minimize the number of places we are calling update_pubkey_cache (#1626)

## Issue Addressed

- Resolves #1080

## Proposed Changes

- Call `update_pubkey_cache` only in the `build_all_caches` method and `get_validator_index` method. 

## Additional Info

This does reduce the number of places the cache is updated, making it simpler. But the `get_validator_index` method is used a couple times when we are iterating through the entire validator registry (or set of active validators). Before, we would only call `update_pubkey_cache` once before iterating through all validators.  So I'm not _totally_ sure this change is worth it.

beacon_node/rest_api/src/beacon.rs

@@ -192,12 +192,11 @@ pub fn get_all_validators<T: BeaconChainTypes>(
     };
 
     let mut state = get_state_from_root_opt(&ctx.beacon_chain, state_root_opt)?;
-    state.update_pubkey_cache()?;
 
-    state
-        .validators
+    let validators = state.validators.clone();
+    validators
         .iter()
-        .map(|validator| validator_response_by_pubkey(&state, validator.pubkey.clone()))
+        .map(|validator| validator_response_by_pubkey(&mut state, validator.pubkey.clone()))
         .collect::<Result<Vec<_>, _>>()
 }
 
@@ -215,13 +214,14 @@ pub fn get_active_validators<T: BeaconChainTypes>(
     };
 
     let mut state = get_state_from_root_opt(&ctx.beacon_chain, state_root_opt)?;
-    state.update_pubkey_cache()?;
 
-    state
-        .validators
+    let validators = state.validators.clone();
+    let current_epoch = state.current_epoch();
+
+    validators
         .iter()
-        .filter(|validator| validator.is_active_at(state.current_epoch()))
-        .map(|validator| validator_response_by_pubkey(&state, validator.pubkey.clone()))
+        .filter(|validator| validator.is_active_at(current_epoch))
+        .map(|validator| validator_response_by_pubkey(&mut state, validator.pubkey.clone()))
         .collect::<Result<Vec<_>, _>>()
 }
 
@@ -279,11 +279,10 @@ fn validator_responses_by_pubkey<T: BeaconChainTypes>(
     validator_pubkeys: Vec<PublicKeyBytes>,
 ) -> Result<Vec<ValidatorResponse>, ApiError> {
     let mut state = get_state_from_root_opt(beacon_chain, state_root_opt)?;
-    state.update_pubkey_cache()?;
 
     validator_pubkeys
         .into_iter()
-        .map(|validator_pubkey| validator_response_by_pubkey(&state, validator_pubkey))
+        .map(|validator_pubkey| validator_response_by_pubkey(&mut state, validator_pubkey))
         .collect::<Result<Vec<_>, ApiError>>()
 }
 
@@ -291,7 +290,7 @@ fn validator_responses_by_pubkey<T: BeaconChainTypes>(
 ///
 /// The provided `state` must have a fully up-to-date pubkey cache.
 fn validator_response_by_pubkey<E: EthSpec>(
-    state: &BeaconState<E>,
+    state: &mut BeaconState<E>,
     validator_pubkey: PublicKeyBytes,
 ) -> Result<ValidatorResponse, ApiError> {
     let validator_index_opt = state

beacon_node/rest_api/src/consensus.rs

@@ -92,10 +92,6 @@ pub fn post_individual_votes<T: BeaconChainTypes>(
             let mut validator_statuses = ValidatorStatuses::new(&state, spec)?;
             validator_statuses.process_attestations(&state, spec)?;
 
-            state.update_pubkey_cache().map_err(|e| {
-                ApiError::ServerError(format!("Unable to build pubkey cache: {:?}", e))
-            })?;
-
             body.pubkeys
                 .into_iter()
                 .map(|pubkey| {

beacon_node/rest_api/src/validator.rs

@@ -156,9 +156,6 @@ fn return_validator_duties<T: BeaconChainTypes>(
     state
         .build_committee_cache(relative_epoch, &beacon_chain.spec)
         .map_err(|e| ApiError::ServerError(format!("Unable to build committee cache: {:?}", e)))?;
-    state
-        .update_pubkey_cache()
-        .map_err(|e| ApiError::ServerError(format!("Unable to build pubkey cache: {:?}", e)))?;
 
     // Get a list of all validators for this epoch.
     //

consensus/state_processing/src/per_block_processing.rs

@@ -446,10 +446,6 @@ pub fn process_deposit<T: EthSpec>(
 
     state.eth1_deposit_index.increment()?;
 
-    // Ensure the state's pubkey cache is fully up-to-date, it will be used to check to see if the
-    // depositing validator already exists in the registry.
-    state.update_pubkey_cache()?;
-
     // Get an `Option<u64>` where `u64` is the validator index if this deposit public key
     // already exists in the beacon_state.
     let validator_index = get_existing_validator_index(state, &deposit.data.pubkey)

consensus/state_processing/src/per_block_processing/verify_deposit.rs

@@ -35,7 +35,7 @@ pub fn verify_deposit_signature(deposit_data: &DepositData, spec: &ChainSpec) ->
 ///
 /// Errors if the state's `pubkey_cache` is not current.
 pub fn get_existing_validator_index<T: EthSpec>(
-    state: &BeaconState<T>,
+    state: &mut BeaconState<T>,
     pub_key: &PublicKeyBytes,
 ) -> Result<Option<u64>> {
     let validator_index = state.get_validator_index(pub_key)?;

consensus/types/src/beacon_state.rs

@@ -300,19 +300,12 @@ impl<T: EthSpec> BeaconState<T> {
         }
     }
 
-    /// If a validator pubkey exists in the validator registry, returns `Some(i)`, otherwise
-    /// returns `None`.
-    ///
-    /// Requires a fully up-to-date `pubkey_cache`, returns an error if this is not the case.
-    pub fn get_validator_index(&self, pubkey: &PublicKeyBytes) -> Result<Option<usize>, Error> {
-        if self.pubkey_cache.len() == self.validators.len() {
-            Ok(self.pubkey_cache.get(pubkey))
-        } else {
-            Err(Error::PubkeyCacheIncomplete {
-                cache_len: self.pubkey_cache.len(),
-                registry_len: self.validators.len(),
-            })
-        }
+    /// This method ensures the state's pubkey cache is fully up-to-date before checking if the validator
+    /// exists in the registry. If a validator pubkey exists in the validator registry, returns `Some(i)`,
+    /// otherwise returns `None`.
+    pub fn get_validator_index(&mut self, pubkey: &PublicKeyBytes) -> Result<Option<usize>, Error> {
+        self.update_pubkey_cache()?;
+        Ok(self.pubkey_cache.get(pubkey))
     }
 
     /// The epoch corresponding to `self.slot`.