Fix the incorrect size calculation logic of FileSink. (#9429)

Summary:
I was writing unit tests for the Textfile writer internally and found
that data written to `MemorySink` may be overwritten.

I investigated the reason and found that `FileSink::writeImpl` can accept multiple buffers.
 https://github.com/facebookincubator/velox/blob/main/velox/dwio/common/FileSink.cpp#L65-L80
Every time the data of a buffer is written, we should update `FileSink#size_`
 instead of updating after writing all buffers. Because `MemorySink::write`
relies on `FileSink#size_` to write data to `MemorySink#data_`.
https://github.com/facebookincubator/velox/blob/main/velox/dwio/common/FileSink.cpp#L184-L189

CC: mbasmanova xiaoxmeng

Pull Request resolved: #9429

Reviewed By: amitkdutta, kewang1024

Differential Revision: D56004384

Pulled By: xiaoxmeng

fbshipit-source-id: c824c5e481866abef12f99d570d41a852bb8b2e0

velox/dwio/common/FileSink.cpp

@@ -66,13 +66,15 @@ void FileSink::writeImpl(
     std::vector<DataBuffer<char>>& buffers,
     const std::function<uint64_t(const DataBuffer<char>&)>& callback) {
   DWIO_ENSURE(!isClosed(), "Cannot write to closed sink.");
-  uint64_t size = 0;
+  const uint64_t oldSize = size_;
   for (auto& buf : buffers) {
-    size += callback(buf);
+    // NOTE: we need to update 'size_' after each 'callback' invocation as some
+    // file sink implementation like MemorySink depends on the updated 'size_'
+    // for new write.
+    size_ += callback(buf);
   }
-  size_ += size;
   if (stats_ != nullptr) {
-    stats_->incRawBytesWritten(size);
+    stats_->incRawBytesWritten(size_ - oldSize);
   }
   // Writing buffer is treated as transferring ownership. So clearing the
   // buffers after all buffers are written.

velox/dwio/common/tests/CMakeLists.txt

@@ -25,6 +25,7 @@ add_executable(
   ExecutorBarrierTest.cpp
   OnDemandUnitLoaderTests.cpp
   LocalFileSinkTest.cpp
+  MemorySinkTest.cpp
   LoggedExceptionTest.cpp
   ParallelForTest.cpp
   RangeTests.cpp

velox/dwio/common/tests/MemorySinkTest.cpp

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * 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 "velox/dwio/common/FileSink.h"
+
+#include <gtest/gtest.h>
+
+namespace facebook::velox::dwio::common {
+
+class MemorySinkTest : public testing::Test {
+ protected:
+  static void SetUpTestCase() {
+    memory::MemoryManager::testingSetInstance({});
+  }
+
+  std::shared_ptr<velox::memory::MemoryPool> pool_{
+      memory::memoryManager()->addLeafPool()};
+};
+
+TEST_F(MemorySinkTest, create) {
+  std::string chars("abcdefghijklmnopqrst");
+  std::vector<DataBuffer<char>> buffers;
+
+  // Add 'abcdefghij' to first buffer
+  buffers.emplace_back(*pool_);
+  buffers.back().append(0, chars.data(), 10);
+
+  // Add 'klmnopqrst' to second buffer
+  buffers.emplace_back(*pool_);
+  buffers.back().append(0, chars.data() + 10, 10);
+
+  ASSERT_EQ(buffers.size(), 2);
+
+  auto memorySink = std::make_unique<MemorySink>(
+      1024, dwio::common::FileSink::Options{.pool = pool_.get()});
+
+  ASSERT_TRUE(memorySink->isBuffered());
+  // Write data to MemorySink.
+  memorySink->write(buffers);
+  ASSERT_EQ(memorySink->size(), chars.length());
+  ASSERT_EQ(memorySink->data(), chars);
+  memorySink->close();
+}
+} // namespace facebook::velox::dwio::common