Introduce VTTScanner - a parser helper for various VTT parsing needs

Source/core/html/track/vtt/VTTScanner.h

Index: Source/core/html/track/vtt/VTTScanner.h
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+/*
+ * Copyright (c) 2013, Opera Software ASA. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Opera Software ASA nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef VTTScanner_h
+#define VTTScanner_h
+
+#include "platform/ParsingUtilities.h"
+#include "wtf/text/WTFString.h"
+
+namespace WebCore {
+
+// Helper class for "scanning" an input string and performing parsing of
+// "micro-syntax"-like constructs.
+//
+// There's two primary operations: match and scan.
+//
+// The 'match' operation matches an explicitly or implicitly specified sequence
+// against the characters ahead of the current input pointer, and returns true
+// if the sequence can be matched.
+//
+// The 'scan' operation performs a 'match', and if the match is successful it
+// advance the input pointer past the matched sequence.
+class VTTScanner {
+    WTF_MAKE_NONCOPYABLE(VTTScanner);
+public:
+    explicit VTTScanner(const String& line);
+
+    typedef const LChar* Position;
+
+    class Run {
+    public:
+        Run(Position start, Position end, bool is8Bit)
+            : m_start(start), m_end(end), m_is8Bit(is8Bit) { }
+
+        Position end() const { return m_end; }
+
+        bool isEmpty() const { return m_start == m_end; }
+        size_t length() const;
+
+    private:
+        Position m_start;
+        Position m_end;
+        bool m_is8Bit;
+    };
+
+    // Check if the input pointer points at the specified position.
+    bool isAt(Position checkPosition) const { return position() == checkPosition; }
+    // Check if the input pointer points at the end of the input.
+    bool isAtEnd() const { return position() == end(); }
+    // Match the character |c| against the character at the input pointer (~lookahead).
+    bool match(char c) const { return !isAtEnd() && currentChar() == c; }
+    // Scan the character |c|.
+    bool scan(char);
+    // Scan the first |charactersCount| characters of the string |characters|.
+    bool scan(const LChar* characters, size_t charactersCount);
+
+    // Scan the literal |characters|.
+    template<unsigned charactersCount>
+    bool scan(const char (&characters)[charactersCount]);
+
+    // Skip (advance the input pointer) as long as the specified
+    // |characterPredicate| returns true, and the input pointer is not passed
+    // the end of the input.
+    template<bool characterPredicate(UChar)>
+    void skipWhile();
+
+    // Return the run of characters for which the specified
+    // |characterPredicate| returns true. The start of the run will be the
+    // current input pointer.
+    template<bool characterPredicate(UChar)>
+    Run collectWhile();
+
+    // Return a String constructed from the rest of the input (between input
+    // pointer and end of input), and advance the input pointer accordingly.
+    String restOfInputAsString();
+
+    // Scan a set of ASCII digits from the input. Return the number of digits
+    // scanned, and set |number| to the computed value. If the digits make up a
+    // number that does not fit the 'int' type, |number| is set to INT_MAX.
+    // Note: Does not handle sign.
+    unsigned scanDigits(int& number);
+
+protected:
+    Position position() const { return m_data.characters8; }
+    Position end() const { return m_end.characters8; }
+    void seekTo(Position);
+    UChar currentChar() const;
+    void advance(unsigned amount = 1);
+    // Adapt a UChar-predicate to an LChar-predicate.
+    // (For use with skipWhile/Until from ParsingUtilities.h).
+    template<bool characterPredicate(UChar)>
+    static inline bool LCharPredicateAdapter(LChar c) { return characterPredicate(c); }
+    union {
+        const LChar* characters8;
+        const UChar* characters16;
+    } m_data;
+    union {
+        const LChar* characters8;
+        const UChar* characters16;
+    } m_end;
+    bool m_is8Bit;
+};
+
+inline size_t VTTScanner::Run::length() const
+{
+    if (m_is8Bit)
+        return m_end - m_start;
+    return reinterpret_cast<const UChar*>(m_end) - reinterpret_cast<const UChar*>(m_start);
+}
+
+template<unsigned charactersCount>
+inline bool VTTScanner::scan(const char (&characters)[charactersCount])
+{
+    return scan(reinterpret_cast<const LChar*>(characters), charactersCount - 1);
+}
+
+template<bool characterPredicate(UChar)>
+inline void VTTScanner::skipWhile()
+{
+    if (m_is8Bit)
+        ::skipWhile<LChar, LCharPredicateAdapter<characterPredicate> >(m_data.characters8, m_end.characters8);
+    else
+        ::skipWhile<UChar, characterPredicate>(m_data.characters16, m_end.characters16);
+}
+
+template<bool characterPredicate(UChar)>
+inline VTTScanner::Run VTTScanner::collectWhile()
+{
+    if (m_is8Bit) {
+        const LChar* current = m_data.characters8;
+        ::skipWhile<LChar, LCharPredicateAdapter<characterPredicate> >(current, m_end.characters8);
+        return Run(position(), current, m_is8Bit);
+    }
+    const UChar* current = m_data.characters16;
+    ::skipWhile<UChar, characterPredicate>(current, m_end.characters16);
+    return Run(position(), reinterpret_cast<Position>(current), m_is8Bit);
+}
+
+inline void VTTScanner::seekTo(Position position)
+{
+    ASSERT(position <= end());
+    m_data.characters8 = position;
+}
+
+inline UChar VTTScanner::currentChar() const
+{
+    ASSERT(position() < end());
+    return m_is8Bit ? *m_data.characters8 : *m_data.characters16;
+}
+
+inline void VTTScanner::advance(unsigned amount)
+{
+    ASSERT(position() < end());
+    if (m_is8Bit)
+        m_data.characters8 += amount;
+    else
+        m_data.characters16 += amount;
+}
+
+// Wrapper of VTTScanner that allows easy interaction with a parsing model
+// where a <String, index> tuple is used.
+class VTTLegacyScanner : public VTTScanner {
+    WTF_MAKE_NONCOPYABLE(VTTLegacyScanner);
+public:
+    VTTLegacyScanner(const String& line, unsigned* outPosition)
+        : VTTScanner(line)
+        , m_outPosition(outPosition)
+    {
+        ASSERT(outPosition && *outPosition <= line.length());
+        // Adjust state according to |*outPosition|.
+        advance(*outPosition);
+        // Save the start position to allow adjusting |*outPosition|.
+        if (m_is8Bit)
+            m_start.characters8 = m_data.characters8;
+        else
+            m_start.characters16 = m_data.characters16;
+    }
+    ~VTTLegacyScanner()
+    {
+        // "Export" the updated position.
+        unsigned advancedChars = m_is8Bit ? m_data.characters8 - m_start.characters8 : m_data.characters16 - m_start.characters16;
+        *m_outPosition += advancedChars;
+    }
+
+private:
+    unsigned* m_outPosition;
+    union {
+        const LChar* characters8;
+        const UChar* characters16;
+    } m_start;
+};
+
+}
+
+#endif