Attestation processing (#497)

* Renamed fork_choice::process_attestation_from_block

* Processing attestation in fork choice

* Retrieving state from store and checking signature

* Looser check on beacon state validity.

* Cleaned up get_attestation_state

* Expanded fork choice api to provide latest validator message.

* Checking if the an attestation contains a latest message

* Correct process_attestation error handling.

* Copy paste error in comment fixed.

* Tidy ancestor iterators

* Getting attestation slot via helper method

* Refactored attestation creation in test utils

* Revert "Refactored attestation creation in test utils"

This reverts commit 4d277fe4239a7194758b18fb5c00dfe0b8231306.

* Integration tests for free attestation processing

* Implicit conflicts resolved.

* formatting

* Do first pass on Grants code

* Add another attestation processing test

* Tidy attestation processing

* Remove old code fragment

* Add non-compiling half finished changes

* Simplify, fix bugs, add tests for chain iters

* Remove attestation processing from op pool

* Fix bug with fork choice, tidy

* Fix overly restrictive check in fork choice.

* Ensure committee cache is build during attn proc

* Ignore unknown blocks at fork choice

* Various minor fixes

* Make fork choice write lock in to read lock

* Remove unused method

* Tidy comments

* Fix attestation prod. target roots change

* Fix compile error in store iters

* Reject any attestation prior to finalization

* Fix minor PR comments

* Remove duplicated attestation finalization check

* Remove awkward `let` statement

eth2/lmd_ghost/src/lib.rs

@@ -43,4 +43,7 @@ pub trait LmdGhost<S: Store, E: EthSpec>: Send + Sync {
         finalized_block: &BeaconBlock<E>,
         finalized_block_root: Hash256,
     ) -> Result<()>;
+
+    /// Returns the latest message for a given validator index.
+    fn latest_message(&self, validator_index: usize) -> Option<(Hash256, Slot)>;
 }

eth2/lmd_ghost/src/reduced_tree.rs

@@ -109,6 +109,10 @@ where
             .update_root(new_block.slot, new_root)
             .map_err(|e| format!("update_finalized_root failed: {:?}", e))
     }
+
+    fn latest_message(&self, validator_index: usize) -> Option<(Hash256, Slot)> {
+        self.core.read().latest_message(validator_index)
+    }
 }
 
 struct ReducedTree<T, E> {
@@ -254,6 +258,13 @@ where
         Ok(head_node.block_hash)
     }
 
+    pub fn latest_message(&self, validator_index: usize) -> Option<(Hash256, Slot)> {
+        match self.latest_votes.get_ref(validator_index) {
+            Some(Some(v)) => Some((v.hash.clone(), v.slot.clone())),
+            _ => None,
+        }
+    }
+
     fn find_head_from<'a>(&'a self, start_node: &'a Node) -> Result<&'a Node> {
         if start_node.does_not_have_children() {
             Ok(start_node)
@@ -600,11 +611,7 @@ where
         let block = self.get_block(child)?;
         let state = self.get_state(block.state_root)?;
 
-        Ok(BlockRootsIterator::owned(
-            self.store.clone(),
-            state,
-            block.slot - 1,
-        ))
+        Ok(BlockRootsIterator::owned(self.store.clone(), state))
     }
 
     /// Verify the integrity of `self`. Returns `Ok(())` if the tree has integrity, otherwise returns `Err(description)`.
@@ -769,6 +776,10 @@ where
         &self.0[i]
     }
 
+    pub fn get_ref(&self, i: usize) -> Option<&T> {
+        self.0.get(i)
+    }
+
     pub fn insert(&mut self, i: usize, element: T) {
         self.ensure(i);
         self.0[i] = element;