simplify kernel_pos index, need undo list per block to handle rewind/…

…undo

this is conceptually similar to output_pos but we support duplicates rather than spending to remove

chain/src/chain.rs

@@ -1107,7 +1107,7 @@ impl Chain {
 
 		// Remove historical blocks from the db unless we are running in archive mode.
 		if !self.archive_mode {
-			self.remove_historical_blocks(&header_pmmr, &mut batch)?;
+			self.remove_historical_blocks(&header_pmmr, &batch)?;
 		}
 
 		// Compact the txhashset itself (rewriting the pruned backend files).
@@ -1154,7 +1154,7 @@ impl Chain {
 	/// Get the position of the kernel if it exists in the kernel_pos index.
 	/// The index is limited to 14 days of recent kernels.
 	pub fn get_kernel_pos(&self, excess: Commitment) -> Result<u64, Error> {
-		Ok(self.txhashset.read().get_kernel_pos(excess)?)
+		self.txhashset.read().get_kernel_pos(excess)
 	}
 
 	/// outputs by insertion index

chain/src/store.rs

@@ -38,6 +38,7 @@ const KERNEL_POS_PREFIX: u8 = b'k';
 const BLOCK_INPUT_BITMAP_PREFIX: u8 = b'B';
 const BLOCK_SUMS_PREFIX: u8 = b'M';
 const BLOCK_SPENT_PREFIX: u8 = b'S';
+const BLOCK_KERNEL_UNDO_PREFIX: u8 = b'U';
 
 /// All chain-related database operations
 pub struct ChainStore {
@@ -208,6 +209,16 @@ impl<'a> Batch<'a> {
 		Ok(())
 	}
 
+	/// We maintain an "undo" index for each full block to allow the kernel_pos
+	/// to be easily reverted during rewind.
+	/// We allow duplicate kernels so we need to know what to revert the kernel_pos
+	/// index to if we "undo" a kernel when rewinding a block.
+	pub fn save_kernel_undo_index(&self, h: &Hash, pos: &Vec<CommitPos>) -> Result<(), Error> {
+		self.db
+			.put_ser(&to_key(BLOCK_KERNEL_UNDO_PREFIX, &mut h.to_vec())[..], pos)?;
+		Ok(())
+	}
+
 	/// Migrate a block stored in the db by serializing it using the provided protocol version.
 	/// Block may have been read using a previous protocol version but we do not actually care.
 	pub fn migrate_block(&self, b: &Block, version: ProtocolVersion) -> Result<(), Error> {

chain/src/txhashset/txhashset.rs

@@ -348,20 +348,13 @@ impl TxHashSet {
 		Ok(self.commit_index.get_output_pos(&commit)?)
 	}
 
-	/// TODO - This needs to be a multi-step process.
-	/// TODO - Rename this.
-	/// First we need to look the entry up in the index.
-	/// This entry will be a vec of (pos, height).
-	/// The entry may be an empty vec.
-	/// We then need to filter this vec by height (discounting anything beyond current head)
-	/// and then actually look the kernels up, filtering out any that do not align with the index.
-	///
 	/// Get the position of the kernel if it exists in the kernel_pos index.
 	/// The index is limited to 14 days of recent kernels.
-	pub fn get_kernel_pos(&self, excess: Commitment) -> Result<Vec<(TxKernel, u64)>, Error> {
-		let pos = self.commit_index.get_kernel_pos_height(&excess);
-		// .map(|entry| entry)?;
-		Ok(pos)
+	pub fn get_kernel_pos(&self, excess: Commitment) -> Result<u64, Error> {
+		Ok(self
+			.commit_index
+			.get_kernel_pos_height(&excess)
+			.map(|x| x.1)?)
 	}
 
 	/// build a new merkle proof for the given position.