oggiterator.cpp

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#include "./oggiterator.h"
 
#include "../exceptions.h"
 
#include <c++utilities/io/binaryreader.h>
 
#include <iostream>
#include <limits>
 
using namespace std;
using namespace CppUtilities;
 
namespace TagParser {
 
void OggIterator::clear(istream &stream, std::uint64_t startOffset, std::uint64_t streamSize)
{
    m_stream = &stream;
    m_startOffset = startOffset;
    m_streamSize = streamSize;
    m_pages.clear();
}
 
void OggIterator::reset()
{
    for (m_page = m_segment = m_offset = 0; m_page < m_pages.size() || fetchNextPage(); ++m_page) {
        const OggPage &page = m_pages[m_page];
        if (!page.segmentSizes().empty() && matchesFilter(page)) {
            // page is not empty and matches ID filter if set
            m_offset = page.startOffset() + page.headerSize();
            break;
        }
    }
    // no matching page found -> iterator is invalid
}
 
void OggIterator::nextPage()
{
    while (++m_page < m_pages.size() || fetchNextPage()) {
        const OggPage &page = m_pages[m_page];
        if (!page.segmentSizes().empty() && matchesFilter(page)) {
            // page is not empty and matches ID filter if set
            m_segment = m_bytesRead = 0;
            m_offset = page.startOffset() + page.headerSize();
            return;
        }
    }
    // no next page available -> iterator is in invalid state
}
 
void OggIterator::nextSegment()
{
    const OggPage &page = m_pages[m_page];
    if (matchesFilter(page) && ++m_segment < page.segmentSizes().size()) {
        // current page has next segment
        m_bytesRead = 0;
        m_offset += page.segmentSizes()[m_segment - 1];
    } else {
        // next (matching) page has next segment
        nextPage();
    }
}
 
void OggIterator::previousPage()
{
    while (m_page) {
        const OggPage &page = m_pages[--m_page];
        if (matchesFilter(page)) {
            m_offset = page.dataOffset(m_segment = page.segmentSizes().size() - 1);
            return;
        }
    }
}
 
void OggIterator::previousSegment()
{
    const OggPage &page = m_pages[m_page];
    if (m_segment && matchesFilter(page)) {
        m_offset -= page.segmentSizes()[m_segment--];
    } else {
        previousPage();
    }
}
 
void OggIterator::read(char *buffer, std::size_t count)
{
    std::size_t bytesRead = 0;
    while (*this && count) {
        const auto available = remainingBytesInCurrentSegment();
        stream().seekg(static_cast<std::streamoff>(currentCharacterOffset()));
        if (count <= available) {
            stream().read(buffer + bytesRead, static_cast<std::streamsize>(count));
            m_bytesRead += count;
            return;
        }
        stream().read(buffer + bytesRead, static_cast<std::streamsize>(available));
        nextSegment();
        bytesRead += available;
        count -= available;
    }
    if (count) {
        // still bytes to read but no more available
        throw TruncatedDataException();
    }
}
 
std::size_t OggIterator::readAll(char *buffer, std::size_t max)
{
    auto bytesRead = std::size_t(0);
    while (*this && max) {
        const auto available = remainingBytesInCurrentSegment();
        stream().seekg(static_cast<std::streamoff>(currentCharacterOffset()), std::ios_base::beg);
        if (max <= available) {
            stream().read(buffer + bytesRead, static_cast<std::streamsize>(max));
            m_bytesRead += max;
            return bytesRead + max;
        } else {
            stream().read(buffer + bytesRead, static_cast<std::streamsize>(available));
            nextSegment();
            bytesRead += available;
            max -= available;
        }
    }
    return bytesRead;
}
 
void OggIterator::ignore(std::size_t count)
{
    while (*this) {
        const auto available = currentSegmentSize() - m_bytesRead;
        if (count <= available) {
            m_bytesRead += count;
            return;
        } else {
            nextSegment();
            count -= available;
        }
    }
    throw TruncatedDataException();
}
 
bool OggIterator::resyncAt(std::uint64_t offset)
{
    // check whether offset is valid
    if (offset >= streamSize() || offset < (m_pages.empty() ? m_startOffset : m_pages.back().startOffset() + m_pages.back().totalSize())) {
        return false;
    }
 
    // find capture pattern 'OggS'
    stream().seekg(static_cast<streamoff>(offset));
    std::uint8_t lettersFound = 0;
    for (std::uint64_t bytesAvailable = max<std::uint64_t>(streamSize() - offset, 65307ul); bytesAvailable >= 27; --bytesAvailable) {
        switch (static_cast<char>(stream().get())) {
        case 'O':
            lettersFound = 1;
            break;
        case 'g':
            lettersFound = lettersFound == 1 || lettersFound == 2 ? lettersFound + 1 : 0;
            break;
        case 'S':
            if (lettersFound == 3) {
                // capture pattern found
                const auto currentOffset = stream().tellg();
                // -> try to parse an Ogg page at this position
                try {
                    m_pages.emplace_back(stream(), static_cast<std::uint64_t>(stream().tellg()) - 4,
                        bytesAvailable > numeric_limits<std::int32_t>::max() ? numeric_limits<std::int32_t>::max()
                                                                             : static_cast<std::int32_t>(bytesAvailable));
                    setPageIndex(m_pages.size() - 1);
                    return true;
                } catch (const Failure &) {
                    stream().seekg(currentOffset);
                }
            }
            [[fallthrough]];
        default:
            lettersFound = 0;
        }
    }
    return false;
}
 
bool OggIterator::fetchNextPage()
{
    if (m_page == m_pages.size()) { // can only fetch the next page if the current page is the last page
        m_offset = m_pages.empty() ? m_startOffset : m_pages.back().startOffset() + m_pages.back().totalSize();
        if (m_offset < m_streamSize) {
            const std::uint64_t bytesAvailable = m_streamSize - m_offset;
            m_pages.emplace_back(*m_stream, m_offset,
                bytesAvailable > numeric_limits<std::int32_t>::max() ? numeric_limits<std::int32_t>::max()
                                                                     : static_cast<std::int32_t>(bytesAvailable));
            return true;
        }
    }
    return false;
}
 
} // namespace TagParser