A thread-safe Media Query Parser

Source/core/css/parser/MediaQueryTokenizer.cpp

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "core/css/parser/MediaQueryTokenizer.h"
+
+#include "core/css/parser/MediaQueryInputStream.h"
+#include "core/html/parser/HTMLParserIdioms.h"
+#include "wtf/unicode/CharacterNames.h"
+
+namespace WebCore {
+
+// http://dev.w3.org/csswg/css-syntax/#name-start-code-point
+static bool isNameStart(UChar c)
+{
+    if (isASCIIAlpha(c))
+        return true;
+    if (c == '_')
+        return true;
+    return !isASCII(c);
+}
+
+// http://www.w3.org/TR/css-syntax-3/#name-code-point
+static bool isNameChar(UChar c)
+{
+    return isNameStart(c) || isASCIIDigit(c) || c == '-';
+}
+
+// http://www.w3.org/TR/css-syntax-3/#check-if-two-code-points-are-a-valid-escape
+static bool twoCharsAreValidEscape(UChar first, UChar second)
+{
+    return ((first == '\\') && (second != '\n') && (second != kEndOfFileMarker));
+}
+
+MediaQueryTokenizer::MediaQueryTokenizer()
+{
+}
+
+void MediaQueryTokenizer::reconsume(UChar c)
+{
+    m_input->pushBack(c);
+}
+
+UChar MediaQueryTokenizer::consume()
+{
+    UChar current = m_input->currentInputChar();
+    m_input->advance();
+    return current;
+}
+
+void MediaQueryTokenizer::consume(unsigned offset)
+{
+    m_input->advance(offset);
+}
+
+MediaQueryToken MediaQueryTokenizer::whiteSpace(UChar cc)
+{
+    // CSS Tokenization is currently lossy, but we could record
+    // the exact whitespace instead of discarding it here.
+    consumeUntilNotWhitespace();
+    return MediaQueryToken(WhitespaceToken);
+}
+
+MediaQueryToken MediaQueryTokenizer::leftParen(UChar cc)
+{
+    return MediaQueryToken(LeftParenToken);
+}
+
+MediaQueryToken MediaQueryTokenizer::rightParen(UChar cc)
+{
+    return MediaQueryToken(RightParenToken);
+}
+
+MediaQueryToken MediaQueryTokenizer::plusOrFullStop(UChar cc)
+{
+    if (nextCharsAreNumber()) {
+        reconsume(cc);
+        return consumeNumericToken();
+    }
+    return MediaQueryToken(DelimToken, cc);
+}
+
+MediaQueryToken MediaQueryTokenizer::comma(UChar cc)
+{
+    return MediaQueryToken(CommaToken);
+}
+
+MediaQueryToken MediaQueryTokenizer::hyphenMinus(UChar cc)
+{
+    if (nextCharsAreNumber()) {
+        reconsume(cc);
+        return consumeNumericToken();
+    }
+    if (nextCharsAreIdentifier()) {
+        reconsume(cc);
+        return consumeIdentLikeToken();
+    }
+    return MediaQueryToken(DelimToken, cc);
+}
+
+MediaQueryToken MediaQueryTokenizer::solidus(UChar cc)
+{
+    return MediaQueryToken(DelimToken, cc);
+}
+
+MediaQueryToken MediaQueryTokenizer::colon(UChar cc)
+{
+    return MediaQueryToken(ColonToken);
+}
+
+MediaQueryToken MediaQueryTokenizer::semiColon(UChar cc)
+{
+    return MediaQueryToken(SemicolonToken);
+}
+
+MediaQueryToken MediaQueryTokenizer::reverseSolidus(UChar cc)
+{
+    if (twoCharsAreValidEscape(cc, m_input->currentInputChar())) {
+        reconsume(cc);
+        return consumeIdentLikeToken();
+    }
+    return MediaQueryToken(DelimToken, cc);
+}
+
+MediaQueryToken MediaQueryTokenizer::asciiDigit(UChar cc)
+{
+    reconsume(cc);
+    return consumeNumericToken();
+}
+
+MediaQueryToken MediaQueryTokenizer::nameStart(UChar cc)
+{
+    reconsume(cc);
+    return consumeIdentLikeToken();
+}
+
+MediaQueryToken MediaQueryTokenizer::endOfFile(UChar cc)
+{
+    return MediaQueryToken(EOFToken);
+}
+
+void MediaQueryTokenizer::tokenize(String string, Vector<MediaQueryToken>& outTokens)
+{
+    MediaQueryTokenizer tokenizer;
+    // According to the spec, we should perform preprocessing here.
+    // See: http://www.w3.org/TR/css-syntax-3/#input-preprocessing
+    //
+    // However, we can skip this step since:
+    // * We're using HTML spaces (which accept \r and \f as a valid white space)
+    // * Do not count white spaces
+    // * consumeEscape replaces NULLs for replacement characters
+
+    MediaQueryInputStream input(string);
+    while (true) {
+        outTokens.append(tokenizer.nextToken(input));
+        if (outTokens.last().type() == EOFToken)
+            return;
+    }
+}
+
+MediaQueryToken MediaQueryTokenizer::nextToken(MediaQueryInputStream& input)
+{
+    // Unlike the HTMLTokenizer, the CSS Syntax spec is written
+    // as a stateless, (fixed-size) look-ahead tokenizer.
+    // We could move to the stateful model and instead create
+    // states for all the "next 3 codepoints are X" cases.
+    // State-machine tokenizers are easier to write to handle
+    // incremental tokenization of partial sources.
+    // However, for now we follow the spec exactly.
+    m_input = &input;
+    UChar cc = consume();
+    CodePoint codePointFunc = 0;
+
+    if (isASCII(cc)) {
+        ASSERT_WITH_SECURITY_IMPLICATION(cc < CODE_POINTS_NUM);
+        codePointFunc = getCodePoints()->codePoints[cc];
+    } else {
+        codePointFunc = &MediaQueryTokenizer::nameStart;
+    }
+
+    if (codePointFunc)
+        return ((this)->*(codePointFunc))(cc);
+
+    return MediaQueryToken(DelimToken, cc);
+}
+
+// This method merges the following spec sections for efficiency
+// http://www.w3.org/TR/css3-syntax/#consume-a-number
+// http://www.w3.org/TR/css3-syntax/#convert-a-string-to-a-number
+MediaQueryToken MediaQueryTokenizer::consumeNumber()
+{
+    ASSERT(nextCharsAreNumber());
+    NumericValueType type = IntegerValueType;
+    double value = 0;
+    int sign = 1;
+    unsigned peekOffset = 0;
+    int exponentSign = 1;
+    unsigned exponentStartPos = 0;
+    unsigned exponentEndPos = 0;
+    unsigned fractionStartPos = 0;
+    unsigned fractionEndPos = 0;
+    unsigned long long integerPart;
+    double fractionPart;
+    unsigned fractionDigits;
+    unsigned long long exponentPart;
+    if (m_input->currentInputChar() == '+') {
+        ++peekOffset;
+    } else if (m_input->peek(peekOffset) == '-') {
+        sign = -1;
+        ++peekOffset;
+    }
+    unsigned intStartPos = peekOffset;
+    peekOffset = m_input->skipWhilePredicate<isASCIIDigit>(peekOffset);
+    unsigned intEndPos = peekOffset;
+    if (m_input->peek(peekOffset) == '.' && isASCIIDigit(m_input->peek(++peekOffset))) {
+        fractionStartPos = peekOffset - 1;
+        peekOffset = m_input->skipWhilePredicate<isASCIIDigit>(peekOffset);
+        fractionEndPos = peekOffset;
+    }
+    if ((m_input->peek(peekOffset) == 'E' || m_input->peek(peekOffset) == 'e')) {
+        int peekOffsetBeforeExponent = peekOffset;
+        ++peekOffset;
+        if (m_input->peek(peekOffset) == '+') {
+            ++peekOffset;
+        } else if (m_input->peek(peekOffset) =='-') {
+            exponentSign = -1;
+            ++peekOffset;
+        }
+        exponentStartPos = peekOffset;
+        peekOffset = m_input->skipWhilePredicate<isASCIIDigit>(peekOffset);
+        exponentEndPos = peekOffset;
+        if (exponentEndPos == exponentStartPos)
+            peekOffset = peekOffsetBeforeExponent;
+    }
+    integerPart = m_input->getUInt(intStartPos, intEndPos);
+    fractionDigits = fractionEndPos - fractionStartPos;
+    unsigned floatingFractionEndPos = fractionEndPos;
+    fractionPart = m_input->getDouble(fractionStartPos, floatingFractionEndPos);
+    exponentPart = m_input->getUInt(exponentStartPos, exponentEndPos);
+    double exponent = pow(10, (float)exponentSign * (double)exponentPart);
+    value = (double)sign * ((double)integerPart + fractionPart) * exponent;
+
+    m_input->advance(peekOffset);
+    if (fractionDigits > 0)
+        type = NumberValueType;
+
+    return MediaQueryToken(NumberToken, value, type);
+}
+
+// http://www.w3.org/TR/css3-syntax/#consume-a-numeric-token
+MediaQueryToken MediaQueryTokenizer::consumeNumericToken()
+{
+    MediaQueryToken token = consumeNumber();
+    if (nextCharsAreIdentifier())
+        token.convertToDimensionWithUnit(consumeName());
+    else if (consumeIfNext('%'))
+        token.convertToPercentage();
+    return token;
+}
+
+// http://www.w3.org/TR/css3-syntax/#consume-an-ident-like-token
+MediaQueryToken MediaQueryTokenizer::consumeIdentLikeToken()
+{
+    String name = consumeName();
+    if (consumeIfNext('('))
+        return MediaQueryToken(FunctionToken, name);
+    return MediaQueryToken(IdentToken, name);
+}
+
+void MediaQueryTokenizer::consumeUntilNotWhitespace()
+{
+    // Using HTML space here rather than CSS space since we don't do preprocessing
+    while (isHTMLSpace<UChar>(m_input->currentInputChar()))
+        consume();
+}
+
+bool MediaQueryTokenizer::consumeIfNext(UChar character)
+{
+    if (m_input->currentInputChar() == character) {
+        consume();
+        return true;
+    }
+    return false;
+}
+
+// http://www.w3.org/TR/css3-syntax/#consume-a-name
+String MediaQueryTokenizer::consumeName()
+{
+    // FIXME: Is this as efficient as it can be?
+    // The possibility of escape chars mandates a copy AFAICT.
+    Vector<UChar> result;
+    while (true) {
+        if (isNameChar(m_input->currentInputChar())) {
+            result.append(consume());
+            continue;
+        }
+        if (nextTwoCharsAreValidEscape()) {
+            // "consume()" fixes a spec bug.
+            // The first code point should be consumed before consuming the escaped code point.
+            consume();
+            result.append(consumeEscape());
+            continue;
+        }
+        return String(result);
+    }
+}
+
+// http://www.w3.org/TR/css-syntax-3/#consume-an-escaped-code-point
+UChar MediaQueryTokenizer::consumeEscape()
+{
+    UChar cc = consume();
+    ASSERT(cc != '\n');
+    if (isASCIIHexDigit(cc)) {
+        unsigned consumedHexDigits = 1;
+        String hexChars;
+        do {
+            hexChars.append(cc);
+            cc = consume();
+            consumedHexDigits++;
+        } while (consumedHexDigits < 6 && isASCIIHexDigit(cc));
+        bool ok = false;
+        UChar codePoint = hexChars.toUIntStrict(&ok, 16);
+        if (!ok)
+            return WTF::Unicode::replacementCharacter;
+        return codePoint;
+    }
+
+    // Replaces NULLs with replacement characters, since we do not perform preprocessing
+    if (cc == kEndOfFileMarker)
+        return WTF::Unicode::replacementCharacter;
+    return cc;
+}
+
+bool MediaQueryTokenizer::nextTwoCharsAreValidEscape()
+{
+    return twoCharsAreValidEscape(m_input->peek(1), m_input->peek(2));
+}
+
+// http://www.w3.org/TR/css3-syntax/#starts-with-a-number
+bool MediaQueryTokenizer::nextCharsAreNumber()
+{
+    UChar first = m_input->currentInputChar();
+    UChar second = m_input->peek(1);
+    if (isASCIIDigit(first))
+        return true;
+    if (first == '+' || first == '-')
+        return ((isASCIIDigit(second)) || (second == '.' && isASCIIDigit(m_input->peek(2))));
+    if (first =='.')
+        return (isASCIIDigit(second));
+    return false;
+}
+
+// http://www.w3.org/TR/css3-syntax/#would-start-an-identifier
+bool MediaQueryTokenizer::nextCharsAreIdentifier()
+{
+    UChar firstChar = m_input->currentInputChar();
+    if (isNameStart(firstChar) || nextTwoCharsAreValidEscape())
+        return true;
+
+    if (firstChar == '-') {
+        if (isNameStart(m_input->peek(1)))
+            return true;
+        return twoCharsAreValidEscape(m_input->peek(1), m_input->peek(2));
+    }
+
+    return false;
+}
+
+} // namespace WebCore