net: Move data reading functionalities from UploadElement to UploadElementReader

net/base/upload_element_reader.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_BASE_UPLOAD_ELEMENT_READER_H_
+#define NET_BASE_UPLOAD_ELEMENT_READER_H_
+
+#include "base/basictypes.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+class UploadElement;
+
+// An interface to read an upload data element.
+class NET_EXPORT UploadElementReader {
+ public:
+  UploadElementReader() {}
+  virtual ~UploadElementReader() {}
+
+  // Creates an appropriate UploadElementReader instance for the given element.
+  static UploadElementReader* Create(const UploadElement& element);
+
+  // Initializes the instance synchronously.
+  virtual int InitSync() = 0;
+
+  // Returns the byte-length of the element.  For files that do not exist, 0
+  // is returned.  This is done for consistency with Mozilla.
+  virtual uint64 GetContentLength() const = 0;
+
+  // Returns the number of bytes remaining to read.
+  virtual uint64 BytesRemaining() const = 0;
+
+  // Returns true if the upload element is entirely in memory.
+  // The default implementation returns false.
+  virtual bool IsInMemory() const;
+
+  // Reads up to |buf_length| bytes synchronously. Returns the number of bytes

[willchan no longer on Chromium, 2012/09/06 01:06:01]

Is it valid to read 0 bytes? What happens when BytesRemaining() == 0 and
ReadSync() is called?

[hashimoto, 2012/09/06 01:55:39]

No behavior change from the current code.

Reading 0 bytes results in returning 0 and no-op.
When BytesRemaining() == 0 and ReadSync() is called, it also results in
returning 0 and no-op.

+  // read. This function never fails. If there's less data to read than we
+  // initially observed, then pad with zero (this can happen with files).
+  // |buf_length| must be greater than 0.
+  virtual int ReadSync(char* buf, int buf_length) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(UploadElementReader);
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_UPLOAD_ELEMENT_READER_H_