Implement basic classes for HPACK (HTTP/2 compression)

net/spdy/hpack_entry.h

+#ifndef NET_SPDY_HPACK_ENTRY_H_
+#define NET_SPDY_HPACK_ENTRY_H_
+
+#include <cstddef>
+#include <deque>
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/macros.h"
+#include "base/strings/string_piece.h"
+
+namespace net {
+
+// All section references below are to
+// http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-04
+// .
+
+// A structure for an entry in the header table (3.1.2) and the
+// reference set (3.1.3). This structure also keeps track of how many
+// times the entry has been 'touched', which is useful for both
+// encoding and decoding.
+class HpackEntry {
+ public:
+  // The constant amount added to name().size() and value().size() to
+  // get the size of an HpackEntry as defined in 3.3.1.
+  static const uint32 kSizeOverhead = 32;
+
+  // The constant returned by touch_count() if an entry hasn't been
+  // touched (which is distinct from an entry having a touch count of
+  // 0).
+  //
+  // TODO(akalin): The distinction between untouched and having a
+  // touch count of 0 is confusing. Think of a better way to represent
+  // this state.
+  static const uint32 kUntouched = 0x7fffffff;
+
+  // Creates an entry with empty name a value. Only defined so that
+  // entries can be stored in STL containers.
+  HpackEntry();
+
+  // Creates an entry with a copy is made of the given name and value.
+  //
+  // TODO(akalin): Add option to not make a copy (for static table
+  // entries).
+  HpackEntry(base::StringPiece name, base::StringPiece value);
+
+  // Copy constructor and assignment operator welcome.
+
+  // The name() and value() StringPieces have the same lifetime as
+  // this entry.
+
+  base::StringPiece name() const { return base::StringPiece(name_); }
+  base::StringPiece value() const { return base::StringPiece(value_); }
+
+  // Returns whether or not this entry is in the reference set.
+  bool IsReferenced() const;
+
+  // Returns how many touches this entry has, or kUntouched if this
+  // entry hasn't been touched at all. The meaning of the touch count
+  // is defined by whatever is calling
+  // AddTouchCount()/ClearTouchCount() (i.e., the encoder or decoder).
+  uint32 TouchCount() const;
+
+  // Returns the size of an entry as defined in 3.3.1. The returned
+  // value may not necessarily fit in 32 bits.
+  size_t Size() const;
+
+  std::string GetDebugString() const;
+
+  // Returns whether this entry has the same name, value, referenced
+  // state, and touch count as the given one.
+  bool Equals(const HpackEntry& other) const;
+
+  void SetReferenced(bool referenced);
+
+  // Adds the given number of touches to this entry (see
+  // TouchCount()). The total number of touches must not exceed 2^31 -
+  // 2. It is guaranteed that this entry's touch count will not equal
+  // kUntouched after this function is called (even if touch_count ==
+  // 0).
+  void AddTouches(uint32 additional_touch_count);
+
+  // Sets the touch count of this entry to kUntouched.
+  void ClearTouches();
+
+ private:
+  std::string name_;
+  std::string value_;
+
+  // The high bit stores 'referenced' and the rest stores the touch
+  // count.
+  uint32 referenced_and_touch_count_;
+};
+
+}  // namespace net
+
+#endif  // NET_SPDY_HPACK_ENTRY_H_