From a42a86080cbf96375922086e90f8cd367c21a98c Mon Sep 17 00:00:00 2001
From: refcell <abigger87@gmail.com>
Date: Mon, 30 Sep 2024 21:56:00 -0400
Subject: [PATCH] feat(protocol): block conversion utilities

---
 crates/protocol/src/lib.rs   |   2 +-
 crates/protocol/src/utils.rs | 104 +++++++++++++++++++++++++++++++++++
 2 files changed, 105 insertions(+), 1 deletion(-)

diff --git a/crates/protocol/src/lib.rs b/crates/protocol/src/lib.rs
index b78d9243..1edf8579 100644
--- a/crates/protocol/src/lib.rs
+++ b/crates/protocol/src/lib.rs
@@ -27,7 +27,7 @@ pub use frame::{
 };
 
 mod utils;
-pub use utils::starts_with_2718_deposit;
+pub use utils::{starts_with_2718_deposit, to_system_config, OpBlockConversionError};
 
 mod channel;
 pub use channel::{
diff --git a/crates/protocol/src/utils.rs b/crates/protocol/src/utils.rs
index 166f7509..895af25f 100644
--- a/crates/protocol/src/utils.rs
+++ b/crates/protocol/src/utils.rs
@@ -1,5 +1,13 @@
 //! Utility methods used by protocol types.
 
+use crate::{
+    block_info::DecodeError, L1BlockInfoBedrock, L1BlockInfoEcotone, L1BlockInfoHolocene,
+    L1BlockInfoTx,
+};
+use alloy_primitives::B256;
+use op_alloy_consensus::{OpBlock, OpTxEnvelope};
+use op_alloy_genesis::{RollupConfig, SystemConfig};
+
 /// Returns if the given `value` is a deposit transaction.
 pub fn starts_with_2718_deposit<B>(value: &B) -> bool
 where
@@ -8,6 +16,102 @@ where
     value.as_ref().first() == Some(&0x7E)
 }
 
+/// An error encountered during [OpBlock] conversion.
+#[derive(Debug, derive_more::Display)]
+pub enum OpBlockConversionError {
+    /// Invalid genesis hash.
+    #[display("Invalid genesis hash. Expected {_0}, got {_1}")]
+    InvalidGenesisHash(B256, B256),
+    /// Invalid transaction type.
+    #[display("First payload transaction has unexpected type: {_0}")]
+    InvalidTxType(u8),
+    /// L1 Info error
+    #[display("Failed to decode L1 info: {_0}")]
+    L1InfoError(DecodeError),
+    /// Missing system config in genesis block.
+    #[display("Missing system config in genesis block")]
+    MissingSystemConfigGenesis,
+    /// Empty transactions.
+    #[display("Empty transactions in payload. Block hash: {_0}")]
+    EmptyTransactions(B256),
+}
+
+impl core::error::Error for OpBlockConversionError {
+    fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
+        match self {
+            Self::L1InfoError(err) => Some(err),
+            _ => None,
+        }
+    }
+}
+
+impl From<DecodeError> for OpBlockConversionError {
+    fn from(e: DecodeError) -> Self {
+        Self::L1InfoError(e)
+    }
+}
+
+/// Converts the [OpBlock] to a partial [SystemConfig].
+pub fn to_system_config(
+    block: &OpBlock,
+    rollup_config: &RollupConfig,
+) -> Result<SystemConfig, OpBlockConversionError> {
+    if block.header.number == rollup_config.genesis.l2.number {
+        if block.header.hash_slow() != rollup_config.genesis.l2.hash {
+            return Err(OpBlockConversionError::InvalidGenesisHash(
+                rollup_config.genesis.l2.hash,
+                block.header.hash_slow(),
+            ));
+        }
+        return rollup_config
+            .genesis
+            .system_config
+            .ok_or(OpBlockConversionError::MissingSystemConfigGenesis);
+    }
+
+    if block.body.transactions.is_empty() {
+        return Err(OpBlockConversionError::EmptyTransactions(block.header.hash_slow()));
+    }
+    let OpTxEnvelope::Deposit(ref tx) = block.body.transactions[0] else {
+        return Err(OpBlockConversionError::InvalidTxType(
+            block.body.transactions[0].tx_type() as u8
+        ));
+    };
+
+    let l1_info = L1BlockInfoTx::decode_calldata(tx.input.as_ref())?;
+    let l1_fee_scalar = match l1_info {
+        L1BlockInfoTx::Bedrock(L1BlockInfoBedrock { l1_fee_scalar, .. }) => l1_fee_scalar,
+        L1BlockInfoTx::Ecotone(L1BlockInfoEcotone {
+            base_fee_scalar,
+            blob_base_fee_scalar,
+            ..
+        })
+        | L1BlockInfoTx::Holocene(L1BlockInfoHolocene {
+            base_fee_scalar,
+            blob_base_fee_scalar,
+            ..
+        }) => {
+            // Translate Ecotone values back into encoded scalar if needed.
+            // We do not know if it was derived from a v0 or v1 scalar,
+            // but v1 is fine, a 0 blob base fee has the same effect.
+            let mut buf = B256::ZERO;
+            buf[0] = 0x01;
+            buf[24..28].copy_from_slice(blob_base_fee_scalar.to_be_bytes().as_ref());
+            buf[28..32].copy_from_slice(base_fee_scalar.to_be_bytes().as_ref());
+            buf.into()
+        }
+    };
+
+    Ok(SystemConfig {
+        batcher_address: l1_info.batcher_address(),
+        overhead: l1_info.l1_fee_overhead(),
+        scalar: l1_fee_scalar,
+        gas_limit: block.header.gas_limit,
+        base_fee_scalar: None,
+        blob_base_fee_scalar: None,
+    })
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;