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      1 // Copyright 2014 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef NET_SPDY_HPACK_HEADER_TABLE_H_
      6 #define NET_SPDY_HPACK_HEADER_TABLE_H_
      7 
      8 #include <cstddef>
      9 #include <deque>
     10 #include <set>
     11 
     12 #include "base/basictypes.h"
     13 #include "base/macros.h"
     14 #include "net/base/net_export.h"
     15 #include "net/spdy/hpack_entry.h"
     16 
     17 // All section references below are to
     18 // http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-08
     19 
     20 namespace net {
     21 
     22 using base::StringPiece;
     23 
     24 namespace test {
     25 class HpackHeaderTablePeer;
     26 }  // namespace test
     27 
     28 // A data structure for the static table (3.3.1) and the header table (3.3.2).
     29 class NET_EXPORT_PRIVATE HpackHeaderTable {
     30  public:
     31   friend class test::HpackHeaderTablePeer;
     32 
     33   // HpackHeaderTable takes advantage of the deque property that references
     34   // remain valid, so long as insertions & deletions are at the head & tail.
     35   // If this changes (eg we start to drop entries from the middle of the table),
     36   // this needs to be a std::list, in which case |*_index_| can be trivially
     37   // extended to map to list iterators.
     38   typedef std::deque<HpackEntry> EntryTable;
     39 
     40   // Implements a total ordering of HpackEntry on name(), value(), then index
     41   // ascending. Note that index may change over the lifetime of an HpackEntry,
     42   // but the relative index order of two entries will not. This comparator is
     43   // composed with the 'lookup' HpackEntry constructor to allow for efficient
     44   // lower-bounding of matching entries.
     45   struct NET_EXPORT_PRIVATE EntryComparator {
     46     bool operator() (const HpackEntry* lhs, const HpackEntry* rhs) const;
     47   };
     48   typedef std::set<HpackEntry*, EntryComparator> OrderedEntrySet;
     49 
     50   HpackHeaderTable();
     51 
     52   ~HpackHeaderTable();
     53 
     54   // Last-aknowledged value of SETTINGS_HEADER_TABLE_SIZE.
     55   size_t settings_size_bound() { return settings_size_bound_; }
     56 
     57   // Current and maximum estimated byte size of the table, as described in
     58   // 5.1. Notably, this is /not/ the number of entries in the table.
     59   size_t size() const { return size_; }
     60   size_t max_size() const { return max_size_; }
     61 
     62   // Returns the entry matching the index, or NULL.
     63   const HpackEntry* GetByIndex(size_t index);
     64 
     65   // Returns the lowest-value entry having |name|, or NULL.
     66   const HpackEntry* GetByName(StringPiece name);
     67 
     68   // Returns the lowest-index matching entry, or NULL.
     69   const HpackEntry* GetByNameAndValue(StringPiece name, StringPiece value);
     70 
     71   // Returns the index of an entry within this header table.
     72   size_t IndexOf(const HpackEntry* entry) const;
     73 
     74   // Sets the maximum size of the header table, evicting entries if
     75   // necessary as described in 5.2.
     76   void SetMaxSize(size_t max_size);
     77 
     78   // Sets the SETTINGS_HEADER_TABLE_SIZE bound of the table. Will call
     79   // SetMaxSize() as needed to preserve max_size() <= settings_size_bound().
     80   void SetSettingsHeaderTableSize(size_t settings_size);
     81 
     82   // Determine the set of entries which would be evicted by the insertion
     83   // of |name| & |value| into the table, as per section 3.3.3. No eviction
     84   // actually occurs. The set is returned via range [begin_out, end_out).
     85   void EvictionSet(StringPiece name,
     86                    StringPiece value,
     87                    EntryTable::iterator* begin_out,
     88                    EntryTable::iterator* end_out);
     89 
     90   // Adds an entry for the representation, evicting entries as needed. |name|
     91   // and |value| must not be owned by an entry which could be evicted. The
     92   // added HpackEntry is returned, or NULL is returned if all entries were
     93   // evicted and the empty table is of insufficent size for the representation.
     94   const HpackEntry* TryAddEntry(StringPiece name, StringPiece value);
     95 
     96   void DebugLogTableState() const;
     97 
     98  private:
     99   // Returns number of evictions required to enter |name| & |value|.
    100   size_t EvictionCountForEntry(StringPiece name, StringPiece value) const;
    101 
    102   // Returns number of evictions required to reclaim |reclaim_size| table size.
    103   size_t EvictionCountToReclaim(size_t reclaim_size) const;
    104 
    105   // Evicts |count| oldest entries from the table.
    106   void Evict(size_t count);
    107 
    108   // |static_entries_| and |static_index_| are owned by HpackStaticTable
    109   // singleton.
    110   const EntryTable& static_entries_;
    111   EntryTable dynamic_entries_;
    112 
    113   const OrderedEntrySet& static_index_;
    114   OrderedEntrySet dynamic_index_;
    115 
    116   // Last acknowledged value for SETTINGS_HEADER_TABLE_SIZE.
    117   size_t settings_size_bound_;
    118 
    119   // Estimated current and maximum byte size of the table.
    120   // |max_size_| <= |settings_header_table_size_|
    121   size_t size_;
    122   size_t max_size_;
    123 
    124   // Total number of table insertions which have occurred. Referenced by
    125   // IndexOf() for determination of an HpackEntry's table index.
    126   size_t total_insertions_;
    127 
    128   DISALLOW_COPY_AND_ASSIGN(HpackHeaderTable);
    129 };
    130 
    131 }  // namespace net
    132 
    133 #endif  // NET_SPDY_HPACK_HEADER_TABLE_H_
    134