From e1c8dc5a3a8b556fabaea8e4db77656763d72ceb Mon Sep 17 00:00:00 2001
From: Gary Yu <gairy.yu@gmail.com>
Date: Thu, 20 Sep 2018 07:29:24 +0800
Subject: [PATCH] fix: reset sync_head to header_head on initial transition to
 HeaderSync (#1531)

* fix for bug #1524, reset sync_head to header_head on initial transition to HeaderSync.
* using @antiochp fix solution in #1539
---
 chain/src/chain.rs       |  8 ++++++++
 chain/src/pipe.rs        | 10 ++++++++--
 servers/src/grin/sync.rs | 34 +++++++++++++++++++++++++---------
 3 files changed, 41 insertions(+), 11 deletions(-)

diff --git a/chain/src/chain.rs b/chain/src/chain.rs
index d64e66984..835938a7a 100644
--- a/chain/src/chain.rs
+++ b/chain/src/chain.rs
@@ -931,6 +931,14 @@ impl Chain {
 			.block_exists(&h)
 			.map_err(|e| ErrorKind::StoreErr(e, "chain block exists".to_owned()).into())
 	}
+
+	/// reset sync_head to header_head
+	pub fn init_sync_head(&self, header_head: &Tip) -> Result<(), Error> {
+		let batch = self.store.batch()?;
+		batch.init_sync_head(header_head)?;
+		batch.commit()?;
+		Ok(())
+	}
 }
 
 fn setup_head(
diff --git a/chain/src/pipe.rs b/chain/src/pipe.rs
index 7f2e1b9c5..bd144bf3d 100644
--- a/chain/src/pipe.rs
+++ b/chain/src/pipe.rs
@@ -215,9 +215,15 @@ pub fn sync_block_header(
 	validate_header(&bh, sync_ctx)?;
 	add_block_header(bh, batch)?;
 
-	// now update the header_head (if new header with most work) and the sync_head
-	// (always)
+	// Update header_head (but only if this header increases our total known work).
+	// i.e. Only if this header is now the head of the current "most work" chain.
 	update_header_head(bh, header_ctx, batch)?;
+
+	// Update sync_head regardless of total work.
+	// We may be syncing a long fork that will *eventually* increase the work
+	// and become the "most work" chain.
+	// header_head and sync_head will diverge in this situation until we switch to
+	// a single "most work" chain.
 	update_sync_head(bh, sync_ctx, batch)
 }
 
diff --git a/servers/src/grin/sync.rs b/servers/src/grin/sync.rs
index 8d63feb10..9dedd1269 100644
--- a/servers/src/grin/sync.rs
+++ b/servers/src/grin/sync.rs
@@ -141,18 +141,34 @@ pub fn run_sync(
 
 						// run the header sync every 10s
 						if si.header_sync_due(&header_head) {
-							header_sync(peers.clone(), chain.clone(), &mut history_locators);
-
 							let status = sync_state.status();
-							match status {
-								SyncStatus::TxHashsetDownload => (),
-								_ => {
-									sync_state.update(SyncStatus::HeaderSync {
-										current_height: header_head.height,
-										highest_height: si.highest_height,
-									});
+							let update_sync_state = match status {
+								SyncStatus::TxHashsetDownload => false,
+								SyncStatus::NoSync | SyncStatus::Initial => {
+									// Reset sync_head to header_head on transition to HeaderSync,
+									// but ONLY on initial transition to HeaderSync state.
+									let sync_head = chain.get_sync_head().unwrap();
+									debug!(
+										LOGGER,
+										"sync: initial transition to HeaderSync. sync_head: {} at {}, reset to: {} at {}",
+										sync_head.hash(),
+										sync_head.height,
+										header_head.hash(),
+										header_head.height,
+									);
+									chain.init_sync_head(&header_head).unwrap();
+									history_locators.clear();
+									true
 								}
+								_ => true,
 							};
+							if update_sync_state {
+								sync_state.update(SyncStatus::HeaderSync {
+									current_height: header_head.height,
+									highest_height: si.highest_height,
+								});
+							}
+							header_sync(peers.clone(), chain.clone(), &mut history_locators);
 						}
 
 						if fast_sync_enabled {