Merge pull request #2134 from kcalvinalvin/2024-03-07-make-duplicate-…

…entries-on-mapslice-impossible

blockchain: fix a bug where a duplicate entry is possible in the mapslice

blockchain/utxocache.go

@@ -99,14 +99,19 @@ func (ms *mapSlice) put(op wire.OutPoint, entry *UtxoEntry, totalEntryMemory uin
 	ms.mtx.Lock()
 	defer ms.mtx.Unlock()
 
-	for i, maxNum := range ms.maxEntries {
+	// Look for the key in the maps.
+	for i := range ms.maxEntries {
 		m := ms.maps[i]
 		_, found := m[op]
 		if found {
 			// If the key is found, overwrite it.
 			m[op] = entry
 			return // Return as we were successful in adding the entry.
 		}
+	}
+
+	for i, maxNum := range ms.maxEntries {
+		m := ms.maps[i]
 		if len(m) >= maxNum {
 			// Don't try to insert if the map already at max since
 			// that'll force the map to allocate double the memory it's

blockchain/utxocache_test.go

@@ -69,6 +69,26 @@ func TestMapSlice(t *testing.T) {
 			t.Fatalf("expected len of %d, got %d", len(m), ms.length())
 		}
 
+		// Delete the first element in the first map.
+		ms.delete(test.keys[0])
+		delete(m, test.keys[0])
+
+		// Try to insert the last element in the mapslice again.
+		ms.put(test.keys[len(test.keys)-1], &UtxoEntry{}, 0)
+		m[test.keys[len(test.keys)-1]] = &UtxoEntry{}
+
+		// Check that the duplicate didn't make it in.
+		if len(m) != ms.length() {
+			t.Fatalf("expected len of %d, got %d", len(m), ms.length())
+		}
+
+		ms.put(test.keys[0], &UtxoEntry{}, 0)
+		m[test.keys[0]] = &UtxoEntry{}
+
+		if len(m) != ms.length() {
+			t.Fatalf("expected len of %d, got %d", len(m), ms.length())
+		}
+
 		for _, key := range test.keys {
 			expected, found := m[key]
 			if !found {