create helper class to read blob data

atom/browser/atom_blob_reader.h

@@ -0,0 +1,80 @@
+// Copyright (c) 2016 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef ATOM_BROWSER_ATOM_BLOB_READER_H_
+#define ATOM_BROWSER_ATOM_BLOB_READER_H_
+
+#include <string>
+
+#include "base/callback.h"
+
+namespace content {
+class ChromeBlobStorageContext;
+}
+
+namespace net {
+class IOBuffer;
+}
+
+namespace storage {
+class BlobDataHandle;
+class BlobReader;
+class FileSystemContext;
+}
+
+namespace v8 {
+template <class T>
+class Local;
+class Value;
+}
+
+namespace atom {
+
+// A class to keep track of the blob context. All methods,
+// except Ctor are expected to be called on IO thread.
+class AtomBlobReader {
+ public:
+  using CompletionCallback = base::Callback<void(v8::Local<v8::Value>)>;
+
+  AtomBlobReader(content::ChromeBlobStorageContext* blob_context,
+                 storage::FileSystemContext* file_system_context);
+  ~AtomBlobReader();
+
+  void StartReading(
+      const std::string& uuid,
+      const AtomBlobReader::CompletionCallback& callback);
+
+ private:
+  // A self-destroyed helper class to read the blob data.
+  // Must be accessed on IO thread.
+  class BlobReadHelper {
+   public:
+    using CompletionCallback = base::Callback<void(char*, int)>;
+
+    BlobReadHelper(std::unique_ptr<storage::BlobReader> blob_reader,
+                   const BlobReadHelper::CompletionCallback& callback);
+    ~BlobReadHelper();
+
+    void Read();
+
+   private:
+    void DidCalculateSize(int result);
+    void DidReadBlobData(const scoped_refptr<net::IOBuffer>& blob_data,
+                         int bytes_read);
+
+    std::unique_ptr<storage::BlobReader> blob_reader_;
+    BlobReadHelper::CompletionCallback completion_callback_;
+
+    DISALLOW_COPY_AND_ASSIGN(BlobReadHelper);
+  };
+
+  scoped_refptr<content::ChromeBlobStorageContext> blob_context_;
+  scoped_refptr<storage::FileSystemContext> file_system_context_;
+
+  DISALLOW_COPY_AND_ASSIGN(AtomBlobReader);
+};
+
+}  // namespace atom
+
+#endif  // ATOM_BROWSER_ATOM_BLOB_READER_H_