Backport upstream #563: Detect reorgs that occur while the server is down

common/cache.go

@@ -221,6 +221,12 @@ func NewBlockCache(dbPath string, chainName string, startHeight int, syncFromHei
 		c.nextBlock++
 	}
 	Log.Info("Done reading ", c.nextBlock-c.firstBlock, " blocks from disk cache")
+
+	// Initialize latestHash from the last block on disk so that the first
+	// block ingested after a restart is checked against the cache tip.
+	// Otherwise, a reorg that occurred while the server was down would go
+	// undetected, permanently leaving orphan blocks in the cache.
+	c.setLatestHash()
 	return c
 }
 

common/cache_test.go

@@ -81,6 +81,21 @@ func TestCache(t *testing.T) {
 	if cache.nextBlock != 289466 {
 		t.Fatal("unexpected nextBlock height")
 	}
+	// The hash of the top block must be restored from disk so that a reorg
+	// that occurred while the server was down can be detected (the first
+	// block ingested after a restart must connect to the cache tip).
+	if cache.latestHash == hash32.Nil {
+		t.Fatal("latestHash not initialized after restart")
+	}
+	if cache.latestHash != hash32.FromSlice(compacts[5].Hash) {
+		t.Fatal("unexpected latestHash after restart")
+	}
+	if cache.HashMatch(hash32.FromSlice(compacts[4].Hash)) {
+		t.Fatal("HashMatch should reject a non-connecting block after restart")
+	}
+	if !cache.HashMatch(hash32.FromSlice(compacts[5].Hash)) {
+		t.Fatal("HashMatch should accept a block connecting to the cache tip")
+	}
 	reorgCache(t)
 
 	// Reorg to before the first block moves back to only the first block