Make HPACK static table static and immutable.

net/spdy/hpack_header_table.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_HEADER_TABLE_H_
 #define NET_SPDY_HPACK_HEADER_TABLE_H_
 
 #include <cstddef>
 #include <deque>
 #include <set>
 
 #include "base/basictypes.h"
 #include "base/macros.h"
 #include "net/base/net_export.h"
 #include "net/spdy/hpack_entry.h"
 
 // All section references below are to
 // http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-08
 
 namespace net {
 
+using base::StringPiece;
+
 namespace test {
 class HpackHeaderTablePeer;
 }  // namespace test
 
 // A data structure for the static table (3.3.1) and the header table (3.3.2).
 class NET_EXPORT_PRIVATE HpackHeaderTable {
  public:
   friend class test::HpackHeaderTablePeer;
 
   // HpackHeaderTable takes advantage of the deque property that references
   // remain valid, so long as insertions & deletions are at the head & tail.
   // If this changes (eg we start to drop entries from the middle of the table),
-  // this needs to be a std::list, in which case |index_| can be trivially
+  // this needs to be a std::list, in which case |*_index_| can be trivially
   // extended to map to list iterators.
   typedef std::deque<HpackEntry> EntryTable;
 
   // Implements a total ordering of HpackEntry on name(), value(), then index
   // ascending. Note that index may change over the lifetime of an HpackEntry,
   // but the relative index order of two entries will not. This comparator is
   // composed with the 'lookup' HpackEntry constructor to allow for efficient
   // lower-bounding of matching entries.
   struct NET_EXPORT_PRIVATE EntryComparator {
-    explicit EntryComparator(HpackHeaderTable* table) : table_(table) {}
-
     bool operator() (const HpackEntry* lhs, const HpackEntry* rhs) const;
-
-   private:
-    HpackHeaderTable* table_;
   };
   typedef std::set<HpackEntry*, EntryComparator> OrderedEntrySet;
 
   HpackHeaderTable();
 
   ~HpackHeaderTable();
 
   // Last-aknowledged value of SETTINGS_HEADER_TABLE_SIZE.
   size_t settings_size_bound() { return settings_size_bound_; }
 
   // Current and maximum estimated byte size of the table, as described in
   // 5.1. Notably, this is /not/ the number of entries in the table.
   size_t size() const { return size_; }
   size_t max_size() const { return max_size_; }
 
   // Returns the entry matching the index, or NULL.
-  HpackEntry* GetByIndex(size_t index);
+  const HpackEntry* GetByIndex(size_t index);
 
   // Returns the lowest-value entry having |name|, or NULL.
-  HpackEntry* GetByName(base::StringPiece name);
+  const HpackEntry* GetByName(StringPiece name);
 
   // Returns the lowest-index matching entry, or NULL.
-  HpackEntry* GetByNameAndValue(base::StringPiece name,
-                                base::StringPiece value);
+  const HpackEntry* GetByNameAndValue(StringPiece name, StringPiece value);
 
   // Returns the index of an entry within this header table.
   size_t IndexOf(const HpackEntry* entry) const;
 
   // Sets the maximum size of the header table, evicting entries if
   // necessary as described in 5.2.
   void SetMaxSize(size_t max_size);
 
   // Sets the SETTINGS_HEADER_TABLE_SIZE bound of the table. Will call
   // SetMaxSize() as needed to preserve max_size() <= settings_size_bound().
   void SetSettingsHeaderTableSize(size_t settings_size);
 
   // Determine the set of entries which would be evicted by the insertion
   // of |name| & |value| into the table, as per section 3.3.3. No eviction
   // actually occurs. The set is returned via range [begin_out, end_out).
-  void EvictionSet(base::StringPiece name, base::StringPiece value,
+  void EvictionSet(StringPiece name,
+                   StringPiece value,
                    EntryTable::iterator* begin_out,
                    EntryTable::iterator* end_out);
 
   // Adds an entry for the representation, evicting entries as needed. |name|
   // and |value| must not be owned by an entry which could be evicted. The
   // added HpackEntry is returned, or NULL is returned if all entries were
   // evicted and the empty table is of insufficent size for the representation.
-  HpackEntry* TryAddEntry(base::StringPiece name, base::StringPiece value);
+  const HpackEntry* TryAddEntry(StringPiece name, StringPiece value);
 
   void DebugLogTableState() const;
 
  private:
   // Returns number of evictions required to enter |name| & |value|.
-  size_t EvictionCountForEntry(base::StringPiece name,
-                               base::StringPiece value) const;
+  size_t EvictionCountForEntry(StringPiece name, StringPiece value) const;
 
   // Returns number of evictions required to reclaim |reclaim_size| table size.
   size_t EvictionCountToReclaim(size_t reclaim_size) const;
 
   // Evicts |count| oldest entries from the table.
   void Evict(size_t count);
 
+  // |static_entries_| and |static_index_| are owned by HpackStaticTable
+  // singleton.
+  const EntryTable& static_entries_;
   EntryTable dynamic_entries_;
-  EntryTable static_entries_;
 
-  // Full table index, over |dynamic_entries_| and |static_entries_|.
-  OrderedEntrySet index_;
+  const OrderedEntrySet& static_index_;
+  OrderedEntrySet dynamic_index_;
 
   // Last acknowledged value for SETTINGS_HEADER_TABLE_SIZE.
   size_t settings_size_bound_;
 
   // Estimated current and maximum byte size of the table.
   // |max_size_| <= |settings_header_table_size_|
   size_t size_;
   size_t max_size_;
 
   // Total number of table insertions which have occurred. Referenced by
   // IndexOf() for determination of an HpackEntry's table index.
   size_t total_insertions_;
 
   DISALLOW_COPY_AND_ASSIGN(HpackHeaderTable);
 };
 
 }  // namespace net
 
 #endif  // NET_SPDY_HPACK_HEADER_TABLE_H_