net/spdy/hpack_header_table.h

   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_