From 94c3b6fdb5d25674a1b17b344d4af3e99d440dcc Mon Sep 17 00:00:00 2001
From: glihm <dev@glihm.net>
Date: Fri, 3 Nov 2023 20:48:53 -0600
Subject: [PATCH] feat: `MsgToL1` hash computation (#476)

---
 starknet-core/src/types/msg.rs | 63 +++++++++++++++++++++++++++++++++-
 1 file changed, 62 insertions(+), 1 deletion(-)

diff --git a/starknet-core/src/types/msg.rs b/starknet-core/src/types/msg.rs
index da5ad5e4..aa621fbe 100644
--- a/starknet-core/src/types/msg.rs
+++ b/starknet-core/src/types/msg.rs
@@ -3,7 +3,7 @@ use alloc::vec::Vec;
 use sha3::{Digest, Keccak256};
 use starknet_ff::FieldElement;
 
-use super::{EthAddress, Hash256};
+use super::{EthAddress, Hash256, MsgToL1};
 
 #[derive(Debug, Clone)]
 pub struct MsgToL2 {
@@ -51,6 +51,35 @@ impl MsgToL2 {
     }
 }
 
+impl MsgToL1 {
+    /// Calculates the message hash based on the algorithm documented here:
+    ///
+    /// https://docs.starknet.io/documentation/architecture_and_concepts/Network_Architecture/messaging-mechanism/#structure_and_hashing_l2-l1
+    pub fn hash(&self) -> Hash256 {
+        let mut hasher = Keccak256::new();
+
+        // FromAddress
+        hasher.update(self.from_address.to_bytes_be());
+
+        // ToAddress
+        hasher.update(self.to_address.to_bytes_be());
+
+        // Payload.length
+        hasher.update([0u8; 24]);
+        hasher.update((self.payload.len() as u64).to_be_bytes());
+
+        // Payload
+        for item in self.payload.iter() {
+            hasher.update(item.to_bytes_be());
+        }
+
+        let hash = hasher.finalize();
+
+        // Because we know hash is always 32 bytes
+        Hash256::from_bytes(unsafe { *(hash[..].as_ptr() as *const [u8; 32]) })
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -88,4 +117,36 @@ mod tests {
 
         assert_eq!(msg.hash(), expected_hash);
     }
+
+    #[test]
+    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test::wasm_bindgen_test)]
+    fn test_msg_to_l1_hash() {
+        // Goerli-1 tx (L1): 59e37da138dcf7ab9ca4fc7fde15d3f113a06781c4181dfcf0d74753023060b1 Log #40.
+        // Goerli-1 tx (L2): 4e0bbc07ff29e5df13dfbcb7e4746fdde52c3649a6a69bd86b15397769722fd
+
+        let msg = MsgToL1 {
+            from_address: FieldElement::from_hex_be(
+                "0x0164cba33fb7152531f6b4cfc3fff26b4d7b26b4900e0881042edd607b428a92",
+            )
+            .unwrap(),
+            to_address: FieldElement::from_hex_be(
+                "0x000000000000000000000000b6dbfaa86bb683152e4fc2401260f9ca249519c0",
+            )
+            .unwrap(),
+            payload: vec![
+                FieldElement::from_hex_be("0x0").unwrap(),
+                FieldElement::from_hex_be("0x0").unwrap(),
+                FieldElement::from_hex_be("0x0182b8").unwrap(),
+                FieldElement::from_hex_be("0x0").unwrap(),
+                FieldElement::from_hex_be("0x0384").unwrap(),
+                FieldElement::from_hex_be("0x0").unwrap(),
+            ],
+        };
+
+        let expected_hash =
+            Hash256::from_hex("0x326a04493fc8f24ac6c6ae7bdba23243ce03ec3aae53f0ed3a0d686eb8cac930")
+                .unwrap();
+
+        assert_eq!(msg.hash(), expected_hash);
+    }
 }