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

net/filter/gzip_stream_source.h

Index: net/filter/gzip_stream_source.h
diff --git a/net/filter/gzip_stream_source.h b/net/filter/gzip_stream_source.h
new file mode 100644
index 0000000000000000000000000000000000000000..3afb3336010dfe159086098f32cbe84bd639f228
--- /dev/null
+++ b/net/filter/gzip_stream_source.h
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+// 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_GZIP_STREAM_SOURCE_H_
+#define NET_FILTER_GZIP_STREAM_SOURCE_H_
+
+#include <memory>
+
+#include "net/filter/filter_stream_source.h"
+#include "net/filter/gzip_header.h"
+
+typedef struct z_stream_s z_stream;
+
+namespace net {
+
+class BlockBuffer;
+
+class GzipStreamSource : public FilterStreamSource {
+ public:
+  enum GzipStreamSourceMode {
+    GZIP_STREAM_SOURCE_DEFLATE,
+    GZIP_STREAM_SOURCE_GZIP,
+    // Same as GZIP_STREAM_SOURCE_GZIP, but allow fallback to plain text.
+    GZIP_STREAM_SOURCE_GZIP_WITH_FALLBACK,
+  };
+
+  explicit GzipStreamSource(std::unique_ptr<StreamSource> previous,
+                            GzipStreamSourceMode mode);
+  ~GzipStreamSource() override;
+
+  bool Init() override;
+
+ private:
+  enum GzipStreamState {
+    GZIP_STREAM_ERROR,
+    GZIP_STREAM_MORE_INPUT,
+    GZIP_STREAM_MORE_OUTPUT_SPACE,
+  };
+
+  // StreamSource implementation
+  Error ReadInternal(IOBuffer* dest_buffer,
+                     size_t buffer_size,
+                     size_t* bytes_read) override;
+
+  GzipStreamState Decompress(IOBuffer* dest_buffer,
+                             size_t buffer_size,
+                             size_t* bytes_read);
+
+  GzipStreamState Passthrough(IOBuffer* dest_buffer,
+                              size_t buffer_size,
+                              size_t* bytes_read);
+
+  void OnReadComplete(const OnReadCompleteCallback& callback,
+                      IOBuffer* dest_buffer,
+                      size_t dest_buffer_size,
+                      Error error,
+                      size_t bytes_read);
+
+  bool InsertZlibHeader();
+
+  // Returns whether an invalid GZip header has been observed. This method
+  // returns true as soon as an invalid GZip header is observed; it returns
+  // false if a complete, valid header has been observed, or not enough bytes
+  // have been seen to be sure. This method pulls its input from |buffer_|.
+  bool IsGzipHeaderInvalid();
+
+  // Returns whether this stream looks like it could be plain text (ie, not
+  // actually gzipped). Right now this uses an extremely simple heuristic; see
+  // the source for details. This method checks the input in |buffer_|, but does
+  // not drain from it.
+  bool ShouldFallbackToPlain();
+
+  // Skips gzip footer bytes if necessary. Might drain input from |buffer_| if
+  // there are still footer bytes to read.
+  void SkipGzipFooterIfNeeded();
+
+  scoped_refptr<IOBuffer> pending_read_buffer_;
+
+  // Indicates the type of content decoding the stream source is performing.
+  // This variable is set only once by Init.
+  GzipStreamSourceMode mode_;
+  // The control block of zlib which actually does the decoding.
+  // This data structure is initialized by Init and updated only by
+  // Decompress, with InsertZlibHeader being the exception as a workaround.
+  std::unique_ptr<z_stream> zlib_stream_;
+  // Whether end of stream has been reached.
+  bool zlib_eof_;
+  // A flag used by Decompress to record whether we've successfully added
+  // a zlib header to this stream.
+  bool zlib_header_added_;
+  // Used to parse the gzip header in gzip stream.
+  // It is used when the decoding mode is GZIP_STREAM_SOURCE_GZIP.
+  GZipHeader gzip_header_;
+  // Whether gzip header should be checked for validity.
+  bool should_check_gzip_header_;
+  // Tracks how many bytes of gzip footer are yet to be filtered.
+  size_t gzip_footer_bytes_left_;
+};
+
+}  // namespace net
+
+#endif  // NET_FILTER_GZIP_STREAM_SOURCE_H__