Implement Cancel() for MemoryFileStreamWriter

In preparation of shared unit tests between the various FileStreamWriter
implementations.

Merge this before https://crrev.com/c/2422682

Change-Id: I56e4a3f5973a13a2bb39108114be5462296ff8e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425429Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Austin Sullivan <asully@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810731}

storage/browser/file_system/local_file_stream_writer_unittest.cc

@@ -24,6 +24,12 @@
 
 namespace storage {
 
+namespace {
+void NeverCalled(int unused) {
+  ADD_FAILURE();
+}
+}  // namespace
+
 class LocalFileStreamWriterTest : public testing::Test {
  public:
   LocalFileStreamWriterTest() : file_thread_("TestFileThread") {}
@@ -75,10 +81,6 @@ class LocalFileStreamWriterTest : public testing::Test {
   base::ScopedTempDir temp_dir_;
 };
 
-void NeverCalled(int unused) {
-  ADD_FAILURE();
-}
-
 TEST_F(LocalFileStreamWriterTest, Write) {
   base::FilePath path = CreateFileWithContent("file_a", std::string());
   std::unique_ptr<LocalFileStreamWriter> writer(CreateWriter(path, 0));

storage/browser/file_system/memory_file_stream_writer.cc

@@ -34,6 +34,7 @@ MemoryFileStreamWriter::MemoryFileStreamWriter(
       file_path_(file_path),
       offset_(initial_offset) {
   DCHECK(memory_file_util_.MaybeValid());
+  has_pending_operation_ = false;
 }
 
 MemoryFileStreamWriter::~MemoryFileStreamWriter() = default;
@@ -41,6 +42,11 @@ MemoryFileStreamWriter::~MemoryFileStreamWriter() = default;
 int MemoryFileStreamWriter::Write(net::IOBuffer* buf,
                                   int buf_len,
                                   net::CompletionOnceCallback callback) {
+  DCHECK(!has_pending_operation_);
+  DCHECK(cancel_callback_.is_null());
+
+  has_pending_operation_ = true;
+
   task_runner_->PostTaskAndReplyWithResult(
       FROM_HERE,
       base::BindOnce(
@@ -66,17 +72,43 @@ int MemoryFileStreamWriter::Write(net::IOBuffer* buf,
 void MemoryFileStreamWriter::OnWriteCompleted(
     net::CompletionOnceCallback callback,
     int result) {
+  DCHECK(has_pending_operation_);
+
+  if (CancelIfRequested())
+    return;
+  has_pending_operation_ = false;
+
   if (result > 0)
     offset_ += result;
 
   std::move(callback).Run(result);
 }
 
-int MemoryFileStreamWriter::Cancel(net::CompletionOnceCallback /*callback*/) {
-  return net::ERR_UNEXPECTED;
+int MemoryFileStreamWriter::Cancel(net::CompletionOnceCallback callback) {
+  if (!has_pending_operation_)
+    return net::ERR_UNEXPECTED;
+
+  DCHECK(!callback.is_null());
+  cancel_callback_ = std::move(callback);
+  return net::ERR_IO_PENDING;
 }
 
 int MemoryFileStreamWriter::Flush(net::CompletionOnceCallback /*callback*/) {
+  DCHECK(!has_pending_operation_);
+  DCHECK(cancel_callback_.is_null());
+
   return net::OK;
 }
+
+bool MemoryFileStreamWriter::CancelIfRequested() {
+  DCHECK(has_pending_operation_);
+
+  if (cancel_callback_.is_null())
+    return false;
+
+  has_pending_operation_ = false;
+  std::move(cancel_callback_).Run(net::OK);
+  return true;
+}
+
 }  // namespace storage

storage/browser/file_system/memory_file_stream_writer.h

@@ -37,14 +37,20 @@ class COMPONENT_EXPORT(STORAGE_BROWSER) MemoryFileStreamWriter
 
   void OnWriteCompleted(net::CompletionOnceCallback callback, int result);
 
+  // Stops the in-flight operation and calls |cancel_callback_| if it has been
+  // set by Cancel() for the current operation.
+  bool CancelIfRequested();
+
   base::WeakPtr<ObfuscatedFileUtilMemoryDelegate> memory_file_util_;
 
   const scoped_refptr<base::TaskRunner> task_runner_;
   const base::FilePath file_path_;
   int64_t offset_;
 
-  base::WeakPtrFactory<MemoryFileStreamWriter> weak_factory_{this};
+  bool has_pending_operation_;
+  net::CompletionOnceCallback cancel_callback_;
 
+  base::WeakPtrFactory<MemoryFileStreamWriter> weak_factory_{this};
   DISALLOW_COPY_AND_ASSIGN(MemoryFileStreamWriter);
 };
 

storage/browser/file_system/memory_file_stream_writer_unittest.cc

@@ -16,6 +16,7 @@
 #include "base/test/task_environment.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
+#include "net/base/test_completion_callback.h"
 #include "storage/browser/file_system/file_stream_test_utils.h"
 #include "storage/browser/file_system/file_stream_writer.h"
 #include "storage/browser/file_system/obfuscated_file_util_memory_delegate.h"
@@ -23,6 +24,12 @@
 
 namespace storage {
 
+namespace {
+void NeverCalled(int unused) {
+  ADD_FAILURE();
+}
+}  // namespace
+
 class MemoryFileStreamWriterTest : public testing::Test {
  public:
   MemoryFileStreamWriterTest() {}
@@ -159,6 +166,25 @@ TEST_F(MemoryFileStreamWriterTest, CancelAfterFinishedOperation) {
   EXPECT_EQ("foo", GetFileContent(path));
 }
 
+TEST_F(MemoryFileStreamWriterTest, CancelWrite) {
+  base::FilePath path = Path("file_a");
+  bool created;
+  EXPECT_EQ(base::File::FILE_OK, file_util()->EnsureFileExists(path, &created));
+
+  std::unique_ptr<FileStreamWriter> writer(CreateWriter(path, 0));
+
+  scoped_refptr<net::StringIOBuffer> buffer(
+      base::MakeRefCounted<net::StringIOBuffer>("xxx"));
+  int result =
+      writer->Write(buffer.get(), buffer->size(), base::BindOnce(&NeverCalled));
+  ASSERT_EQ(net::ERR_IO_PENDING, result);
+
+  net::TestCompletionCallback callback;
+  writer->Cancel(callback.callback());
+  int cancel_result = callback.WaitForResult();
+  EXPECT_EQ(net::OK, cancel_result);
+}
+
 TEST_F(MemoryFileStreamWriterTest, FlushBeforeWriting) {
   base::FilePath path = Path("file_a");
   bool created;