From 4bfc2364e3a58b19ad042b8abd9ab12658f9efc4 Mon Sep 17 00:00:00 2001
From: bitfalt <75431447+bitfalt@users.noreply.github.com>
Date: Thu, 12 Sep 2024 12:32:02 -0600
Subject: [PATCH] feat: add eth_chain_id entrypoint

---
 crates/contracts/src/kakarot_core/interface.cairo | 4 ++++
 crates/contracts/src/kakarot_core/kakarot.cairo   | 7 +++++++
 crates/utils/src/constants.cairo                  | 1 +
 3 files changed, 12 insertions(+)

diff --git a/crates/contracts/src/kakarot_core/interface.cairo b/crates/contracts/src/kakarot_core/interface.cairo
index 8c014f3b..e3a6f07a 100644
--- a/crates/contracts/src/kakarot_core/interface.cairo
+++ b/crates/contracts/src/kakarot_core/interface.cairo
@@ -31,6 +31,10 @@ pub trait IKakarotCore<TContractState> {
         self: @TContractState, origin: EthAddress, tx: Transaction
     ) -> (bool, Span<u8>, u64);
 
+    // Getter for the transaction chain_id
+    // Returns the chain_id of the transaction after applying modulo 2^53
+    fn eth_chain_id(self: @TContractState) -> u64;
+
     /// Transaction entrypoint into the EVM
     /// Executes an EVM transaction and possibly modifies the state
     fn eth_send_transaction(ref self: TContractState, tx: Transaction) -> (bool, Span<u8>, u64);
diff --git a/crates/contracts/src/kakarot_core/kakarot.cairo b/crates/contracts/src/kakarot_core/kakarot.cairo
index 1a605665..77c9da1f 100644
--- a/crates/contracts/src/kakarot_core/kakarot.cairo
+++ b/crates/contracts/src/kakarot_core/kakarot.cairo
@@ -34,6 +34,7 @@ pub mod KakarotCore {
     use utils::eth_transaction::transaction::{Transaction, TransactionTrait};
     use utils::helpers::compute_starknet_address;
     use utils::set::{Set, SetTrait};
+    use utils::constants::POW_2_53;
 
     component!(path: ownable_component, storage: ownable, event: OwnableEvent);
     component!(path: upgradeable_component, storage: upgradeable, event: UpgradeableEvent);
@@ -164,6 +165,12 @@ pub mod KakarotCore {
             (success, return_data, gas_used)
         }
 
+        fn eth_chain_id(self: @ContractState) -> u64 {
+            let tx_info = get_tx_info().unbox();
+            let tx_chain_id: u64 = tx_info.chain_id.try_into().unwrap();
+            tx_chain_id % POW_2_53.try_into().unwrap()
+        }
+
         fn eth_send_transaction(ref self: ContractState, tx: Transaction) -> (bool, Span<u8>, u64) {
             let gas_price = validate_eth_tx(@self, tx);
 
diff --git a/crates/utils/src/constants.cairo b/crates/utils/src/constants.cairo
index bb97faa8..899b1382 100644
--- a/crates/utils/src/constants.cairo
+++ b/crates/utils/src/constants.cairo
@@ -216,6 +216,7 @@ pub const POW_2_24: u128 = 0x1000000;
 pub const POW_2_32: u128 = 0x100000000;
 pub const POW_2_40: u128 = 0x10000000000;
 pub const POW_2_48: u128 = 0x1000000000000;
+pub const POW_2_53: u128 = 0x20000000000000;
 pub const POW_2_56: u128 = 0x100000000000000;
 pub const POW_2_64: u128 = 0x10000000000000000;
 pub const POW_2_72: u128 = 0x1000000000000000000;