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XCM: Remote account converter (#6662)
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* Draft remote account converter

* Tests and doc comments

* Adapt naming, tests fix

* Try with prefix in account

* Revert "Try with prefix in account"

This reverts commit 4617597.

* Adapt code and test to review suggestions

* adapt to take into account parent in conversion

* fix: docs

* fix: try doc fix v2
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@mustermeiszer
mustermeiszer authored Apr 24, 2023
1 parent c9f89da commit 887e38f
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316 changes: 316 additions & 0 deletions xcm/xcm-builder/src/location_conversion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,111 @@ use sp_std::{borrow::Borrow, marker::PhantomData};
use xcm::latest::prelude::*;
use xcm_executor::traits::Convert;

/// Prefix for generating alias account for accounts coming
/// from chains that use 32 byte long representations.
pub const FOREIGN_CHAIN_PREFIX_PARA_32: [u8; 37] = *b"ForeignChainAliasAccountPrefix_Para32";

/// Prefix for generating alias account for accounts coming
/// from chains that use 20 byte long representations.
pub const FOREIGN_CHAIN_PREFIX_PARA_20: [u8; 37] = *b"ForeignChainAliasAccountPrefix_Para20";

/// Prefix for generating alias account for accounts coming
/// from the relay chain using 32 byte long representations.
pub const FOREIGN_CHAIN_PREFIX_RELAY: [u8; 36] = *b"ForeignChainAliasAccountPrefix_Relay";

/// This converter will for a given `AccountId32`/`AccountKey20`
/// always generate the same "remote" account for a specific
/// sending chain.
/// I.e. the user gets the same remote account
/// on every consuming para-chain and relay chain.
///
/// Can be used as a converter in `SovereignSignedViaLocation`
///
/// ## Example
/// Assuming the following network layout.
///
/// ```notrust
/// R
/// / \
/// / \
/// P1 P2
/// / \ / \
/// / \ / \
/// P1.1 P1.2 P2.1 P2.2
/// ```
/// Then a given account A will have the same alias accounts in the
/// same plane. So, it is important which chain account A acts from.
/// E.g.
/// * From P1.2 A will act as
/// * hash(ParaPrefix, A, 1, 1) on P1.2
/// * hash(ParaPrefix, A, 1, 0) on P1
/// * From P1 A will act as
/// * hash(RelayPrefix, A, 1) on P1.2 & P1.1
/// * hash(ParaPrefix, A, 1, 1) on P2
/// * hash(ParaPrefix, A, 1, 0) on R
///
/// Note that the alias accounts have overlaps but never on the same
/// chain when the sender comes from different chains.
pub struct ForeignChainAliasAccount<AccountId>(PhantomData<AccountId>);
impl<AccountId: From<[u8; 32]> + Clone> Convert<MultiLocation, AccountId>
for ForeignChainAliasAccount<AccountId>
{
fn convert_ref(location: impl Borrow<MultiLocation>) -> Result<AccountId, ()> {
let entropy = match location.borrow() {
// Used on the relay chain for sending paras that use 32 byte accounts
MultiLocation {
parents: 0,
interior: X2(Parachain(para_id), AccountId32 { id, .. }),
} => ForeignChainAliasAccount::<AccountId>::from_para_32(para_id, id, 0),

// Used on the relay chain for sending paras that use 20 byte accounts
MultiLocation {
parents: 0,
interior: X2(Parachain(para_id), AccountKey20 { key, .. }),
} => ForeignChainAliasAccount::<AccountId>::from_para_20(para_id, key, 0),

// Used on para-chain for sending paras that use 32 byte accounts
MultiLocation {
parents: 1,
interior: X2(Parachain(para_id), AccountId32 { id, .. }),
} => ForeignChainAliasAccount::<AccountId>::from_para_32(para_id, id, 1),

// Used on para-chain for sending paras that use 20 byte accounts
MultiLocation {
parents: 1,
interior: X2(Parachain(para_id), AccountKey20 { key, .. }),
} => ForeignChainAliasAccount::<AccountId>::from_para_20(para_id, key, 1),

// Used on para-chain for sending from the relay chain
MultiLocation { parents: 1, interior: X1(AccountId32 { id, .. }) } =>
ForeignChainAliasAccount::<AccountId>::from_relay_32(id, 1),

// No other conversions provided
_ => return Err(()),
};

Ok(entropy.into())
}

fn reverse_ref(_: impl Borrow<AccountId>) -> Result<MultiLocation, ()> {
Err(())
}
}

impl<AccountId> ForeignChainAliasAccount<AccountId> {
fn from_para_32(para_id: &u32, id: &[u8; 32], parents: u8) -> [u8; 32] {
(FOREIGN_CHAIN_PREFIX_PARA_32, para_id, id, parents).using_encoded(blake2_256)
}

fn from_para_20(para_id: &u32, id: &[u8; 20], parents: u8) -> [u8; 32] {
(FOREIGN_CHAIN_PREFIX_PARA_20, para_id, id, parents).using_encoded(blake2_256)
}

fn from_relay_32(id: &[u8; 32], parents: u8) -> [u8; 32] {
(FOREIGN_CHAIN_PREFIX_RELAY, id, parents).using_encoded(blake2_256)
}
}

pub struct Account32Hash<Network, AccountId>(PhantomData<(Network, AccountId)>);
impl<Network: Get<Option<NetworkId>>, AccountId: From<[u8; 32]> + Into<[u8; 32]> + Clone>
Convert<MultiLocation, AccountId> for Account32Hash<Network, AccountId>
Expand Down Expand Up @@ -225,4 +330,215 @@ mod tests {
let inverted = UniversalLocation::get().invert_target(&input);
assert_eq!(inverted, Err(()));
}

#[test]
fn remote_account_convert_on_para_sending_para_32() {
let mul = MultiLocation {
parents: 1,
interior: X2(Parachain(1), AccountId32 { network: None, id: [0u8; 32] }),
};
let rem_1 = ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap();

assert_eq!(
[
181, 186, 132, 152, 52, 210, 226, 199, 8, 235, 213, 242, 94, 70, 250, 170, 19, 163,
196, 102, 245, 14, 172, 184, 2, 148, 108, 87, 230, 163, 204, 32
],
rem_1
);

let mul = MultiLocation {
parents: 1,
interior: X2(
Parachain(1),
AccountId32 { network: Some(NetworkId::Polkadot), id: [0u8; 32] },
),
};

assert_eq!(ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap(), rem_1);

let mul = MultiLocation {
parents: 1,
interior: X2(Parachain(2), AccountId32 { network: None, id: [0u8; 32] }),
};
let rem_2 = ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap();

assert_eq!(
[
183, 188, 66, 169, 82, 250, 45, 30, 142, 119, 184, 55, 177, 64, 53, 114, 12, 147,
128, 10, 60, 45, 41, 193, 87, 18, 86, 49, 127, 233, 243, 143
],
rem_2
);

assert_ne!(rem_1, rem_2);
}

#[test]
fn remote_account_convert_on_para_sending_para_20() {
let mul = MultiLocation {
parents: 1,
interior: X2(Parachain(1), AccountKey20 { network: None, key: [0u8; 20] }),
};
let rem_1 = ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap();

assert_eq!(
[
210, 60, 37, 255, 116, 38, 221, 26, 85, 82, 252, 125, 220, 19, 41, 91, 185, 69,
102, 83, 120, 63, 15, 212, 74, 141, 82, 203, 187, 212, 77, 120
],
rem_1
);

let mul = MultiLocation {
parents: 1,
interior: X2(
Parachain(1),
AccountKey20 { network: Some(NetworkId::Polkadot), key: [0u8; 20] },
),
};

assert_eq!(ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap(), rem_1);

let mul = MultiLocation {
parents: 1,
interior: X2(Parachain(2), AccountKey20 { network: None, key: [0u8; 20] }),
};
let rem_2 = ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap();

assert_eq!(
[
197, 16, 31, 199, 234, 80, 166, 55, 178, 135, 95, 48, 19, 128, 9, 167, 51, 99, 215,
147, 94, 171, 28, 157, 29, 107, 240, 22, 10, 104, 99, 186
],
rem_2
);

assert_ne!(rem_1, rem_2);
}

#[test]
fn remote_account_convert_on_para_sending_relay() {
let mul = MultiLocation {
parents: 1,
interior: X1(AccountId32 { network: None, id: [0u8; 32] }),
};
let rem_1 = ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap();

assert_eq!(
[
227, 12, 152, 241, 220, 53, 26, 27, 1, 167, 167, 214, 61, 161, 255, 96, 56, 16,
221, 59, 47, 45, 40, 193, 88, 92, 4, 167, 164, 27, 112, 99
],
rem_1
);

let mul = MultiLocation {
parents: 1,
interior: X1(AccountId32 { network: Some(NetworkId::Polkadot), id: [0u8; 32] }),
};

assert_eq!(ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap(), rem_1);

let mul = MultiLocation {
parents: 1,
interior: X1(AccountId32 { network: None, id: [1u8; 32] }),
};
let rem_2 = ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap();

assert_eq!(
[
143, 195, 87, 73, 129, 2, 163, 211, 239, 51, 55, 235, 82, 173, 162, 206, 158, 237,
166, 73, 254, 62, 131, 6, 170, 241, 209, 116, 105, 69, 29, 226
],
rem_2
);

assert_ne!(rem_1, rem_2);
}

#[test]
fn remote_account_convert_on_relay_sending_para_20() {
let mul = MultiLocation {
parents: 0,
interior: X2(Parachain(1), AccountKey20 { network: None, key: [0u8; 20] }),
};
let rem_1 = ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap();

assert_eq!(
[
25, 251, 15, 92, 148, 141, 236, 238, 50, 108, 133, 56, 118, 11, 250, 122, 81, 160,
104, 160, 97, 200, 210, 49, 208, 142, 64, 144, 24, 110, 246, 101
],
rem_1
);

let mul = MultiLocation {
parents: 0,
interior: X2(Parachain(2), AccountKey20 { network: None, key: [0u8; 20] }),
};
let rem_2 = ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap();

assert_eq!(
[
88, 157, 224, 235, 76, 88, 201, 143, 206, 227, 14, 192, 177, 245, 75, 62, 41, 10,
107, 182, 61, 57, 239, 112, 43, 151, 58, 111, 150, 153, 234, 189
],
rem_2
);

assert_ne!(rem_1, rem_2);
}

#[test]
fn remote_account_convert_on_relay_sending_para_32() {
let mul = MultiLocation {
parents: 0,
interior: X2(Parachain(1), AccountId32 { network: None, id: [0u8; 32] }),
};
let rem_1 = ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap();

assert_eq!(
[
45, 120, 232, 0, 226, 49, 106, 48, 65, 181, 184, 147, 224, 235, 198, 152, 183, 156,
67, 57, 67, 67, 187, 104, 171, 23, 140, 21, 183, 152, 63, 20
],
rem_1
);

let mul = MultiLocation {
parents: 0,
interior: X2(
Parachain(1),
AccountId32 { network: Some(NetworkId::Polkadot), id: [0u8; 32] },
),
};

assert_eq!(ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap(), rem_1);

let mul = MultiLocation {
parents: 0,
interior: X2(Parachain(2), AccountId32 { network: None, id: [0u8; 32] }),
};
let rem_2 = ForeignChainAliasAccount::<[u8; 32]>::convert(mul).unwrap();

assert_eq!(
[
97, 119, 110, 66, 239, 113, 96, 234, 127, 92, 66, 204, 53, 129, 33, 119, 213, 192,
171, 100, 139, 51, 39, 62, 196, 163, 16, 213, 160, 44, 100, 228
],
rem_2
);

assert_ne!(rem_1, rem_2);
}

#[test]
fn remote_account_fails_with_bad_multilocation() {
let mul = MultiLocation {
parents: 1,
interior: X1(AccountKey20 { network: None, key: [0u8; 20] }),
};
assert!(ForeignChainAliasAccount::<[u8; 32]>::convert(mul).is_err());
}
}

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