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28
29#ifndef URLBuffer_h
30#define URLBuffer_h
31
32namespace 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.
42template<typename CHAR>
43class URLBuffer {
44public:
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
114protected:
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
137