a `AssetPricePair` where `base` is the configured `SelfAssetId`.
+        fn get_price(quote: T::AssetId) -> Result<AssetPricePair<T::AssetId>, DispatchError> {
+            Self::get_price_pair(T::SelfAssetId::get(), quote)
+        }
+
+        fn get_price_pair(
+            base: T::AssetId,
+            quote: T::AssetId,
+        ) -> Result<AssetPricePair<T::AssetId>, DispatchError> {
+            let base_feed_id =
+                Self::get_asset_feed_id(&base).ok_or(Error::<T>::AssetPriceFeedNotFound)?;
+            let quote_feed_id =
+                Self::get_asset_feed_id(&quote).ok_or(Error::<T>::AssetPriceFeedNotFound)?;
+
+            let (last_base_value, base_decimals) = Self::get_latest_valid_value(base_feed_id)?;
+            let (last_quote_value, quote_decimals) = Self::get_latest_valid_value(quote_feed_id)?;
+
+            let mut last_base_value = last_base_value
+                .try_into()
+                .map_err(|_| Error::<T>::ExceededAccuracy)?;
+            let mut last_quote_value = last_quote_value
+                .try_into()
+                .map_err(|_| Error::<T>::ExceededAccuracy)?;
+
+            // upscale the precision of the feed, which measures in fewer decimals
+            match base_decimals.cmp(&quote_decimals) {
+                Ordering::Less => {
+                    last_base_value = Self::adjust_with_multiplier(
+                        last_base_value,
+                        quote_decimals - base_decimals,
+                    )?;
+                }
+                Ordering::Greater => {
+                    last_quote_value = Self::adjust_with_multiplier(
+                        last_quote_value,
+                        base_decimals - quote_decimals,
+                    )?;
+                }
+                _ => {}
+            }
+
+            let price = Price::checked_from_rational(last_base_value, last_quote_value)
+                .ok_or(Error::<T>::ExceededAccuracy)?;
+
+            Ok(AssetPricePair { base, quote, price })
+        }
+    }
+}