chore: a set of minor improvements for engine (#916)

## Description

A set of minor changes and clean-ups for overall codebase.

## Performance / NEAR gas cost considerations

No changes should affect gas cost. 

## Testing

Automated tests

## How should this be reviewed

Patches are minor and do not introduce any behaviour changes

---------

Co-authored-by: Oleksandr Anyshchenko <[email protected]>

engine-precompiles/src/lib.rs

@@ -7,6 +7,7 @@
     clippy::missing_errors_doc,
     clippy::unreadable_literal
 )]
+#![forbid(unsafe_code)]
 pub mod account_ids;
 pub mod alt_bn256;
 pub mod blake2;

engine-precompiles/src/xcc.rs

@@ -1,7 +1,6 @@
 //! Cross contract call precompile.
 //!
 //! Allow Aurora users interacting with NEAR smart contracts using cross contract call primitives.
-//! TODO: How they work (low level explanation with examples)
 
 use crate::{utils, HandleBasedPrecompile, PrecompileOutput};
 use aurora_engine_sdk::io::IO;
@@ -80,7 +79,7 @@ pub mod cross_contract_call {
         H256,
     };
 
-    /// Exit to Ethereum precompile address
+    /// NEAR Cross Contract Call precompile address
     ///
     /// Address: `0x516cded1d16af10cad47d6d49128e2eb7d27b372`
     /// This address is computed as: `&keccak("nearCrossContractCall")[12..]`

engine-standalone-storage/src/engine_state.rs

@@ -102,7 +102,7 @@ impl<'db, 'input: 'db, 'output: 'db> IO for EngineStateAccess<'db, 'input, 'outp
         let value = iter.next().and_then(|maybe_elem| {
             maybe_elem
                 .ok()
-                .map(|(_, value)| DiffValue::try_from_bytes(&value).unwrap())
+                .map(|(_, value)| DiffValue::try_from_bytes(&value).expect("diff value is invalid"))
         })?;
         value.take_value().map(EngineStorageValue::Vec)
     }

engine-standalone-storage/src/lib.rs

@@ -198,7 +198,7 @@ impl Storage {
         let storage_key = construct_storage_key(StoragePrefix::Diff, &tx_included.to_bytes());
         self.db
             .get_pinned(storage_key)?
-            .map(|slice| Diff::try_from_bytes(slice.as_ref()).unwrap())
+            .map(|slice| Diff::try_from_bytes(slice.as_ref()).expect("transaction_diff is invalid"))
             .ok_or(Error::TransactionNotFound(tx_included))
     }
 
@@ -249,12 +249,12 @@ impl Storage {
         action(&mut batch, &storage_key, &msg_bytes);
 
         let storage_key = construct_storage_key(StoragePrefix::Diff, &tx_included_bytes);
-        let diff_bytes = diff.try_to_bytes().unwrap();
+        let diff_bytes = diff.try_to_bytes().expect("diff should is invalid");
         action(&mut batch, &storage_key, &diff_bytes);
 
         for (key, value) in diff {
             let storage_key = construct_engine_key(key, block_height, tx_included.position);
-            let value_bytes = value.try_to_bytes().unwrap();
+            let value_bytes = value.try_to_bytes().expect("value is invalid");
             action(&mut batch, &storage_key, &value_bytes);
         }
 
@@ -275,7 +275,7 @@ impl Storage {
             if k.len() < n || k[0..n] != db_key_prefix {
                 break;
             }
-            let value = DiffValue::try_from_bytes(v.as_ref()).unwrap();
+            let value = DiffValue::try_from_bytes(v.as_ref()).expect("diff should is invalid");
             let block_height = {
                 let mut buf = [0u8; 8];
                 buf.copy_from_slice(&k[n..(n + 8)]);
@@ -314,7 +314,7 @@ impl Storage {
 
         while iter.valid() {
             // unwrap is safe because the iterator is valid
-            let db_key = iter.key().unwrap().to_vec();
+            let db_key = iter.key().expect("iterator should is invalid").to_vec();
             if db_key.get(0..engine_prefix_len) != Some(&engine_prefix) {
                 break;
             }
@@ -335,7 +335,7 @@ impl Storage {
                 iter.seek_for_prev(&desired_db_key);
 
                 let value = if iter.valid() {
-                    let bytes = iter.value().unwrap();
+                    let bytes = iter.value().expect("iterator is invalid");
                     DiffValue::try_from_bytes(bytes).unwrap_or_else(|e| {
                         panic!(
                             "Could not deserialize key={} value={} error={:?}",

engine-standalone-storage/src/relayer_db/types.rs

@@ -183,7 +183,7 @@ impl TryFrom<postgres::Row> for TransactionRow {
             near_hash,
             near_receipt_hash,
             from,
-            to: to.map(|arr| Address::try_from_slice(arr).unwrap()),
+            to: to.map(|arr| Address::try_from_slice(arr).expect("address is invalid")),
             nonce,
             gas_price,
             gas_limit,
@@ -221,7 +221,7 @@ impl From<TransactionRow> for EthTransactionKind {
 
 fn get_numeric(row: &postgres::Row, field: &str) -> U256 {
     let value: PostgresNumeric = row.get(field);
-    U256::try_from(value).unwrap()
+    U256::try_from(value).expect("postgres numeric is invalid")
 }
 
 fn get_hash(row: &postgres::Row, field: &str) -> H256 {
@@ -231,7 +231,7 @@ fn get_hash(row: &postgres::Row, field: &str) -> H256 {
 
 fn get_address(row: &postgres::Row, field: &str) -> Address {
     let value: &[u8] = row.get(field);
-    Address::try_from_slice(value).unwrap()
+    Address::try_from_slice(value).expect("address is invalid")
 }
 
 fn get_timestamp(row: &postgres::Row, field: &str) -> Option<u64> {

engine-standalone-storage/src/sync/types.rs

@@ -69,7 +69,7 @@ impl TransactionMessage {
     #[must_use]
     pub fn to_bytes(&self) -> Vec<u8> {
         let borshable: BorshableTransactionMessage = self.into();
-        borsh::to_vec(&borshable).unwrap()
+        borsh::to_vec(&borshable).expect("self to be valid")
     }
 
     pub fn try_from_slice(bytes: &[u8]) -> Result<Self, std::io::Error> {

engine-transactions/src/lib.rs

@@ -6,6 +6,7 @@
     clippy::missing_panics_doc,
     clippy::missing_errors_doc
 )]
+#![forbid(unsafe_code)]
 
 use aurora_engine_types::types::{Address, Wei};
 use aurora_engine_types::{vec, Vec, H160, U256};

engine/src/contract_methods/connector/deposit_event.rs

@@ -80,9 +80,10 @@ impl FtTransferMessageData {
             }
         })?;
 
-        // Parse the fee from the message slice. It should contain 32 bytes,
-        // but after that, it will be parsed to u128.
-        // This logic is for compatibility.
+        // Parse the fee from the message slice.
+        // The fee is expected to be represented as a 32-byte value in the message.
+        // However, it will be parsed and converted to a u128 for further processing.
+        // This parsing logic is implemented to ensure compatibility
         let fee_u128: u128 = U256::from_little_endian(&data[..32])
             .try_into()
             .map_err(|_| errors::ParseOnTransferMessageError::OverflowNumber)?;

engine/src/lib.rs

@@ -698,11 +698,14 @@ mod contract {
             .sdk_unwrap();
     }
 
-    /// Allow receiving NEP141 tokens to the EVM contract.
+    /// Allows receiving NEP141 tokens in the EVM contract.
     ///
-    /// This function returns the amount of tokens to return to the sender.
-    /// Either all tokens are transferred and tokens are returned
-    /// in case of an error, or no token is returned if the transaction was successful.
+    /// This function is called when NEP141 tokens are transferred to the contract.
+    /// It returns the amount of tokens that should be returned to the sender.
+    ///
+    /// There are two possible outcomes:
+    /// 1. If an error occurs during the token transfer, all the transferred tokens are returned to the sender.
+    /// 2. If the token transfer is successful, no tokens are returned, and the contract keeps the transferred tokens.
     #[no_mangle]
     pub extern "C" fn ft_on_transfer() {
         let io = Runtime;