Source/WebCore/html/track/BufferedLineReader.cpp

/*
 * 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:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * 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
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 * 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
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#include "config.h"
#include "BufferedLineReader.h"

#include <wtf/unicode/CharacterNames.h>

namespace WebCore {

std::optional<String> BufferedLineReader::nextLine()
{
    if (m_maybeSkipLF) {
        // We ran out of data after a CR (U+000D), which means that we may be
        // in the middle of a CRLF pair. If the next character is a LF (U+000A)
        // then skip it, and then (unconditionally) return the buffered line.
        if (!m_buffer.isEmpty()) {
            if (m_buffer.currentCharacter() == newlineCharacter)
                m_buffer.advancePastNewline();
            m_maybeSkipLF = false;
        }
        // If there was no (new) data available, then keep m_maybeSkipLF set,
        // and fall through all the way down to the EOS check at the end of the function.
    }

    bool shouldReturnLine = false;
    bool checkForLF = false;
    while (!m_buffer.isEmpty()) {
        UChar character = m_buffer.currentCharacter();
        m_buffer.advance();

        if (character == newlineCharacter || character == carriageReturn) {
            // We found a line ending. Return the accumulated line.
            shouldReturnLine = true;
            checkForLF = (character == carriageReturn);
            break;
        }

        // NULs are transformed into U+FFFD (REPLACEMENT CHAR.) in step 1 of
        // the WebVTT parser algorithm.
        if (character == '\0')
            character = replacementCharacter;

        m_lineBuffer.append(character);
    }

    if (checkForLF) {
        // May be in the middle of a CRLF pair.
        if (!m_buffer.isEmpty()) {
            if (m_buffer.currentCharacter() == newlineCharacter)
                m_buffer.advancePastNewline();
        } else {
            // Check for the newline on the next call (unless we reached EOS, in
            // which case we'll return the contents of the line buffer, and
            // reset state for the next line.)
            m_maybeSkipLF = true;
        }
    }

    if (isAtEndOfStream()) {
        // We've reached the end of the stream proper. Emit a line if the
        // current line buffer is non-empty. (Note that if shouldReturnLine is
        // set already, we want to return a line nonetheless.)
        shouldReturnLine |= !m_lineBuffer.isEmpty();
    }

    if (shouldReturnLine) {
        auto line = m_lineBuffer.toString();
        m_lineBuffer.clear();
        return line;
    }

    ASSERT(m_buffer.isEmpty());
    return std::nullopt;
}

} // namespace WebCore