[testnet2] Store output sum (#1043)

* block sums and reworked block validation
read and write block_sums
refactor validate on both block and txhashset
write block_sum on fast sync
we store the kernel_sum (need to account for the offset)

* block_sums

* rustfmt

* cleanup

chain/src/types.rs

@@ -17,6 +17,7 @@
 use std::{error, fmt, io};
 
 use util::secp;
+use util::secp_static;
 use util::secp::pedersen::Commitment;
 
 use core::core::hash::{Hash, Hashed};
@@ -328,6 +329,15 @@ pub trait ChainStore: Send + Sync {
 	/// Deletes a block marker associated with the provided hash
 	fn delete_block_marker(&self, bh: &Hash) -> Result<(), store::Error>;
 
+	/// Save block sums for the given block hash.
+	fn save_block_sums(&self, bh: &Hash, marker: &BlockSums) -> Result<(), store::Error>;
+
+	/// Get block sums for the given block hash.
+	fn get_block_sums(&self, bh: &Hash) -> Result<BlockSums, store::Error>;
+
+	/// Delete block sums for the given block hash.
+	fn delete_block_sums(&self, bh: &Hash) -> Result<(), store::Error>;
+
 	/// Saves the provided block header at the corresponding height. Also check
 	/// the consistency of the height chain in store by assuring previous
 	/// headers are also at their respective heights.
@@ -389,3 +399,42 @@ impl Default for BlockMarker {
 		}
 	}
 }
+
+/// The output_sum and kernel_sum for a given block.
+/// This is used to validate the next block being processed by applying
+/// the inputs, outputs, kernels and kernel_offset from the new block
+/// and checking everything sums correctly.
+#[derive(Debug, Clone)]
+pub struct BlockSums {
+	/// The total output sum so far.
+	pub output_sum: Commitment,
+	/// The total kernel sum so far.
+	pub kernel_sum: Commitment,
+}
+
+impl Writeable for BlockSums {
+	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
+		writer.write_fixed_bytes(&self.output_sum)?;
+		writer.write_fixed_bytes(&self.kernel_sum)?;
+		Ok(())
+	}
+}
+
+impl Readable for BlockSums {
+	fn read(reader: &mut Reader) -> Result<BlockSums, ser::Error> {
+		Ok(BlockSums {
+			output_sum: Commitment::read(reader)?,
+			kernel_sum: Commitment::read(reader)?,
+		})
+	}
+}
+
+impl Default for BlockSums {
+	fn default() -> BlockSums {
+		let zero_commit = secp_static::commit_to_zero_value();
+		BlockSums {
+			output_sum: zero_commit.clone(),
+			kernel_sum: zero_commit.clone(),
+		}
+	}
+}