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// Copyright (C) Parity Technologies (UK) Ltd.
// This file is part of Polkadot.
// Polkadot is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// Polkadot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with Polkadot. If not, see <http://www.gnu.org/licenses/>.
use primitives::Id as ParaId;
use runtime_parachains::{
configuration::{self, HostConfiguration},
use sp_runtime::FixedPointNumber;
use sp_std::{marker::PhantomData, prelude::*};
use xcm::prelude::*;
use SendError::*;
/// Simple value-bearing trait for determining/expressing the assets required to be paid for a
/// messages to be delivered to a parachain.
pub trait PriceForParachainDelivery {
/// Return the assets required to deliver `message` to the given `para` destination.
fn price_for_parachain_delivery(para: ParaId, message: &Xcm<()>) -> MultiAssets;
}
impl PriceForParachainDelivery for () {
fn price_for_parachain_delivery(_: ParaId, _: &Xcm<()>) -> MultiAssets {
MultiAssets::new()
}
}
/// Implementation of `PriceForParachainDelivery` which returns a fixed price.
pub struct ConstantPrice<T>(sp_std::marker::PhantomData<T>);
impl<T: Get<MultiAssets>> PriceForParachainDelivery for ConstantPrice<T> {
fn price_for_parachain_delivery(_: ParaId, _: &Xcm<()>) -> MultiAssets {
T::get()
}
}
/// Implementation of `PriceForParachainDelivery` which returns an exponentially increasing price.
/// The `A` type parameter is used to denote the asset ID that will be used for paying the delivery
/// fee.
///
/// The formula for the fee is based on the sum of a base fee plus a message length fee, multiplied
/// by a specified factor. In mathematical form, it is `F * (B + encoded_msg_len * M)`.
pub struct ExponentialPrice<A, B, M, F>(sp_std::marker::PhantomData<(A, B, M, F)>);
impl<A: Get<AssetId>, B: Get<u128>, M: Get<u128>, F: FeeTracker> PriceForParachainDelivery
for ExponentialPrice<A, B, M, F>
{
fn price_for_parachain_delivery(para: ParaId, msg: &Xcm<()>) -> MultiAssets {
let msg_fee = (msg.encoded_size() as u128).saturating_mul(M::get());
let fee_sum = B::get().saturating_add(msg_fee);
let amount = F::get_fee_factor(para).saturating_mul_int(fee_sum);
(A::get(), amount).into()
}
}
/// XCM sender for relay chain. It only sends downward message.
pub struct ChildParachainRouter<T, W, P>(PhantomData<(T, W, P)>);
impl<T: configuration::Config + dmp::Config, W: xcm::WrapVersion, P: PriceForParachainDelivery>
SendXcm for ChildParachainRouter<T, W, P>
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type Ticket = (HostConfiguration<T::BlockNumber>, ParaId, Vec<u8>);
fn validate(
dest: &mut Option<MultiLocation>,
msg: &mut Option<Xcm<()>>,
) -> SendResult<(HostConfiguration<T::BlockNumber>, ParaId, Vec<u8>)> {
let d = dest.take().ok_or(MissingArgument)?;
let id = if let MultiLocation { parents: 0, interior: X1(Parachain(id)) } = &d {
*id
} else {
*dest = Some(d);
return Err(NotApplicable)
};
// Downward message passing.
let xcm = msg.take().ok_or(MissingArgument)?;
let config = <configuration::Pallet<T>>::config();
let para = id.into();
let price = P::price_for_parachain_delivery(para, &xcm);
let blob = W::wrap_version(&d, xcm).map_err(|()| DestinationUnsupported)?.encode();
<dmp::Pallet<T>>::can_queue_downward_message(&config, ¶, &blob)
.map_err(Into::<SendError>::into)?;
Ok(((config, para, blob), price))
}
fn deliver(
(config, para, blob): (HostConfiguration<T::BlockNumber>, ParaId, Vec<u8>),
) -> Result<XcmHash, SendError> {
let hash = sp_io::hashing::blake2_256(&blob[..]);
<dmp::Pallet<T>>::queue_downward_message(&config, para, blob)
.map(|()| hash)
.map_err(|_| SendError::Transport(&"Error placing into DMP queue"))
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#[cfg(test)]
mod tests {
use super::*;
use frame_support::parameter_types;
use runtime_parachains::FeeTracker;
use sp_runtime::FixedU128;
parameter_types! {
pub const BaseDeliveryFee: u128 = 300_000_000;
pub const TransactionByteFee: u128 = 1_000_000;
pub FeeAssetId: AssetId = Concrete(Here.into());
}
struct TestFeeTracker;
impl FeeTracker for TestFeeTracker {
fn get_fee_factor(_: ParaId) -> FixedU128 {
FixedU128::from_rational(101, 100)
}
}
type TestExponentialPrice =
ExponentialPrice<FeeAssetId, BaseDeliveryFee, TransactionByteFee, TestFeeTracker>;
#[test]
fn exponential_price_correct_price_calculation() {
let id: ParaId = 123.into();
let b: u128 = BaseDeliveryFee::get();
let m: u128 = TransactionByteFee::get();
// F * (B + msg_length * M)
// message_length = 1
let result: u128 = TestFeeTracker::get_fee_factor(id.clone()).saturating_mul_int(b + m);
assert_eq!(
TestExponentialPrice::price_for_parachain_delivery(id.clone(), &Xcm(vec![])),
(FeeAssetId::get(), result).into()
);
// message size = 2
let result: u128 =
TestFeeTracker::get_fee_factor(id.clone()).saturating_mul_int(b + (2 * m));
assert_eq!(
TestExponentialPrice::price_for_parachain_delivery(id.clone(), &Xcm(vec![ClearOrigin])),
(FeeAssetId::get(), result).into()
);
// message size = 4
let result: u128 =
TestFeeTracker::get_fee_factor(id.clone()).saturating_mul_int(b + (4 * m));
assert_eq!(
TestExponentialPrice::price_for_parachain_delivery(
id.clone(),
&Xcm(vec![SetAppendix(Xcm(vec![ClearOrigin]))])
),
(FeeAssetId::get(), result).into()
);
}
}