Avoid string construction overhead for lookup-only HpackEntry objects.

net/spdy/hpack/hpack_entry.h

 // Copyright 2014 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_SPDY_HPACK_ENTRY_H_
 #define NET_SPDY_HPACK_ENTRY_H_
 
-#include <cstddef>
-#include <set>
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/macros.h"
 #include "base/strings/string_piece.h"
 #include "net/base/net_export.h"
 
 // All section references below are to
 // http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-08
 
 namespace net {
 
 // A structure for an entry in the static table (3.3.1)
 // and the header table (3.3.2).
 class NET_EXPORT_PRIVATE HpackEntry {
  public:
   // The constant amount added to name().size() and value().size() to
   // get the size of an HpackEntry as defined in 5.1.
   static const size_t kSizeOverhead;
 
   // Creates an entry. Preconditions:
   // - |is_static| captures whether this entry is a member of the static
   //   or dynamic header table.
   // - |insertion_index| is this entry's index in the total set of entries ever
   //   inserted into the header table (including static entries).
   //
   // The combination of |is_static| and |insertion_index| allows an
   // HpackEntryTable to determine the index of an HpackEntry in O(1) time.
+  // Copies |name| and |value|.
   HpackEntry(base::StringPiece name,
              base::StringPiece value,
              bool is_static,
              size_t insertion_index);
 
   // Create a 'lookup' entry (only) suitable for querying a HpackEntrySet. The
   // instance InsertionIndex() always returns 0 and IsLookup() returns true.
+  // The memory backing |name| and |value| must outlive this object.
   HpackEntry(base::StringPiece name, base::StringPiece value);
 
+  HpackEntry(const HpackEntry& other);
+  HpackEntry& operator=(const HpackEntry& other);
+
   // Creates an entry with empty name and value. Only defined so that
   // entries can be stored in STL containers.
   HpackEntry();
 
   ~HpackEntry();
 
-  const std::string& name() const { return name_; }
-  const std::string& value() const { return value_; }
+  base::StringPiece name() const { return name_ref_; }
+  base::StringPiece value() const { return value_ref_; }
 
   // Returns whether this entry is a member of the static (as opposed to
   // dynamic) table.
   bool IsStatic() const { return type_ == STATIC; }
 
   // Returns whether this entry is a lookup-only entry.
   bool IsLookup() const { return type_ == LOOKUP; }
 
   // Used to compute the entry's index in the header table.
   size_t InsertionIndex() const { return insertion_index_; }
 
   // Returns the size of an entry as defined in 5.1.
   static size_t Size(base::StringPiece name, base::StringPiece value);
   size_t Size() const;
 
   std::string GetDebugString() const;
 
  private:
   enum EntryType {
     LOOKUP,
     DYNAMIC,
     STATIC,
   };
 
-  // TODO(jgraettinger): Reduce copies, possibly via SpdyPinnableBufferPiece.
+  // These members are not used for LOOKUP entries.
   std::string name_;
   std::string value_;
 
+  // These members are always valid. For DYNAMIC and STATIC entries, they
+  // always point to |name_| and |value_|.
+  base::StringPiece name_ref_;
+  base::StringPiece value_ref_;
+
   // The entry's index in the total set of entries ever inserted into the header
   // table.
   size_t insertion_index_;
 
   EntryType type_;
 };
 
 }  // namespace net
 
 #endif  // NET_SPDY_HPACK_ENTRY_H_