Add graffiti cli flag to the validator client. (#1425)

## Issue Addressed

#1419

## Proposed Changes

Creates a `--graffiti` cli flag in the validator client. If the flag is set, it overrides graffiti in the beacon node. 

## Additional Info

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -1564,12 +1564,13 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         &self,
         randao_reveal: Signature,
         slot: Slot,
+        validator_graffiti: Option<Graffiti>,
     ) -> Result<BeaconBlockAndState<T::EthSpec>, BlockProductionError> {
         let state = self
             .state_at_slot(slot - 1, StateSkipConfig::WithStateRoots)
             .map_err(|_| BlockProductionError::UnableToProduceAtSlot(slot))?;
 
-        self.produce_block_on_state(state, slot, randao_reveal)
+        self.produce_block_on_state(state, slot, randao_reveal, validator_graffiti)
     }
 
     /// Produce a block for some `slot` upon the given `state`.
@@ -1585,6 +1586,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         mut state: BeaconState<T::EthSpec>,
         produce_at_slot: Slot,
         randao_reveal: Signature,
+        validator_graffiti: Option<Graffiti>,
     ) -> Result<BeaconBlockAndState<T::EthSpec>, BlockProductionError> {
         metrics::inc_counter(&metrics::BLOCK_PRODUCTION_REQUESTS);
         let timer = metrics::start_timer(&metrics::BLOCK_PRODUCTION_TIMES);
@@ -1652,6 +1654,12 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             }
         }
 
+        // Override the beacon node's graffiti with graffiti from the validator, if present.
+        let graffiti = match validator_graffiti {
+            Some(graffiti) => graffiti,
+            None => self.graffiti,
+        };
+
         let mut block = SignedBeaconBlock {
             message: BeaconBlock {
                 slot: state.slot,
@@ -1661,7 +1669,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                 body: BeaconBlockBody {
                     randao_reveal,
                     eth1_data,
-                    graffiti: self.graffiti,
+                    graffiti,
                     proposer_slashings: proposer_slashings.into(),
                     attester_slashings: attester_slashings.into(),
                     attestations: self

beacon_node/beacon_chain/src/test_utils.rs

@@ -520,7 +520,7 @@ where
 
         let (block, state) = self
             .chain
-            .produce_block_on_state(state, slot, randao_reveal)
+            .produce_block_on_state(state, slot, randao_reveal, None)
             .expect("should produce block");
 
         let signed_block = block.sign(sk, &state.fork, state.genesis_validators_root, &self.spec);

beacon_node/rest_api/src/validator.rs

@@ -1,4 +1,6 @@
-use crate::helpers::{check_content_type_for_json, publish_beacon_block_to_network};
+use crate::helpers::{
+    check_content_type_for_json, parse_hex_ssz_bytes, publish_beacon_block_to_network,
+};
 use crate::response_builder::ResponseBuilder;
 use crate::{ApiError, ApiResult, NetworkChannel, UrlQuery};
 use beacon_chain::{
@@ -288,8 +290,14 @@ pub fn get_new_beacon_block<T: BeaconChainTypes>(
     let slot = query.slot()?;
     let randao_reveal = query.randao_reveal()?;
 
+    let validator_graffiti = if let Some((_key, value)) = query.first_of_opt(&["graffiti"]) {
+        Some(parse_hex_ssz_bytes(&value)?)
+    } else {
+        None
+    };
+
     let (new_block, _state) = beacon_chain
-        .produce_block(randao_reveal, slot)
+        .produce_block(randao_reveal, slot, validator_graffiti)
         .map_err(|e| {
             error!(
                 log,

beacon_node/rest_api/tests/test.rs

@@ -460,7 +460,7 @@ fn validator_block_post() {
             remote_node
                 .http
                 .validator()
-                .produce_block(slot, randao_reveal),
+                .produce_block(slot, randao_reveal, None),
         )
         .expect("should fetch block from http api");
 
@@ -547,7 +547,7 @@ fn validator_block_get() {
             remote_node
                 .http
                 .validator()
-                .produce_block(slot, randao_reveal.clone()),
+                .produce_block(slot, randao_reveal.clone(), None),
         )
         .expect("should fetch block from http api");
 
@@ -555,7 +555,50 @@ fn validator_block_get() {
         .client
         .beacon_chain()
         .expect("client should have beacon chain")
-        .produce_block(randao_reveal, slot)
+        .produce_block(randao_reveal, slot, None)
+        .expect("should produce block");
+
+    assert_eq!(
+        block, expected_block,
+        "the block returned from the API should be as expected"
+    );
+}
+
+#[test]
+fn validator_block_get_with_graffiti() {
+    let mut env = build_env();
+
+    let spec = &E::default_spec();
+
+    let node = build_node(&mut env, testing_client_config());
+    let remote_node = node.remote_node().expect("should produce remote node");
+
+    let beacon_chain = node
+        .client
+        .beacon_chain()
+        .expect("client should have beacon chain");
+
+    let slot = Slot::new(1);
+    let randao_reveal = get_randao_reveal(beacon_chain, slot, spec);
+
+    let block = env
+        .runtime()
+        .block_on(remote_node.http.validator().produce_block(
+            slot,
+            randao_reveal.clone(),
+            Some(*b"test-graffiti-test-graffiti-test"),
+        ))
+        .expect("should fetch block from http api");
+
+    let (expected_block, _state) = node
+        .client
+        .beacon_chain()
+        .expect("client should have beacon chain")
+        .produce_block(
+            randao_reveal,
+            slot,
+            Some(*b"test-graffiti-test-graffiti-test"),
+        )
         .expect("should produce block");
 
     assert_eq!(