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