pow-migration: Fix accounts migration

Fix accounts migration by setting the `Policy.NUM_SNAPSHOTS_MAX`
constant that allows to get accounts tree chunks for blocks that are
this value below the head of the chain.

pow-migration/src/lib.rs

@@ -22,7 +22,7 @@ use crate::{
         check_validators_ready, generate_ready_tx, get_ready_txns, send_tx,
         types::ValidatorsReadiness,
     },
-    state::{get_stakers, get_validators},
+    state::{get_stakers, get_validators, setup_pow_rpc_server},
 };
 
 static TESTNET_BLOCK_WINDOWS: &BlockWindows = &BlockWindows {
@@ -150,7 +150,10 @@ pub async fn migrate(
     validator_address: &Address,
     network_id: NetworkId,
 ) -> Result<Option<GenesisConfig>, Error> {
-    // First we obtain the list of registered validators
+    // First set up the PoW client for accounts migration
+    setup_pow_rpc_server(pow_client).await?;
+
+    // Now we obtain the list of registered validators
     let registered_validators = get_validators(
         pow_client,
         block_windows.registration_start..block_windows.registration_end,

pow-migration/src/state/mod.rs

@@ -20,9 +20,13 @@ use nimiq_transaction::account::htlc_contract::{AnyHash, AnyHash32, AnyHash64};
 
 use crate::state::types::{Error, GenesisAccounts, GenesisValidator};
 
-// POW estimated block time in milliseconds
+// PoW estimated block time in milliseconds
 const POW_BLOCK_TIME_MS: u64 = 60 * 1000; // 1 min
 
+// PoW maximum amount of snapshots. This is a constant that needs to be set in the PoW client
+// such that we can get accounts snapshots of blocks within [head - `POW_MAX_SNAPSHOTS`, head].
+const POW_MAX_SNAPSHOTS: u64 = 2000;
+
 fn pos_basic_account_from_account(pow_account: &PoWBasicAccount) -> Result<GenesisAccount, Error> {
     let address = Address::from_user_friendly_address(&pow_account.address)?;
     let balance = Coin::try_from(pow_account.balance)?;
@@ -111,6 +115,18 @@ fn pos_anyhash_from_hash_root(hash_root: &str, algorithm: u8) -> Result<AnyHash,
     }
 }
 
+/// Sets up the POW RPC server for migrating accounts
+pub async fn setup_pow_rpc_server(client: &Client) -> Result<(), Error> {
+    let _ = client
+        .set_constant("Policy.NUM_SNAPSHOTS_MAX", POW_MAX_SNAPSHOTS)
+        .await
+        .map_err(|e| {
+            log::error!("Could not set `Policy.NUM_SNAPSHOTS_MAX` constant. Check your client or try updating it.");
+            e
+        })?;
+    Ok(())
+}
+
 /// Gets the set of the Genesis Accounts by taking a snapshot of the accounts in
 /// a specific block number defined by `cutting_block`.
 pub async fn get_accounts(
@@ -125,6 +141,15 @@ pub async fn get_accounts(
         htlc_accounts: vec![],
     };
     let mut start_prefix = "".to_string();
+
+    // Check that the PoW client is already set up
+    if client.get_constant("Policy.NUM_SNAPSHOTS_MAX").await? != POW_MAX_SNAPSHOTS {
+        log::error!(
+            "RPC client is not set up for accounts migration. Call `setup_pow_rpc_server` first"
+        );
+        return Err(Error::RPCServerNotReady);
+    }
+
     loop {
         let chunk = client
             .get_accounts_tree_chunk(&cutting_block.hash, &start_prefix)

pow-migration/src/state/types.rs

@@ -25,6 +25,9 @@ pub enum Error {
     /// Invalid Genesis timestamp
     #[error("Invalid genesis timestamp: {0}")]
     InvalidTimestamp(u64),
+    /// RPC server not ready
+    #[error("RPC server is not ready")]
+    RPCServerNotReady,
 }
 
 /// Genesis accounts for the genesis state