Fix on-disk consensus context format (#5598)

* Fix on-disk consensus context format

* Keep indexed attestations, thanks Sean

beacon_node/store/src/consensus_context.rs

@@ -0,0 +1,66 @@
+use ssz_derive::{Decode, Encode};
+use state_processing::ConsensusContext;
+use std::collections::HashMap;
+use types::{AttestationData, BitList, EthSpec, Hash256, IndexedAttestation, Slot};
+
+/// The consensus context is stored on disk as part of the data availability overflow cache.
+///
+/// We use this separate struct to keep the on-disk format stable in the presence of changes to the
+/// in-memory `ConsensusContext`. You MUST NOT change the fields of this struct without
+/// superstructing it and implementing a schema migration.
+#[derive(Debug, PartialEq, Clone, Encode, Decode)]
+pub struct OnDiskConsensusContext<E: EthSpec> {
+    /// Slot to act as an identifier/safeguard
+    slot: Slot,
+    /// Proposer index of the block at `slot`.
+    proposer_index: Option<u64>,
+    /// Block root of the block at `slot`.
+    current_block_root: Option<Hash256>,
+    /// We keep the indexed attestations in the *in-memory* version of this struct so that we don't
+    /// need to regenerate them if roundtripping via this type *without* going to disk.
+    ///
+    /// They are not part of the on-disk format.
+    #[ssz(skip_serializing, skip_deserializing)]
+    indexed_attestations:
+        HashMap<(AttestationData, BitList<E::MaxValidatorsPerCommittee>), IndexedAttestation<E>>,
+}
+
+impl<E: EthSpec> OnDiskConsensusContext<E> {
+    pub fn from_consensus_context(ctxt: ConsensusContext<E>) -> Self {
+        // Match exhaustively on fields here so we are forced to *consider* updating the on-disk
+        // format when the `ConsensusContext` fields change.
+        let ConsensusContext {
+            slot,
+            previous_epoch: _,
+            current_epoch: _,
+            proposer_index,
+            current_block_root,
+            indexed_attestations,
+        } = ctxt;
+        OnDiskConsensusContext {
+            slot,
+            proposer_index,
+            current_block_root,
+            indexed_attestations,
+        }
+    }
+
+    pub fn into_consensus_context(self) -> ConsensusContext<E> {
+        let OnDiskConsensusContext {
+            slot,
+            proposer_index,
+            current_block_root,
+            indexed_attestations,
+        } = self;
+
+        let mut ctxt = ConsensusContext::new(slot);
+
+        if let Some(proposer_index) = proposer_index {
+            ctxt = ctxt.set_proposer_index(proposer_index);
+        }
+        if let Some(block_root) = current_block_root {
+            ctxt = ctxt.set_current_block_root(block_root);
+        }
+        ctxt.set_indexed_attestations(indexed_attestations)
+    }
+}

beacon_node/store/src/lib.rs

@@ -14,6 +14,7 @@ mod chunk_writer;
 pub mod chunked_iter;
 pub mod chunked_vector;
 pub mod config;
+pub mod consensus_context;
 pub mod errors;
 mod forwards_iter;
 mod garbage_collection;
@@ -30,6 +31,7 @@ pub mod iter;
 
 pub use self::chunk_writer::ChunkWriter;
 pub use self::config::StoreConfig;
+pub use self::consensus_context::OnDiskConsensusContext;
 pub use self::hot_cold_store::{HotColdDB, HotStateSummary, Split};
 pub use self::leveldb_store::LevelDB;
 pub use self::memory_store::MemoryStore;