[AHM] Sovereign Account Translation

integration-tests/ahm/Cargo.toml

@@ -35,3 +35,7 @@ sp-runtime = { workspace = true, default-features = true }
 sp-storage = { workspace = true, default-features = true }
 sp-tracing = { workspace = true, default-features = true }
 tokio = { features = ["full", "macros"], workspace = true }
+xcm-builder = { workspace = true, default-features = true }
+xcm-emulator = { workspace = true, default-features = true }
+polkadot-runtime-common = { workspace = true, default-features = true }
+codec = { workspace = true, default-features = true }

integration-tests/ahm/src/tests.rs

@@ -31,13 +31,15 @@
 //! SNAP_RC="../../polkadot.snap" SNAP_AH="../../ah-polkadot.snap" RUST_LOG="info" ct polkadot-integration-tests-ahm -r on_initialize_works -- --nocapture
 //! ```
 
-use cumulus_primitives_core::{AggregateMessageOrigin, ParaId};
+use asset_hub_polkadot_runtime::Runtime as AssetHub;
+use cumulus_primitives_core::{AggregateMessageOrigin, Junction, Location, ParaId};
 use frame_support::traits::*;
 use pallet_rc_migrator::{types::PalletMigrationChecks, MigrationStage, RcMigrationStage};
-use std::str::FromStr;
-
-use asset_hub_polkadot_runtime::Runtime as AssetHub;
 use polkadot_runtime::Runtime as Polkadot;
+use polkadot_runtime_common::paras_registrar;
+use sp_runtime::AccountId32;
+use std::{collections::BTreeMap, str::FromStr};
+use xcm_emulator::ConvertLocation;
 
 use super::mock::*;
 
@@ -113,3 +115,86 @@ async fn account_migration_works() {
 		// some overweight ones.
 	});
 }
+
+#[test]
+fn sovereign_account_translation() {
+	let good_cases = [
+		(
+			// para 2094 account https://polkadot.subscan.io/account/13YMK2dzLWfnGZXSLuAxgZbBiNMHLfnPZ8itzwXryJ9FcWsE
+			"13YMK2dzLWfnGZXSLuAxgZbBiNMHLfnPZ8itzwXryJ9FcWsE",
+			// on ah (different account id) https://assethub-polkadot.subscan.io/account/13cKp88oRErgQAFatu83oCvzxr2b45qVcnNLFu4Mr2ApU6ZC
+			"13cKp88oRErgQAFatu83oCvzxr2b45qVcnNLFu4Mr2ApU6ZC",
+		),
+		(
+			"13YMK2dsXbyC866w2tFM4vH52nRs3uTwac32jh1FNXZBXv18",
+			"13cKp88gcLA6Fgq5atCSBZctHG7AmKX3eFgTzeXkFFakPWuo",
+		),
+	];
+
+	for (rc_acc, ah_acc) in good_cases {
+		let rc_acc = AccountId32::from_str(rc_acc).unwrap();
+		let ah_acc = AccountId32::from_str(ah_acc).unwrap();
+
+		let (translated, _para_id) = pallet_rc_migrator::accounts::AccountsMigrator::<Polkadot>::try_translate_rc_sovereign_to_ah(rc_acc).unwrap().unwrap();
+		assert_eq!(translated, ah_acc);
+	}
+
+	let bad_cases = [
+		"13yJaZUmhMDG91AftfdNeJm6hMVSL9Jq2gqiyFdhiJgXf6AY", // wrong prefix
+		"13ddruDZgGbfVmbobzfNLV4momSgjkFnMXkfogizb4uEbHtQ", // "
+		"13cF4T4kfi8VYw2nTZfkYkn9BjGpmRDsivYxFqGYUWkU8L2d", // "
+		"13cKp88gcLA6Fgq5atCSBZctHG7AmKX3eFgTzeXkFFakPo6e", // last byte not 0
+		"13cF4T4kfiJ39NqGh4DAZSMo6NuWT1fYfZzCo9f5HH8dUFBJ", // 7 byte not zero
+		"13cKp88gcLA6Fgq5atCSBZctHGenFzUo3qmmReNVKzpnGvFg", // some center byte not zero
+	];
+
+	for rc_acc in bad_cases {
+		let rc_acc = AccountId32::from_str(rc_acc).unwrap();
+
+		let translated = pallet_rc_migrator::accounts::AccountsMigrator::<Polkadot>::try_translate_rc_sovereign_to_ah(rc_acc).unwrap();
+		assert!(translated.is_none());
+	}
+}
+
+/// For human consumption.
+#[tokio::test]
+async fn print_sovereign_account_translation() {
+	let (mut rc, mut ah) = load_externalities().await.unwrap();
+
+	let mut rc_to_ah = BTreeMap::new();
+
+	rc.execute_with(|| {
+		for para_id in paras_registrar::Paras::<Polkadot>::iter_keys().collect::<Vec<_>>() {
+			let rc_acc = xcm_builder::ChildParachainConvertsVia::<ParaId, AccountId32>::convert_location(&Location::new(0, Junction::Parachain(para_id.into()))).unwrap();
+
+			let (ah_acc, para_id) = pallet_rc_migrator::accounts::AccountsMigrator::<Polkadot>::try_translate_rc_sovereign_to_ah(rc_acc.clone()).unwrap().unwrap();
+			rc_to_ah.insert(rc_acc, (ah_acc, para_id));
+		}
+
+		for account in frame_system::Account::<Polkadot>::iter_keys() {
+			let translated = pallet_rc_migrator::accounts::AccountsMigrator::<Polkadot>::try_translate_rc_sovereign_to_ah(account.clone()).unwrap();
+
+			if let Some((ah_acc, para_id)) = translated {
+				if !rc_to_ah.contains_key(&account) {
+					println!("Account belongs to an unregistered para {}: {}", para_id, account);
+					rc_to_ah.insert(account, (ah_acc, para_id));
+				}
+			}
+		}
+	});
+
+	let mut csv: String = "para,rc,ah\n".into();
+
+	// Sanity check that they all exist. Note that they dont *have to*, but all do.
+	println!("Translating {} RC accounts to AH", rc_to_ah.len());
+	ah.execute_with(|| {
+		for (rc_acc, (ah_acc, para_id)) in rc_to_ah.iter() {
+			println!("[{}] {} -> {}", para_id, rc_acc, ah_acc);
+
+			csv.push_str(&format!("{},{},{}\n", para_id, rc_acc, ah_acc));
+		}
+	});
+
+	//std::fs::write("../../pallets/rc-migrator/src/sovereign_account_translation.csv",
+	// csv).unwrap();
+}

pallets/rc-migrator/src/accounts.md

@@ -0,0 +1,32 @@
+# Account Migration
+
+Accounts are migrated with all their balance, locks and reserves at the beginning of the Asset Hub
+migration.
+
+## User Impact
+
+Users need to be aware that all of their funds will be moved from the Relay chain to the Asset Hub.
+The Account ID will stay the same. This ensures that normal user accounts will be to control their
+funds on Asset Hub.
+
+## Sovereign Account Translation
+
+For parachain sovereign accounts, it is not possible to just use the same account ID. The sovereign
+account address of a parachain is calculated differently, depending on whether it is the account on
+the Relay or a parachain (like Asset Hub).  
+
+There are different kinds of sovereign accounts. In this context, we only focus on these parachain
+sovereign accounts:
+- On the Relay: derived from `"para" ++ para_id ++ 00..`
+- On the Asset Hub and all other sibling parachains: derived from `"sibl" ++ para_id ++ 00..`
+
+Our translation logic inverts the derivation and changes the prefix from `"para"` to `"sibl"` for
+all accounts that match the pattern `"para" ++ para_id ++ 00..`. The full list of translated
+accounts is in [this CSV file](./sovereign_account_translation.csv).
+
+It is advised that parachains check that they can control their account on Asset Hub. They can also
+forego this check if they do not need control thereof - for example when they are not holding any
+funds on their relay sovereign account. However, please note that someone could still send funds to
+that address before or after the migration.
+
+Example for Bifrost: this is the [relay sovereign account](https://polkadot.subscan.io/account/13YMK2eeopZtUNpeHnJ1Ws2HqMQG6Ts9PGCZYGyFbSYoZfcm) and it gets translated to this [sibling sovereign account](https://assethub-polkadot.subscan.io/account/13cKp89TtYknbyYnqnF6dWN75q5ZosvFSuqzoEVkUAaNR47A).

pallets/rc-migrator/src/accounts.rs

@@ -71,9 +71,11 @@ AH: mint_into(checking, checking_total - total_issuance) // publishes Balances::
 */
 
 use crate::{types::*, *};
+use codec::DecodeAll;
 use frame_support::{traits::tokens::IdAmount, weights::WeightMeter};
 use frame_system::Account as SystemAccount;
 use pallet_balances::{AccountData, BalanceLock};
+use sp_core::ByteArray;
 use sp_runtime::traits::Zero;
 
 /// Account type meant to transfer data between RC and AH.
@@ -542,4 +544,34 @@ impl<T: Config> AccountsMigrator<T> {
 		// TODO: define actual weight
 		Weight::from_all(1)
 	}
+
+	/// Try to translate a Parachain sovereign account to the Parachain AH sovereign account.
+	///
+	/// Returns:
+	/// - `Ok(None)` if the account is not a Parachain sovereign account
+	/// - `Ok(Some((ah_account, para_id)))` with the translated account and the para id
+	/// - `Err(())` otherwise
+	pub fn try_translate_rc_sovereign_to_ah(
+		acc: T::AccountId,
+	) -> Result<Option<(T::AccountId, u16)>, ()> {
+		let raw = acc.to_raw_vec();
+
+		// Must start with "para"
+		let Some(raw) = raw.strip_prefix(b"para") else {
+			return Ok(None);
+		};
+		// Must end with 26 zero bytes
+		let Some(raw) = raw.strip_suffix(&[0u8; 26]) else {
+			return Ok(None);
+		};
+		let para_id = u16::decode_all(&mut &raw[..]).map_err(|_| ())?;
+
+		// Translate to AH sibling account
+		let mut ah_raw = [0u8; 32];
+		ah_raw[0..4].copy_from_slice(b"sibl");
+		ah_raw[4..6].copy_from_slice(&para_id.encode());
+		let ah_acc = ah_raw.try_into().map_err(|_| ()).defensive()?;
+
+		Ok(Some((ah_acc, para_id)))
+	}
 }