Implement basic BeaconChain persistence.

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -1,5 +1,6 @@
 use crate::checkpoint::CheckPoint;
 use crate::errors::{BeaconChainError as Error, BlockProductionError};
+use crate::persisted_beacon_chain::{PersistedBeaconChain, BEACON_CHAIN_DB_KEY};
 use fork_choice::{ForkChoice, ForkChoiceError};
 use log::{debug, trace};
 use operation_pool::DepositInsertStatus;
@@ -140,6 +141,51 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         })
     }
 
+    /// Attempt to load an existing instance from the given `store`.
+    pub fn from_store(store: Arc<T::Store>) -> Result<Option<BeaconChain<T>>, Error> {
+        let key = Hash256::from_slice(&BEACON_CHAIN_DB_KEY.as_bytes());
+        let p: PersistedBeaconChain<T> = match store.get(&key) {
+            Err(e) => return Err(e.into()),
+            Ok(None) => return Ok(None),
+            Ok(Some(p)) => p,
+        };
+
+        let spec = T::EthSpec::spec();
+
+        let slot_clock = T::SlotClock::new(
+            spec.genesis_slot,
+            p.state.genesis_time,
+            spec.seconds_per_slot,
+        );
+
+        let fork_choice = T::ForkChoice::new(store.clone());
+
+        Ok(Some(BeaconChain {
+            store,
+            slot_clock,
+            op_pool: OperationPool::default(),
+            canonical_head: RwLock::new(p.canonical_head),
+            finalized_head: RwLock::new(p.finalized_head),
+            state: RwLock::new(p.state),
+            spec,
+            fork_choice: RwLock::new(fork_choice),
+        }))
+    }
+
+    /// Attempt to save this instance to `self.store`.
+    pub fn persist(&self) -> Result<(), Error> {
+        let p: PersistedBeaconChain<T> = PersistedBeaconChain {
+            canonical_head: self.canonical_head.read().clone(),
+            finalized_head: self.finalized_head.read().clone(),
+            state: self.state.read().clone(),
+        };
+
+        let key = Hash256::from_slice(&BEACON_CHAIN_DB_KEY.as_bytes());
+        self.store.put(&key, &p)?;
+
+        Ok(())
+    }
+
     /// Returns the beacon block body for each beacon block root in `roots`.
     ///
     /// Fails if any root in `roots` does not have a corresponding block.

beacon_node/beacon_chain/src/checkpoint.rs

@@ -1,9 +1,10 @@
 use serde_derive::Serialize;
+use ssz_derive::{Decode, Encode};
 use types::{BeaconBlock, BeaconState, EthSpec, Hash256};
 
 /// Represents some block and it's associated state. Generally, this will be used for tracking the
 /// head, justified head and finalized head.
-#[derive(Clone, Serialize, PartialEq, Debug)]
+#[derive(Clone, Serialize, PartialEq, Debug, Encode, Decode)]
 pub struct CheckPoint<E: EthSpec> {
     pub beacon_block: BeaconBlock,
     pub beacon_block_root: Hash256,

beacon_node/beacon_chain/src/lib.rs

@@ -1,6 +1,7 @@
 mod beacon_chain;
 mod checkpoint;
 mod errors;
+mod persisted_beacon_chain;
 
 pub use self::beacon_chain::{
     BeaconChain, BeaconChainTypes, BlockProcessingOutcome, InvalidBlock, ValidBlock,

beacon_node/beacon_chain/src/persisted_beacon_chain.rs

@@ -0,0 +1,30 @@
+use crate::{BeaconChainTypes, CheckPoint};
+use ssz::{Decode, Encode};
+use ssz_derive::{Decode, Encode};
+use store::{DBColumn, Error as StoreError, StoreItem};
+use types::BeaconState;
+
+/// 32-byte key for accessing the `PersistedBeaconChain`.
+pub const BEACON_CHAIN_DB_KEY: &str = "PERSISTEDBEACONCHAINPERSISTEDBEA";
+
+#[derive(Encode, Decode)]
+pub struct PersistedBeaconChain<T: BeaconChainTypes> {
+    pub canonical_head: CheckPoint<T::EthSpec>,
+    pub finalized_head: CheckPoint<T::EthSpec>,
+    // TODO: operations pool.
+    pub state: BeaconState<T::EthSpec>,
+}
+
+impl<T: BeaconChainTypes> StoreItem for PersistedBeaconChain<T> {
+    fn db_column() -> DBColumn {
+        DBColumn::BeaconChain
+    }
+
+    fn as_store_bytes(&self) -> Vec<u8> {
+        self.as_ssz_bytes()
+    }
+
+    fn from_store_bytes(bytes: &mut [u8]) -> Result<Self, StoreError> {
+        Self::from_ssz_bytes(bytes).map_err(Into::into)
+    }
+}