[ON HOLD] Implement pull-based design for content decoding

net/filter/stream_source.h

+// Copyright 2016 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_FILTER_STREAM_SOURCE_H_
+#define NET_FILTER_STREAM_SOURCE_H_
+
+#include <string>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "net/base/completion_callback.h"
+#include "net/base/net_errors.h"
+
+namespace net {
+
+class IOBuffer;
+
+// The StreamSource class implements a producer of bytes. Sources often
+// incorporate a previous source from which they read undecoded input. Those
+// which incorporate a previous source take ownership of the previous source
+// when they are created.
+class NET_EXPORT_PRIVATE StreamSource {
+ public:
+  enum SourceType {
+#define STREAM_SOURCE_TYPE(label) TYPE_##label,
+#include "net/filter/stream_source_type_list.h"
+#undef STREAM_SOURCE_TYPE
+    // Used for UMA.
+    TYPE_MAX,
+  };
+
+  // |type| is the type of the StreamSource.
+  explicit StreamSource(SourceType type);
+
+  virtual ~StreamSource();
+
+  // Initiaties a read from the filter chain starting at this stream source.
+  // If it completes synchronously, it:
+  //   - Returns an int representing the number of bytes read. If 0, EOF has
+  //     been reached
+  //   - Bytes will be written into |*dest_buffer|
+  //   - Does not call |callback|
+  // If it completes asynchronously, it:
+  //   - Returns ERR_IO_PENDING
+  //   - Calls |callback| when it does complete, with an error code and a count
+  //     of bytes read and written into |*dest_buffer|.
+  // This method takes a reference to |*dest_buffer| if it completes
+  // asynchronously to ensure it does not get freed mid-read.
+  virtual int Read(IOBuffer* dest_buffer,
+                   size_t buffer_size,
+                   const CompletionCallback& callback) = 0;
+
+  // Returns a string that represents the filter chain that starts at and
+  // includes |this|. This is for UMA logging.
+  virtual std::string OrderedTypeStringList() const;
+
+  SourceType type() const { return type_; }
+
+ private:
+  SourceType type_;
+
+  DISALLOW_COPY_AND_ASSIGN(StreamSource);
+};
+
+}  // namespace net
+
+#endif  // NET_FILTER_STREAM_SOURCE_H_