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

net/filter/source_stream.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_SOURCE_STREAM_H_
+#define NET_FILTER_SOURCE_STREAM_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 SourceStream class implements a producer of bytes.
+class NET_EXPORT_PRIVATE SourceStream {
+ public:
+  enum SourceType {
+#define SOURCE_STREAM_TYPE(label) TYPE_##label,
+#include "net/filter/source_stream_type_list.h"
+#undef SOURCE_STREAM_TYPE
+    // Used for UMA.
+    TYPE_MAX,
+  };
+
+  // |type| is the type of the SourceStream.
+  explicit SourceStream(SourceType type);
+
+  virtual ~SourceStream();
+
+  // Initiaties a read from the stream.
+  // 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

[Randy Smith (Not in Mondays), 2016/08/09 20:28:30]

nit, suggestion "an error code *or* a count"?

[xunjieli, 2016/08/15 15:19:08]

Done.

+  //     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 stream. This is for UMA logging.
+  virtual std::string OrderedTypeStringList() const;

[Randy Smith (Not in Mondays), 2016/08/09 20:28:30]

Why is this named OrderedTypeStringList()?  I'm not sure what that name means.

[Randy Smith (Not in Mondays), 2016/08/09 20:28:30]

Suggestion: If I'm reading the code correctly, the reason this isn't a pure
virtual is because URLRequestJobSourceStream doesn't implement it, and hence
ends up using this implementation.  Would it make sense to move this
implementation into URLRJSS and make this a pure virtual?  

[xunjieli, 2016/08/15 15:19:07]

Done.

[xunjieli, 2016/08/15 15:19:08]

This is moved over from the original code.
The original name is:

std::string OrderedFilterList() const;

https://cs.chromium.org/chromium/src/net/filter/filter.h?rcl=0&l=238

[Randy Smith (Not in Mondays), 2016/08/22 22:04:32]

Yeah, but that code was more explicit about filters being in a chain.  This code
is being a little more abstract; at each level the SourceStream looks opaque to
what calls it; it's just a producer of bytes.  And this is really nothing more
than a string that describes the stream.  So I'd vote in favor of just calling
it "Description()" and commenting that this is for UMA and net logging.

ETA: Actually, it looks like it's used for testing as well (which scares me a
bit, but I'm not going to worry about that for now).

+
+  SourceType type() const { return type_; }
+
+ private:
+  SourceType type_;
+
+  DISALLOW_COPY_AND_ASSIGN(SourceStream);
+};
+
+}  // namespace net
+
+#endif  // NET_FILTER_SOURCE_STREAM_H_