feat(protocol): BatchValidationProvider (#189)

### Description

Part of a port migrating the batch types from `kona-derive` to
`op-alloy`. See
[`kona#695`](anton-rs/kona#695).

This PR introduces a validation trait that is used for span batch
validity checks.

Cargo.toml

@@ -85,6 +85,7 @@ jsonrpsee-core = "0.24"
 jsonrpsee-types = "0.24"
 
 # misc
+async-trait = "0.1.83"
 cfg-if = "1"
 spin = { version = "0.9.8", features = ["mutex"] }
 derive_more = { version = "1.0", default-features = false }

crates/protocol/Cargo.toml

@@ -27,6 +27,7 @@ alloy-consensus.workspace = true
 
 # Misc
 derive_more.workspace = true
+async-trait.workspace = true
 
 # `arbitrary` feature
 arbitrary = { workspace = true, features = ["derive"], optional = true }

crates/protocol/src/batch/mod.rs

@@ -8,3 +8,6 @@ pub use validity::BatchValidity;
 
 mod single;
 pub use single::SingleBatch;
+
+mod traits;
+pub use traits::BatchValidationProvider;

crates/protocol/src/batch/traits.rs

@@ -0,0 +1,25 @@
+//! Traits for working with protocol types.
+
+use alloc::{boxed::Box, string::ToString};
+use async_trait::async_trait;
+use core::fmt::Display;
+use op_alloy_consensus::OpBlock;
+
+use crate::L2BlockInfo;
+
+/// Describes the functionality of a data source that fetches safe blocks.
+#[async_trait]
+pub trait BatchValidationProvider {
+    /// The error type for the [BatchValidationProvider].
+    type Error: Display + ToString;
+
+    /// Returns the [L2BlockInfo] given a block number.
+    ///
+    /// Errors if the block does not exist.
+    async fn l2_block_info_by_number(&mut self, number: u64) -> Result<L2BlockInfo, Self::Error>;
+
+    /// Returns the [OpBlock] for a given number.
+    ///
+    /// Errors if no block is available for the given block number.
+    async fn block_by_number(&mut self, number: u64) -> Result<OpBlock, Self::Error>;
+}

crates/protocol/src/lib.rs

@@ -10,7 +10,10 @@
 extern crate alloc;
 
 mod batch;
-pub use batch::{BatchType, BatchValidity, SingleBatch, SINGLE_BATCH_TYPE, SPAN_BATCH_TYPE};
+pub use batch::{
+    BatchType, BatchValidationProvider, BatchValidity, SingleBatch, SINGLE_BATCH_TYPE,
+    SPAN_BATCH_TYPE,
+};
 
 mod block;
 pub use block::{BlockInfo, FromBlockError, L2BlockInfo};