Merge branch 'rh-grandpa-dynamic2' of github.com:paritytech/substrate

2026-05-31 08:41:02 +00:00 · 2018-11-15 17:49:36 +01:00
parent 4307a55505 3cd2739f66
commit 913513d983
29 changed files with 1833 additions and 478 deletions
@@ -663,11 +663,12 @@ dependencies = [

 [[package]]
 name = "finality-grandpa"
-version = "0.2.0"
+version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
 "futures 0.1.25 (registry+https://github.com/rust-lang/crates.io-index)",
 "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num-traits 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)",
 "parity-codec 2.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
 "parity-codec-derive 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "parking_lot 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1803,6 +1804,7 @@ dependencies = [
 "srml-treasury 0.1.0",
 "srml-upgrade-key 0.1.0",
 "substrate-client 0.1.0",
+ "substrate-fg-primitives 0.1.0",
 "substrate-keyring 0.1.0",
 "substrate-primitives 0.1.0",
 ]
@@ -3178,20 +3180,37 @@ dependencies = [
 "wasmi 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "substrate-fg-primitives"
+version = "0.1.0"
+dependencies = [
+ "parity-codec 2.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "parity-codec-derive 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sr-primitives 0.1.0",
+ "sr-std 0.1.0",
+ "substrate-client 0.1.0",
+ "substrate-primitives 0.1.0",
+]
+
 [[package]]
 name = "substrate-finality-grandpa"
 version = "0.1.0"
 dependencies = [
- "finality-grandpa 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "env_logger 0.5.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "finality-grandpa 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "futures 0.1.25 (registry+https://github.com/rust-lang/crates.io-index)",
 "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
 "parity-codec 2.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "parity-codec-derive 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "parking_lot 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
 "sr-primitives 0.1.0",
 "substrate-client 0.1.0",
+ "substrate-consensus-common 0.1.0",
+ "substrate-fg-primitives 0.1.0",
 "substrate-keyring 0.1.0",
 "substrate-network 0.1.0",
 "substrate-primitives 0.1.0",
+ "substrate-test-client 0.1.0",
 "tokio 0.1.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

@@ -4362,7 +4381,7 @@ dependencies = [
 "checksum failure_derive 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "64c2d913fe8ed3b6c6518eedf4538255b989945c14c2a7d5cbff62a5e2120596"
 "checksum fake-simd 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "e88a8acf291dafb59c2d96e8f59828f3838bb1a70398823ade51a84de6a6deed"
 "checksum fdlimit 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b1ee15a7050e5580b3712877157068ea713b245b080ff302ae2ca973cfcd9baa"
-"checksum finality-grandpa 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "20d8cf871510f0d57630e75f9e65f87cba29581ccab1f78666d8b2e422d0baa6"
+"checksum finality-grandpa 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "be6d2735e8f570474c7925a60ebe04ec0bdd9eea7cc4fddab78a0ecfdefec20e"
 "checksum fixed-hash 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a557e80084b05c32b455963ff565a9de6f2866da023d6671705c6aff6f65e01c"
 "checksum fnv 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)" = "2fad85553e09a6f881f739c29f0b00b0f01357c743266d478b68951ce23285f3"
 "checksum foreign-types 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "f6f339eb8adc052cd2ca78910fda869aefa38d22d5cb648e6485e4d3fc06f3b1"
@@ -27,6 +27,7 @@ members = [
 	"core/consensus/rhd",
 	"core/executor",
 	"core/finality-grandpa",
+	"core/finality-grandpa/primitives",
 	"core/keyring",
 	"core/network",
 	"core/primitives",
@@ -274,6 +274,18 @@ pub struct BlockImportOperation<Block: BlockT, H: Hasher> {
 	updates: MemoryDB<H>,
 	changes_trie_updates: MemoryDB<H>,
 	pending_block: Option<PendingBlock<Block>>,
+	aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
+}
+
+impl<Block: BlockT, H: Hasher> BlockImportOperation<Block, H> {
+	fn apply_aux(&mut self, transaction: &mut DBTransaction) {
+		for (key, maybe_val) in self.aux_ops.drain(..) {
+			match maybe_val {
+				Some(val) => transaction.put_vec(columns::AUX, &key, val),
+				None => transaction.delete(columns::AUX, &key),
+			}
+		}
+	}
 }

 impl<Block> client::backend::BlockImportOperation<Block, Blake2Hasher>
@@ -345,6 +357,13 @@ where Block: BlockT<Hash=H256>,
 		self.changes_trie_updates = update;
 		Ok(())
 	}
+
+	fn set_aux<I>(&mut self, ops: I) -> Result<(), client::error::Error>
+		where I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>
+	{
+		self.aux_ops = ops.into_iter().collect();
+		Ok(())
+	}
 }

 struct StorageDb<Block: BlockT> {
@@ -636,6 +655,7 @@ impl<Block> client::backend::Backend<Block, Blake2Hasher> for Backend<Block> whe
 			old_state: state,
 			updates: MemoryDB::default(),
 			changes_trie_updates: MemoryDB::default(),
+			aux_ops: Vec::new(),
 		})
 	}

@@ -643,6 +663,7 @@ impl<Block> client::backend::Backend<Block, Blake2Hasher> for Backend<Block> whe
 		-> Result<(), client::error::Error>
 	{
 		let mut transaction = DBTransaction::new();
+		operation.apply_aux(&mut transaction);

 		if let Some(pending_block) = operation.pending_block {
 			let hash = pending_block.header.hash();
@@ -43,6 +43,7 @@ pub(crate) mod columns {
 	pub const HEADER: Option<u32> = Some(2);
 	pub const CACHE: Option<u32> = Some(3);
 	pub const CHT: Option<u32> = Some(4);
+	pub const AUX: Option<u32> = Some(5);
 }

 /// Prefix for headers CHT.
@@ -285,6 +286,7 @@ impl<Block> LightBlockchainStorage<Block> for LightStorage<Block>
 		header: Block::Header,
 		authorities: Option<Vec<AuthorityId>>,
 		leaf_state: NewBlockState,
+		aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	) -> ClientResult<()> {
 		let mut transaction = DBTransaction::new();

@@ -300,6 +302,13 @@ impl<Block> LightBlockchainStorage<Block> for LightStorage<Block>
 			::utils::number_and_hash_to_lookup_key(number, hash)
 		};

+		for (key, maybe_val) in aux_ops {
+			match maybe_val {
+				Some(val) => transaction.put_vec(columns::AUX, &key, val),
+				None => transaction.delete(columns::AUX, &key),
+			}
+		}
+
 		if leaf_state.is_best() {
 			// handle reorg.
 			{
@@ -471,16 +480,17 @@ pub(crate) mod tests {
 		}
 	}

-	fn header_with_changes_trie(parent: &Hash, number: u64) -> Header {
-		let mut header = default_header(parent, number);
-		header.digest.logs.push(DigestItem::ChangesTrieRoot([(number % 256) as u8; 32].into()));
-		header
-	}
-
-	fn header_with_extrinsics_root(parent: &Hash, number: u64, extrinsics_root: Hash) -> Header {
-		let mut header = default_header(parent, number);
-		header.extrinsics_root = extrinsics_root;
-		header
+	pub fn insert_block_with_extrinsics_root(
+		db: &LightStorage<Block>,
+		parent: &Hash,
+		number: u64,
+		authorities: Option<Vec<AuthorityId>>,
+		extrinsics_root: Hash,
+	) -> Hash {
+		let header = prepare_header(parent, number, extrinsics_root);
+		let hash = header.hash();
+		db.import_header(header, authorities, NewBlockState::Best, Vec::new()).unwrap();
+		hash
 	}

 	pub fn insert_block<F: Fn() -> Header>(
@@ -490,7 +500,7 @@ pub(crate) mod tests {
 	) -> Hash {
 		let header = header();
 		let hash = header.hash();
-		db.import_header(header, authorities, NewBlockState::Best).unwrap();
+		db.import_header(header, authorities, NewBlockState::Best, Vec::new()).unwrap();
 		hash
 	}

@@ -501,7 +511,7 @@ pub(crate) mod tests {
 	) -> Hash {
 		let header = header();
 		let hash = header.hash();
-		db.import_header(header, authorities, NewBlockState::Final).unwrap();
+		db.import_header(header, authorities, NewBlockState::Final, Vec::new()).unwrap();
 		hash
 	}

@@ -512,7 +522,7 @@ pub(crate) mod tests {
 	) -> Hash {
 		let header = header();
 		let hash = header.hash();
-		db.import_header(header, authorities, NewBlockState::Normal).unwrap();
+		db.import_header(header, authorities, NewBlockState::Normal, Vec::new()).unwrap();
 		hash
 	}

@@ -74,6 +74,9 @@ pub trait BlockImportOperation<Block, H> where
 	fn reset_storage(&mut self, top: StorageMap, children: ChildrenStorageMap) -> error::Result<H::Out>;
 	/// Inject changes trie data into the database.
 	fn update_changes_trie(&mut self, update: MemoryDB<H>) -> error::Result<()>;
+	/// Update auxiliary keys. Values are `None` if should be deleted.
+	fn set_aux<I>(&mut self, ops: I) -> error::Result<()>
+		where I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>;
 }

 /// Client backend. Manages the data layer.
@@ -602,6 +602,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		body: Option<Vec<Block::Extrinsic>>,
 		authorities: Option<Vec<AuthorityId>>,
 		finalized: bool,
+		aux: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	) -> error::Result<ImportResult> where
 		RA: TaggedTransactionQueue<Block>,
 		E: CallExecutor<Block, Blake2Hasher> + Send + Sync + Clone,
@@ -695,6 +696,8 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		if let Some(Some(changes_update)) = changes_update {
 			transaction.update_changes_trie(changes_update)?;
 		}
+
+		transaction.set_aux(aux)?;
 		self.backend.commit_operation(transaction)?;

 		if make_notifications {
@@ -880,7 +883,9 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 	/// TODO [snd] possibly implement this on blockchain::Backend and just redirect here
 	/// Returns `Ok(None)` if `target_hash` is not found in search space.
 	/// TODO [snd] write down time complexity
-	pub fn best_containing(&self, target_hash: Block::Hash, maybe_max_number: Option<NumberFor<Block>>) -> error::Result<Option<Block::Hash>> {
+	pub fn best_containing(&self, target_hash: Block::Hash, maybe_max_number: Option<NumberFor<Block>>)
+		-> error::Result<Option<Block::Hash>>
+	{
 		let target_header = {
 			match self.backend.blockchain().header(BlockId::Hash(target_hash))? {
 				Some(x) => x,
@@ -1016,7 +1021,8 @@ impl<B, E, Block, RA> CallApiAt<Block> for Client<B, E, Block, RA> where
 	B: backend::Backend<Block, Blake2Hasher>,
 	E: CallExecutor<Block, Blake2Hasher> + Clone + Send + Sync,
 	Block: BlockT<Hash=H256>,
-	RA: CoreAPI<Block>
+	RA: CoreAPI<Block>, // not strictly necessary at the moment
+						// but we want to bound to make sure the API is actually available.
 {
 	fn call_api_at(
 		&self,
@@ -1071,7 +1077,7 @@ impl<B, E, Block, RA> consensus::BlockImport<Block> for Client<B, E, Block, RA>
 			post_digests,
 			body,
 			finalized,
-			..
+			auxiliary,
 		} = import_block;
 		let parent_hash = header.parent_hash().clone();

@@ -1103,6 +1109,7 @@ impl<B, E, Block, RA> consensus::BlockImport<Block> for Client<B, E, Block, RA>
 			body,
 			new_authorities,
 			finalized,
+			auxiliary,
 		);

 		*self.importing_block.write() = None;
@@ -97,6 +97,7 @@ struct BlockchainStorage<Block: BlockT> {
 	header_cht_roots: HashMap<NumberFor<Block>, Block::Hash>,
 	changes_trie_cht_roots: HashMap<NumberFor<Block>, Block::Hash>,
 	leaves: LeafSet<Block::Hash, NumberFor<Block>>,
+	aux: HashMap<Vec<u8>, Vec<u8>>,
 }

 /// In-memory blockchain. Supports concurrent reads.
@@ -146,6 +147,7 @@ impl<Block: BlockT> Blockchain<Block> {
 				header_cht_roots: HashMap::new(),
 				changes_trie_cht_roots: HashMap::new(),
 				leaves: LeafSet::new(),
+				aux: HashMap::new(),
 			}));
 		Blockchain {
 			storage: storage.clone(),
@@ -249,6 +251,16 @@ impl<Block: BlockT> Blockchain<Block> {
 		self.storage.write().finalized_hash = hash;
 		Ok(())
 	}
+
+	fn write_aux(&self, ops: Vec<(Vec<u8>, Option<Vec<u8>>)>) {
+		let mut storage = self.storage.write();
+		for (k, v) in ops {
+			match v {
+				Some(v) => storage.aux.insert(k, v),
+				None => storage.aux.remove(&k),
+			};
+		}
+	}
 }

 impl<Block: BlockT> HeaderBackend<Block> for Blockchain<Block> {
@@ -322,6 +334,7 @@ impl<Block: BlockT> light::blockchain::Storage<Block> for Blockchain<Block>
 		header: Block::Header,
 		authorities: Option<Vec<AuthorityId>>,
 		state: NewBlockState,
+		aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	) -> error::Result<()> {
 		let hash = header.hash();
 		let parent_hash = *header.parent_hash();
@@ -330,6 +343,7 @@ impl<Block: BlockT> light::blockchain::Storage<Block> for Blockchain<Block>
 			self.cache.insert(parent_hash, authorities);
 		}

+		self.write_aux(aux_ops);
 		Ok(())
 	}

@@ -363,6 +377,7 @@ pub struct BlockImportOperation<Block: BlockT, H: Hasher> {
 	old_state: InMemory<H>,
 	new_state: Option<InMemory<H>>,
 	changes_trie_update: Option<MemoryDB<H>>,
+	aux: Option<Vec<(Vec<u8>, Option<Vec<u8>>)>>,
 }

 impl<Block, H> backend::BlockImportOperation<Block, H> for BlockImportOperation<Block, H>
@@ -433,6 +448,13 @@ where
 		self.new_state = Some(InMemory::from(transaction));
 		Ok(root)
 	}
+
+	fn set_aux<I>(&mut self, ops: I) -> error::Result<()>
+		where I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>
+	{
+		self.aux = Some(ops.into_iter().collect());
+		Ok(())
+	}
 }

 /// In-memory backend. Keeps all states and blocks in memory. Useful for testing.
@@ -445,7 +467,6 @@ where
 	states: RwLock<HashMap<Block::Hash, InMemory<H>>>,
 	changes_trie_storage: InMemoryChangesTrieStorage<H>,
 	blockchain: Blockchain<Block>,
-	aux: RwLock<HashMap<Vec<u8>, Vec<u8>>>,
 }

 impl<Block, H> Backend<Block, H>
@@ -460,7 +481,6 @@ where
 			states: RwLock::new(HashMap::new()),
 			changes_trie_storage: InMemoryChangesTrieStorage::new(),
 			blockchain: Blockchain::new(),
-			aux: RwLock::new(HashMap::new()),
 		}
 	}
 }
@@ -488,6 +508,7 @@ where
 			old_state: state,
 			new_state: None,
 			changes_trie_update: None,
+			aux: None,
 		})
 	}

@@ -515,6 +536,10 @@ where
 				self.blockchain.cache.insert(parent_hash, operation.pending_authorities);
 			}
 		}
+
+		if let Some(ops) = operation.aux {
+			self.blockchain.write_aux(ops);
+		}
 		Ok(())
 	}

@@ -542,18 +567,18 @@ where
 	}

 	fn insert_aux<'a, 'b: 'a, 'c: 'a, I: IntoIterator<Item=&'a (&'c [u8], &'c [u8])>, D: IntoIterator<Item=&'a &'b [u8]>>(&self, insert: I, delete: D) -> error::Result<()> {
-		let mut aux = self.aux.write();
+		let mut storage = self.blockchain.storage.write();
 		for (k, v) in insert {
-			aux.insert(k.to_vec(), v.to_vec());
+			storage.aux.insert(k.to_vec(), v.to_vec());
 		}
 		for k in delete {
-			aux.remove(*k);
+			storage.aux.remove(*k);
 		}
 		Ok(())
 	}

 	fn get_aux(&self, key: &[u8]) -> error::Result<Option<Vec<u8>>> {
-		Ok(self.aux.read().get(key).cloned())
+		Ok(self.blockchain.storage.read().aux.get(key).cloned())
 	}
 }

@@ -46,6 +46,7 @@ pub struct ImportOperation<Block: BlockT, S, F> {
 	header: Option<Block::Header>,
 	authorities: Option<Vec<AuthorityId>>,
 	leaf_state: NewBlockState,
+	aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	_phantom: ::std::marker::PhantomData<(S, F)>,
 }

@@ -86,6 +87,7 @@ impl<S, F, Block, H> ClientBackend<Block, H> for Backend<S, F> where
 			header: None,
 			authorities: None,
 			leaf_state: NewBlockState::Normal,
+			aux_ops: Vec::new(),
 			_phantom: Default::default(),
 		})
 	}
@@ -96,6 +98,7 @@ impl<S, F, Block, H> ClientBackend<Block, H> for Backend<S, F> where
 			header,
 			operation.authorities,
 			operation.leaf_state,
+			operation.aux_ops,
 		)
 	}

@@ -193,6 +196,13 @@ where
 		let mut op = in_mem.begin_operation(BlockId::Hash(Default::default()))?;
 		op.reset_storage(top, children)
 	}
+
+	fn set_aux<I>(&mut self, ops: I) -> ClientResult<()>
+		where I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>
+	{
+		self.aux_ops = ops.into_iter().collect();
+		Ok(())
+	}
 }

 impl<Block, S, F, H> StateBackend<H> for OnDemandState<Block, S, F>
@@ -35,11 +35,15 @@ use light::fetcher::{Fetcher, RemoteHeaderRequest};
 /// Light client blockchain storage.
 pub trait Storage<Block: BlockT>: BlockchainHeaderBackend<Block> {
 	/// Store new header. Should refuse to revert any finalized blocks.
+	///
+	/// Takes new authorities, the leaf state of the new block, and
+	/// any auxiliary storage updates to place in the same operation.
 	fn import_header(
 		&self,
 		header: Block::Header,
 		authorities: Option<Vec<AuthorityId>>,
 		state: NewBlockState,
+		aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	) -> ClientResult<()>;

 	/// Mark historic header as finalized.
@@ -16,6 +16,9 @@

 //! Macros for declaring and implementing the runtime APIs.

+// these are part of the public API, so need to be re-exported
+pub use runtime_version::{ApiId, RuntimeVersion};
+
 /// Declare the given API traits.
 ///
 /// # Example:
@@ -24,12 +24,11 @@ pub use state_machine::OverlayedChanges;
 pub use runtime_primitives::{traits::Block as BlockT, generic::BlockId};
 #[cfg(feature = "std")]
 use runtime_primitives::traits::ApiRef;
-use runtime_version::ApiId;
+pub use runtime_version::ApiId;
 #[doc(hidden)]
 pub use rstd::slice;
 #[cfg(feature = "std")]
 use rstd::result;
-#[doc(hidden)]
 pub use codec::{Encode, Decode};
 #[cfg(feature = "std")]
 use error;
@@ -73,6 +72,30 @@ pub trait CallApiAt<Block: BlockT> {
 		changes: &mut OverlayedChanges,
 		initialised_block: &mut Option<BlockId<Block>>,
 	) -> error::Result<Vec<u8>>;
+
+	/// Call the given api function with strong arguments at the given block
+	/// and returns the decoded result.
+	fn call_api_at_strong<In: Encode, Out: Decode>(
+		&self,
+		at: &BlockId<Block>,
+		function: &'static str,
+		args: &In,
+		changes: &mut OverlayedChanges,
+		initialised_block: &mut Option<BlockId<Block>>,
+	) -> error::Result<Out> where Self: Sized {
+		let raw = self.call_api_at(
+			at,
+			function,
+			args.encode(),
+			changes,
+			initialised_block,
+		)?;
+
+		match Out::decode(&mut &raw[..]) {
+			Some(out) => Ok(out),
+			None => bail!(error::ErrorKind::CallResultDecode(function)),
+		}
+	}
 }

 /// The ApiIds for the various standard runtime APIs.
@@ -389,11 +389,11 @@ pub type AuraImportQueue<B, C> = BasicQueue<B, AuraVerifier<C>>;
 /// Start an import queue for the Aura consensus algorithm.
 pub fn import_queue<B, C>(config: Config, client: Arc<C>) -> AuraImportQueue<B, C> where
 	B: Block,
-	C: Authorities<B> + BlockImport<B> + Send + Sync,
+	C: Authorities<B> + BlockImport<B,Error=client::error::Error> + Send + Sync,
 	DigestItemFor<B>: CompatibleDigestItem,
 {
-	let verifier = Arc::new(AuraVerifier { config, client });
-	BasicQueue::new(verifier)
+	let verifier = Arc::new(AuraVerifier { config, client: client.clone() });
+	BasicQueue::new(verifier, client)
 }


@@ -443,12 +443,13 @@ mod tests {
 	const TEST_ROUTING_INTERVAL: Duration = Duration::from_millis(50);

 	pub struct AuraTestNet {
-		peers: Vec<Arc<Peer<AuraVerifier<PeersClient>>>>,
+		peers: Vec<Arc<Peer<AuraVerifier<PeersClient>, ()>>>,
 		started: bool
 	}

 	impl TestNetFactory for AuraTestNet {
 		type Verifier = AuraVerifier<PeersClient>;
+		type PeerData = ();

 		/// Create new test network with peers and given config.
 		fn from_config(_config: &ProtocolConfig) -> Self {
@@ -465,15 +466,15 @@ mod tests {
 			Arc::new(AuraVerifier { client, config })
 		}

-		fn peer(&self, i: usize) -> &Peer<Self::Verifier> {
+		fn peer(&self, i: usize) -> &Peer<Self::Verifier, ()> {
 			&self.peers[i]
 		}

-		fn peers(&self) -> &Vec<Arc<Peer<Self::Verifier>>> {
+		fn peers(&self) -> &Vec<Arc<Peer<Self::Verifier, ()>>> {
 			&self.peers
 		}

-		fn mut_peers<F: Fn(&mut Vec<Arc<Peer<Self::Verifier>>>)>(&mut self, closure: F ) {
+		fn mut_peers<F: Fn(&mut Vec<Arc<Peer<Self::Verifier, ()>>>)>(&mut self, closure: F) {
 			closure(&mut self.peers);
 		}

@@ -6,17 +6,22 @@ authors = ["Parity Technologies <admin@parity.io>"]
 [dependencies]
 futures = "0.1.17"
 parity-codec = "2.1"
+parity-codec-derive = "2.0"
 sr-primitives = { path = "../sr-primitives" }
+substrate-consensus-common = { path = "../consensus/common" }
 substrate-primitives = { path = "../primitives" }
 substrate-client = { path = "../client" }
 log = "0.4"
+parking_lot = "0.4"
 tokio = "0.1.7"
+substrate-fg-primitives = { path = "primitives" }

 [dependencies.finality-grandpa]
-version = "0.2.0"
+version = "0.3.0"
 features = ["derive-codec"]

 [dev-dependencies]
 substrate-network = { path = "../network", features = ["test-helpers"] }
-parking_lot = "0.4"
 substrate-keyring = { path = "../keyring" }
+substrate-test-client = { path = "../test-client"}
+env_logger = "0.5"
@@ -0,0 +1,23 @@
+[package]
+name = "substrate-fg-primitives"
+version = "0.1.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+
+[dependencies]
+substrate-client = { path = "../../client", default-features = false }
+substrate-primitives = { path = "../../primitives", default-features = false }
+parity-codec = { version = "2.1", default-features = false }
+parity-codec-derive = { version = "2.1", default-features = false }
+sr-primitives = { path = "../../sr-primitives", default-features = false }
+sr-std = { path = "../../sr-std", default-features = false }
+
+[features]
+default = ["std"]
+std = [
+	"substrate-primitives/std",
+	"substrate-client/std",
+	"parity-codec/std",
+	"parity-codec-derive/std",
+	"sr-primitives/std",
+	"sr-std/std",
+]
@@ -0,0 +1,86 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Primitives for GRANDPA integration, suitable for WASM compilation.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+extern crate substrate_primitives;
+extern crate sr_primitives;
+extern crate parity_codec;
+
+#[macro_use]
+extern crate parity_codec_derive;
+
+#[macro_use]
+extern crate substrate_client as client;
+
+extern crate sr_std as rstd;
+
+use substrate_primitives::AuthorityId;
+use sr_primitives::traits::{Block as BlockT, DigestFor, NumberFor};
+use rstd::vec::Vec;
+
+/// A scheduled change of authority set.
+#[cfg_attr(feature = "std", derive(Debug, PartialEq))]
+#[derive(Clone, Encode, Decode)]
+pub struct ScheduledChange<N> {
+	/// The new authorities after the change, along with their respective weights.
+	pub next_authorities: Vec<(AuthorityId, u64)>,
+	/// The number of blocks to delay.
+	pub delay: N,
+}
+
+/// WASM function call to check for pending changes.
+pub const PENDING_CHANGE_CALL: &str = "grandpa_pending_change";
+/// WASM function call to get current GRANDPA authorities.
+pub const AUTHORITIES_CALL: &str = "grandpa_authorities";
+
+/// The ApiIds for GRANDPA API.
+pub mod id {
+	use client::runtime_api::ApiId;
+
+	/// ApiId for the GrandpaApi trait.
+	pub const GRANDPA_API: ApiId = *b"fgrandpa";
+}
+
+decl_runtime_apis! {
+	/// APIs for integrating the GRANDPA finality gadget into runtimes.
+	/// This should be implemented on the runtime side.
+	///
+	/// This is primarily used for negotiating authority-set changes for the
+	/// gadget. GRANDPA uses a signalling model of changing authority sets:
+	/// changes should be signalled with a delay of N blocks, and then automatically
+	/// applied in the runtime after those N blocks have passed.
+	///
+	/// The consensus protocol will coordinate the handoff externally.
+	pub trait GrandpaApi<Block: BlockT> {
+		/// Check a digest for pending changes.
+		/// Return `None` if there are no pending changes.
+		///
+		/// Precedence towards earlier or later digest items can be given
+		/// based on the rules of the chain.
+		///
+		/// No change should be scheduled if one is already and the delay has not
+		/// passed completely.
+		fn grandpa_pending_change(digest: DigestFor<Block>)
+			-> Option<ScheduledChange<NumberFor<Block>>>;
+
+		/// Get the current GRANDPA authorities and weights. This should not change except
+		/// for when changes are scheduled and the corresponding delay has passed.
+		fn grandpa_authorities() -> Vec<(AuthorityId, u64)>;
+	}
+}
@@ -0,0 +1,344 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Utilities for dealing with authorities, authority sets, and handoffs.
+
+use parking_lot::RwLock;
+use substrate_primitives::AuthorityId;
+
+use std::cmp::Ord;
+use std::fmt::Debug;
+use std::ops::Add;
+use std::sync::Arc;
+
+/// A shared authority set.
+pub(crate) struct SharedAuthoritySet<H, N> {
+	inner: Arc<RwLock<AuthoritySet<H, N>>>,
+}
+
+impl<H, N> Clone for SharedAuthoritySet<H, N> {
+	fn clone(&self) -> Self {
+		SharedAuthoritySet { inner: self.inner.clone() }
+	}
+}
+
+impl<H, N> SharedAuthoritySet<H, N> {
+	/// The genesis authority set.
+	pub(crate) fn genesis(initial: Vec<(AuthorityId, u64)>) -> Self {
+		SharedAuthoritySet {
+			inner: Arc::new(RwLock::new(AuthoritySet::genesis(initial)))
+		}
+	}
+
+	/// Acquire a reference to the inner read-write lock.
+	pub(crate) fn inner(&self) -> &RwLock<AuthoritySet<H, N>> {
+		&*self.inner
+	}
+}
+
+impl<H: Eq, N> SharedAuthoritySet<H, N>
+	where N: Add<Output=N> + Ord + Clone + Debug
+{
+	/// Get the earliest limit-block number, if any.
+	pub(crate) fn current_limit(&self) -> Option<N> {
+		self.inner.read().current_limit()
+	}
+
+	/// Get the current set ID. This is incremented every time the set changes.
+	pub(crate) fn set_id(&self) -> u64 {
+		self.inner.read().set_id
+	}
+}
+
+impl<H, N> From<AuthoritySet<H, N>> for SharedAuthoritySet<H, N> {
+	fn from(set: AuthoritySet<H, N>) -> Self {
+		SharedAuthoritySet { inner: Arc::new(RwLock::new(set)) }
+	}
+}
+
+/// Status of the set after changes were applied.
+pub(crate) struct Status<H, N> {
+	/// Whether internal changes were made.
+	pub(crate) changed: bool,
+	/// `Some` when underlying authority set has changed, containing the
+	/// block where that set changed.
+	pub(crate) new_set_block: Option<(H, N)>,
+}
+
+/// A set of authorities.
+#[derive(Debug, Clone, Encode, Decode)]
+pub(crate) struct AuthoritySet<H, N> {
+	current_authorities: Vec<(AuthorityId, u64)>,
+	set_id: u64,
+	pending_changes: Vec<PendingChange<H, N>>,
+}
+
+impl<H, N> AuthoritySet<H, N> {
+	/// Get a genesis set with given authorities.
+	pub(crate) fn genesis(initial: Vec<(AuthorityId, u64)>) -> Self {
+		AuthoritySet {
+			current_authorities: initial,
+			set_id: 0,
+			pending_changes: Vec::new(),
+		}
+	}
+
+	/// Get the current set id and a reference to the current authority set.
+	pub(crate) fn current(&self) -> (u64, &[(AuthorityId, u64)]) {
+		(self.set_id, &self.current_authorities[..])
+	}
+}
+
+impl<H: Eq, N> AuthoritySet<H, N>
+	where N: Add<Output=N> + Ord + Clone + Debug,
+{
+	/// Note an upcoming pending transition.
+	pub(crate) fn add_pending_change(&mut self, pending: PendingChange<H, N>) {
+		// ordered first by effective number and then by signal-block number.
+		let key = (pending.effective_number(), pending.canon_height.clone());
+		let idx = self.pending_changes
+			.binary_search_by_key(&key, |change| (
+				change.effective_number(),
+				change.canon_height.clone(),
+			))
+			.unwrap_or_else(|i| i);
+
+		self.pending_changes.insert(idx, pending);
+	}
+
+	/// Inspect pending changes.
+	#[cfg(test)]
+	pub(crate) fn pending_changes(&self) -> &[PendingChange<H, N>] {
+		&self.pending_changes
+	}
+
+	/// Get the earliest limit-block number, if any.
+	pub(crate) fn current_limit(&self) -> Option<N> {
+		self.pending_changes.get(0).map(|change| change.effective_number().clone())
+	}
+
+	/// Apply or prune any pending transitions. Provide a closure that can be used to check for the
+	/// finalized block with given number.
+	///
+	/// When the set has changed, the return value will be `Ok(Some((H, N)))` which is the cnaonical
+	/// block where the set last changed.
+	pub(crate) fn apply_changes<F, E>(&mut self, just_finalized: N, mut canonical: F)
+		-> Result<Status<H, N>, E>
+		where F: FnMut(N) -> Result<H, E>
+	{
+		let mut status = Status {
+			changed: false,
+			new_set_block: None,
+		};
+		loop {
+			let remove_up_to = match self.pending_changes.first() {
+				None => break,
+				Some(change) => {
+					let effective_number = change.effective_number();
+					if effective_number > just_finalized { break }
+
+					// check if the block that signalled the change is canonical in
+					// our chain.
+					if canonical(change.canon_height.clone())? == change.canon_hash {
+						// apply this change: make the set canonical
+						info!(target: "finality", "Applying authority set change scheduled at block #{:?}",
+							change.canon_height);
+
+						self.current_authorities = change.next_authorities.clone();
+						self.set_id += 1;
+
+						status.new_set_block = Some((
+							canonical(effective_number.clone())?,
+							effective_number.clone(),
+						));
+
+						// discard any signalled changes
+						// that happened before or equal to the effective number of the change.
+						self.pending_changes.iter()
+							.take_while(|c| c.canon_height <= effective_number)
+							.count()
+					} else {
+						1 // prune out this entry; it's no longer relevant.
+					}
+				}
+			};
+
+			let remove_up_to = ::std::cmp::min(remove_up_to, self.pending_changes.len());
+			self.pending_changes.drain(..remove_up_to);
+			status.changed = true; // always changed because we strip at least the first change.
+		}
+
+		Ok(status)
+	}
+}
+
+/// A pending change to the authority set.
+///
+/// This will be applied when the announcing block is at some depth within
+/// the finalized chain.
+#[derive(Debug, Clone, Encode, Decode, PartialEq)]
+pub(crate) struct PendingChange<H, N> {
+	/// The new authorities and weights to apply.
+	pub(crate) next_authorities: Vec<(AuthorityId, u64)>,
+	/// How deep in the finalized chain the announcing block must be
+	/// before the change is applied.
+	pub(crate) finalization_depth: N,
+	/// The announcing block's height.
+	pub(crate) canon_height: N,
+	/// The announcing block's hash.
+	pub(crate) canon_hash: H,
+}
+
+impl<H, N: Add<Output=N> + Clone> PendingChange<H, N> {
+	/// Returns the effective number this change will be applied at.
+	fn effective_number(&self) -> N {
+		self.canon_height.clone() + self.finalization_depth.clone()
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn changes_sorted_in_correct_order() {
+		let mut authorities = AuthoritySet {
+			current_authorities: Vec::new(),
+			set_id: 0,
+			pending_changes: Vec::new(),
+		};
+
+		let change_a = PendingChange {
+			next_authorities: Vec::new(),
+			finalization_depth: 10,
+			canon_height: 5,
+			canon_hash: "hash_a",
+		};
+
+		let change_b = PendingChange {
+			next_authorities: Vec::new(),
+			finalization_depth: 0,
+			canon_height: 16,
+			canon_hash: "hash_b",
+		};
+
+		let change_c = PendingChange {
+			next_authorities: Vec::new(),
+			finalization_depth: 5,
+			canon_height: 10,
+			canon_hash: "hash_c",
+		};
+
+		authorities.add_pending_change(change_a.clone());
+		authorities.add_pending_change(change_b.clone());
+		authorities.add_pending_change(change_c.clone());
+
+		assert_eq!(authorities.pending_changes, vec![change_a, change_c, change_b]);
+	}
+
+	#[test]
+	fn apply_change() {
+		let mut authorities = AuthoritySet {
+			current_authorities: Vec::new(),
+			set_id: 0,
+			pending_changes: Vec::new(),
+		};
+
+		let set_a = vec![([1; 32].into(), 5)];
+		let set_b = vec![([2; 32].into(), 5)];
+
+		let change_a = PendingChange {
+			next_authorities: set_a.clone(),
+			finalization_depth: 10,
+			canon_height: 5,
+			canon_hash: "hash_a",
+		};
+
+		let change_b = PendingChange {
+			next_authorities: set_b.clone(),
+			finalization_depth: 10,
+			canon_height: 5,
+			canon_hash: "hash_b",
+		};
+
+		authorities.add_pending_change(change_a.clone());
+		authorities.add_pending_change(change_b.clone());
+
+		authorities.apply_changes(10, |_| Err(())).unwrap();
+		assert!(authorities.current_authorities.is_empty());
+
+		authorities.apply_changes(15, |n| match n {
+			5 => Ok("hash_a"),
+			15 => Ok("hash_15_canon"),
+			_ => Err(()),
+		}).unwrap();
+
+		assert_eq!(authorities.current_authorities, set_a);
+		assert_eq!(authorities.set_id, 1);
+		assert!(authorities.pending_changes.is_empty());
+	}
+
+	#[test]
+	fn apply_many_changes_at_once() {
+		let mut authorities = AuthoritySet {
+			current_authorities: Vec::new(),
+			set_id: 0,
+			pending_changes: Vec::new(),
+		};
+
+		let set_a = vec![([1; 32].into(), 5)];
+		let set_b = vec![([2; 32].into(), 5)];
+		let set_c = vec![([3; 32].into(), 5)];
+
+		let change_a = PendingChange {
+			next_authorities: set_a.clone(),
+			finalization_depth: 10,
+			canon_height: 5,
+			canon_hash: "hash_a",
+		};
+
+		// will be ignored because it was signalled when change_a still pending.
+		let change_b = PendingChange {
+			next_authorities: set_b.clone(),
+			finalization_depth: 10,
+			canon_height: 15,
+			canon_hash: "hash_b",
+		};
+
+		let change_c = PendingChange {
+			next_authorities: set_c.clone(),
+			finalization_depth: 10,
+			canon_height: 16,
+			canon_hash: "hash_c",
+		};
+
+		authorities.add_pending_change(change_a.clone());
+		authorities.add_pending_change(change_b.clone());
+		authorities.add_pending_change(change_c.clone());
+
+		authorities.apply_changes(26, |n| match n {
+			5 => Ok("hash_a"),
+			15 => Ok("hash_b"),
+			16 => Ok("hash_c"),
+			26 => Ok("hash_26"),
+			_ => Err(()),
+		}).unwrap();
+
+		assert_eq!(authorities.current_authorities, set_c);
+		assert_eq!(authorities.set_id, 2); // has been bumped only twice
+		assert!(authorities.pending_changes.is_empty());
+	}
+}
@@ -16,15 +16,50 @@

 //! Integration of the GRANDPA finality gadget into substrate.
 //!
-//! This is a long-running future that produces finality notifications.
+//! This crate provides a long-running future that produces finality notifications.
+//!
+//! # Usage
+//!
+//! First, create a block-import wrapper with the `block_import` function.
+//! The GRANDPA worker needs to be linked together with this block import object,
+//! so a `LinkHalf` is returned as well. All blocks imported (from network or consensus or otherwise)
+//! must pass through this wrapper, otherwise consensus is likely to break in
+//! unexpected ways.
+//!
+//! Next, use the `LinkHalf` and a local configuration to `run_grandpa`. This requires a
+//! `Network` implementation. The returned future should be driven to completion and
+//! will finalize blocks in the background.
+//!
+//! # Changing authority sets
+//!
+//! The rough idea behind changing authority sets in GRANDPA is that at some point,
+//! we obtain agreement for some maximum block height that the current set can
+//! finalize, and once a block with that height is finalized the next set will
+//! pick up finalization from there.
+//!
+//! Technically speaking, this would be implemented as a voting rule which says,
+//! "if there is a signal for a change in N blocks in block B, only vote on
+//! chains with length NUM(B) + N if they contain B". This conditional-inclusion
+//! logic is complex to compute because it requires looking arbitrarily far
+//! back in the chain.
+//!
+//! Instead, we keep track of a list of all signals we've seen so far,
+//! sorted ascending by the block number they would be applied at. We never vote
+//! on chains with number higher than the earliest handoff block number
+//! (this is num(signal) + N). When finalizing a block, we either apply or prune
+//! any signaled changes based on whether the signaling block is included in the
+//! newly-finalized chain.

 extern crate finality_grandpa as grandpa;
 extern crate futures;
 extern crate substrate_client as client;
 extern crate sr_primitives as runtime_primitives;
+extern crate substrate_consensus_common as consensus_common;
 extern crate substrate_primitives;
 extern crate tokio;
+extern crate parking_lot;
 extern crate parity_codec as codec;
+extern crate substrate_fg_primitives as fg_primitives;

 #[macro_use]
 extern crate log;
@@ -33,44 +68,84 @@ extern crate log;
 extern crate substrate_network as network;

 #[cfg(test)]
-extern crate parking_lot;
+extern crate substrate_keyring as keyring;

 #[cfg(test)]
-extern crate substrate_keyring as keyring;
+extern crate substrate_test_client as test_client;
+
+#[cfg(test)]
+extern crate env_logger;
+
+#[macro_use]
+extern crate parity_codec_derive;

 use futures::prelude::*;
 use futures::stream::Fuse;
 use futures::sync::mpsc;
-use client::{Client, ImportNotifications, backend::Backend, CallExecutor, blockchain::HeaderBackend};
+use client::{Client, error::Error as ClientError, ImportNotifications, backend::Backend, CallExecutor};
+use client::blockchain::HeaderBackend;
+use client::runtime_api::TaggedTransactionQueue;
 use codec::{Encode, Decode};
-use runtime_primitives::traits::{As, NumberFor, Block as BlockT, Header as HeaderT};
+use consensus_common::{BlockImport, ImportBlock, ImportResult};
+use runtime_primitives::traits::{
+	NumberFor, Block as BlockT, Header as HeaderT, DigestFor, ProvideRuntimeApi
+};
+use fg_primitives::GrandpaApi;
 use runtime_primitives::generic::BlockId;
 use substrate_primitives::{ed25519, H256, AuthorityId, Blake2Hasher};
 use tokio::timer::Interval;

 use grandpa::Error as GrandpaError;
-use grandpa::{voter, round::State as RoundState, Prevote, Precommit, Equivocation};
+use grandpa::{voter, round::State as RoundState, Equivocation, BlockNumberOps};

 use std::collections::{VecDeque, HashMap};
 use std::sync::Arc;
 use std::time::{Instant, Duration};

+use authorities::SharedAuthoritySet;
+
+pub use fg_primitives::ScheduledChange;
+
+mod authorities;
+
+#[cfg(test)]
+mod tests;
+
 const LAST_COMPLETED_KEY: &[u8] = b"grandpa_completed_round";
+const AUTHORITY_SET_KEY: &[u8] = b"grandpa_voters";
+
+/// round-number, round-state
+type LastCompleted<H, N> = (u64, RoundState<H, N>);

 /// A GRANDPA message for a substrate chain.
-pub type Message<Block> = grandpa::Message<<Block as BlockT>::Hash>;
+pub type Message<Block> = grandpa::Message<<Block as BlockT>::Hash, NumberFor<Block>>;
 /// A signed message.
-pub type SignedMessage<Block> = grandpa::SignedMessage<<Block as BlockT>::Hash, ed25519::Signature, AuthorityId>;
+pub type SignedMessage<Block> = grandpa::SignedMessage<
+	<Block as BlockT>::Hash,
+	NumberFor<Block>,
+	ed25519::Signature,
+	AuthorityId,
+>;
+/// A prevote message for this chain's block type.
+pub type Prevote<Block> = grandpa::Prevote<<Block as BlockT>::Hash, NumberFor<Block>>;
+/// A precommit message for this chain's block type.
+pub type Precommit<Block> = grandpa::Precommit<<Block as BlockT>::Hash, NumberFor<Block>>;

 /// Configuration for the GRANDPA service.
+#[derive(Clone)]
 pub struct Config {
 	/// The expected duration for a message to be gossiped across the network.
 	pub gossip_duration: Duration,
-	/// The voters.
-	// TODO: make dynamic
-	pub voters: Vec<AuthorityId>,
 	/// The local signing key.
 	pub local_key: Option<Arc<ed25519::Pair>>,
+	/// Some local identifier of the voter.
+	pub name: Option<String>,
+}
+
+impl Config {
+	fn name(&self) -> &str {
+		self.name.as_ref().map(|s| s.as_str()).unwrap_or("<unknown>")
+	}
 }

 /// Errors that can occur while voting in GRANDPA.
@@ -83,7 +158,7 @@ pub enum Error {
 	/// A blockchain error.
 	Blockchain(String),
 	/// Could not complete a round on disk.
-	CouldNotCompleteRound(::client::error::Error),
+	Client(ClientError),
 	/// A timer failed to fire.
 	Timer(::tokio::timer::Error),
 }
@@ -104,13 +179,13 @@ pub trait Network: Clone {

 	/// Get a stream of messages for a specific round. This stream should
 	/// never logically conclude.
-	fn messages_for(&self, round: u64) -> Self::In;
+	fn messages_for(&self, round: u64, set_id: u64) -> Self::In;

 	/// Send a message at a specific round out.
-	fn send_message(&self, round: u64, message: Vec<u8>);
+	fn send_message(&self, round: u64, set_id: u64, message: Vec<u8>);

 	/// Clean up messages for a round.
-	fn drop_messages(&self, round: u64);
+	fn drop_messages(&self, round: u64, set_id: u64);
 }

 /// Something which can determine if a block is known.
@@ -118,24 +193,23 @@ pub trait BlockStatus<Block: BlockT> {
 	/// Return `Ok(Some(number))` or `Ok(None)` depending on whether the block
 	/// is definitely known and has been imported.
 	/// If an unexpected error occurs, return that.
-	fn block_number(&self, hash: Block::Hash) -> Result<Option<u32>, Error>;
+	fn block_number(&self, hash: Block::Hash) -> Result<Option<NumberFor<Block>>, Error>;
 }

 impl<B, E, Block: BlockT<Hash=H256>, RA> BlockStatus<Block> for Arc<Client<B, E, Block, RA>> where
 	B: Backend<Block, Blake2Hasher>,
 	E: CallExecutor<Block, Blake2Hasher> + Send + Sync,
 	RA: Send + Sync,
-	NumberFor<Block>: As<u32>,
+	NumberFor<Block>: BlockNumberOps,
 {
-	fn block_number(&self, hash: Block::Hash) -> Result<Option<u32>, Error> {
+	fn block_number(&self, hash: Block::Hash) -> Result<Option<NumberFor<Block>>, Error> {
 		self.block_number_from_id(&BlockId::Hash(hash))
 			.map_err(|e| Error::Blockchain(format!("{:?}", e)))
-			.map(|num| num.map(|n| n.as_()))
 	}
 }

 /// Buffering imported messages until blocks with given hashes are imported.
-pub struct UntilImported<Block: BlockT, Status, I> {
+struct UntilImported<Block: BlockT, Status, I> {
 	import_notifications: Fuse<ImportNotifications<Block>>,
 	status_check: Status,
 	inner: Fuse<I>,
@@ -270,6 +344,7 @@ impl<Block: BlockT, Status: BlockStatus<Block>, I> Stream for UntilImported<Bloc
 // clears the network messages for inner round on drop.
 struct ClearOnDrop<I, N: Network> {
 	round: u64,
+	set_id: u64,
 	inner: I,
 	network: N,
 }
@@ -293,13 +368,27 @@ impl<I: Sink, N: Network> Sink for ClearOnDrop<I, N> {

 impl<I, N: Network> Drop for ClearOnDrop<I, N> {
 	fn drop(&mut self) {
-		self.network.drop_messages(self.round);
+		self.network.drop_messages(self.round, self.set_id);
 	}
 }

+fn localized_payload<E: Encode>(round: u64, set_id: u64, message: &E) -> Vec<u8> {
+	let mut v = message.encode();
+
+	round.using_encoded(|s| v.extend(s));
+	set_id.using_encoded(|s| v.extend(s));
+
+	v
+}
+
 // converts a message stream into a stream of signed messages.
 // the output stream checks signatures also.
-fn checked_message_stream<Block: BlockT, S>(inner: S, voters: Vec<AuthorityId>)
+fn checked_message_stream<Block: BlockT, S>(
+	round: u64,
+	set_id: u64,
+	inner: S,
+	voters: Arc<HashMap<AuthorityId, u64>>,
+)
 	-> impl Stream<Item=SignedMessage<Block>,Error=Error> where
 	S: Stream<Item=Vec<u8>,Error=()>
 {
@@ -313,13 +402,13 @@ fn checked_message_stream<Block: BlockT, S>(inner: S, voters: Vec<AuthorityId>)
 		})
 		.and_then(move |msg| {
 			// check signature.
-			if !voters.contains(&msg.id) {
+			if !voters.contains_key(&msg.id) {
 				debug!(target: "afg", "Skipping message from unknown voter {}", msg.id);
 				return Ok(None);
 			}

 			let as_public = ::ed25519::Public::from_raw(msg.id.0);
-			let encoded_raw = msg.message.encode();
+			let encoded_raw = localized_payload(round, set_id, &msg.message);
 			if ::ed25519::verify_strong(&msg.signature, &encoded_raw, as_public) {
 				Ok(Some(msg))
 			} else {
@@ -332,9 +421,10 @@ fn checked_message_stream<Block: BlockT, S>(inner: S, voters: Vec<AuthorityId>)
 }

 fn outgoing_messages<Block: BlockT, N: Network>(
-	local_key: Option<Arc<ed25519::Pair>>,
-	voters: Vec<AuthorityId>,
 	round: u64,
+	set_id: u64,
+	local_key: Option<Arc<ed25519::Pair>>,
+	voters: Arc<HashMap<AuthorityId, u64>>,
 	network: N,
 ) -> (
 	impl Stream<Item=SignedMessage<Block>,Error=Error>,
@@ -342,15 +432,20 @@ fn outgoing_messages<Block: BlockT, N: Network>(
 ) {
 	let locals = local_key.and_then(|pair| {
 		let public = pair.public();
-		voters.iter().find(|id| id.0 == public.0).map(move |id| (pair, id.clone()))
+		let id = AuthorityId(public.0);
+		if voters.contains_key(&id) {
+			Some((pair, id))
+		} else {
+			None
+		}
 	});

 	let (tx, rx) = mpsc::unbounded();
 	let rx = rx
 		.map(move |msg: Message<Block>| {
-			// when locals exist. sign messages on import
+			// when locals exist, sign messages on import
 			if let Some((ref pair, local_id)) = locals {
-				let encoded = msg.encode();
+				let encoded = localized_payload(round, set_id, &msg);
 				let signature = pair.sign(&encoded[..]);
 				let signed = SignedMessage::<Block> {
 					message: msg,
@@ -359,7 +454,7 @@ fn outgoing_messages<Block: BlockT, N: Network>(
 				};

 				// forward to network.
-				network.send_message(round, signed.encode());
+				network.send_message(round, set_id, signed.encode());
 				Some(signed)
 			} else {
 				None
@@ -377,20 +472,22 @@ fn outgoing_messages<Block: BlockT, N: Network>(
 }

 /// The environment we run GRANDPA in.
-pub struct Environment<B, E, Block: BlockT, N: Network, RA> {
+struct Environment<B, E, Block: BlockT, N: Network, RA> {
 	inner: Arc<Client<B, E, Block, RA>>,
-	voters: HashMap<AuthorityId, usize>,
+	voters: Arc<HashMap<AuthorityId, u64>>,
 	config: Config,
+	authority_set: SharedAuthoritySet<Block::Hash, NumberFor<Block>>,
 	network: N,
+	set_id: u64,
 }

-impl<Block: BlockT<Hash=H256>, B, E, N, RA> grandpa::Chain<Block::Hash> for Environment<B, E, Block, N, RA> where
+impl<Block: BlockT<Hash=H256>, B, E, N, RA> grandpa::Chain<Block::Hash, NumberFor<Block>> for Environment<B, E, Block, N, RA> where
 	Block: 'static,
 	B: Backend<Block, Blake2Hasher> + 'static,
 	E: CallExecutor<Block, Blake2Hasher> + 'static,
 	N: Network + 'static,
 	N::In: 'static,
-	NumberFor<Block>: As<u32>,
+	NumberFor<Block>: BlockNumberOps,
 {
 	fn ancestry(&self, base: Block::Hash, block: Block::Hash) -> Result<Vec<Block::Hash>, GrandpaError> {
 		if base == block { return Err(NotDescendent) }
@@ -420,14 +517,23 @@ impl<Block: BlockT<Hash=H256>, B, E, N, RA> grandpa::Chain<Block::Hash> for Envi
 		Ok(tree_route.retracted().iter().skip(1).map(|e| e.hash).collect())
 	}

-	fn best_chain_containing(&self, block: Block::Hash) -> Option<(Block::Hash, u32)> {
-		match self.inner.best_containing(block, None) {
+	fn best_chain_containing(&self, block: Block::Hash) -> Option<(Block::Hash, NumberFor<Block>)> {
+		// we refuse to vote beyond the current limit number where transitions are scheduled to
+		// occur.
+		// once blocks are finalized that make that transition irrelevant or activate it,
+		// we will proceed onwards. most of the time there will be no pending transition.
+		let limit = self.authority_set.current_limit();
+		trace!(target: "afg", "Finding best chain containing block {:?} with number limit {:?}", block, limit);
+
+		match self.inner.best_containing(block, limit) {
 			Ok(Some(hash)) => {
 				let header = self.inner.header(&BlockId::Hash(hash)).ok()?
 					.expect("Header known to exist after `best_containing` call; qed");

-				Some((hash, header.number().as_()))
+				Some((hash, header.number().clone()))
 			}
+			// Ok(None) can be returned when `block` is after `limit`. That might cause issues.
+			// might be better to return the header itself in this (rare) case.
 			Ok(None) => None,
 			Err(e) => {
 				debug!(target: "afg", "Encountered error finding best chain containing {:?}: {:?}", block, e);
@@ -437,22 +543,65 @@ impl<Block: BlockT<Hash=H256>, B, E, N, RA> grandpa::Chain<Block::Hash> for Envi
 	}
 }

-impl<B, E, Block: BlockT<Hash=H256>, N, RA> voter::Environment<Block::Hash> for Environment<B, E, Block, N, RA> where
+/// A new authority set along with the canonical block it changed at.
+#[derive(Debug)]
+struct NewAuthoritySet<H, N> {
+	canon_number: N,
+	canon_hash: H,
+	set_id: u64,
+	authorities: Vec<(AuthorityId, u64)>,
+}
+
+/// Signals either an early exit of a voter or an error.
+#[derive(Debug)]
+enum ExitOrError<H, N> {
+	/// An error occurred.
+	Error(Error),
+	/// Early exit of the voter: the new set ID and the new authorities along with respective weights.
+	AuthoritiesChanged(NewAuthoritySet<H, N>),
+}
+
+impl<H, N> From<Error> for ExitOrError<H, N> {
+	fn from(e: Error) -> Self {
+		ExitOrError::Error(e)
+	}
+}
+
+impl<H, N> From<ClientError> for ExitOrError<H, N> {
+	fn from(e: ClientError) -> Self {
+		ExitOrError::Error(Error::Client(e))
+	}
+}
+
+impl<H, N> From<grandpa::Error> for ExitOrError<H, N> {
+	fn from(e: grandpa::Error) -> Self {
+		ExitOrError::Error(Error::from(e))
+	}
+}
+
+impl<B, E, Block: BlockT<Hash=H256>, N, RA> voter::Environment<Block::Hash, NumberFor<Block>> for Environment<B, E, Block, N, RA> where
 	Block: 'static,
 	B: Backend<Block, Blake2Hasher> + 'static,
 	E: CallExecutor<Block, Blake2Hasher> + 'static + Send + Sync,
 	N: Network + 'static,
 	N::In: 'static,
 	RA: 'static + Send + Sync,
-	NumberFor<Block>: As<u32>,
+	NumberFor<Block>: BlockNumberOps,
 {
 	type Timer = Box<Future<Item = (), Error = Self::Error>>;
 	type Id = AuthorityId;
 	type Signature = ed25519::Signature;
-	type In = Box<Stream<Item = ::grandpa::SignedMessage<Block::Hash, Self::Signature, Self::Id>, Error = Self::Error>>;
-	type Out = Box<Sink<SinkItem = ::grandpa::Message<Block::Hash>, SinkError = Self::Error>>;
-	type Error = Error;
+	type In = Box<Stream<
+		Item = ::grandpa::SignedMessage<Block::Hash, NumberFor<Block>, Self::Signature, Self::Id>,
+		Error = Self::Error,
+	>>;
+	type Out = Box<Sink<
+		SinkItem = ::grandpa::Message<Block::Hash, NumberFor<Block>>,
+		SinkError = Self::Error,
+	>>;
+	type Error = ExitOrError<Block::Hash, NumberFor<Block>>;

+	#[allow(unreachable_code)]
 	fn round_data(
 		&self,
 		round: u64
@@ -466,14 +615,17 @@ impl<B, E, Block: BlockT<Hash=H256>, N, RA> voter::Environment<Block::Hash> for

 		// TODO: dispatch this with `mpsc::spawn`.
 		let incoming = checked_message_stream::<Block, _>(
-			self.network.messages_for(round),
-			self.config.voters.clone(),
+			round,
+			self.set_id,
+			self.network.messages_for(round, self.set_id),
+			self.voters.clone(),
 		);

 		let (out_rx, outgoing) = outgoing_messages::<Block, _>(
-			self.config.local_key.clone(),
-			self.config.voters.clone(),
 			round,
+			self.set_id,
+			self.config.local_key.clone(),
+			self.voters.clone(),
 			self.network.clone(),
 		);

@@ -486,51 +638,121 @@ impl<B, E, Block: BlockT<Hash=H256>, N, RA> voter::Environment<Block::Hash> for
 		);

 		// join incoming network messages with locally originating ones.
-		let incoming = Box::new(incoming.select(out_rx));
+		let incoming = Box::new(out_rx.select(incoming).map_err(Into::into));

 		// schedule network message cleanup when sink drops.
 		let outgoing = Box::new(ClearOnDrop {
 			round,
+			set_id: self.set_id,
 			network: self.network.clone(),
-			inner: outgoing,
+			inner: outgoing.sink_map_err(Into::into),
 		});

 		voter::RoundData {
-			prevote_timer: Box::new(prevote_timer.map_err(Error::Timer)),
-			precommit_timer: Box::new(precommit_timer.map_err(Error::Timer)),
-			voters: self.voters.clone(),
+			prevote_timer: Box::new(prevote_timer.map_err(|e| Error::Timer(e).into())),
+			precommit_timer: Box::new(precommit_timer.map_err(|e| Error::Timer(e).into())),
+			voters: (&*self.voters).clone(),
 			incoming,
 			outgoing,
 		}
 	}

-	fn completed(&self, round: u64, state: RoundState<Block::Hash>) -> Result<(), Self::Error> {
+	fn completed(&self, round: u64, state: RoundState<Block::Hash, NumberFor<Block>>) -> Result<(), Self::Error> {
+		debug!(
+			target: "afg", "Voter {} completed round {} in set {}. Estimate = {:?}, Finalized in round = {:?}",
+			self.config.name(),
+			round,
+			self.set_id,
+			state.estimate.as_ref().map(|e| e.1),
+			state.finalized.as_ref().map(|e| e.1),
+		);
+
 		let encoded_state = (round, state).encode();
 		if let Err(e) = self.inner.backend()
 			.insert_aux(&[(LAST_COMPLETED_KEY, &encoded_state[..])], &[])
 		{
 			warn!(target: "afg", "Shutting down voter due to error bookkeeping last completed round in DB: {:?}", e);
-			Err(Error::CouldNotCompleteRound(e))
+			Err(Error::Client(e).into())
 		} else {
 			Ok(())
 		}
 	}

-	fn finalize_block(&self, hash: Block::Hash, number: u32) -> Result<(), Self::Error> {
-		// TODO: don't unconditionally notify.
+	fn finalize_block(&self, hash: Block::Hash, number: NumberFor<Block>) -> Result<(), Self::Error> {
+		// ideally some handle to a synchronization oracle would be used
+		// to avoid unconditionally notifying.
 		if let Err(e) = self.inner.finalize_block(BlockId::Hash(hash), true) {
 			warn!(target: "afg", "Error applying finality to block {:?}: {:?}", (hash, number), e);
+
+			// we return without error because not being able to finalize (temporarily) is
+			// non-fatal.
+			return Ok(());
 		}

-		// we return without error in all cases because not being able to finalize is
-		// non-fatal.
+		// lock must be held through writing to DB to avoid race
+		let mut authority_set = self.authority_set.inner().write();
+		let client = &self.inner;
+		let status = authority_set.apply_changes(number, |canon_number| {
+			client.block_hash_from_id(&BlockId::number(canon_number))
+				.map(|h| h.expect("given number always less than newly-finalized number; \
+					thus there is a block with that number finalized already; qed"))
+		})?;
+
+		if status.changed {
+			// write new authority set state to disk.
+			let encoded_set = authority_set.encode();
+
+			let write_result = if let Some((ref canon_hash, ref canon_number)) = status.new_set_block {
+				// we also overwrite the "last completed round" entry with a blank slate
+				// because from the perspective of the finality gadget, the chain has
+				// reset.
+				let round_state = RoundState::genesis((*canon_hash, *canon_number));
+				let last_completed: LastCompleted<_, _> = (0, round_state);
+				let encoded = last_completed.encode();
+
+				client.backend().insert_aux(
+					&[
+						(AUTHORITY_SET_KEY, &encoded_set[..]),
+						(LAST_COMPLETED_KEY, &encoded[..]),
+					],
+					&[]
+				)
+			} else {
+				client.backend().insert_aux(&[(AUTHORITY_SET_KEY, &encoded_set[..])], &[])
+			};
+
+			if let Err(e) = write_result {
+				warn!(target: "finality", "Failed to write updated authority set to disk. Bailing.");
+				warn!(target: "finality", "Node is in a potentially inconsistent state.");
+
+				return Err(e.into());
+			}
+		}
+
+		if let Some((canon_hash, canon_number)) = status.new_set_block {
+			// the authority set has changed.
+			let (new_id, set_ref) = authority_set.current();
+
+			if set_ref.len() > 16 {
+				info!("Applying GRANDPA set change to new set with {} authorities", set_ref.len());
+			} else {
+				info!("Applying GRANDPA set change to new set {:?}", set_ref);
+			}
+			Err(ExitOrError::AuthoritiesChanged(NewAuthoritySet {
+				canon_hash,
+				canon_number,
+				set_id: new_id,
+				authorities: set_ref.to_vec(),
+			}))
+		} else {
 			Ok(())
 		}
+	}

 	fn prevote_equivocation(
 		&self,
 		_round: u64,
-		equivocation: ::grandpa::Equivocation<Self::Id, Prevote<Block::Hash>, Self::Signature>
+		equivocation: ::grandpa::Equivocation<Self::Id, Prevote<Block>, Self::Signature>
 	) {
 		warn!(target: "afg", "Detected prevote equivocation in the finality worker: {:?}", equivocation);
 		// nothing yet; this could craft misbehavior reports of some kind.
@@ -539,232 +761,209 @@ impl<B, E, Block: BlockT<Hash=H256>, N, RA> voter::Environment<Block::Hash> for
 	fn precommit_equivocation(
 		&self,
 		_round: u64,
-		equivocation: Equivocation<Self::Id, Precommit<Block::Hash>, Self::Signature>
+		equivocation: Equivocation<Self::Id, Precommit<Block>, Self::Signature>
 	) {
 		warn!(target: "afg", "Detected precommit equivocation in the finality worker: {:?}", equivocation);
 		// nothing yet
 	}
 }

-/// Run a GRANDPA voter as a task. The returned future should be executed in a tokio runtime.
-pub fn run_grandpa<B, E: Send + Sync, Block: BlockT<Hash=H256>, N, RA: Send + Sync + 'static>(
-	config: Config,
+
+
+/// A block-import handler for GRANDPA.
+///
+/// This scans each imported block for signals of changing authority set.
+/// When using GRANDPA, the block import worker should be using this block import
+/// object.
+pub struct GrandpaBlockImport<B, E, Block: BlockT<Hash=H256>, RA> {
+	inner: Arc<Client<B, E, Block, RA>>,
+	authority_set: SharedAuthoritySet<Block::Hash, NumberFor<Block>>,
+}
+
+impl<B, E, Block: BlockT<Hash=H256>, RA> BlockImport<Block> for GrandpaBlockImport<B, E, Block, RA> where
+	B: Backend<Block, Blake2Hasher> + 'static,
+	E: CallExecutor<Block, Blake2Hasher> + 'static + Clone + Send + Sync,
+	DigestFor<Block>: Encode,
+	RA: GrandpaApi<Block> + TaggedTransactionQueue<Block>,
+{
+	type Error = ClientError;
+
+	fn import_block(&self, mut block: ImportBlock<Block>, new_authorities: Option<Vec<AuthorityId>>)
+		-> Result<ImportResult, Self::Error>
+	{
+		use authorities::PendingChange;
+
+		let maybe_change = self.inner.runtime_api().grandpa_pending_change(
+			&BlockId::hash(*block.header.parent_hash()),
+			&block.header.digest().clone(),
+		)?;
+
+		// when we update the authorities, we need to hold the lock
+		// until the block is written to prevent a race if we need to restore
+		// the old authority set on error.
+		let just_in_case = maybe_change.map(|change| {
+			let hash = block.header.hash();
+			let number = block.header.number().clone();
+
+			let mut authorities = self.authority_set.inner().write();
+			let old_set = authorities.clone();
+			authorities.add_pending_change(PendingChange {
+				next_authorities: change.next_authorities,
+				finalization_depth: change.delay,
+				canon_height: number,
+				canon_hash: hash,
+			});
+
+			block.auxiliary.push((AUTHORITY_SET_KEY.to_vec(), Some(authorities.encode())));
+			(old_set, authorities)
+		});
+
+		let result = self.inner.import_block(block, new_authorities);
+		if let Err(ref e) = result {
+			if let Some((old_set, mut authorities)) = just_in_case {
+				debug!(target: "afg", "Restoring old set after block import error: {:?}", e);
+				*authorities = old_set;
+			}
+		}
+
+		result
+	}
+}
+
+/// Half of a link between a block-import worker and a the background voter.
+// This should remain non-clone.
+pub struct LinkHalf<B, E, Block: BlockT<Hash=H256>, RA> {
 	client: Arc<Client<B, E, Block, RA>>,
-	voters: HashMap<AuthorityId, usize>,
+	authority_set: SharedAuthoritySet<Block::Hash, NumberFor<Block>>,
+}
+
+/// Make block importer and link half necessary to tie the background voter
+/// to it.
+pub fn block_import<B, E, Block: BlockT<Hash=H256>, RA>(client: Arc<Client<B, E, Block, RA>>)
+	-> Result<(GrandpaBlockImport<B, E, Block, RA>, LinkHalf<B, E, Block, RA>), ClientError>
+	where
+		B: Backend<Block, Blake2Hasher> + 'static,
+		E: CallExecutor<Block, Blake2Hasher> + 'static + Clone + Send + Sync,
+		RA: GrandpaApi<Block>,
+{
+	use runtime_primitives::traits::Zero;
+	let authority_set = match client.backend().get_aux(AUTHORITY_SET_KEY)? {
+		None => {
+			info!(target: "afg", "Loading GRANDPA authorities \
+				from genesis on what appears to be first startup.");
+
+			// no authority set on disk: fetch authorities from genesis state.
+			// if genesis state is not available, we may be a light client, but these
+			// are unsupported for following GRANDPA directly.
+			let genesis_authorities = client.runtime_api()
+				.grandpa_authorities(&BlockId::number(Zero::zero()))?;
+
+			let authority_set = SharedAuthoritySet::genesis(genesis_authorities);
+			let encoded = authority_set.inner().read().encode();
+			client.backend().insert_aux(&[(AUTHORITY_SET_KEY, &encoded[..])], &[])?;
+
+			authority_set
+		}
+		Some(raw) => ::authorities::AuthoritySet::decode(&mut &raw[..])
+			.ok_or_else(|| ::client::error::ErrorKind::Backend(
+				format!("GRANDPA authority set kept in invalid format")
+			))?
+			.into(),
+	};
+
+	Ok((
+		GrandpaBlockImport { inner: client.clone(), authority_set: authority_set.clone() },
+		LinkHalf { client, authority_set },
+	))
+}
+
+/// Run a GRANDPA voter as a task. Provide configuration and a link to a
+/// block import worker that has already been instantiated with `block_import`.
+pub fn run_grandpa<B, E, Block: BlockT<Hash=H256>, N, RA>(
+	config: Config,
+	link: LinkHalf<B, E, Block, RA>,
 	network: N,
-) -> Result<impl Future<Item=(),Error=()>,client::error::Error> where
+) -> ::client::error::Result<impl Future<Item=(),Error=()>> where
 	Block::Hash: Ord,
 	B: Backend<Block, Blake2Hasher> + 'static,
-	E: CallExecutor<Block, Blake2Hasher> + 'static,
+	E: CallExecutor<Block, Blake2Hasher> + Send + Sync + 'static,
 	N: Network + 'static,
 	N::In: 'static,
-	NumberFor<Block>: As<u32>,
+	NumberFor<Block>: BlockNumberOps,
+	DigestFor<Block>: Encode,
+	RA: Send + Sync + 'static,
 {
+	use futures::future::{self, Loop as FutureLoop};
+	use runtime_primitives::traits::Zero;
+
+	let LinkHalf { client, authority_set } = link;
 	let chain_info = client.info()?;
 	let genesis_hash = chain_info.chain.genesis_hash;
-	let last_finalized = (
-		chain_info.chain.finalized_hash,
-		chain_info.chain.finalized_number.as_()
-	);

 	let (last_round_number, last_state) = match client.backend().get_aux(LAST_COMPLETED_KEY)? {
-		None => (0, RoundState::genesis((genesis_hash, 0))),
-		Some(raw) => <(u64, RoundState<Block::Hash>)>::decode(&mut &raw[..])
+		None => (0, RoundState::genesis((genesis_hash, <NumberFor<Block>>::zero()))),
+		Some(raw) => LastCompleted::decode(&mut &raw[..])
 			.ok_or_else(|| ::client::error::ErrorKind::Backend(
 				format!("Last GRANDPA round state kept in invalid format")
 			))?
 	};

-	let environment = Arc::new(Environment {
+	let voters = authority_set.inner().read().current().1.iter()
+		.cloned()
+		.collect();
+
+	let initial_environment = Arc::new(Environment {
+		inner: client.clone(),
+		config: config.clone(),
+		voters: Arc::new(voters),
+		network: network.clone(),
+		set_id: authority_set.set_id(),
+		authority_set: authority_set.clone(),
+	});
+
+	let work = future::loop_fn((initial_environment, last_round_number, last_state), move |params| {
+		let (env, last_round_number, last_state) = params;
+		debug!(target: "afg", "{}: Starting new voter with set ID {}", config.name(), env.set_id);
+
+		let chain_info = match client.info() {
+			Ok(i) => i,
+			Err(e) => return future::Either::B(future::err(Error::Client(e))),
+		};
+
+		let last_finalized = (
+			chain_info.chain.finalized_hash,
+			chain_info.chain.finalized_number,
+		);
+
+		let voter = voter::Voter::new(env, last_round_number, last_state, last_finalized);
+		let client = client.clone();
+		let config = config.clone();
+		let network = network.clone();
+		let authority_set = authority_set.clone();
+		future::Either::A(voter.then(move |res| match res {
+			// voters don't conclude naturally; this could reasonably be an error.
+			Ok(()) => Ok(FutureLoop::Break(())),
+			Err(ExitOrError::Error(e)) => Err(e),
+			Err(ExitOrError::AuthoritiesChanged(new)) => {
+				let env = Arc::new(Environment {
 					inner: client,
 					config,
-		voters,
+					voters: Arc::new(new.authorities.into_iter().collect()),
+					set_id: new.set_id,
 					network,
+					authority_set,
 				});

-	let voter = voter::Voter::new(
-		environment,
-		last_round_number,
-		last_state,
-		last_finalized,
-	);
-
-	Ok(voter.map_err(|e| warn!("GRANDPA Voter failed: {:?}", e)))
-}
-
-#[cfg(test)]
-mod tests {
-	use super::*;
-	use network::test::*;
-	use parking_lot::Mutex;
-	use tokio::runtime::current_thread;
-	use keyring::Keyring;
-	use client::BlockchainEvents;
-
-	#[derive(Clone)]
-	struct TestGrandpaNetwork {
-		inner: Arc<Mutex<TestNet>>,
-		peer_id: usize,
+				// start the new authority set using the block where the
+				// set changed (not where the signal happened!) as the base.
+				Ok(FutureLoop::Continue((
+					env,
+					0, // always start at round 0 when changing sets.
+					RoundState::genesis((new.canon_hash, new.canon_number)),
+				)))
 			}
-
-	impl TestGrandpaNetwork {
-		fn new(inner: Arc<Mutex<TestNet>>, peer_id: usize,) -> Self {
-			TestGrandpaNetwork {
-				inner,
-				peer_id,
-			}
-		}
-	}
-
-	fn round_to_topic(round: u64) -> Hash {
-		let mut hash = Hash::default();
-		round.using_encoded(|s| {
-			let raw = hash.as_mut();
-			raw[..8].copy_from_slice(s);
+		}))
 	});
-		hash
-	}

-	impl Network for TestGrandpaNetwork {
-		type In = Box<Stream<Item=Vec<u8>,Error=()>>;
-
-		fn messages_for(&self, round: u64) -> Self::In {
-			let messages = self.inner.lock().peer(self.peer_id)
-				.with_spec(|spec, _| spec.gossip.messages_for(round_to_topic(round)));
-
-			let messages = messages.map_err(
-				move |_| panic!("Messages for round {} dropped too early", round)
-			);
-
-			Box::new(messages)
-		}
-
-		fn send_message(&self, round: u64, message: Vec<u8>) {
-			let mut inner = self.inner.lock();
-			inner.peer(self.peer_id).gossip_message(round_to_topic(round), message);
-			inner.route();
-		}
-
-		fn drop_messages(&self, round: u64) {
-			let topic = round_to_topic(round);
-			self.inner.lock().peer(self.peer_id)
-				.with_spec(|spec, _| spec.gossip.collect_garbage(|t| t == &topic));
-		}
-	}
-
-	const TEST_GOSSIP_DURATION: Duration = Duration::from_millis(500);
-	const TEST_ROUTING_INTERVAL: Duration = Duration::from_millis(50);
-
-	#[test]
-	fn finalize_20_unanimous_3_peers() {
-		let mut net = TestNet::new(3);
-		net.peer(0).push_blocks(20, false);
-		net.sync();
-
-		let net = Arc::new(Mutex::new(net));
-		let peers = &[
-			(0, Keyring::Alice),
-			(1, Keyring::Bob),
-			(2, Keyring::Charlie),
-		];
-
-		let voters: Vec<_> = peers.iter()
-			.map(|&(_, ref key)| AuthorityId(key.to_raw_public()))
-			.collect();
-
-		let mut finality_notifications = Vec::new();
-
-		let mut runtime = current_thread::Runtime::new().unwrap();
-		for (peer_id, key) in peers {
-			let client = net.lock().peer(*peer_id).client().clone();
-			finality_notifications.push(
-				client.finality_notification_stream()
-					.take_while(|n| Ok(n.header.number() < &20))
-					.for_each(move |_| Ok(()))
-			);
-			let voter = run_grandpa(
-				Config {
-					gossip_duration: TEST_GOSSIP_DURATION,
-					voters: voters.clone(),
-					local_key: Some(Arc::new(key.clone().into())),
-				},
-				client,
-				voters.iter().map(|&id| (id, 1)).collect(),
-				TestGrandpaNetwork::new(net.clone(), *peer_id),
-			).expect("all in order with client and network");
-
-			runtime.spawn(voter);
-		}
-
-		// wait for all finalized on each.
-		let wait_for = ::futures::future::join_all(finality_notifications)
-			.map(|_| ())
-			.map_err(|_| ());
-
-		let drive_to_completion = ::tokio::timer::Interval::new_interval(TEST_ROUTING_INTERVAL)
-			.for_each(move |_| { net.lock().route_until_complete(); Ok(()) })
-			.map(|_| ())
-			.map_err(|_| ());
-
-		runtime.block_on(wait_for.select(drive_to_completion).map_err(|_| ())).unwrap();
-	}
-
-	#[test]
-	fn observer_can_finalize() {
-		let mut net = TestNet::new(4);
-		net.peer(0).push_blocks(20, false);
-		net.sync();
-
-		let net = Arc::new(Mutex::new(net));
-		let peers = &[
-			(0, Keyring::Alice),
-			(1, Keyring::Bob),
-			(2, Keyring::Charlie),
-		];
-
-		let voters: HashMap<_, _> = peers.iter()
-			.map(|&(_, ref key)| (AuthorityId(key.to_raw_public()), 1))
-			.collect();
-
-		let mut finality_notifications = Vec::new();
-
-		let mut runtime = current_thread::Runtime::new().unwrap();
-		let all_peers = peers.iter()
-			.cloned()
-			.map(|(id, key)| (id, Some(Arc::new(key.into()))))
-			.chain(::std::iter::once((3, None)));
-
-		for (peer_id, local_key) in all_peers {
-			let client = net.lock().peer(peer_id).client().clone();
-			finality_notifications.push(
-				client.finality_notification_stream()
-					.take_while(|n| Ok(n.header.number() < &20))
-					.for_each(move |_| Ok(()))
-			);
-			let voter = run_grandpa(
-				Config {
-					gossip_duration: TEST_GOSSIP_DURATION,
-					voters: voters.keys().cloned().collect(),
-					local_key,
-				},
-				client,
-				voters.clone(),
-				TestGrandpaNetwork::new(net.clone(), peer_id),
-			).expect("all in order with client and network");
-
-			runtime.spawn(voter);
-		}
-
-		// wait for all finalized on each.
-		let wait_for = ::futures::future::join_all(finality_notifications)
-			.map(|_| ())
-			.map_err(|_| ());
-
-		let drive_to_completion = ::tokio::timer::Interval::new_interval(TEST_ROUTING_INTERVAL)
-			.for_each(move |_| { net.lock().route_until_complete(); Ok(()) })
-			.map(|_| ())
-			.map_err(|_| ());
-
-		runtime.block_on(wait_for.select(drive_to_completion).map_err(|_| ())).unwrap();
-	}
+	Ok(work.map_err(|e| warn!("GRANDPA Voter failed: {:?}", e)))
 }
@@ -0,0 +1,460 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Tests and test helpers for GRANDPA.
+
+use super::*;
+use network::test::{Block, Hash, TestNetFactory, Peer, PeersClient};
+use network::import_queue::{PassThroughVerifier};
+use network::config::{ProtocolConfig, Roles};
+use parking_lot::Mutex;
+use tokio::runtime::current_thread;
+use keyring::Keyring;
+use client::BlockchainEvents;
+use test_client::{self, runtime::BlockNumber};
+use codec::Decode;
+use consensus_common::BlockOrigin;
+use std::collections::HashSet;
+
+use authorities::AuthoritySet;
+
+type PeerData = Mutex<Option<LinkHalf<test_client::Backend, test_client::Executor, Block, test_client::runtime::ClientWithApi>>>;
+type GrandpaPeer = Peer<PassThroughVerifier, PeerData>;
+
+struct GrandpaTestNet {
+	peers: Vec<Arc<GrandpaPeer>>,
+	test_config: TestApi,
+	started: bool
+}
+
+impl GrandpaTestNet {
+	fn new(test_config: TestApi, n_peers: usize) -> Self {
+		let mut net = GrandpaTestNet {
+			peers: Vec::with_capacity(n_peers),
+			started: false,
+			test_config,
+		};
+		let config = Self::default_config();
+
+		for _ in 0..n_peers {
+			net.add_peer(&config);
+		}
+
+		net
+	}
+}
+
+impl TestNetFactory for GrandpaTestNet {
+	type Verifier = PassThroughVerifier;
+	type PeerData = PeerData;
+
+	/// Create new test network with peers and given config.
+	fn from_config(_config: &ProtocolConfig) -> Self {
+		GrandpaTestNet {
+			peers: Vec::new(),
+			test_config: Default::default(),
+			started: false
+		}
+	}
+
+	fn default_config() -> ProtocolConfig {
+		// the authority role ensures gossip hits all nodes here.
+		ProtocolConfig {
+			roles: Roles::AUTHORITY,
+		}
+	}
+
+	fn make_verifier(&self, _client: Arc<PeersClient>, _cfg: &ProtocolConfig)
+		-> Arc<Self::Verifier>
+	{
+		Arc::new(PassThroughVerifier(false)) // use non-instant finality.
+	}
+
+	fn make_block_import(&self, client: Arc<PeersClient>)
+		-> (Arc<BlockImport<Block,Error=ClientError> + Send + Sync>, PeerData)
+	{
+		let (import, link) = block_import(client, self.test_config.clone()).expect("Could not create block import for fresh peer.");
+		(Arc::new(import), Mutex::new(Some(link)))
+	}
+
+	fn peer(&self, i: usize) -> &GrandpaPeer {
+		&self.peers[i]
+	}
+
+	fn peers(&self) -> &Vec<Arc<GrandpaPeer>> {
+		&self.peers
+	}
+
+	fn mut_peers<F: Fn(&mut Vec<Arc<GrandpaPeer>>)>(&mut self, closure: F) {
+		closure(&mut self.peers);
+	}
+
+	fn started(&self) -> bool {
+		self.started
+	}
+
+	fn set_started(&mut self, new: bool) {
+		self.started = new;
+	}
+}
+
+#[derive(Clone)]
+struct MessageRouting {
+	inner: Arc<Mutex<GrandpaTestNet>>,
+	peer_id: usize,
+}
+
+impl MessageRouting {
+	fn new(inner: Arc<Mutex<GrandpaTestNet>>, peer_id: usize,) -> Self {
+		MessageRouting {
+			inner,
+			peer_id,
+		}
+	}
+}
+
+fn make_topic(round: u64, set_id: u64) -> Hash {
+	let mut hash = Hash::default();
+	round.using_encoded(|s| {
+		let raw = hash.as_mut();
+		raw[..8].copy_from_slice(s);
+	});
+	set_id.using_encoded(|s| {
+		let raw = hash.as_mut();
+		raw[8..16].copy_from_slice(s);
+	});
+	hash
+}
+
+impl Network for MessageRouting {
+	type In = Box<Stream<Item=Vec<u8>,Error=()>>;
+
+	fn messages_for(&self, round: u64, set_id: u64) -> Self::In {
+		let messages = self.inner.lock().peer(self.peer_id)
+			.with_spec(|spec, _| spec.gossip.messages_for(make_topic(round, set_id)));
+
+		let messages = messages.map_err(
+			move |_| panic!("Messages for round {} dropped too early", round)
+		);
+
+		Box::new(messages)
+	}
+
+	fn send_message(&self, round: u64, set_id: u64, message: Vec<u8>) {
+		let mut inner = self.inner.lock();
+		inner.peer(self.peer_id).gossip_message(make_topic(round, set_id), message);
+		inner.route_until_complete();
+	}
+
+	fn drop_messages(&self, round: u64, set_id: u64) {
+		let topic = make_topic(round, set_id);
+		self.inner.lock().peer(self.peer_id)
+			.with_spec(|spec, _| spec.gossip.collect_garbage(|t| t == &topic));
+	}
+}
+
+#[derive(Default, Clone)]
+struct TestApi {
+	genesis_authorities: Vec<(AuthorityId, u64)>,
+	scheduled_changes: Arc<Mutex<HashMap<Hash, ScheduledChange<BlockNumber>>>>,
+}
+
+impl TestApi {
+	fn new(genesis_authorities: Vec<(AuthorityId, u64)>) -> Self {
+		TestApi {
+			genesis_authorities,
+			scheduled_changes: Arc::new(Mutex::new(HashMap::new())),
+		}
+	}
+}
+
+impl ApiClient<Block> for TestApi {
+	fn genesis_authorities(&self) -> Result<Vec<(AuthorityId, u64)>, ClientError> {
+		Ok(self.genesis_authorities.clone())
+	}
+
+	fn scheduled_change(&self, header: &<Block as BlockT>::Header)
+		-> Result<Option<ScheduledChange<NumberFor<Block>>>, ClientError>
+	{
+		// we take only scheduled changes at given block number where there are no
+		// extrinsics.
+		Ok(self.scheduled_changes.lock().get(&header.hash()).map(|c| c.clone()))
+	}
+}
+
+const TEST_GOSSIP_DURATION: Duration = Duration::from_millis(500);
+const TEST_ROUTING_INTERVAL: Duration = Duration::from_millis(50);
+
+fn make_ids(keys: &[Keyring]) -> Vec<(AuthorityId, u64)> {
+	keys.iter()
+		.map(|key| AuthorityId(key.to_raw_public()))
+		.map(|id| (id, 1))
+		.collect()
+}
+
+#[test]
+fn finalize_3_voters_no_observers() {
+	let peers = &[Keyring::Alice, Keyring::Bob, Keyring::Charlie];
+	let voters = make_ids(peers);
+
+	let mut net = GrandpaTestNet::new(TestApi::new(voters), 3);
+	net.peer(0).push_blocks(20, false);
+	net.sync();
+
+	for i in 0..3 {
+		assert_eq!(net.peer(i).client().info().unwrap().chain.best_number, 20,
+			"Peer #{} failed to sync", i);
+	}
+
+	let net = Arc::new(Mutex::new(net));
+
+	let mut finality_notifications = Vec::new();
+	let mut runtime = current_thread::Runtime::new().unwrap();
+
+	for (peer_id, key) in peers.iter().enumerate() {
+		let (client, link) = {
+			let mut net = net.lock();
+			// temporary needed for some reason
+			let link = net.peers[peer_id].data.lock().take().expect("link initialized at startup; qed");
+			(
+				net.peers[peer_id].client().clone(),
+				link,
+			)
+		};
+		finality_notifications.push(
+			client.finality_notification_stream()
+				.take_while(|n| Ok(n.header.number() < &20))
+				.for_each(|_| Ok(()))
+		);
+		let voter = run_grandpa(
+			Config {
+				gossip_duration: TEST_GOSSIP_DURATION,
+				local_key: Some(Arc::new(key.clone().into())),
+				name: Some(format!("peer#{}", peer_id)),
+			},
+			link,
+			MessageRouting::new(net.clone(), peer_id),
+		).expect("all in order with client and network");
+
+		runtime.spawn(voter);
+	}
+
+	// wait for all finalized on each.
+	let wait_for = ::futures::future::join_all(finality_notifications)
+		.map(|_| ())
+		.map_err(|_| ());
+
+	let drive_to_completion = ::tokio::timer::Interval::new_interval(TEST_ROUTING_INTERVAL)
+		.for_each(move |_| { net.lock().route_until_complete(); Ok(()) })
+		.map(|_| ())
+		.map_err(|_| ());
+
+	runtime.block_on(wait_for.select(drive_to_completion).map_err(|_| ())).unwrap();
+}
+
+#[test]
+fn finalize_3_voters_1_observer() {
+	let peers = &[Keyring::Alice, Keyring::Bob, Keyring::Charlie];
+	let voters = make_ids(peers);
+
+	let mut net = GrandpaTestNet::new(TestApi::new(voters), 4);
+	net.peer(0).push_blocks(20, false);
+	net.sync();
+
+	let net = Arc::new(Mutex::new(net));
+	let mut finality_notifications = Vec::new();
+
+	let mut runtime = current_thread::Runtime::new().unwrap();
+	let all_peers = peers.iter()
+		.cloned()
+		.map(|key| Some(Arc::new(key.into())))
+		.chain(::std::iter::once(None));
+
+	for (peer_id, local_key) in all_peers.enumerate() {
+		let (client, link) = {
+			let mut net = net.lock();
+			let link = net.peers[peer_id].data.lock().take().expect("link initialized at startup; qed");
+			(
+				net.peers[peer_id].client().clone(),
+				link,
+			)
+		};
+		finality_notifications.push(
+			client.finality_notification_stream()
+				.take_while(|n| Ok(n.header.number() < &20))
+				.for_each(move |_| Ok(()))
+		);
+		let voter = run_grandpa(
+			Config {
+				gossip_duration: TEST_GOSSIP_DURATION,
+				local_key,
+				name: Some(format!("peer#{}", peer_id)),
+			},
+			link,
+			MessageRouting::new(net.clone(), peer_id),
+		).expect("all in order with client and network");
+
+		runtime.spawn(voter);
+	}
+
+	// wait for all finalized on each.
+	let wait_for = ::futures::future::join_all(finality_notifications)
+		.map(|_| ())
+		.map_err(|_| ());
+
+	let drive_to_completion = ::tokio::timer::Interval::new_interval(TEST_ROUTING_INTERVAL)
+		.for_each(move |_| { net.lock().route_until_complete(); Ok(()) })
+		.map(|_| ())
+		.map_err(|_| ());
+
+	runtime.block_on(wait_for.select(drive_to_completion).map_err(|_| ())).unwrap();
+}
+
+#[test]
+fn transition_3_voters_twice_1_observer() {
+	let peers_a = &[
+		Keyring::Alice,
+		Keyring::Bob,
+		Keyring::Charlie,
+	];
+
+	let peers_b = &[
+		Keyring::Dave,
+		Keyring::Eve,
+		Keyring::Ferdie,
+	];
+
+	let peers_c = &[
+		Keyring::Alice,
+		Keyring::Eve,
+		Keyring::Two,
+	];
+
+	let observer = &[Keyring::One];
+
+	let genesis_voters = make_ids(peers_a);
+
+	let api = TestApi::new(genesis_voters);
+	let transitions = api.scheduled_changes.clone();
+	let add_transition = move |hash, change| {
+		transitions.lock().insert(hash, change);
+	};
+
+	let mut net = GrandpaTestNet::new(api, 9);
+
+	// first 20 blocks: transition at 15, applied at 20.
+	{
+		net.peer(0).push_blocks(14, false);
+		net.peer(0).generate_blocks(1, BlockOrigin::File, |builder| {
+			let block = builder.bake().unwrap();
+			add_transition(block.header.hash(), ScheduledChange {
+				next_authorities: make_ids(peers_b),
+				delay: 4,
+			});
+
+			block
+		});
+		net.peer(0).push_blocks(5, false);
+	}
+
+	// at block 21 we do another transition, but this time instant.
+	// add more until we have 30.
+	{
+		net.peer(0).generate_blocks(1, BlockOrigin::File, |builder| {
+			let block = builder.bake().unwrap();
+			add_transition(block.header.hash(), ScheduledChange {
+				next_authorities: make_ids(peers_c),
+				delay: 0,
+			});
+
+			block
+		});
+
+		net.peer(0).push_blocks(9, false);
+	}
+	net.sync();
+
+	for (i, peer) in net.peers().iter().enumerate() {
+		assert_eq!(peer.client().info().unwrap().chain.best_number, 30,
+			"Peer #{} failed to sync", i);
+
+		let set_raw = peer.client().backend().get_aux(::AUTHORITY_SET_KEY).unwrap().unwrap();
+		let set = AuthoritySet::<Hash, BlockNumber>::decode(&mut &set_raw[..]).unwrap();
+
+		assert_eq!(set.current(), (0, make_ids(peers_a).as_slice()));
+		assert_eq!(set.pending_changes().len(), 2);
+	}
+
+	let net = Arc::new(Mutex::new(net));
+	let mut finality_notifications = Vec::new();
+
+	let mut runtime = current_thread::Runtime::new().unwrap();
+	let all_peers = peers_a.iter()
+		.chain(peers_b)
+		.chain(peers_c)
+		.chain(observer)
+		.cloned()
+		.collect::<HashSet<_>>() // deduplicate
+		.into_iter()
+		.map(|key| Some(Arc::new(key.into())))
+		.enumerate();
+
+	for (peer_id, local_key) in all_peers {
+		let (client, link) = {
+			let mut net = net.lock();
+			let link = net.peers[peer_id].data.lock().take().expect("link initialized at startup; qed");
+			(
+				net.peers[peer_id].client().clone(),
+				link,
+			)
+		};
+		finality_notifications.push(
+			client.finality_notification_stream()
+				.take_while(|n| Ok(n.header.number() < &30))
+				.for_each(move |_| Ok(()))
+				.map(move |()| {
+					let set_raw = client.backend().get_aux(::AUTHORITY_SET_KEY).unwrap().unwrap();
+					let set = AuthoritySet::<Hash, BlockNumber>::decode(&mut &set_raw[..]).unwrap();
+
+					assert_eq!(set.current(), (2, make_ids(peers_c).as_slice()));
+					assert!(set.pending_changes().is_empty());
+				})
+		);
+		let voter = run_grandpa(
+			Config {
+				gossip_duration: TEST_GOSSIP_DURATION,
+				local_key,
+				name: Some(format!("peer#{}", peer_id)),
+			},
+			link,
+			MessageRouting::new(net.clone(), peer_id),
+		).expect("all in order with client and network");
+
+		runtime.spawn(voter);
+	}
+
+	// wait for all finalized on each.
+	let wait_for = ::futures::future::join_all(finality_notifications)
+		.map(|_| ())
+		.map_err(|_| ());
+
+	let drive_to_completion = ::tokio::timer::Interval::new_interval(TEST_ROUTING_INTERVAL)
+		.for_each(move |_| { net.lock().route_until_complete(); Ok(()) })
+		.map(|_| ())
+		.map_err(|_| ());
+
+	runtime.block_on(wait_for.select(drive_to_completion).map_err(|_| ())).unwrap();
+}
@@ -34,14 +34,16 @@ use primitives::AuthorityId;
 use runtime_primitives::traits::{Block as BlockT, Header as HeaderT, NumberFor, Zero};

 pub use blocks::BlockData;
-use chain::Client;
+use client::error::Error as ClientError;
 use error::{ErrorKind, Error};
 use protocol::Context;
 use service::ExecuteInContext;
 use sync::ChainSync;

-pub use consensus::{ImportBlock, ImportResult, BlockOrigin};
+pub use consensus::{ImportBlock, BlockImport, ImportResult, BlockOrigin};

+/// Shared block import struct used by the queue.
+pub type SharedBlockImport<B> = Arc<dyn BlockImport<B,Error=ClientError> + Send + Sync>;

 #[cfg(any(test, feature = "test-helpers"))]
 use std::cell::RefCell;
@@ -66,14 +68,9 @@ pub trait ImportQueue<B: BlockT>: Send + Sync {
 	///
 	/// This is called automatically by the network service when synchronization
 	/// begins.
-	fn start<E>(
-		&self,
-		_sync: Weak<RwLock<ChainSync<B>>>,
-		_service: Weak<E>,
-		_chain: Weak<Client<B>>
-	) -> Result<(), Error> where
+	fn start<L>(&self, _link: L) -> Result<(), Error> where
 		Self: Sized,
-		E: 'static + ExecuteInContext<B>,
+		L: 'static + Link<B>,
 	{
 		Ok(())
 	}
@@ -103,6 +100,7 @@ pub struct BasicQueue<B: BlockT, V: 'static + Verifier<B>> {
 	handle: Mutex<Option<::std::thread::JoinHandle<()>>>,
 	data: Arc<AsyncImportQueueData<B>>,
 	verifier: Arc<V>,
+	block_import: SharedBlockImport<B>,
 }

 /// Locks order: queue, queue_blocks, best_importing_number
@@ -116,11 +114,12 @@ struct AsyncImportQueueData<B: BlockT> {

 impl<B: BlockT, V: Verifier<B>> BasicQueue<B, V> {
 	/// Instantiate a new basic queue, with given verifier.
-	pub fn new(verifier: Arc<V>) -> Self {
+	pub fn new(verifier: Arc<V>, block_import: SharedBlockImport<B>) -> Self {
 		Self {
 			handle: Mutex::new(None),
 			data: Arc::new(AsyncImportQueueData::new()),
 			verifier,
+			block_import,
 		}
 	}
 }
@@ -138,18 +137,17 @@ impl<B: BlockT> AsyncImportQueueData<B> {
 }

 impl<B: BlockT, V: 'static + Verifier<B>> ImportQueue<B> for BasicQueue<B, V> {
-	fn start<E: 'static + ExecuteInContext<B>>(
+	fn start<L: 'static + Link<B>>(
 		&self,
-		sync: Weak<RwLock<ChainSync<B>>>,
-		service: Weak<E>,
-		chain: Weak<Client<B>>
+		link: L,
 	) -> Result<(), Error> {
 		debug_assert!(self.handle.lock().is_none());

 		let qdata = self.data.clone();
 		let verifier = self.verifier.clone();
+		let block_import = self.block_import.clone();
 		*self.handle.lock() = Some(::std::thread::Builder::new().name("ImportQueue".into()).spawn(move || {
-			import_thread(sync, service, chain, qdata, verifier)
+			import_thread(block_import, link, qdata, verifier)
 		}).map_err(|err| Error::from(ErrorKind::Io(err)))?);
 		Ok(())
 	}
@@ -215,10 +213,9 @@ impl<B: BlockT, V: 'static + Verifier<B>> Drop for BasicQueue<B, V> {
 }

 /// Blocks import thread.
-fn import_thread<B: BlockT, E: ExecuteInContext<B>, V: Verifier<B>>(
-	sync: Weak<RwLock<ChainSync<B>>>,
-	service: Weak<E>,
-	chain: Weak<Client<B>>,
+fn import_thread<B: BlockT, L: Link<B>, V: Verifier<B>>(
+	block_import: SharedBlockImport<B>,
+	link: L,
 	qdata: Arc<AsyncImportQueueData<B>>,
 	verifier: Arc<V>
 ) {
@@ -243,11 +240,10 @@ fn import_thread<B: BlockT, E: ExecuteInContext<B>, V: Verifier<B>>(
 			}
 		};

-		match (sync.upgrade(), service.upgrade(), chain.upgrade()) {
-			(Some(sync), Some(service), Some(chain)) => {
 		let blocks_hashes: Vec<B::Hash> = new_blocks.1.iter().map(|b| b.block.hash.clone()).collect();
 		if !import_many_blocks(
-					&mut SyncLink{chain: &sync, client: &*chain, context: &*service},
+			&*block_import,
+			&link,
 			Some(&*qdata),
 			new_blocks,
 			verifier.clone(),
@@ -259,75 +255,72 @@ fn import_thread<B: BlockT, E: ExecuteInContext<B>, V: Verifier<B>>(
 		for blocks_hash in blocks_hashes {
 			queue_blocks.remove(&blocks_hash);
 		}
-			},
-			_ => break,
-		}
 	}

 	trace!(target: "sync", "Stopping import thread");
 }
-/// ChainSync link trait.
-trait SyncLinkApi<B: BlockT> {
-	/// Get chain reference.
-	fn chain(&self) -> &Client<B>;
+
+/// Hooks that the verification queue can use to influence the synchronization
+/// algorithm.
+pub trait Link<B: BlockT>: Send {
 	/// Block imported.
-	fn block_imported(&mut self, hash: &B::Hash, number: NumberFor<B>);
+	fn block_imported(&self, _hash: &B::Hash, _number: NumberFor<B>) { }
 	/// Maintain sync.
-	fn maintain_sync(&mut self);
+	fn maintain_sync(&self) { }
 	/// Disconnect from peer.
-	fn useless_peer(&mut self, who: NodeIndex, reason: &str);
+	fn useless_peer(&self, _who: NodeIndex, _reason: &str) { }
 	/// Disconnect from peer and restart sync.
-	fn note_useless_and_restart_sync(&mut self, who: NodeIndex, reason: &str);
+	fn note_useless_and_restart_sync(&self, _who: NodeIndex, _reason: &str) { }
 	/// Restart sync.
-	fn restart(&mut self);
+	fn restart(&self) { }
 }

+/// A link implementation that does nothing.
+pub struct NoopLink;

-/// Link with the ChainSync service.
-struct SyncLink<'a, B: 'a + BlockT, E: 'a + ExecuteInContext<B>> {
-	pub chain: &'a RwLock<ChainSync<B>>,
-	pub client: &'a Client<B>,
-	pub context: &'a E,
+impl<B: BlockT> Link<B> for NoopLink { }
+
+/// A link implementation that connects to the network.
+pub struct NetworkLink<B: BlockT, E: ExecuteInContext<B>> {
+	/// The chain-sync handle
+	pub(crate) sync: Weak<RwLock<ChainSync<B>>>,
+	/// Network context.
+	pub(crate) context: Weak<E>,
 }

-impl<'a, B: 'static + BlockT, E: 'a + ExecuteInContext<B>> SyncLink<'a, B, E> {
+impl<B: BlockT, E: ExecuteInContext<B>> NetworkLink<B, E> {
 	/// Execute closure with locked ChainSync.
-	fn with_sync<F: Fn(&mut ChainSync<B>, &mut Context<B>)>(&mut self, closure: F) {
-		let service = self.context;
-		let sync = self.chain;
+	fn with_sync<F: Fn(&mut ChainSync<B>, &mut Context<B>)>(&self, closure: F) {
+		if let (Some(sync), Some(service)) = (self.sync.upgrade(), self.context.upgrade()) {
 			service.execute_in_context(move |protocol| {
 				let mut sync = sync.write();
 				closure(&mut *sync, protocol)
 			});
 		}
+	}
 }

-impl<'a, B: 'static + BlockT, E: 'a + ExecuteInContext<B>> SyncLinkApi<B> for SyncLink<'a, B, E> {
-
-	fn chain(&self) -> &Client<B> {
-		self.client
-	}
-
-	fn block_imported(&mut self, hash: &B::Hash, number: NumberFor<B>) {
+impl<B: BlockT, E: ExecuteInContext<B>> Link<B> for NetworkLink<B, E> {
+	fn block_imported(&self, hash: &B::Hash, number: NumberFor<B>) {
 		self.with_sync(|sync, _| sync.block_imported(&hash, number))
 	}

-	fn maintain_sync(&mut self) {
+	fn maintain_sync(&self) {
 		self.with_sync(|sync, protocol| sync.maintain_sync(protocol))
 	}

-	fn useless_peer(&mut self, who: NodeIndex, reason: &str) {
+	fn useless_peer(&self, who: NodeIndex, reason: &str) {
 		self.with_sync(|_, protocol| protocol.report_peer(who, Severity::Useless(reason)))
 	}

-	fn note_useless_and_restart_sync(&mut self, who: NodeIndex, reason: &str) {
+	fn note_useless_and_restart_sync(&self, who: NodeIndex, reason: &str) {
 		self.with_sync(|sync, protocol| {
 			protocol.report_peer(who, Severity::Useless(reason));	// is this actually malign or just useless?
 			sync.restart(protocol);
 		})
 	}

-	fn restart(&mut self) {
+	fn restart(&self) {
 		self.with_sync(|sync, protocol| sync.restart(protocol))
 	}
 }
@@ -360,7 +353,8 @@ enum BlockImportError {

 /// Import a bunch of blocks.
 fn import_many_blocks<'a, B: BlockT, V: Verifier<B>>(
-	link: &mut SyncLinkApi<B>,
+	import_handle: &BlockImport<B, Error=ClientError>,
+	link: &Link<B>,
 	qdata: Option<&AsyncImportQueueData<B>>,
 	blocks: (BlockOrigin, Vec<BlockData<B>>),
 	verifier: Arc<V>
@@ -383,7 +377,7 @@ fn import_many_blocks<'a, B: BlockT, V: Verifier<B>>(
 	// Blocks in the response/drain should be in ascending order.
 	for block in blocks {
 		let import_result = import_single_block(
-			link.chain(),
+			import_handle,
 			blocks_origin.clone(),
 			block,
 			verifier.clone(),
@@ -407,7 +401,7 @@ fn import_many_blocks<'a, B: BlockT, V: Verifier<B>>(

 /// Single block import function.
 fn import_single_block<B: BlockT, V: Verifier<B>>(
-	chain: &Client<B>,
+	import_handle: &BlockImport<B,Error=ClientError>,
 	block_origin: BlockOrigin,
 	block: BlockData<B>,
 	verifier: Arc<V>
@@ -449,7 +443,7 @@ fn import_single_block<B: BlockT, V: Verifier<B>>(
 			BlockImportError::VerificationFailed(peer, msg)
 		})?;

-	match chain.import(import_block, new_authorities) {
+	match import_handle.import_block(import_block, new_authorities) {
 		Ok(ImportResult::AlreadyInChain) => {
 			trace!(target: "sync", "Block already in chain {}: {:?}", number, hash);
 			Ok(BlockImportResult::ImportedKnown(hash, number))
@@ -478,8 +472,8 @@ fn import_single_block<B: BlockT, V: Verifier<B>>(
 }

 /// Process single block import result.
-fn process_import_result<'a, B: BlockT>(
-	link: &mut SyncLinkApi<B>,
+fn process_import_result<B: BlockT>(
+	link: &Link<B>,
 	result: Result<BlockImportResult<B::Hash, <<B as BlockT>::Header as HeaderT>::Number>, BlockImportError>
 ) -> usize
 {
@@ -576,40 +570,61 @@ impl<B: BlockT> Verifier<B> for PassThroughVerifier {
 	}
 }

-#[cfg(any(test, feature = "test-helpers"))]
 /// Blocks import queue that is importing blocks in the same thread.
 /// The boolean value indicates whether blocks should be imported without instant finality.
-pub struct SyncImportQueue<B: BlockT, V: Verifier<B>>(Arc<V>, ImportCB<B>);
 #[cfg(any(test, feature = "test-helpers"))]
-impl<B: BlockT, V: Verifier<B>> SyncImportQueue<B, V> {
-	/// Create a new SyncImportQueue wrapping the given Verifier
-	pub fn new(verifier: Arc<V>) -> Self {
-		SyncImportQueue(verifier, ImportCB::new())
+pub struct SyncImportQueue<B: BlockT, V: Verifier<B>> {
+	verifier: Arc<V>,
+	link: ImportCB<B>,
+	block_import: SharedBlockImport<B>,
+}
+
+#[cfg(any(test, feature = "test-helpers"))]
+impl<B: 'static + BlockT, V: 'static + Verifier<B>> SyncImportQueue<B, V> {
+	/// Create a new SyncImportQueue wrapping the given Verifier and block import
+	/// handle.
+	pub fn new(verifier: Arc<V>, block_import: SharedBlockImport<B>) -> Self {
+		let queue = SyncImportQueue {
+			verifier,
+			link: ImportCB::new(),
+			block_import,
+		};
+
+		let v = queue.verifier.clone();
+		let import_handle = queue.block_import.clone();
+		queue.link.set(Box::new(move |origin, new_blocks| {
+			let verifier = v.clone();
+			import_many_blocks(
+				&*import_handle,
+				&NoopLink,
+				None,
+				(origin, new_blocks),
+				verifier,
+			)
+		}));
+
+		queue
 	}
 }

 #[cfg(any(test, feature = "test-helpers"))]
 impl<B: 'static + BlockT, V: 'static + Verifier<B>> ImportQueue<B> for SyncImportQueue<B, V>
 {
-	fn start<E: 'static + ExecuteInContext<B>>(
+	fn start<L: 'static + Link<B>>(
 		&self,
-		sync: Weak<RwLock<ChainSync<B>>>,
-		service: Weak<E>,
-		chain: Weak<Client<B>>
+		link: L,
 	) -> Result<(), Error> {
-		let v = self.0.clone();
-		self.1.set(Box::new(move | origin, new_blocks | {
+		let v = self.verifier.clone();
+		let import_handle = self.block_import.clone();
+		self.link.set(Box::new(move |origin, new_blocks| {
 			let verifier = v.clone();
-			match (sync.upgrade(), service.upgrade(), chain.upgrade()) {
-				(Some(sync), Some(service), Some(chain)) =>
 			import_many_blocks(
-						&mut SyncLink{chain: &sync, client: &*chain, context: &*service},
+				&*import_handle,
+				&link,
 				None,
 				(origin, new_blocks),
 				verifier,
-					),
-				_ => false
-			}
+			)
 		}));
 		Ok(())
 	}
@@ -629,7 +644,7 @@ impl<B: 'static + BlockT, V: 'static + Verifier<B>> ImportQueue<B> for SyncImpor
 	}

 	fn import_blocks(&self, origin: BlockOrigin, blocks: Vec<BlockData<B>>) {
-		self.1.call(origin, blocks);
+		self.link.call(origin, blocks);
 	}
 }

@@ -639,42 +654,49 @@ pub mod tests {
 	use message;
 	use test_client::{self, TestClient};
 	use test_client::runtime::{Block, Hash};
-	use on_demand::tests::DummyExecutor;
 	use runtime_primitives::generic::BlockId;
+	use std::cell::Cell;
 	use super::*;

-
 	struct TestLink {
-		chain: Arc<Client<Block>>,
-		imported: usize,
-		maintains: usize,
-		disconnects: usize,
-		restarts: usize,
+		imported: Cell<usize>,
+		maintains: Cell<usize>,
+		disconnects: Cell<usize>,
+		restarts: Cell<usize>,
 	}

 	impl TestLink {
 		fn new() -> TestLink {
 			TestLink {
-				chain: Arc::new(test_client::new()),
-				imported: 0,
-				maintains: 0,
-				disconnects: 0,
-				restarts: 0,
+				imported: Cell::new(0),
+				maintains: Cell::new(0),
+				disconnects: Cell::new(0),
+				restarts: Cell::new(0),
 			}
 		}

 		fn total(&self) -> usize {
-			self.imported + self.maintains + self.disconnects + self.restarts
+			self.imported.get() + self.maintains.get() + self.disconnects.get() + self.restarts.get()
 		}
 	}

-	impl SyncLinkApi<Block> for TestLink {
-		fn chain(&self) -> &Client<Block> { &*self.chain }
-		fn block_imported(&mut self, _hash: &Hash, _number: NumberFor<Block>) { self.imported += 1; }
-		fn maintain_sync(&mut self) { self.maintains += 1; }
-		fn useless_peer(&mut self, _: NodeIndex, _: &str) { self.disconnects += 1; }
-		fn note_useless_and_restart_sync(&mut self, _: NodeIndex, _: &str) { self.disconnects += 1; self.restarts += 1; }
-		fn restart(&mut self) { self.restarts += 1; }
+	impl Link<Block> for TestLink {
+		fn block_imported(&self, _hash: &Hash, _number: NumberFor<Block>) {
+			self.imported.set(self.imported.get() + 1);
+		}
+		fn maintain_sync(&self) {
+			self.maintains.set(self.maintains.get() + 1);
+		}
+		fn useless_peer(&self, _: NodeIndex, _: &str) {
+			self.disconnects.set(self.disconnects.get() + 1);
+		}
+		fn note_useless_and_restart_sync(&self, id: NodeIndex, r: &str) {
+			self.useless_peer(id, r);
+			self.restart();
+		}
+		fn restart(&self) {
+			self.restarts.set(self.restarts.get() + 1);
+		}
 	}

 	fn prepare_good_block() -> (client::Client<test_client::Backend, test_client::Executor, Block, test_client::runtime::ClientWithApi>, Hash, u64, BlockData<Block>) {
@@ -735,39 +757,39 @@ pub mod tests {

 	#[test]
 	fn process_import_result_works() {
-		let mut link = TestLink::new();
-		assert_eq!(process_import_result::<Block>(&mut link, Ok(BlockImportResult::ImportedKnown(Default::default(), 0))), 1);
+		let link = TestLink::new();
+		assert_eq!(process_import_result::<Block>(&link, Ok(BlockImportResult::ImportedKnown(Default::default(), 0))), 1);
 		assert_eq!(link.total(), 1);

-		let mut link = TestLink::new();
-		assert_eq!(process_import_result::<Block>(&mut link, Ok(BlockImportResult::ImportedKnown(Default::default(), 0))), 1);
+		let link = TestLink::new();
+		assert_eq!(process_import_result::<Block>(&link, Ok(BlockImportResult::ImportedKnown(Default::default(), 0))), 1);
 		assert_eq!(link.total(), 1);
-		assert_eq!(link.imported, 1);
+		assert_eq!(link.imported.get(), 1);

-		let mut link = TestLink::new();
-		assert_eq!(process_import_result::<Block>(&mut link, Ok(BlockImportResult::ImportedUnknown(Default::default(), 0))), 1);
+		let link = TestLink::new();
+		assert_eq!(process_import_result::<Block>(&link, Ok(BlockImportResult::ImportedUnknown(Default::default(), 0))), 1);
 		assert_eq!(link.total(), 1);
-		assert_eq!(link.imported, 1);
+		assert_eq!(link.imported.get(), 1);

-		let mut link = TestLink::new();
-		assert_eq!(process_import_result::<Block>(&mut link, Err(BlockImportError::IncompleteHeader(Some(0)))), 0);
+		let link = TestLink::new();
+		assert_eq!(process_import_result::<Block>(&link, Err(BlockImportError::IncompleteHeader(Some(0)))), 0);
 		assert_eq!(link.total(), 1);
-		assert_eq!(link.disconnects, 1);
+		assert_eq!(link.disconnects.get(), 1);

-		let mut link = TestLink::new();
-		assert_eq!(process_import_result::<Block>(&mut link, Err(BlockImportError::IncompleteJustification(Some(0)))), 0);
+		let link = TestLink::new();
+		assert_eq!(process_import_result::<Block>(&link, Err(BlockImportError::IncompleteJustification(Some(0)))), 0);
 		assert_eq!(link.total(), 1);
-		assert_eq!(link.disconnects, 1);
+		assert_eq!(link.disconnects.get(), 1);

-		let mut link = TestLink::new();
-		assert_eq!(process_import_result::<Block>(&mut link, Err(BlockImportError::UnknownParent)), 0);
+		let link = TestLink::new();
+		assert_eq!(process_import_result::<Block>(&link, Err(BlockImportError::UnknownParent)), 0);
 		assert_eq!(link.total(), 1);
-		assert_eq!(link.restarts, 1);
+		assert_eq!(link.restarts.get(), 1);

-		let mut link = TestLink::new();
-		assert_eq!(process_import_result::<Block>(&mut link, Err(BlockImportError::Error)), 0);
+		let link = TestLink::new();
+		assert_eq!(process_import_result::<Block>(&link, Err(BlockImportError::Error)), 0);
 		assert_eq!(link.total(), 1);
-		assert_eq!(link.restarts, 1);
+		assert_eq!(link.restarts.get(), 1);
 	}

 	#[test]
@@ -776,7 +798,9 @@ pub mod tests {
 		let qdata = AsyncImportQueueData::new();
 		let verifier = Arc::new(PassThroughVerifier(true));
 		qdata.is_stopping.store(true, Ordering::SeqCst);
+		let client = test_client::new();
 		assert!(!import_many_blocks(
+			&client,
 			&mut TestLink::new(),
 			Some(&qdata),
 			(BlockOrigin::File, vec![block.clone(), block]),
@@ -789,10 +813,8 @@ pub mod tests {
 		// Perform this test multiple times since it exhibits non-deterministic behavior.
 		for _ in 0..100 {
 			let verifier = Arc::new(PassThroughVerifier(true));
-			let queue = BasicQueue::new(verifier);
-			let service = Arc::new(DummyExecutor);
-			let chain = Arc::new(test_client::new());
-			queue.start(Weak::new(), Arc::downgrade(&service), Arc::downgrade(&chain) as Weak<Client<Block>>).unwrap();
+			let queue = BasicQueue::new(verifier, Arc::new(test_client::new()));
+			queue.start(TestLink::new()).unwrap();
 			drop(queue);
 		}
 	}
@@ -84,7 +84,6 @@ impl<B: BlockT + 'static, S: NetworkSpecialization<B>, H: ExHashT> Service<B, S,
 		protocol_id: ProtocolId,
 		import_queue: I,
 	) -> Result<Arc<Service<B, S, H>>, Error> {
-		let chain = params.chain.clone();
 		let import_queue = Arc::new(import_queue);
 		let handler = Arc::new(Protocol::new(
 			params.config,
@@ -98,20 +97,22 @@ impl<B: BlockT + 'static, S: NetworkSpecialization<B>, H: ExHashT> Service<B, S,
 		let registered = RegisteredProtocol::new(protocol_id, &versions[..]);
 		let (thread, network) = start_thread(params.network_config, handler.clone(), registered)?;

-		let sync = Arc::new(Service {
+		let service = Arc::new(Service {
 			network,
 			protocol_id,
 			handler,
 			bg_thread: Some(thread),
 		});

-		import_queue.start(
-			Arc::downgrade(sync.handler.sync()),
-			Arc::downgrade(&sync),
-			Arc::downgrade(&chain)
-		)?;
+		// connect the import-queue to the network service.
+		let link = ::import_queue::NetworkLink {
+			sync: Arc::downgrade(service.handler.sync()),
+			context: Arc::downgrade(&service),
+		};

-		Ok(sync)
+		import_queue.start(link)?;
+
+		Ok(service)
 	}

 	/// Called when a new block is imported by the client.
@@ -24,6 +24,7 @@ use std::sync::Arc;

 use parking_lot::RwLock;
 use client;
+use client::error::Error as ClientError;
 use client::block_builder::BlockBuilder;
 use runtime_primitives::generic::BlockId;
 use io::SyncIo;
@@ -37,7 +38,7 @@ use import_queue::{SyncImportQueue, PassThroughVerifier, Verifier};
 use consensus::BlockOrigin;
 use specialization::NetworkSpecialization;
 use consensus_gossip::ConsensusGossip;
-use import_queue::ImportQueue;
+use import_queue::{BlockImport, ImportQueue};
 use service::ExecuteInContext;
 use test_client;

@@ -138,33 +139,38 @@ pub struct TestPacket {

 pub type PeersClient = client::Client<test_client::Backend, test_client::Executor, Block, test_client::runtime::ClientWithApi>;

-pub struct Peer<V: Verifier<Block>> {
+pub struct Peer<V: Verifier<Block>, D> {
 	client: Arc<PeersClient>,
 	pub sync: Arc<Protocol<Block, DummySpecialization, Hash>>,
 	pub queue: Arc<RwLock<VecDeque<TestPacket>>>,
 	import_queue: Arc<SyncImportQueue<Block, V>>,
 	executor: Arc<DummyContextExecutor>,
+	/// Some custom data set up at initialization time.
+	pub data: D,
 }

-impl<V: 'static + Verifier<Block>> Peer<V> {
+impl<V: 'static + Verifier<Block>, D> Peer<V, D> {
 	fn new(
 		client: Arc<PeersClient>,
 		sync: Arc<Protocol<Block, DummySpecialization, Hash>>,
 		queue: Arc<RwLock<VecDeque<TestPacket>>>,
 		import_queue: Arc<SyncImportQueue<Block, V>>,
+		data: D,
 	) -> Self {
 		let executor = Arc::new(DummyContextExecutor(sync.clone(), queue.clone()));
-		Peer { client, sync, queue, import_queue, executor}
+		Peer { client, sync, queue, import_queue, executor, data }
 	}
 	/// Called after blockchain has been populated to updated current state.
 	fn start(&self) {
 		// Update the sync state to the latest chain state.
 		let info = self.client.info().expect("In-mem client does not fail");
 		let header = self.client.header(&BlockId::Hash(info.chain.best_hash)).unwrap().unwrap();
-		self.import_queue.start(
-				Arc::downgrade(&self.sync.sync()),
-				Arc::downgrade(&self.executor),
-				Arc::downgrade(&self.sync.context_data().chain)).expect("Test ImportQueue always starts");
+		let network_link = ::import_queue::NetworkLink {
+			sync: Arc::downgrade(self.sync.sync()),
+			context: Arc::downgrade(&self.executor),
+		};
+
+		self.import_queue.start(network_link).expect("Test ImportQueue always starts");
 		self.sync.on_block_imported(&mut TestIo::new(&self.queue, None), info.chain.best_hash, &header);
 	}

@@ -187,6 +193,11 @@ impl<V: 'static + Verifier<Block>> Peer<V> {
 		io.to_disconnect.clone()
 	}

+	fn with_io<'a, F, U>(&'a self, f: F) -> U where F: FnOnce(&mut TestIo<'a>) -> U {
+		let mut io = TestIo::new(&self.queue, None);
+		f(&mut io)
+	}
+
 	/// Produce the next pending message to send to another peer.
 	fn pending_message(&self) -> Option<TestPacket> {
 		self.flush();
@@ -229,25 +240,39 @@ impl<V: 'static + Verifier<Block>> Peer<V> {

 	/// Add blocks to the peer -- edit the block before adding
 	pub fn generate_blocks<F>(&self, count: usize, origin: BlockOrigin, mut edit_block: F)
-	where F: FnMut(&mut BlockBuilder<Block, PeersClient>)
+		where F: FnMut(BlockBuilder<Block, PeersClient>) -> Block
 	{
-		for _ in 0 .. count {
-			let mut builder = self.client.new_block().unwrap();
-			edit_block(&mut builder);
-			let block = builder.bake().unwrap();
+		use blocks::BlockData;
+
+		for _  in 0..count {
+			let builder = self.client.new_block().unwrap();
+			let block = edit_block(builder);
 			let hash = block.header.hash();
 			trace!("Generating {}, (#{}, parent={})", hash, block.header.number, block.header.parent_hash);
 			let header = block.header.clone();
-			self.client.justify_and_import(origin, block).unwrap();
-			self.sync.on_block_imported(&mut TestIo::new(&self.queue, None), hash, &header);
+
+			// NOTE: if we use a non-synchronous queue in the test-net in the future,
+			// this may not work.
+		 	self.import_queue.import_blocks(origin, vec![BlockData {
+				origin: None,
+				block: ::message::BlockData::<Block> {
+					hash,
+					header: Some(header),
+					body: Some(block.extrinsics),
+					receipt: None,
+					message_queue: None,
+					justification: Some(Vec::new()),
+				},
+			}]);
 		}
+
 	}

 	/// Push blocks to the peer (simplified: with or without a TX)
 	pub fn push_blocks(&self, count: usize, with_tx: bool) {
 		let mut nonce = 0;
 		if with_tx {
-			self.generate_blocks(count, BlockOrigin::File, |builder| {
+			self.generate_blocks(count, BlockOrigin::File, |mut builder| {
 				let transfer = Transfer {
 					from: Keyring::Alice.to_raw_public().into(),
 					to: Keyring::Alice.to_raw_public().into(),
@@ -257,9 +282,10 @@ impl<V: 'static + Verifier<Block>> Peer<V> {
 				let signature = Keyring::from_raw_public(transfer.from.to_fixed_bytes()).unwrap().sign(&transfer.encode()).into();
 				builder.push(Extrinsic { transfer, signature }).unwrap();
 				nonce = nonce + 1;
+				builder.bake().unwrap()
 			});
 		} else {
-			self.generate_blocks(count, BlockOrigin::File, |_| ());
+			self.generate_blocks(count, BlockOrigin::File, |builder| builder.bake().unwrap());
 		}
 	}

@@ -292,6 +318,7 @@ impl TransactionPool<Hash, Block> for EmptyTransactionPool {

 pub trait TestNetFactory: Sized {
 	type Verifier: 'static + Verifier<Block>;
+	type PeerData: Default;

 	/// These two need to be implemented!
 	fn from_config(config: &ProtocolConfig) -> Self;
@@ -299,13 +326,20 @@ pub trait TestNetFactory: Sized {


 	/// Get reference to peer.
-	fn peer(&self, i: usize) -> &Peer<Self::Verifier>;
-	fn peers(&self) -> &Vec<Arc<Peer<Self::Verifier>>>;
-	fn mut_peers<F: Fn(&mut Vec<Arc<Peer<Self::Verifier>>>)>(&mut self, closure: F );
+	fn peer(&self, i: usize) -> &Peer<Self::Verifier, Self::PeerData>;
+	fn peers(&self) -> &Vec<Arc<Peer<Self::Verifier, Self::PeerData>>>;
+	fn mut_peers<F: Fn(&mut Vec<Arc<Peer<Self::Verifier, Self::PeerData>>>)>(&mut self, closure: F);

 	fn started(&self) -> bool;
 	fn set_started(&mut self, now: bool);

+	/// Get custom block import handle for fresh client, along with peer data.
+	fn make_block_import(&self, client: Arc<PeersClient>)
+		-> (Arc<BlockImport<Block,Error=ClientError> + Send + Sync>, Self::PeerData)
+	{
+		(client, Default::default())
+	}
+
 	fn default_config() -> ProtocolConfig {
 		ProtocolConfig::default()
 	}
@@ -326,7 +360,9 @@ pub trait TestNetFactory: Sized {
 		let client = Arc::new(test_client::new());
 		let tx_pool = Arc::new(EmptyTransactionPool);
 		let verifier = self.make_verifier(client.clone(), config);
-		let import_queue = Arc::new(SyncImportQueue::new(verifier));
+		let (block_import, data) = self.make_block_import(client.clone());
+
+		let import_queue = Arc::new(SyncImportQueue::new(verifier, block_import));
 		let specialization = DummySpecialization {
 			gossip: ConsensusGossip::new(),
 		};
@@ -343,7 +379,8 @@ pub trait TestNetFactory: Sized {
 			client,
 			Arc::new(sync),
 			Arc::new(RwLock::new(VecDeque::new())),
-			import_queue
+			import_queue,
+			data,
 		));

 		self.mut_peers(|peers| {
@@ -453,12 +490,13 @@ pub trait TestNetFactory: Sized {
 }

 pub struct TestNet {
-	peers: Vec<Arc<Peer<PassThroughVerifier>>>,
+	peers: Vec<Arc<Peer<PassThroughVerifier, ()>>>,
 	started: bool
 }

 impl TestNetFactory for TestNet {
 	type Verifier = PassThroughVerifier;
+	type PeerData = ();

 	/// Create new test network with peers and given config.
 	fn from_config(_config: &ProtocolConfig) -> Self {
@@ -474,15 +512,15 @@ impl TestNetFactory for TestNet {
 		Arc::new(PassThroughVerifier(false))
 	}

-	fn peer(&self, i: usize) -> &Peer<Self::Verifier> {
+	fn peer(&self, i: usize) -> &Peer<Self::Verifier, ()> {
 		&self.peers[i]
 	}

-	fn peers(&self) -> &Vec<Arc<Peer<Self::Verifier>>> {
+	fn peers(&self) -> &Vec<Arc<Peer<Self::Verifier, ()>>> {
 		&self.peers
 	}

-	fn mut_peers<F: Fn(&mut Vec<Arc<Peer<Self::Verifier>>>)>(&mut self, closure: F ) {
+	fn mut_peers<F: Fn(&mut Vec<Arc<Peer<Self::Verifier, ()>>>)>(&mut self, closure: F ) {
 		closure(&mut self.peers);
 	}

@@ -94,7 +94,10 @@ fn own_blocks_are_announced() {
 	::env_logger::init().ok();
 	let mut net = TestNet::new(3);
 	net.sync(); // connect'em
-	net.peer(0).generate_blocks(1, BlockOrigin::Own, |_| ());
+	net.peer(0).generate_blocks(1, BlockOrigin::Own, |builder| builder.bake().unwrap());
+
+	let header = net.peer(0).client().header(&BlockId::Number(1)).unwrap().unwrap();
+	net.peer(0).with_io(|io| net.peer(0).sync.on_block_imported(io, header.hash(), &header));
 	net.sync();
 	assert_eq!(net.peer(0).client.backend().blockchain().info().unwrap().best_number, 1);
 	assert_eq!(net.peer(1).client.backend().blockchain().info().unwrap().best_number, 1);
@@ -21,7 +21,7 @@ use futures::Future;

 use runtime_primitives::generic::{SignedBlock, BlockId};
 use runtime_primitives::traits::{As, Block, Header};
-use network::import_queue::{ImportQueue, BlockData};
+use network::import_queue::{ImportQueue, Link, BlockData};
 use network::message;

 use consensus_common::BlockOrigin;
@@ -90,8 +90,12 @@ pub fn export_blocks<F, E, W>(config: FactoryFullConfiguration<F>, exit: E, mut
 pub fn import_blocks<F, E, R>(config: FactoryFullConfiguration<F>, exit: E, mut input: R) -> error::Result<()>
 	where F: ServiceFactory, E: Future<Item=(),Error=()> + Send + 'static, R: Read,
 {
+	struct DummyLink;
+	impl<B: Block> Link<B> for DummyLink { }
+
 	let client = new_client::<F>(&config)?;
 	let queue = components::FullComponents::<F>::build_import_queue(&config, client.clone())?;
+	queue.start(DummyLink)?;

 	let (exit_send, exit_recv) = std::sync::mpsc::channel();
 	::std::thread::spawn(move || {
@@ -472,8 +472,8 @@ impl<C: Components> network::TransactionPool<ComponentExHash<C>, ComponentBlock<
 ///         // The first one is for the initializing the full import queue and the second for the
 ///         // light import queue.
 /// 		ImportQueue = BasicQueue<Block, NoneVerifier>
-/// 			{ |_, _| Ok(BasicQueue::new(Arc::new(NoneVerifier {}))) }
-/// 			{ |_, _| Ok(BasicQueue::new(Arc::new(NoneVerifier {}))) },
+/// 			{ |_, client| Ok(BasicQueue::new(Arc::new(NoneVerifier {}, client))) }
+/// 			{ |_, client| Ok(BasicQueue::new(Arc::new(NoneVerifier {}, client))) },
 /// 	}
 /// }
 /// ```
@@ -33,7 +33,6 @@ extern crate sr_io as runtime_io;
 #[macro_use]
 extern crate sr_version as runtime_version;

-
 #[cfg(test)]
 #[macro_use]
 extern crate hex_literal;
@@ -14,7 +14,8 @@ parity-codec-derive = "2.1"
 sr-std = { path = "../../core/sr-std" }
 srml-support = { path = "../../srml/support" }
 substrate-primitives = { path = "../../core/primitives" }
-substrate-client = { path = "../../core/client", optional = true }
+substrate-fg-primitives = { path = "../../core/finality-grandpa/primitives" }
+substrate-client = { path = "../../core/client" }
 substrate-keyring = { path = "../../core/keyring" }
 srml-balances = { path = "../../srml/balances" }
 srml-consensus = { path = "../../srml/consensus" }
@@ -57,5 +58,6 @@ std = [
 	"serde_derive",
 	"serde/std",
 	"safe-mix/std",
-	"substrate-client",
+	"substrate-client/std",
+	"substrate-fg-primitives/std",
 ]
@@ -56,6 +56,7 @@ extern crate srml_upgrade_key as upgrade_key;
 #[macro_use]
 extern crate sr_version as version;
 extern crate node_primitives;
+extern crate substrate_fg_primitives;

 #[cfg(feature = "std")]
 use codec::{Encode, Decode};
@@ -72,7 +73,7 @@ use client::runtime_api::ApiExt;
 use runtime_primitives::ApplyResult;
 use runtime_primitives::transaction_validity::TransactionValidity;
 use runtime_primitives::generic;
-use runtime_primitives::traits::{Convert, BlakeTwo256, Block as BlockT};
+use runtime_primitives::traits::{Convert, BlakeTwo256, Block as BlockT, DigestFor, NumberFor};
 #[cfg(feature = "std")]
 use runtime_primitives::traits::ApiRef;
 #[cfg(feature = "std")]
@@ -84,6 +85,7 @@ use council::seats as council_seats;
 #[cfg(any(feature = "std", test))]
 use version::NativeVersion;
 use substrate_primitives::OpaqueMetadata;
+use substrate_fg_primitives::{runtime::GrandpaApi, ScheduledChange};

 #[cfg(any(feature = "std", test))]
 pub use runtime_primitives::BuildStorage;
@@ -395,6 +397,19 @@ impl client::runtime_api::Metadata<GBlock> for ClientWithApi {
 	}
 }

+#[cfg(feature = "std")]
+impl substrate_fg_primitives::GrandpaApi<GBlock> for ClientWithApi {
+	fn grandpa_pending_change(&self, at: &GBlockId, digest: &DigestFor<GBlock>)
+		-> Result<Option<ScheduledChange<NumberFor<GBlock>>>, client::error::Error> {
+		self.call_api_at(at, "grandpa_pending_change", digest)
+	}
+
+	fn grandpa_authorities(&self, at: &GBlockId)
+		-> Result<Vec<(AuthorityId, u64)>, client::error::Error> {
+		self.call_api_at(at, "grandpa_authorities", &())
+	}
+}
+
 impl_runtime_apis! {
 	impl Core<Block> for Runtime {
 		fn version() -> RuntimeVersion {
@@ -447,4 +462,16 @@ impl_runtime_apis! {
 			Executive::validate_transaction(tx)
 		}
 	}
+
+
+	impl GrandpaApi<Block> for ClientWithApi {
+		fn grandpa_pending_change(digest: DigestFor<Block>)
+			-> Option<ScheduledChange<NumberFor<Block>>> {
+			unimplemented!("Robert, where is the impl?")
+		}
+
+		fn grandpa_authorities() -> Vec<(SessionKey, u64)> {
+			unimplemented!("Robert, where is the impl?")
+		}
+	}
 }
@@ -526,6 +526,7 @@ dependencies = [
 "srml-treasury 0.1.0",
 "srml-upgrade-key 0.1.0",
 "substrate-client 0.1.0",
+ "substrate-fg-primitives 0.1.0",
 "substrate-primitives 0.1.0",
 ]

@@ -1272,6 +1273,18 @@ dependencies = [
 "wasmi 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "substrate-fg-primitives"
+version = "0.1.0"
+dependencies = [
+ "parity-codec 2.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "parity-codec-derive 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sr-primitives 0.1.0",
+ "sr-std 0.1.0",
+ "substrate-client 0.1.0",
+ "substrate-primitives 0.1.0",
+]
+
 [[package]]
 name = "substrate-keyring"
 version = "0.1.0"
@@ -12,6 +12,7 @@ safe-mix = { version = "1.0", default-features = false }
 parity-codec-derive = { version = "2.1" }
 parity-codec = { version = "2.1", default-features = false }
 substrate-primitives = { path = "../../../core/primitives", default-features = false }
+substrate-fg-primitives = { path = "../../../core/finality-grandpa/primitives", default-features = false }
 substrate-client = { path = "../../../core/client", default-features = false }
 sr-std = { path = "../../../core/sr-std", default-features = false }
 srml-support = { path = "../../../srml/support", default-features = false }
@@ -38,6 +39,7 @@ std = [
 	"parity-codec/std",
 	"substrate-primitives/std",
 	"substrate-client/std",
+	"substrate-fg-primitives/std",
 	"sr-std/std",
 	"srml-support/std",
 	"srml-balances/std",