Tx kernel entry (#1957)

* Wrap tx kernels in tx kernel entries when storing them in the MMR.
Decouples the storage impl of kernels.

* rustfmt

chain/src/chain.rs

@@ -28,7 +28,9 @@ use lru_cache::LruCache;
 use core::core::hash::{Hash, Hashed, ZERO_HASH};
 use core::core::merkle_proof::MerkleProof;
 use core::core::verifier_cache::VerifierCache;
-use core::core::{Block, BlockHeader, BlockSums, Output, OutputIdentifier, Transaction, TxKernel};
+use core::core::{
+	Block, BlockHeader, BlockSums, Output, OutputIdentifier, Transaction, TxKernelEntry,
+};
 use core::global;
 use core::pow;
 use error::{Error, ErrorKind};
@@ -966,7 +968,7 @@ impl Chain {
 	}
 
 	/// as above, for kernels
-	pub fn get_last_n_kernel(&self, distance: u64) -> Vec<(Hash, TxKernel)> {
+	pub fn get_last_n_kernel(&self, distance: u64) -> Vec<(Hash, TxKernelEntry)> {
 		let mut txhashset = self.txhashset.write();
 		txhashset.last_n_kernel(distance)
 	}

chain/src/txhashset/rewindable_kernel_view.rs

@@ -15,7 +15,7 @@
 //! Lightweight readonly view into kernel MMR for convenience.
 
 use core::core::pmmr::RewindablePMMR;
-use core::core::{BlockHeader, TxKernel};
+use core::core::{BlockHeader, TxKernelEntry};
 
 use error::{Error, ErrorKind};
 use grin_store::pmmr::PMMRBackend;
@@ -23,7 +23,7 @@ use store::Batch;
 
 /// Rewindable (but readonly) view of the kernel set (based on kernel MMR).
 pub struct RewindableKernelView<'a> {
-	pmmr: RewindablePMMR<'a, TxKernel, PMMRBackend<TxKernel>>,
+	pmmr: RewindablePMMR<'a, TxKernelEntry, PMMRBackend<TxKernelEntry>>,
 	batch: &'a Batch<'a>,
 	header: BlockHeader,
 }
@@ -31,7 +31,7 @@ pub struct RewindableKernelView<'a> {
 impl<'a> RewindableKernelView<'a> {
 	/// Build a new readonly kernel view.
 	pub fn new(
-		pmmr: RewindablePMMR<'a, TxKernel, PMMRBackend<TxKernel>>,
+		pmmr: RewindablePMMR<'a, TxKernelEntry, PMMRBackend<TxKernelEntry>>,
 		batch: &'a Batch,
 		header: BlockHeader,
 	) -> RewindableKernelView<'a> {

chain/src/txhashset/txhashset.rs

@@ -29,7 +29,9 @@ use core::core::committed::Committed;
 use core::core::hash::{Hash, Hashed};
 use core::core::merkle_proof::MerkleProof;
 use core::core::pmmr::{self, ReadonlyPMMR, RewindablePMMR, DBPMMR, PMMR};
-use core::core::{Block, BlockHeader, Input, Output, OutputFeatures, OutputIdentifier, TxKernel};
+use core::core::{
+	Block, BlockHeader, Input, Output, OutputFeatures, OutputIdentifier, TxKernel, TxKernelEntry,
+};
 use core::global;
 use core::ser::{PMMRIndexHashable, PMMRable};
 
@@ -119,7 +121,7 @@ pub struct TxHashSet {
 
 	output_pmmr_h: PMMRHandle<OutputIdentifier>,
 	rproof_pmmr_h: PMMRHandle<RangeProof>,
-	kernel_pmmr_h: PMMRHandle<TxKernel>,
+	kernel_pmmr_h: PMMRHandle<TxKernelEntry>,
 
 	// chain store used as index of commitments to MMR positions
 	commit_index: Arc<ChainStore>,
@@ -205,8 +207,8 @@ impl TxHashSet {
 	}
 
 	/// as above, for kernels
-	pub fn last_n_kernel(&mut self, distance: u64) -> Vec<(Hash, TxKernel)> {
+	pub fn last_n_kernel(&mut self, distance: u64) -> Vec<(Hash, TxKernelEntry)> {
-		let kernel_pmmr: PMMR<TxKernel, _> =
+		let kernel_pmmr: PMMR<TxKernelEntry, _> =
 			PMMR::at(&mut self.kernel_pmmr_h.backend, self.kernel_pmmr_h.last_pos);
 		kernel_pmmr.get_last_n_insertions(distance)
 	}
@@ -247,7 +249,7 @@ impl TxHashSet {
 			PMMR::at(&mut self.output_pmmr_h.backend, self.output_pmmr_h.last_pos);
 		let rproof_pmmr: PMMR<RangeProof, _> =
 			PMMR::at(&mut self.rproof_pmmr_h.backend, self.rproof_pmmr_h.last_pos);
-		let kernel_pmmr: PMMR<TxKernel, _> =
+		let kernel_pmmr: PMMR<TxKernelEntry, _> =
 			PMMR::at(&mut self.kernel_pmmr_h.backend, self.kernel_pmmr_h.last_pos);
 
 		TxHashSetRoots {
@@ -733,7 +735,7 @@ pub struct Extension<'a> {
 	header_pmmr: DBPMMR<'a, BlockHeader, HashOnlyMMRBackend>,
 	output_pmmr: PMMR<'a, OutputIdentifier, PMMRBackend<OutputIdentifier>>,
 	rproof_pmmr: PMMR<'a, RangeProof, PMMRBackend<RangeProof>>,
-	kernel_pmmr: PMMR<'a, TxKernel, PMMRBackend<TxKernel>>,
+	kernel_pmmr: PMMR<'a, TxKernelEntry, PMMRBackend<TxKernelEntry>>,
 
 	/// Rollback flag.
 	rollback: bool,
@@ -766,7 +768,7 @@ impl<'a> Committed for Extension<'a> {
 		for n in 1..self.kernel_pmmr.unpruned_size() + 1 {
 			if pmmr::is_leaf(n) {
 				if let Some(kernel) = self.kernel_pmmr.get_data(n) {
-					commitments.push(kernel.excess);
+					commitments.push(kernel.excess());
 				}
 			}
 		}
@@ -951,14 +953,14 @@ impl<'a> Extension<'a> {
 	/// Push kernel onto MMR (hash and data files).
 	fn apply_kernel(&mut self, kernel: &TxKernel) -> Result<(), Error> {
 		self.kernel_pmmr
-			.push(kernel.clone())
+			.push(TxKernelEntry::from(kernel.clone()))
 			.map_err(&ErrorKind::TxHashSetErr)?;
 		Ok(())
 	}
 
 	fn apply_header(&mut self, header: &BlockHeader) -> Result<(), Error> {
 		self.header_pmmr
-			.push(&header)
+			.push(header)
 			.map_err(&ErrorKind::TxHashSetErr)?;
 		Ok(())
 	}

core/src/core/transaction.rs

@@ -250,13 +250,67 @@ impl TxKernel {
 	}
 }
 
-impl FixedLength for TxKernel {
+/// Wrapper around a tx kernel used when maintaining them in the MMR.
+#[derive(Serialize, Deserialize, Debug, Clone)]
+pub struct TxKernelEntry {
+	/// The underlying tx kernel.
+	pub kernel: TxKernel,
+}
+
+impl Writeable for TxKernelEntry {
+	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
+		ser_multiwrite!(
+			writer,
+			[write_u8, self.kernel.features.bits()],
+			[write_u64, self.kernel.fee],
+			[write_u64, self.kernel.lock_height],
+			[write_fixed_bytes, &self.kernel.excess]
+		);
+		self.kernel.excess_sig.write(writer)?;
+		Ok(())
+	}
+}
+
+impl Readable for TxKernelEntry {
+	fn read(reader: &mut Reader) -> Result<TxKernelEntry, ser::Error> {
+		let features =
+			KernelFeatures::from_bits(reader.read_u8()?).ok_or(ser::Error::CorruptedData)?;
+		let kernel = TxKernel {
+			features: features,
+			fee: reader.read_u64()?,
+			lock_height: reader.read_u64()?,
+			excess: Commitment::read(reader)?,
+			excess_sig: secp::Signature::read(reader)?,
+		};
+		Ok(TxKernelEntry { kernel })
+	}
+}
+
+impl TxKernelEntry {
+	/// The excess on the underlying tx kernel.
+	pub fn excess(&self) -> Commitment {
+		self.kernel.excess
+	}
+
+	/// Verify the underlying tx kernel.
+	pub fn verify(&self) -> Result<(), Error> {
+		self.kernel.verify()
+	}
+}
+
+impl From<TxKernel> for TxKernelEntry {
+	fn from(kernel: TxKernel) -> Self {
+		TxKernelEntry { kernel }
+	}
+}
+
+impl FixedLength for TxKernelEntry {
 	const LEN: usize = 17 // features plus fee and lock_height
 		+ secp::constants::PEDERSEN_COMMITMENT_SIZE
 		+ secp::constants::AGG_SIGNATURE_SIZE;
 }
 
-impl PMMRable for TxKernel {}
+impl PMMRable for TxKernelEntry {}
 
 /// TransactionBody is a common abstraction for transaction and block
 #[derive(Serialize, Deserialize, Debug, Clone)]