Fix bad case of trying to rewind to block at height 0 (#271)

* bad case of trying to rewind to block header height 0
* rewind_to_genesis appears to work
* do not assume genesis block at height 0 is empty, pass full block in to rewind, check for last output and kernel, use index 0 if block is empty

chain/src/pipe.rs

@@ -237,14 +237,17 @@ fn validate_block(
 			}
 		}
 
-		// rewind the sum trees up the forking block, providing the height of the
-  // forked block and the last commitment we want to rewind to
 		let forked_block = ctx.store.get_block(&current)?;
-		if forked_block.header.height > 0 {
-			let last_output = &forked_block.outputs[forked_block.outputs.len() - 1];
-			let last_kernel = &forked_block.kernels[forked_block.kernels.len() - 1];
-			ext.rewind(forked_block.header.height, last_output, last_kernel)?;
-		}
+
+		debug!(
+			LOGGER,
+			"validate_block: forked_block: {} at {}",
+			forked_block.header.hash(),
+			forked_block.header.height,
+		);
+
+		// rewind the sum trees up to the forking block
+		ext.rewind(&forked_block)?;
 
 		// apply all forked blocks, including this new one
 		for h in hashes {
@@ -259,6 +262,26 @@ fn validate_block(
 		|| kernel_root.hash != b.header.kernel_root
 	{
 		ext.dump(false);
+
+		debug!(
+			LOGGER,
+			"validate_block: utxo roots - {:?}, {:?}",
+			utxo_root.hash,
+			b.header.utxo_root,
+		);
+		debug!(
+			LOGGER,
+			"validate_block: rproof roots - {:?}, {:?}",
+			rproof_root.hash,
+			b.header.range_proof_root,
+		);
+		debug!(
+			LOGGER,
+			"validate_block: kernel roots - {:?}, {:?}",
+			kernel_root.hash,
+			b.header.kernel_root,
+		);
+
 		return Err(Error::InvalidRoot);
 	}
 

chain/src/sumtree.rs

@@ -22,8 +22,9 @@ use std::sync::Arc;
 
 use util::secp::pedersen::{RangeProof, Commitment};
 
-use core::core::{Block, Output, SumCommit, TxKernel};
+use core::core::{Block, SumCommit, TxKernel};
 use core::core::pmmr::{Backend, HashSum, NoSum, Summable, PMMR};
+use core::core::hash::Hashed;
 use grin_store;
 use grin_store::sumtree::PMMRBackend;
 use types::ChainStore;
@@ -297,11 +298,33 @@ impl<'a> Extension<'a> {
 
 	/// Rewinds the MMRs to the provided position, given the last output and
 	/// last kernel of the block we want to rewind to.
-	pub fn rewind(&mut self, height: u64, output: &Output, kernel: &TxKernel) -> Result<(), Error> {
-		let out_pos_rew = self.commit_index.get_output_pos(&output.commitment())?;
-		let kern_pos_rew = self.commit_index.get_kernel_pos(&kernel.excess)?;
+	pub fn rewind(&mut self, block: &Block) -> Result<(), Error> {
+		debug!(
+			LOGGER,
+			"Rewind sumtrees to header {} at {}",
+			block.header.hash(),
+			block.header.height,
+		);
+
+		let out_pos_rew = match block.outputs.last() {
+			Some(output) => self.commit_index.get_output_pos(&output.commitment())?,
+			None => 0,
+		};
+
+		let kern_pos_rew = match block.kernels.last() {
+			Some(kernel) => self.commit_index.get_kernel_pos(&kernel.excess)?,
+			None => 0,
+		};
+
+		debug!(
+			LOGGER,
+			"Rewind sumtrees to output pos: {}, kernel pos: {}",
+			out_pos_rew,
+			kern_pos_rew,
+		);
+
+		let height = block.header.height;
 
-		debug!(LOGGER, "Rewind sumtrees to {}", out_pos_rew);
 		self.output_pmmr
 			.rewind(out_pos_rew, height as u32)
 			.map_err(&Error::SumTreeErr)?;
@@ -311,6 +334,7 @@ impl<'a> Extension<'a> {
 		self.kernel_pmmr
 			.rewind(kern_pos_rew, height as u32)
 			.map_err(&Error::SumTreeErr)?;
+
 		self.dump(true);
 		Ok(())
 	}

grin/src/adapters.rs

@@ -167,8 +167,8 @@ impl NetAdapter for NetToChainAdapter {
 
 		debug!(
 			LOGGER,
-			"locate_headers: {:?}",
-			header,
+			"locate_headers: common header: {:?}",
+			header.hash(),
 		);
 
 		// looks like we know one, getting as many following headers as allowed

grin/src/sync.rs

@@ -247,10 +247,9 @@ impl Syncer {
 		if let Some(p) = peer {
 			debug!(
 				LOGGER,
-				"Asking peer {} for more block headers starting from {} at {}.",
+				"Asking peer {} for more block headers, locator: {:?}",
 				p.info.addr,
-				tip.last_block_h,
-				tip.height
+				locator,
 			);
 			p.send_header_request(locator)?;
 		} else {
@@ -288,6 +287,11 @@ impl Syncer {
 			})
 			.collect::<Vec<_>>();
 		heights.append(&mut tail);
+
+		// Include the genesis block (height 0) here as a fallback to guarantee
+		// both nodes share at least one common header hash in the locator
+		heights.push(0);
+
 		debug!(LOGGER, "Loc heights: {:?}", heights);
 
 		// Iteratively travel the header chain back from our head and retain the