create helper class to read blob data

atom/browser/atom_blob_reader.cc

@@ -0,0 +1,133 @@
+// Copyright (c) 2016 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "atom/browser/atom_blob_reader.h"
+
+#include "content/browser/blob_storage/chrome_blob_storage_context.h"
+#include "content/public/browser/browser_thread.h"
+#include "net/base/io_buffer.h"
+#include "net/base/net_errors.h"
+#include "storage/browser/blob/blob_data_handle.h"
+#include "storage/browser/blob/blob_reader.h"
+#include "storage/browser/blob/blob_storage_context.h"
+#include "storage/browser/fileapi/file_system_context.h"
+
+#include "atom/common/node_includes.h"
+
+using content::BrowserThread;
+
+namespace atom {
+
+namespace {
+
+void RunCallbackInUI(
+    const AtomBlobReader::CompletionCallback& callback,
+    char* blob_data,
+    int size) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  v8::Isolate* isolate = v8::Isolate::GetCurrent();
+  v8::Locker locker(isolate);
+  v8::HandleScope handle_scope(isolate);
+  if (blob_data) {
+    v8::Local<v8::Value> buffer = node::Buffer::New(isolate,
+        blob_data, static_cast<size_t>(size)).ToLocalChecked();
+    callback.Run(buffer);
+  } else {
+    callback.Run(v8::Null(isolate));
+  }
+}
+
+}  // namespace
+
+AtomBlobReader::AtomBlobReader(
+    content::ChromeBlobStorageContext* blob_context,
+    storage::FileSystemContext* file_system_context)
+    : blob_context_(blob_context),
+      file_system_context_(file_system_context) {
+}
+
+AtomBlobReader::~AtomBlobReader() {
+}
+
+void AtomBlobReader::StartReading(
+    const std::string& uuid,
+    const AtomBlobReader::CompletionCallback& completion_callback) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  auto blob_data_handle =
+      blob_context_->context()->GetBlobDataFromUUID(uuid);
+  auto callback = base::Bind(&RunCallbackInUI,
+                             completion_callback);
+  if (!blob_data_handle) {
+    BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
+        base::Bind(callback, nullptr, 0));
+    return;
+  }
+
+  auto blob_reader = blob_data_handle->CreateReader(
+      file_system_context_.get(),
+      BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE).get());
+  BlobReadHelper* blob_read_helper =
+      new BlobReadHelper(std::move(blob_reader), callback);
+  blob_read_helper->Read();
+}
+
+AtomBlobReader::BlobReadHelper::BlobReadHelper(
+    std::unique_ptr<storage::BlobReader> blob_reader,
+    const BlobReadHelper::CompletionCallback& callback)
+    : blob_reader_(std::move(blob_reader)),
+      completion_callback_(callback) {
+}
+
+AtomBlobReader::BlobReadHelper::~BlobReadHelper() {
+}
+
+void AtomBlobReader::BlobReadHelper::Read() {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  storage::BlobReader::Status size_status = blob_reader_->CalculateSize(
+      base::Bind(&AtomBlobReader::BlobReadHelper::DidCalculateSize,
+                 base::Unretained(this)));
+  if (size_status != storage::BlobReader::Status::IO_PENDING)
+    DidCalculateSize(net::OK);
+}
+
+void AtomBlobReader::BlobReadHelper::DidCalculateSize(int result) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  if (result != net::OK) {
+    DidReadBlobData(nullptr, 0);
+    return;
+  }
+
+  uint64_t total_size = blob_reader_->total_size();
+  int bytes_read = 0;
+  scoped_refptr<net::IOBuffer> blob_data =
+      new net::IOBuffer(static_cast<size_t>(total_size));
+  auto callback = base::Bind(&AtomBlobReader::BlobReadHelper::DidReadBlobData,
+                             base::Unretained(this),
+                             base::RetainedRef(blob_data));
+  storage::BlobReader::Status read_status = blob_reader_->Read(
+      blob_data.get(),
+      total_size,
+      &bytes_read,
+      callback);
+  if (read_status != storage::BlobReader::Status::IO_PENDING)
+    callback.Run(bytes_read);
+}
+
+void AtomBlobReader::BlobReadHelper::DidReadBlobData(
+    const scoped_refptr<net::IOBuffer>& blob_data,
+    int size) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  char* data = new char[size];
+  memcpy(data, blob_data->data(), size);
+  BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
+      base::Bind(completion_callback_, data, size));
+  delete this;
+}
+
+}  // namespace atom