Implement VABCPartitionWriter

Test: treehugger

Change-Id: I7ec47adba0bc095879989b43ec642ea6a7852ab6
diff --git a/payload_consumer/snapshot_extent_writer.cc b/payload_consumer/snapshot_extent_writer.cc
new file mode 100644
index 0000000..882d1f7
--- /dev/null
+++ b/payload_consumer/snapshot_extent_writer.cc
@@ -0,0 +1,54 @@
+//
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#include "update_engine/payload_consumer/snapshot_extent_writer.h"
+
+#include <algorithm>
+#include <cstdint>
+
+#include <libsnapshot/cow_writer.h>
+
+#include "update_engine/update_metadata.pb.h"
+
+namespace chromeos_update_engine {
+SnapshotExtentWriter::SnapshotExtentWriter(
+    android::snapshot::ICowWriter* cow_writer)
+    : cow_writer_(cow_writer) {
+  CHECK_NE(cow_writer, nullptr);
+}
+
+SnapshotExtentWriter::~SnapshotExtentWriter() {
+  CHECK(buffer_.empty());
+}
+
+bool SnapshotExtentWriter::Init(
+    FileDescriptorPtr /*fd*/,
+    const google::protobuf::RepeatedPtrField<Extent>& extents,
+    uint32_t /*block_size*/) {
+  // TODO(zhangkelvin) Implement this
+  return true;
+}
+
+// Returns true on success.
+// This will construct a COW_REPLACE operation and forward it to CowWriter. It
+// is important that caller does not perform SOURCE_COPY operation on this
+// class, otherwise raw data will be stored. Caller should find ways to use
+// COW_COPY whenever possible.
+bool SnapshotExtentWriter::Write(const void* bytes, size_t count) {
+  // TODO(zhangkelvin) Implement this
+  return true;
+}
+
+}  // namespace chromeos_update_engine