Bootstrap (#501)

* 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

* Begin metrics refactor

* Move beacon_chain to new metrics structure.

* Make metrics not panic if already defined

* Use global prometheus gather at rest api

* Unify common metric fns into a crate

* Add heavy metering to block processing

* Remove hypen from prometheus metric name

* Add more beacon chain metrics

* Add beacon chain persistence metric

* Prune op pool on finalization

* Add extra prom beacon chain metrics

* Prefix BeaconChain metrics with "beacon_"

* Add more store metrics

* Add basic metrics to libp2p

* Add metrics to HTTP server

* Remove old `http_server` crate

* Update metrics names to be more like standard

* Fix broken beacon chain metrics, add slot clock metrics

* Add lighthouse_metrics gather fn

* Remove http args

* Fix wrong state given to op pool prune

* Make prom metric names more consistent

* Add more metrics, tidy existing metrics

* Fix store block read metrics

* Tidy attestation metrics

* Fix minor PR comments

* Fix minor PR comments

* Remove duplicated attestation finalization check

* Remove awkward `let` statement

* Add first attempts at HTTP bootstrap

* Add beacon_block methods to rest api

* Fix serde for block.body.grafitti

* Allow travis failures on beta (see desc)

There's a non-backward compatible change in `cargo fmt`. Stable and beta
do not agree.

* Add network routes to API

* Fix rustc warnings

* Add best_slot method

* Add --bootstrap arg to beacon node

* Get bootstrapper working for ENR address

* Store intermediate states during block processing

* Allow bootstrapper to scrape libp2p address

* Update bootstrapper libp2p address finding

* Add comments

* Tidy API to be more consistent with recent decisions

* Address some review comments

* Make BeaconChainTypes Send + Sync + 'static

* Add `/network/listen_port` API endpoint

* Abandon starting the node if libp2p doesn't start

* Update bootstrapper for API changes

* Remove unnecessary trait bounds

beacon_node/rest_api/src/helpers.rs

@@ -31,22 +31,40 @@ pub fn parse_root(string: &str) -> Result<Hash256, ApiError> {
     }
 }
 
-/// Returns a `BeaconState` in the canonical chain of `beacon_chain` at the given `slot`, if
-/// possible.
+/// Returns the root of the `BeaconBlock` in the canonical chain of `beacon_chain` at the given
+/// `slot`, if possible.
+///
+/// May return a root for a previous slot, in the case of skip slots.
+pub fn block_root_at_slot<T: BeaconChainTypes>(
+    beacon_chain: &BeaconChain<T>,
+    target: Slot,
+) -> Option<Hash256> {
+    beacon_chain
+        .rev_iter_block_roots()
+        .take_while(|(_root, slot)| *slot >= target)
+        .find(|(_root, slot)| *slot == target)
+        .map(|(root, _slot)| root)
+}
+
+/// Returns a `BeaconState` and it's root in the canonical chain of `beacon_chain` at the given
+/// `slot`, if possible.
 ///
 /// Will not return a state if the request slot is in the future. Will return states higher than
 /// the current head by skipping slots.
 pub fn state_at_slot<T: BeaconChainTypes>(
     beacon_chain: &BeaconChain<T>,
     slot: Slot,
-) -> Result<BeaconState<T::EthSpec>, ApiError> {
+) -> Result<(Hash256, BeaconState<T::EthSpec>), ApiError> {
     let head_state = &beacon_chain.head().beacon_state;
 
     if head_state.slot == slot {
         // The request slot is the same as the best block (head) slot.
 
         // I'm not sure if this `.clone()` will be optimized out. If not, it seems unnecessary.
-        Ok(beacon_chain.head().beacon_state.clone())
+        Ok((
+            beacon_chain.head().beacon_state_root,
+            beacon_chain.head().beacon_state.clone(),
+        ))
     } else {
         let root = state_root_at_slot(beacon_chain, slot)?;
 
@@ -55,7 +73,7 @@ pub fn state_at_slot<T: BeaconChainTypes>(
             .get(&root)?
             .ok_or_else(|| ApiError::NotFound(format!("Unable to find state at root {}", root)))?;
 
-        Ok(state)
+        Ok((root, state))
     }
 }