Recover from corrupt block maps

internal/files/blockmap.go

@@ -179,6 +179,18 @@ func (f *BlockFinder) Iterate(hash []byte, iterFn func(string, string, uint32) b
 	return false
 }
 
+// A method for repairing incorrect blockmap entries, removes the old entry
+// and replaces it with a new entry for the given block
+func (f *BlockFinder) Fix(folder, file string, index uint32, oldHash, newHash []byte) error {
+	buf := make([]byte, 4)
+	binary.BigEndian.PutUint32(buf, uint32(index))
+
+	batch := new(leveldb.Batch)
+	batch.Delete(toBlockKey(oldHash, folder, file))
+	batch.Put(toBlockKey(newHash, folder, file), buf)
+	return f.db.Write(batch, nil)
+}
+
 // m.blockKey returns a byte slice encoding the following information:
 //	   keyTypeBlock (1 byte)
 //	   folder (64 bytes)

internal/files/blockmap_test.go

@@ -235,3 +235,34 @@ func TestBlockFinderLookup(t *testing.T) {
 
 	f1.Flags = 0
 }
+
+func TestBlockFinderFix(t *testing.T) {
+	db, f := setup()
+
+	iterFn := func(folder, file string, index uint32) bool {
+		return true
+	}
+
+	m := NewBlockMap(db, "folder1")
+	err := m.Add([]protocol.FileInfo{f1})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !f.Iterate(f1.Blocks[0].Hash, iterFn) {
+		t.Fatal("Block not found")
+	}
+
+	err = f.Fix("folder1", f1.Name, 0, f1.Blocks[0].Hash, f2.Blocks[0].Hash)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if f.Iterate(f1.Blocks[0].Hash, iterFn) {
+		t.Fatal("Unexpected block")
+	}
+
+	if !f.Iterate(f2.Blocks[0].Hash, iterFn) {
+		t.Fatal("Block not found")
+	}
+}