parser/html/nsHtml5String.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef nsHtml5String_h
   6 #define nsHtml5String_h
   7
   8 #include "nsAtom.h"
   9 #include "nsString.h"
  10 #include "nsStringBuffer.h"
  11
  12 class nsHtml5TreeBuilder;
  13
  14 /**
  15  * A pass-by-value type that can represent
  16  *  * nullptr
  17  *  * empty string
  18  *  * Non-empty string as exactly-sized (capacity is length) `nsStringBuffer*`
  19  *  * Non-empty string as an nsAtom*
  20  *
  21  * Holding or passing this type is as unsafe as holding or passing
  22  * `nsStringBuffer*`/`nsAtom*`.
  23  */
  24 class nsHtml5String final {
  25  private:
  26   static const uintptr_t kKindMask = uintptr_t(3);
  27
  28   static const uintptr_t kPtrMask = ~kKindMask;
  29
  30   enum Kind : uintptr_t {
  31     eNull = 0,
  32     eEmpty = 1,
  33     eStringBuffer = 2,
  34     eAtom = 3,
  35   };
  36
  37   inline Kind GetKind() const { return (Kind)(mBits & kKindMask); }
  38
  39   inline nsStringBuffer* AsStringBuffer() const {
  40     MOZ_ASSERT(GetKind() == eStringBuffer);
  41     return reinterpret_cast<nsStringBuffer*>(mBits & kPtrMask);
  42   }
  43
  44   inline nsAtom* AsAtom() const {
  45     MOZ_ASSERT(GetKind() == eAtom);
  46     return reinterpret_cast<nsAtom*>(mBits & kPtrMask);
  47   }
  48
  49   inline const char16_t* AsPtr() const {
  50     switch (GetKind()) {
  51       case eStringBuffer:
  52         return reinterpret_cast<char16_t*>(AsStringBuffer()->Data());
  53       case eAtom:
  54         return AsAtom()->GetUTF16String();
  55       default:
  56         return nsCharTraits<char16_t>::sEmptyBuffer;
  57     }
  58   }
  59
  60  public:
  61   /**
  62    * Default constructor.
  63    */
  64   inline nsHtml5String() : nsHtml5String(nullptr) {}
  65
  66   /**
  67    * Constructor from nullptr.
  68    */
  69   inline MOZ_IMPLICIT nsHtml5String(decltype(nullptr)) : mBits(eNull) {}
  70
  71   inline uint32_t Length() const {
  72     switch (GetKind()) {
  73       case eStringBuffer:
  74         return (AsStringBuffer()->StorageSize() / sizeof(char16_t) - 1);
  75       case eAtom:
  76         return AsAtom()->GetLength();
  77       default:
  78         return 0;
  79     }
  80   }
  81
  82   /**
  83    * False iff the string is logically null
  84    */
  85   inline MOZ_IMPLICIT operator bool() const { return mBits; }
  86
  87   /**
  88    * Get the underlying nsAtom* or nullptr if this nsHtml5String
  89    * does not hold an atom.
  90    */
  91   inline nsAtom* MaybeAsAtom() {
  92     if (GetKind() == eAtom) {
  93       return AsAtom();
  94     }
  95     return nullptr;
  96   }
  97
  98   void ToString(nsAString& aString);
  99
 100   void CopyToBuffer(char16_t* aBuffer) const;
 101
 102   bool LowerCaseEqualsASCII(const char* aLowerCaseLiteral) const;
 103
 104   bool EqualsASCII(const char* aLiteral) const;
 105
 106   bool LowerCaseStartsWithASCII(const char* aLowerCaseLiteral) const;
 107
 108   bool Equals(nsHtml5String aOther) const;
 109
 110   nsHtml5String Clone();
 111
 112   void Release();
 113
 114   static nsHtml5String FromBuffer(char16_t* aBuffer, int32_t aLength,
 115                                   nsHtml5TreeBuilder* aTreeBuilder);
 116
 117   static nsHtml5String FromLiteral(const char* aLiteral);
 118
 119   static nsHtml5String FromString(const nsAString& aString);
 120
 121   static nsHtml5String FromAtom(already_AddRefed<nsAtom> aAtom);
 122
 123   static nsHtml5String EmptyString();
 124
 125  private:
 126   /**
 127    * Constructor from raw bits.
 128    */
 129   explicit nsHtml5String(uintptr_t aBits) : mBits(aBits){};
 130
 131   /**
 132    * Zero if null, one if empty, otherwise tagged pointer
 133    * to either nsAtom or nsStringBuffer. The two least-significant
 134    * bits are tag bits.
 135    */
 136   uintptr_t mBits;
 137 };
 138
 139 #endif  // nsHtml5String_h