Grandpa validator set handoff justification (#1190)

* core: make block justification optional

* runtime: update wasm binaries

* core: optionally pass justification on finalize_block

* finality-grandpa: add channel to trigger authority set changes

this will allow the `BlockImport` to trigger an authority set change when
importing a change block that provides a justification (when syncing)

* finality-grandpa: move finalize_block to free function

* finality-grandpa: add GrandpaOracle for auth set liveness checking

this will be used by `BlockImport` to check whether the authority set for a
given block is still live, if the authority set isn't live then importing a
change block requires a justification.

* finality-grandpa: store justification on finalized transition blocks

* finality-grandpa: check justification on authority set change blocks

* finality-grandpa: poll grandpa liveness oracle every 10 seconds

* finality-grandpa: spawn grandpa oracle in service setup

* core: support multiple subscriptions per consensus gossip topic

* finality-grandpa: create and verify justifications

* finality-grandpa: update to local branch of grandpa

* finality-grandpa: update to finality-grandpa v0.5.0

* finality-grandpa: move grandpa oracle code

* finality-grandpa: fix canonality check

* finality-grandpa: clean up error handling

* finality-grandpa: fix canonical_at_height

* finality-grandpa: fix tests

* runtime: update wasm binaries

* core: add tests for finalizing block with justification

* finality-grandpa: improve validation of justifications

* core: remove unused IncompleteJustification block import error

* core: test multiple subscribers for same consensus gossip topic

* Revert "finality-grandpa: improve validation of justifications"

This reverts commit 51eb2c58c2219801e876af6d6c9371bdd9ff2477.

* finality-grandpa: fix commit validation

* finality-grandpa: fix commit ancestry validation

* finality-grandpa: use grandpa v0.5.1

* finality-grandpa: add docs

* finality-grandpa: fix failing test

* finality-grandpa: only allow a pending authority set change per fork

* finality-grandpa: fix validator set transition test

substrate/core/consensus/aura/src/lib.rs

@@ -60,7 +60,7 @@ use codec::Encode;
 use consensus_common::{Authorities, BlockImport, Environment, Proposer};
 use client::ChainHead;
 use consensus_common::{ImportBlock, BlockOrigin};
-use runtime_primitives::{generic, generic::BlockId};
+use runtime_primitives::{generic, generic::BlockId, Justification};
 use runtime_primitives::traits::{Block, Header, Digest, DigestItemFor};
 use network::import_queue::{Verifier, BasicQueue};
 use primitives::{AuthorityId, ed25519};
@@ -244,7 +244,7 @@ pub fn start_aura<B, C, E, I, SO, Error>(
 						let import_block = ImportBlock {
 							origin: BlockOrigin::Own,
 							header,
-							justification: Vec::new(),
+							justification: None,
 							post_digests: vec![item],
 							body: Some(body),
 							finalized: false,
@@ -367,7 +367,7 @@ impl<B: Block, C, E> Verifier<B> for AuraVerifier<C, E> where
 		&self,
 		origin: BlockOrigin,
 		header: B::Header,
-		_justification: Vec<u8>,
+		justification: Option<Justification>,
 		body: Option<Vec<B::Extrinsic>>
 	) -> Result<(ImportBlock<B>, Option<Vec<AuthorityId>>), String> {
 		let slot_now = slot_now(self.config.slot_duration)
@@ -390,13 +390,14 @@ impl<B: Block, C, E> Verifier<B> for AuraVerifier<C, E> where
 				debug!(target: "aura", "Checked {:?}; importing.", pre_header);
 
 				extra_verification.into_future().wait()?;
+
 				let import_block = ImportBlock {
 					origin,
 					header: pre_header,
-					justification: Vec::new(),
 					post_digests: vec![item],
 					body,
 					finalized: false,
+					justification,
 					auxiliary: Vec::new(),
 				};