wtf/url/src/URLBuffer.h

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  28
  29 #ifndef URLBuffer_h
  30 #define URLBuffer_h
  31
  32 namespace WTF {
  33
  34 // Base class for the canonicalizer output, this maintains a buffer and
  35 // supports simple resizing and append operations on it.
  36 //
  37 // It is VERY IMPORTANT that no virtual function calls be made on the common
  38 // code path. We only have two virtual function calls, the destructor and a
  39 // resize function that is called when the existing buffer is not big enough.
  40 // The derived class is then in charge of setting up our buffer which we will
  41 // manage.
  42 template<typename CHAR>
  43 class URLBuffer {
  44 public:
  45     URLBuffer() : m_buffer(0), m_capacity(0), m_length(0) { }
  46     virtual ~URLBuffer() { }
  47
  48     // Implemented to resize the buffer. This function should update the buffer
  49     // pointer to point to the new buffer, and any old data up to |m_length| in
  50     // the buffer must be copied over.
  51     //
  52     // The new size must be larger than m_capacity.
  53     virtual void resize(int) = 0;
  54
  55     inline char at(int offset) const { return m_buffer[offset]; }
  56     inline void set(int offset, CHAR ch)
  57     {
  58         // FIXME: Add ASSERT(offset < length());
  59         m_buffer[offset] = ch;
  60     }
  61
  62     // Returns the current capacity of the buffer. The length() is the number of
  63     // characters that have been declared to be written, but the capacity() is
  64     // the number that can be written without reallocation. If the caller must
  65     // write many characters at once, it can make sure there is enough capacity,
  66     // write the data, then use setLength() to declare the new length().
  67     int capacity() const { return m_capacity; }
  68     int length() const { return m_length; }
  69
  70     // The output will NOT be 0-terminated. Call length() to get the length.
  71     const CHAR* data() const { return m_buffer; }
  72     CHAR* data() { return m_buffer; }
  73
  74     // Shortens the URL to the new length. Used for "backing up" when processing
  75     // relative paths. This can also be used if an external function writes a lot
  76     // of data to the buffer (when using the "Raw" version below) beyond the end,
  77     // to declare the new length.
  78     void setLength(int length)
  79     {
  80         // FIXME: Add ASSERT(length < capacity());
  81         m_length = length;
  82     }
  83
  84     // This is the most performance critical function, since it is called for
  85     // every character.
  86     void append(CHAR ch)
  87     {
  88         // In VC2005, putting this common case first speeds up execution
  89         // dramatically because this branch is predicted as taken.
  90         if (m_length < m_capacity) {
  91             m_buffer[m_length] = ch;
  92             ++m_length;
  93             return;
  94         }
  95
  96         if (!grow(1))
  97             return;
  98
  99         m_buffer[m_length] = ch;
 100         ++m_length;
 101     }
 102
 103     void append(const CHAR* str, int strLength)
 104     {
 105         if (m_length + strLength > m_capacity) {
 106             if (!grow(m_length + strLength - m_capacity))
 107                 return;
 108         }
 109         for (int i = 0; i < strLength; i++)
 110             m_buffer[m_length + i] = str[i];
 111         m_length += strLength;
 112     }
 113
 114 protected:
 115     // Returns true if the buffer could be resized, false on OOM.
 116     bool grow(int minimumAdditionalCapacity)
 117     {
 118         static const int minimumCapacity = 16;
 119         int newCapacity = m_capacity ? m_capacity : minimumCapacity;
 120         do {
 121             if (newCapacity >= (1 << 30)) // Prevent overflow below.
 122                 return false;
 123             newCapacity *= 2;
 124         } while (newCapacity < m_capacity + minimumAdditionalCapacity);
 125         resize(newCapacity);
 126         return true;
 127     }
 128
 129     CHAR* m_buffer;
 130     int m_capacity;
 131     int m_length; // Used characters in the buffer.
 132 };
 133
 134 } // namespace WTF
 135
 136 #endif // URLBuffer_h