Punish offline validators, aura-style (#1216)

* make offline-reporting infrastructure more generic

* add a listener-trait for watching when the timestamp has been set

* prevent inclusion of empty offline reports

* add test for exclusion

* generate aura-offline reports

* ability to slash many times for being offline "multiple" times

* Logic for punishing validators for missing aura steps

* stub tests

* pave way for verification of timestamp vs slot

* alter aura import queue to wait for timestamp

* check timestamp matches seal

* do inherent check properly

* service compiles

* all tests compile

* test srml-aura logic

* aura tests pass

* everything builds

* some more final tweaks to block authorship for aura

* switch to manual delays before step

* restore substrate-consensus-aura to always std and address grumbles

* update some state roots in executor tests

* node-executor tests pass

* get most tests passing

* address grumbles

substrate/core/client/src/backend.rs

@@ -79,6 +79,20 @@ pub trait BlockImportOperation<Block, H> where
 		where I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>;
 }
 
+/// Provides access to an auxiliary database.
+pub trait AuxStore {
+	/// Insert auxiliary data into key-value store. Deletions occur after insertions.
+	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<()>;
+	/// Query auxiliary data from key-value store.
+	fn get_aux(&self, key: &[u8]) -> error::Result<Option<Vec<u8>>>;
+}
+
 /// Client backend. Manages the data layer.
 ///
 /// Note on state pruning: while an object from `state_at` is alive, the state
@@ -87,7 +101,7 @@ pub trait BlockImportOperation<Block, H> where
 ///
 /// The same applies for live `BlockImportOperation`s: while an import operation building on a parent `P`
 /// is alive, the state for `P` should not be pruned.
-pub trait Backend<Block, H>: Send + Sync where
+pub trait Backend<Block, H>: AuxStore + Send + Sync where
 	Block: BlockT,
 	H: Hasher<Out=Block::Hash>,
 {
@@ -117,10 +131,22 @@ pub trait Backend<Block, H>: Send + Sync where
 	/// Attempts to revert the chain by `n` blocks. Returns the number of blocks that were
 	/// successfully reverted.
 	fn revert(&self, n: NumberFor<Block>) -> error::Result<NumberFor<Block>>;
+
 	/// Insert auxiliary data into key-value store.
-	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<()>;
+	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<()>
+	{
+		AuxStore::insert_aux(self, insert, delete)
+	}
 	/// Query auxiliary data from key-value store.
-	fn get_aux(&self, key: &[u8]) -> error::Result<Option<Vec<u8>>>;
+	fn get_aux(&self, key: &[u8]) -> error::Result<Option<Vec<u8>>> {
+		AuxStore::get_aux(self, key)
+	}
 }
 
 /// Mark for all Backend implementations, that are making use of state data, stored locally.