fix: codec issue

Author: greged93

crates/codec/src/lib.rs

@@ -16,7 +16,7 @@ use crate::{
 };
 
 use alloy_eips::eip4844::Blob;
-use alloy_primitives::Bytes;
+use alloy_primitives::{Bytes, U256};
 
 /// The Codec.
 #[derive(Debug)]
@@ -46,7 +46,7 @@ impl Codec {
     /// Decodes the input data and returns the decoded [`Batch`].
     pub fn decode<T: CommitDataSource>(input: &T) -> Result<Batch, CodecError> {
         let calldata = input.calldata();
-        let version = calldata.first().ok_or(DecodingError::MissingCodecVersion)?;
+        let version = get_codec_version(&calldata).ok_or(DecodingError::MissingCodecVersion)?;
 
         let payload = match version {
             0 => decode_v0(calldata)?,
@@ -66,7 +66,7 @@ impl Codec {
                 let blob = input.blob().ok_or(DecodingError::MissingBlob)?;
                 decode_v7(blob.as_ref())?
             }
-            v => return Err(DecodingError::UnsupportedCodecVersion(*v).into()),
+            v => return Err(DecodingError::UnsupportedCodecVersion(v).into()),
         };
 
         Ok(payload)
@@ -80,3 +80,21 @@ pub trait CommitDataSource {
     /// Returns the blob for decoding.
     fn blob(&self) -> Option<&Blob>;
 }
+
+/// Returns the codec version from the calldata.
+fn get_codec_version(calldata: &[u8]) -> Option<u8> {
+    const CODEC_VERSION_OFFSET_START: usize = 4;
+    const CODEC_VERSION_OFFSET_END: usize = 4 + 32;
+    const HIGH_BYTES_FLAG: U256 =
+        U256::from_limbs([u64::MAX, u64::MAX, u64::MAX, 0xffffffffffffff00]);
+    const LOW_BYTES_FLAG: U256 = U256::from_limbs([0, 0, 0, 0xff]);
+
+    let version = calldata.get(CODEC_VERSION_OFFSET_START..CODEC_VERSION_OFFSET_END)?;
+    let version = U256::from_be_slice(version);
+
+    if (version & HIGH_BYTES_FLAG) != U256::ZERO {
+        return None
+    }
+
+    Some((version & LOW_BYTES_FLAG).saturating_to())
+}