expected nbits method & support

db/src/block_provider.rs

@@ -14,6 +14,9 @@ pub trait BlockProvider {
 	/// resolves header bytes by block reference (number/hash)
 	fn block_header_bytes(&self, block_ref: BlockRef) -> Option<Bytes>;
 
+	/// resolves header bytes by block reference (number/hash)
+	fn block_header(&self, block_ref: BlockRef) -> Option<chain::BlockHeader>;
+
 	/// resolves deserialized block body by block reference (number/hash)
 	fn block(&self, block_ref: BlockRef) -> Option<chain::Block>;
 

db/src/storage.rs

@@ -40,6 +40,9 @@ const MAX_FORK_ROUTE_PRESET: usize = 128;
 pub trait Store : BlockProvider + BlockStapler + TransactionProvider + TransactionMetaProvider {
 	/// get best block
 	fn best_block(&self) -> Option<BestBlock>;
+
+	/// get best header
+	fn best_header(&self) -> Option<chain::BlockHeader>;
 }
 
 /// Blockchain storage with rocksdb database
@@ -165,7 +168,6 @@ impl Storage {
 		})
 	}
 
-
 	/// update transactions metadata in the specified database transaction
 	fn update_transactions_meta(&self, context: &mut UpdateContext, number: u32, accepted_txs: &[chain::Transaction])
 		-> Result<(), Error>
@@ -385,6 +387,12 @@ impl BlockProvider for Storage {
 		self.resolve_hash(block_ref).and_then(|h| self.get(COL_BLOCK_HEADERS, &*h))
 	}
 
+	fn block_header(&self, block_ref: BlockRef) -> Option<chain::BlockHeader> {
+		self.block_header_bytes(block_ref).map(
+			|bytes| deserialize::<_, chain::BlockHeader>(bytes.as_ref())
+				.expect("Error deserializing header, possible db corruption"))
+	}
+
 	fn block_transaction_hashes(&self, block_ref: BlockRef) -> Vec<H256> {
 		self.resolve_hash(block_ref)
 			.map(|h| self.block_transaction_hashes_by_hash(&h))
@@ -596,6 +604,12 @@ impl Store for Storage {
 	fn best_block(&self) -> Option<BestBlock> {
 		self.best_block.read().clone()
 	}
+
+	fn best_header(&self) -> Option<chain::BlockHeader> {
+		self.best_block.read().as_ref().and_then(
+			|bb| Some(self.block_header_by_hash(&bb.hash).expect("Best block exists but no such header. Race condition?")),
+		)
+	}
 }
 
 #[cfg(test)]

db/src/test_storage.rs

@@ -81,6 +81,13 @@ impl BlockProvider for TestStorage {
 			.map(|ref block| serialization::serialize(block.header()))
 	}
 
+	fn block_header(&self, block_ref: BlockRef) -> Option<chain::BlockHeader> {
+		let data = self.data.read();
+		self.resolve_hash(block_ref)
+			.and_then(|ref h| data.blocks.get(h))
+			.map(|ref block| block.header().clone())
+	}
+
 	fn block_transaction_hashes(&self, block_ref: BlockRef) -> Vec<H256> {
 		let data = self.data.read();
 		self.resolve_hash(block_ref)
@@ -174,5 +181,11 @@ impl Store for TestStorage {
 	fn best_block(&self) -> Option<BestBlock> {
 		self.data.read().best_block.clone()
 	}
+
+	fn best_header(&self) -> Option<chain::BlockHeader> {
+		self.data.read().best_block.as_ref().and_then(
+			|bb| Some(self.block_header(BlockRef::Hash(bb.hash.clone())).expect("Best block exists but no such header. Race condition?"))
+		)
+	}
 }
 

verification/src/chain_verifier.rs

@@ -54,6 +54,12 @@ impl ChainVerifier {
 	}
 
 	fn ordered_verify(&self, block: &chain::Block, at_height: u32) -> Result<(), Error> {
+		// check that difficulty matches the adjusted level
+		if let Some(expected_nbits) = self.expected_nbits() {
+			if !self.skip_pow && expected_nbits != block.header().nbits {
+				return Err(Error::Difficulty);
+			}
+		}
 
 		let coinbase_spends = block.transactions()[0].total_spends();
 
@@ -258,6 +264,22 @@ impl ChainVerifier {
 			},
 		}
 	}
+
+	fn expected_nbits(&self) -> Option<u32> {
+
+		let best_header = match self.store.best_header() {
+			Some(bb) => bb,
+			None => { return None; }
+		};
+
+		if self.store.best_block().expect("At least genesis should exist at this point").number < 2016 {
+			return Some(best_header.nbits);
+		}
+
+		// todo: calculate difficulty adjustment
+
+		Some(best_header.nbits)
+	}
 }
 
 impl Verify for ChainVerifier {