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/test-client/src/client_ext.rs

@@ -18,18 +18,23 @@
 
 use client::{self, Client};
 use consensus::{ImportBlock, BlockImport, BlockOrigin};
+use runtime_primitives::Justification;
 use runtime_primitives::generic::BlockId;
 use primitives::Blake2Hasher;
 use runtime;
 
 /// Extension trait for a test client.
 pub trait TestClient: Sized {
-	/// Justify and import block to the chain. No finality.
-	fn justify_and_import(&self, origin: BlockOrigin, block: runtime::Block)
+	/// Import block to the chain. No finality.
+	fn import(&self, origin: BlockOrigin, block: runtime::Block)
+		-> client::error::Result<()>;
+
+	/// Import block with justification, finalizes block.
+	fn import_justified(&self, origin: BlockOrigin, block: runtime::Block, justification: Justification)
 		-> client::error::Result<()>;
 
 	/// Finalize a block.
-	fn finalize_block(&self, id: BlockId<runtime::Block>) -> client::error::Result<()>;
+	fn finalize_block(&self, id: BlockId<runtime::Block>, justification: Option<Justification>) -> client::error::Result<()>;
 
 	/// Returns hash of the genesis block.
 	fn genesis_hash(&self) -> runtime::Hash;
@@ -41,13 +46,13 @@ impl<B, E, RA> TestClient for Client<B, E, runtime::Block, RA>
 		E: client::CallExecutor<runtime::Block, Blake2Hasher>,
 		Self: BlockImport<runtime::Block, Error=client::error::Error>,
 {
-	fn justify_and_import(&self, origin: BlockOrigin, block: runtime::Block)
+	fn import(&self, origin: BlockOrigin, block: runtime::Block)
 		-> client::error::Result<()>
 	{
 		let import = ImportBlock {
 			origin,
 			header: block.header,
-			justification: vec![],
+			justification: None,
 			post_digests: vec![],
 			body: Some(block.extrinsics),
 			finalized: false,
@@ -57,8 +62,24 @@ impl<B, E, RA> TestClient for Client<B, E, runtime::Block, RA>
 		self.import_block(import, None).map(|_| ())
 	}
 
-	fn finalize_block(&self, id: BlockId<runtime::Block>) -> client::error::Result<()> {
-		self.finalize_block(id, true)
+	fn import_justified(&self, origin: BlockOrigin, block: runtime::Block, justification: Justification)
+		-> client::error::Result<()>
+	{
+		let import = ImportBlock {
+			origin,
+			header: block.header,
+			justification: Some(justification),
+			post_digests: vec![],
+			body: Some(block.extrinsics),
+			finalized: true,
+			auxiliary: Vec::new(),
+		};
+
+		self.import_block(import, None).map(|_| ())
+	}
+
+	fn finalize_block(&self, id: BlockId<runtime::Block>, justification: Option<Justification>) -> client::error::Result<()> {
+		self.finalize_block(id, justification, true)
 	}
 
 	fn genesis_hash(&self) -> runtime::Hash {