Fix bug when resuming from DB prior to genesis (#946)

* Use default client genesis if no chain in store

* Always use resume if there is a beacon chain

beacon_node/beacon_chain/src/builder.rs

@@ -178,6 +178,19 @@ where
             .map_err(|e| format!("DB error whilst reading eth1 cache: {:?}", e))
     }
 
+    /// Returns true if `self.store` contains a persisted beacon chain.
+    pub fn store_contains_beacon_chain(&self) -> Result<bool, String> {
+        let store = self
+            .store
+            .clone()
+            .ok_or_else(|| "load_from_store requires a store.".to_string())?;
+
+        Ok(store
+            .get::<PersistedBeaconChain>(&Hash256::from_slice(&BEACON_CHAIN_DB_KEY))
+            .map_err(|e| format!("DB error when reading persisted beacon chain: {:?}", e))?
+            .is_some())
+    }
+
     /// Attempt to load an existing chain from the builder's `Store`.
     ///
     /// May initialize several components; including the op_pool and finalized checkpoints.

beacon_node/client/src/builder.rs

@@ -151,6 +151,26 @@ where
                 Ok((builder, spec, context))
             })
             .and_then(move |(builder, spec, context)| {
+                let chain_exists = builder
+                    .store_contains_beacon_chain()
+                    .unwrap_or_else(|_| false);
+
+                // If the client is expect to resume but there's no beacon chain in the database,
+                // use the `DepositContract` method. This scenario is quite common when the client
+                // is shutdown before finding genesis via eth1.
+                //
+                // Alternatively, if there's a beacon chain in the database then always resume
+                // using it.
+                let client_genesis = if client_genesis == ClientGenesis::Resume && !chain_exists {
+                    info!(context.log, "Defaulting to deposit contract genesis");
+
+                    ClientGenesis::DepositContract
+                } else if chain_exists {
+                    ClientGenesis::Resume
+                } else {
+                    client_genesis
+                };
+
                 let genesis_state_future: Box<dyn Future<Item = _, Error = _> + Send> =
                     match client_genesis {
                         ClientGenesis::Interop {

beacon_node/client/src/config.rs

@@ -12,7 +12,7 @@ const TESTNET_SPEC_CONSTANTS: &str = "minimal";
 const DEFAULT_FREEZER_DB_DIR: &str = "freezer_db";
 
 /// Defines how the client should initialize the `BeaconChain` and other components.
-#[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(PartialEq, Debug, Clone, Serialize, Deserialize)]
 pub enum ClientGenesis {
     /// Reads the genesis state and other persisted data from the `Store`.
     Resume,