Fix light sync deadlock (blocks import queue) (#260)

* fix light sync deadlock

* some more docs

Author: svyatonik

substrate/network/src/chain.rs

@@ -25,7 +25,7 @@ use runtime_primitives::bft::Justification;
 /// Local client abstraction for the network.
 pub trait Client<Block: BlockT>: Send + Sync {
 	/// Import a new block. Parent is supposed to be existing in the blockchain.
-	fn import(&self, is_best: bool, header: Block::Header, justification: Justification<Block::Hash>, body: Option<Vec<Block::Extrinsic>>) -> Result<ImportResult, Error>;
+	fn import(&self, origin: BlockOrigin, header: Block::Header, justification: Justification<Block::Hash>, body: Option<Vec<Block::Extrinsic>>) -> Result<ImportResult, Error>;
 
 	/// Get blockchain info.
 	fn info(&self) -> Result<ClientInfo<Block>, Error>;
@@ -54,10 +54,9 @@ impl<B, E, Block> Client<Block> for SubstrateClient<B, E, Block> where
 	E: CallExecutor<Block> + Send + Sync + 'static,
 	Block: BlockT,
 {
-	fn import(&self, is_best: bool, header: Block::Header, justification: Justification<Block::Hash>, body: Option<Vec<Block::Extrinsic>>) -> Result<ImportResult, Error> {
+	fn import(&self, origin: BlockOrigin, header: Block::Header, justification: Justification<Block::Hash>, body: Option<Vec<Block::Extrinsic>>) -> Result<ImportResult, Error> {
 		// TODO: defer justification check.
 		let justified_header = self.check_justification(header, justification.into())?;
-		let origin = if is_best { BlockOrigin::NetworkBroadcast } else { BlockOrigin::NetworkInitialSync };
 		(self as &SubstrateClient<B, E, Block>).import_block(origin, justified_header, body)
 	}
 

substrate/network/src/error.rs

@@ -16,12 +16,14 @@
 
 //! Polkadot service possible errors.
 
+use std::io::Error as IoError;
 use network_libp2p::Error as NetworkError;
 use client;
 
 error_chain! {
 	foreign_links {
 		Network(NetworkError) #[doc = "Devp2p error."];
+		Io(IoError) #[doc = "IO error."];
 	}
 
 	links {