/src/qpdf/libqpdf/QPDF_objects.cc

Source
#include <qpdf/qpdf-config.h> // include first for large file support

#include <qpdf/QPDF_private.hh>

#include <qpdf/InputSource_private.hh>
#include <qpdf/OffsetInputSource.hh>
#include <qpdf/Pipeline.hh>
#include <qpdf/QPDFExc.hh>
#include <qpdf/QPDFLogger.hh>
#include <qpdf/QPDFObjectHandle_private.hh>
#include <qpdf/QPDFObject_private.hh>
#include <qpdf/QPDFParser.hh>
#include <qpdf/QTC.hh>
#include <qpdf/QUtil.hh>
#include <qpdf/Util.hh>

#include <array>
#include <atomic>
#include <cstring>
#include <limits>
#include <map>
#include <vector>

using namespace qpdf;
using namespace std::literals;

using Objects = QPDF::Doc::Objects;
using Parser = impl::Parser;

QPDFXRefEntry::QPDFXRefEntry() = default;

QPDFXRefEntry::QPDFXRefEntry(int type, qpdf_offset_t field1, int field2) :
    type(type),
    field1(field1),
    field2(field2)
{
    util::assertion(type == 1 || type == 2, "invalid xref type " + std::to_string(type));
}

int
QPDFXRefEntry::getType() const
{
    return type;
}

qpdf_offset_t
QPDFXRefEntry::getOffset() const
{
    util::assertion(type == 1, "getOffset called for xref entry of type != 1");
    return this->field1;
}

int
QPDFXRefEntry::getObjStreamNumber() const
{
    util::assertion(type == 2, "getObjStreamNumber called for xref entry of type != 2");
    return QIntC::to_int(field1);
}

int
QPDFXRefEntry::getObjStreamIndex() const
{
    util::assertion(type == 2, "getObjStreamIndex called for xref entry of type != 2");
    return field2;
}

namespace
{
    class InvalidInputSource: public InputSource
    {
      public:
        ~InvalidInputSource() override = default;
        qpdf_offset_t
        findAndSkipNextEOL() override
        {
            throwException();
            return 0;
        }
        std::string const&
        getName() const override
        {
            static std::string name("closed input source");
            return name;
        }
        qpdf_offset_t
        tell() override
        {
            throwException();
            return 0;
        }
        void
        seek(qpdf_offset_t offset, int whence) override
        {
            throwException();
        }
        void
        rewind() override
        {
            throwException();
        }
        size_t
        read(char* buffer, size_t length) override
        {
            throwException();
            return 0;
        }
        void
        unreadCh(char ch) override
        {
            throwException();
        }

      private:
        void
        throwException()
        {
            throw std::logic_error(
                "QPDF operation attempted on a QPDF object with no input "
                "source. QPDF operations are invalid before processFile (or "
                "another process method) or after closeInputSource");
        }
    };
} // namespace

class QPDF::ResolveRecorder final
{
  public:
    ResolveRecorder(QPDF& qpdf, QPDFObjGen const& og) :
        qpdf(qpdf),
        iter(qpdf.m->resolving.insert(og).first)
    {
    }
    ~ResolveRecorder()
    {
        qpdf.m->resolving.erase(iter);
    }

  private:
    QPDF& qpdf;
    std::set<QPDFObjGen>::const_iterator iter;
};

class Objects::PatternFinder final: public InputSource::Finder
{
  public:
    PatternFinder(Objects& o, bool (Objects::*checker)()) :
        o(o),
        checker(checker)
    {
    }
    ~PatternFinder() final = default;
    bool
    check() final
    {
        return (this->o.*checker)();
    }

  private:
    Objects& o;
    bool (Objects::*checker)();
};

bool
Objects::validatePDFVersion(char const*& p, std::string& version)
{
    if (!util::is_digit(*p)) {
        return false;
    }
    while (util::is_digit(*p)) {
        version.append(1, *p++);
    }
    if (!(*p == '.' && util::is_digit(*(p + 1)))) {
        return false;
    }
    version.append(1, *p++);
    while (util::is_digit(*p)) {
        version.append(1, *p++);
    }
    return true;
}

bool
Objects::findHeader()
{
    qpdf_offset_t global_offset = m->file->tell();
    std::string line = m->file->readLine(1024);
    char const* p = line.data();
    util::assertion(strncmp(p, "%PDF-", 5) == 0, "findHeader is not looking at %PDF-");
    p += 5;
    std::string version;
    // Note: The string returned by line.data() is always null-terminated. The code below never
    // overruns the buffer because a null character always short-circuits further advancement.
    if (!validatePDFVersion(p, version)) {
        return false;
    }
    m->pdf_version = version;
    if (global_offset != 0) {
        // Empirical evidence strongly suggests (codified in PDF 2.0 spec) that when there is
        // leading material prior to the PDF header, all explicit offsets in the file are such that
        // 0 points to the beginning of the header.
        m->file = std::make_shared<OffsetInputSource>(m->file, global_offset);
    }
    return true;
}

bool
Objects::findStartxref()
{
    if (readToken(*m->file).isWord("startxref") && readToken(*m->file).isInteger()) {
        // Position in front of offset token
        m->file->seek(m->file->getLastOffset(), SEEK_SET);
        return true;
    }
    return false;
}

void
Objects::parse(char const* password)
{
    if (password) {
        m->encp->provided_password = password;
    }

    // Find the header anywhere in the first 1024 bytes of the file.
    PatternFinder hf(*this, &Objects::findHeader);
    if (!m->file->findFirst("%PDF-", 0, 1024, hf)) {
        warn(damagedPDF("", -1, "can't find PDF header"));
        // QPDFWriter writes files that usually require at least version 1.2 for /FlateDecode
        m->pdf_version = "1.2";
    }

    // PDF spec says %%EOF must be found within the last 1024 bytes of/ the file.  We add an extra
    // 30 characters to leave room for the startxref stuff.
    m->file->seek(0, SEEK_END);
    qpdf_offset_t end_offset = m->file->tell();
    m->xref_table_max_offset = end_offset;
    // Sanity check on object ids. All objects must appear in xref table / stream. In all realistic
    // scenarios at least 3 bytes are required.
    if (m->xref_table_max_id > m->xref_table_max_offset / 3) {
        m->xref_table_max_id = static_cast<int>(m->xref_table_max_offset / 3);
    }
    qpdf_offset_t start_offset = (end_offset > 1054 ? end_offset - 1054 : 0);
    PatternFinder sf(*this, &Objects::findStartxref);
    qpdf_offset_t xref_offset = 0;
    if (m->file->findLast("startxref", start_offset, 0, sf)) {
        xref_offset = QUtil::string_to_ll(readToken(*m->file).getValue().c_str());
    }

    try {
        if (xref_offset == 0) {
            throw damagedPDF("", -1, "can't find startxref");
        }
        try {
            read_xref(xref_offset);
        } catch (QPDFExc&) {
            throw;
        } catch (std::exception& e) {
            throw damagedPDF("", -1, std::string("error reading xref: ") + e.what());
        }
    } catch (QPDFExc& e) {
        if (global::Options::inspection_mode()) {
            try {
                reconstruct_xref(e, xref_offset > 0);
            } catch (std::exception& er) {
                warn(damagedPDF("", -1, "error reconstructing xref: "s + er.what()));
            }
            if (!m->trailer) {
                m->trailer = Dictionary::empty();
            }
            return;
        }
        if (cf.surpress_recovery()) {
            throw;
        }
        reconstruct_xref(e, xref_offset > 0);
    }

    m->encp->initialize(qpdf);
    m->parsed = true;
    if (!m->xref_table.empty() && !qpdf.getRoot().getKey("/Pages").isDictionary()) {
        // QPDFs created from JSON have an empty xref table and no root object yet.
        throw damagedPDF("", -1, "unable to find page tree");
    }
    if (m->cf.max_warnings()) {
        if (m->pages.empty()) {
            throw damagedPDF("", -1, "no pages found");
        }
        (void)m->cf.max_warnings(0);
    }
}

void
Objects::inParse(bool v)
{
    util::internal_error_if(
        m->in_parse == v, "QPDF: re-entrant parsing detected"
        // This happens if QPDFParser::parse tries to resolve an indirect object while it is
        // parsing.
    );
    m->in_parse = v;
}

void
Objects::setTrailer(QPDFObjectHandle obj)
{
    if (m->trailer) {
        return;
    }
    m->trailer = obj;
}

void
Objects::reconstruct_xref(QPDFExc& e, bool found_startxref)
{
    if (m->reconstructed_xref) {
        // Avoid xref reconstruction infinite loops. This is getting very hard to reproduce because
        // qpdf is throwing many fewer exceptions while parsing. Most situations are warnings now.
        throw e;
    }

    // If recovery generates more than 1000 warnings, the file is so severely damaged that there
    // probably is no point trying to continue.
    const auto max_warnings = m->warnings.size() + 1000U;
    auto check_warnings = [this, max_warnings]() {
        if (m->warnings.size() > max_warnings) {
            throw damagedPDF("", -1, "too many errors while reconstructing cross-reference table");
        }
    };

    m->reconstructed_xref = true;
    // We may find more objects, which may contain dangling references.
    m->fixed_dangling_refs = false;

    warn(damagedPDF("", -1, "file is damaged"));
    warn(e);
    warn(damagedPDF("", -1, "Attempting to reconstruct cross-reference table"));

    // Delete all references to type 1 (uncompressed) objects
    std::vector<QPDFObjGen> to_delete;
    for (auto const& iter: m->xref_table) {
        if (iter.second.getType() == 1) {
            to_delete.emplace_back(iter.first);
        }
    }
    for (auto const& iter: to_delete) {
        m->xref_table.erase(iter);
    }

    std::vector<std::tuple<int, int, qpdf_offset_t>> found_objects;
    std::vector<qpdf_offset_t> trailers;
    std::vector<qpdf_offset_t> startxrefs;

    m->file->seek(0, SEEK_END);
    qpdf_offset_t eof = m->file->tell();
    m->file->seek(0, SEEK_SET);
    // Don't allow very long tokens here during recovery. All the interesting tokens are covered.
    static size_t const MAX_LEN = 10;
    while (m->file->tell() < eof) {
        QPDFTokenizer::Token t1 = m->objects.readToken(*m->file, MAX_LEN);
        qpdf_offset_t token_start = m->file->tell() - toO(t1.getValue().length());
        if (t1.isInteger()) {
            auto pos = m->file->tell();
            auto t2 = m->objects.readToken(*m->file, MAX_LEN);
            if (t2.isInteger() && m->objects.readToken(*m->file, MAX_LEN).isWord("obj")) {
                int obj = QUtil::string_to_int(t1.getValue().c_str());
                int gen = QUtil::string_to_int(t2.getValue().c_str());
                if (obj <= m->xref_table_max_id) {
                    found_objects.emplace_back(obj, gen, token_start);
                } else {
                    warn(damagedPDF(
                        "", -1, "ignoring object with impossibly large id " + std::to_string(obj)));
                }
            }
            m->file->seek(pos, SEEK_SET);
        } else if (!m->trailer && t1.isWord("trailer")) {
            trailers.emplace_back(m->file->tell());
        } else if (!found_startxref && t1.isWord("startxref")) {
            startxrefs.emplace_back(m->file->tell());
        }
        check_warnings();
        m->file->findAndSkipNextEOL();
    }

    if (!found_startxref && !startxrefs.empty() && !found_objects.empty() &&
        startxrefs.back() > std::get<2>(found_objects.back())) {
        auto xref_backup{m->xref_table};
        try {
            m->file->seek(startxrefs.back(), SEEK_SET);
            if (auto offset = QUtil::string_to_ll(readToken(*m->file).getValue().data())) {
                read_xref(offset);

                if (qpdf.getRoot().getKey("/Pages").isDictionary()) {
                    warn(damagedPDF(
                        "", -1, "startxref was more than 1024 bytes before end of file"));
                    m->encp->initialize(qpdf);
                    m->parsed = true;
                    m->reconstructed_xref = false;
                    return;
                }
            }
        } catch (...) {
            // ok, bad luck. Do recovery.
        }
        m->xref_table = std::move(xref_backup);
    }

    auto rend = found_objects.rend();
    for (auto it = found_objects.rbegin(); it != rend; it++) {
        auto [obj, gen, token_start] = *it;
        insertXrefEntry(obj, 1, token_start, gen);
        check_warnings();
    }
    m->deleted_objects.clear();

    // Search at most the last 100 trailer candidates. If none of them are valid, odds are this file
    // is deliberately broken.
    int end_index = trailers.size() > 100 ? static_cast<int>(trailers.size()) - 100 : 0;
    for (auto it = trailers.rbegin(); it != std::prev(trailers.rend(), end_index); it++) {
        m->file->seek(*it, SEEK_SET);
        auto t = readTrailer();
        if (!t.isDictionary()) {
            // Oh well.  It was worth a try.
        } else {
            if (t.hasKey("/Root")) {
                m->trailer = t;
                break;
            }
            warn(damagedPDF("trailer", *it, "recovered trailer has no /Root entry"));
        }
        check_warnings();
    }

    if (!m->trailer) {
        qpdf_offset_t max_offset{0};
        size_t max_size{0};
        // If there are any xref streams, take the last one to appear.
        for (auto const& iter: m->xref_table) {
            auto entry = iter.second;
            if (entry.getType() != 1) {
                continue;
            }
            auto oh = qpdf.getObject(iter.first);
            try {
                if (!oh.isStreamOfType("/XRef")) {
                    continue;
                }
            } catch (std::exception&) {
                continue;
            }
            auto offset = entry.getOffset();
            auto size = oh.getDict().getKey("/Size").getUIntValueAsUInt();
            if (size > max_size || (size == max_size && offset > max_offset)) {
                max_offset = offset;
                setTrailer(oh.getDict());
            }
            check_warnings();
        }
        if (max_offset > 0) {
            try {
                read_xref(max_offset, true);
            } catch (std::exception&) {
                warn(damagedPDF(
                    "", -1, "error decoding candidate xref stream while recovering damaged file"));
            }
            QTC::TC("qpdf", "QPDF recover xref stream");
        }
    }

    if (!m->trailer || (!m->parsed && !m->trailer.getKey("/Root").isDictionary())) {
        // Try to find a Root dictionary. As a quick fix try the one with the highest object id.
        QPDFObjectHandle root;
        for (auto const& iter: m->obj_cache) {
            try {
                if (QPDFObjectHandle(iter.second.object).isDictionaryOfType("/Catalog")) {
                    root = iter.second.object;
                }
            } catch (std::exception&) {
                continue;
            }
        }
        if (root) {
            if (!m->trailer) {
                warn(damagedPDF(
                    "", -1, "unable to find trailer dictionary while recovering damaged file"));
                m->trailer = QPDFObjectHandle::newDictionary();
            }
            m->trailer.replaceKey("/Root", root);
        }
    }

    if (!m->trailer) {
        // We could check the last encountered object to see if it was an xref stream.  If so, we
        // could try to get the trailer from there.  This may make it possible to recover files with
        // bad startxref pointers even when they have object streams.

        throw damagedPDF("", -1, "unable to find trailer dictionary while recovering damaged file");
    }
    if (m->xref_table.empty()) {
        // We cannot check for an empty xref table in parse because empty tables are valid when
        // creating QPDF objects from JSON.
        throw damagedPDF("", -1, "unable to find objects while recovering damaged file");
    }
    check_warnings();
    if (!m->parsed) {
        m->parsed = !m->pages.empty();
        if (!m->parsed) {
            throw damagedPDF("", -1, "unable to find any pages while recovering damaged file");
        }
        check_warnings();
    }

    // We could iterate through the objects looking for streams and try to find objects inside of
    // them, but it's probably not worth the trouble.  Acrobat can't recover files with any errors
    // in an xref stream, and this would be a real long shot anyway.  If we wanted to do anything
    // that involved looking at stream contents, we'd also have to call initializeEncryption() here.
    // It's safe to call it more than once.
}

void
Objects::read_xref(qpdf_offset_t xref_offset, bool in_stream_recovery)
{
    std::map<int, int> free_table;
    std::set<qpdf_offset_t> visited;
    while (xref_offset) {
        visited.insert(xref_offset);
        char buf[7];
        memset(buf, 0, sizeof(buf));
        m->file->seek(xref_offset, SEEK_SET);
        // Some files miss the mark a little with startxref. We could do a better job of searching
        // in the neighborhood for something that looks like either an xref table or stream, but the
        // simple heuristic of skipping whitespace can help with the xref table case and is harmless
        // with the stream case.
        bool done = false;
        bool skipped_space = false;
        while (!done) {
            char ch;
            if (1 == m->file->read(&ch, 1)) {
                if (util::is_space(ch)) {
                    skipped_space = true;
                } else {
                    m->file->unreadCh(ch);
                    done = true;
                }
            } else {
                QTC::TC("qpdf", "QPDF eof skipping spaces before xref", skipped_space ? 0 : 1);
                done = true;
            }
        }

        m->file->read(buf, sizeof(buf) - 1);
        // The PDF spec says xref must be followed by a line terminator, but files exist in the wild
        // where it is terminated by arbitrary whitespace.
        if ((strncmp(buf, "xref", 4) == 0) && util::is_space(buf[4])) {
            if (skipped_space) {
                warn(damagedPDF("", -1, "extraneous whitespace seen before xref"));
            }
            QTC::TC(
                "qpdf",
                "QPDF xref space",
                ((buf[4] == '\n')       ? 0
                     : (buf[4] == '\r') ? 1
                     : (buf[4] == ' ')  ? 2
                                        : 9999));
            int skip = 4;
            // buf is null-terminated, and util::is_space('\0') is false, so this won't overrun.
            while (util::is_space(buf[skip])) {
                ++skip;
            }
            xref_offset = read_xrefTable(xref_offset + skip);
        } else {
            xref_offset = read_xrefStream(xref_offset, in_stream_recovery);
        }
        if (visited.contains(xref_offset)) {
            throw damagedPDF("", -1, "loop detected following xref tables");
        }
    }

    if (!m->trailer) {
        throw damagedPDF("", -1, "unable to find trailer while reading xref");
    }
    int size = m->trailer.getKey("/Size").getIntValueAsInt();
    int max_obj = 0;
    if (!m->xref_table.empty()) {
        max_obj = m->xref_table.rbegin()->first.getObj();
    }
    if (!m->deleted_objects.empty()) {
        max_obj = std::max(max_obj, *(m->deleted_objects.rbegin()));
    }
    if (size < 1 || (size - 1) != max_obj) {
        if (size == (max_obj + 2) && qpdf.getObject(max_obj + 1, 0).isStreamOfType("/XRef")) {
            warn(damagedPDF(
                "",
                -1,
                "xref entry for the xref stream itself is missing - a common error handled "
                "correctly by qpdf and most other applications"));
        } else {
            warn(damagedPDF(
                "",
                -1,
                ("reported number of objects (" + std::to_string(size) +
                 ") is not one plus the highest object number (" + std::to_string(max_obj) + ")")));
        }
    }

    // We no longer need the deleted_objects table, so go ahead and clear it out to make sure we
    // never depend on its being set.
    m->deleted_objects.clear();

    // Make sure we keep only the highest generation for any object.
    QPDFObjGen last_og{-1, 0};
    for (auto const& item: m->xref_table) {
        auto id = item.first.getObj();
        if (id == last_og.getObj() && id > 0) {
            qpdf.removeObject(last_og);
        }
        last_og = item.first;
    }
}

bool
Objects::parse_xrefFirst(std::string const& line, int& obj, int& num, int& bytes)
{
    // is_space and is_digit both return false on '\0', so this will not overrun the null-terminated
    // buffer.
    char const* p = line.c_str();
    char const* start = line.c_str();

    // Skip zero or more spaces
    while (util::is_space(*p)) {
        ++p;
    }
    // Require digit
    if (!util::is_digit(*p)) {
        return false;
    }
    // Gather digits
    std::string obj_str;
    while (util::is_digit(*p)) {
        obj_str.append(1, *p++);
    }
    // Require space
    if (!util::is_space(*p)) {
        return false;
    }
    // Skip spaces
    while (util::is_space(*p)) {
        ++p;
    }
    // Require digit
    if (!util::is_digit(*p)) {
        return false;
    }
    // Gather digits
    std::string num_str;
    while (util::is_digit(*p)) {
        num_str.append(1, *p++);
    }
    // Skip any space including line terminators
    while (util::is_space(*p)) {
        ++p;
    }
    bytes = toI(p - start);
    obj = QUtil::string_to_int(obj_str.c_str());
    num = QUtil::string_to_int(num_str.c_str());
    return true;
}

bool
Objects::read_bad_xrefEntry(qpdf_offset_t& f1, int& f2, char& type)
{
    // Reposition after initial read attempt and reread.
    m->file->seek(m->file->getLastOffset(), SEEK_SET);
    auto line = m->file->readLine(30);

    // is_space and is_digit both return false on '\0', so this will not overrun the null-terminated
    // buffer.
    char const* p = line.data();

    // Skip zero or more spaces. There aren't supposed to be any.
    bool invalid = false;
    while (util::is_space(*p)) {
        ++p;
        invalid = true;
    }
    // Require digit
    if (!util::is_digit(*p)) {
        return false;
    }
    // Gather digits
    std::string f1_str;
    while (util::is_digit(*p)) {
        f1_str.append(1, *p++);
    }
    // Require space
    if (!util::is_space(*p)) {
        return false;
    }
    if (util::is_space(*(p + 1))) {
        invalid = true;
    }
    // Skip spaces
    while (util::is_space(*p)) {
        ++p;
    }
    // Require digit
    if (!util::is_digit(*p)) {
        return false;
    }
    // Gather digits
    std::string f2_str;
    while (util::is_digit(*p)) {
        f2_str.append(1, *p++);
    }
    // Require space
    if (!util::is_space(*p)) {
        return false;
    }
    if (util::is_space(*(p + 1))) {
        invalid = true;
    }
    // Skip spaces
    while (util::is_space(*p)) {
        ++p;
    }
    if ((*p == 'f') || (*p == 'n')) {
        type = *p;
    } else {
        return false;
    }
    if ((f1_str.length() != 10) || (f2_str.length() != 5)) {
        invalid = true;
    }

    if (invalid) {
        warn(damagedPDF("xref table", "accepting invalid xref table entry"));
    }

    f1 = QUtil::string_to_ll(f1_str.c_str());
    f2 = QUtil::string_to_int(f2_str.c_str());

    return true;
}

// Optimistically read and parse xref entry. If entry is bad, call read_bad_xrefEntry and return
// result.
bool
Objects::read_xrefEntry(qpdf_offset_t& f1, int& f2, char& type)
{
    std::array<char, 21> line;
    if (m->file->read(line.data(), 20) != 20) {
        // C++20: [[unlikely]]
        return false;
    }
    line[20] = '\0';
    char const* p = line.data();

    int f1_len = 0;
    int f2_len = 0;

    // is_space and is_digit both return false on '\0', so this will not overrun the null-terminated
    // buffer.

    // Gather f1 digits. NB No risk of overflow as 9'999'999'999 < max long long.
    while (*p == '0') {
        ++f1_len;
        ++p;
    }
    while (util::is_digit(*p) && f1_len++ < 10) {
        f1 *= 10;
        f1 += *p++ - '0';
    }
    // Require space
    if (!util::is_space(*p++)) {
        // Entry doesn't start with space or digit.
        // C++20: [[unlikely]]
        return false;
    }
    // Gather digits. NB No risk of overflow as 99'999 < max int.
    while (*p == '0') {
        ++f2_len;
        ++p;
    }
    while (util::is_digit(*p) && f2_len++ < 5) {
        f2 *= 10;
        f2 += static_cast<int>(*p++ - '0');
    }
    if (util::is_space(*p++) && (*p == 'f' || *p == 'n')) {
        // C++20: [[likely]]
        type = *p;
        // No test for valid line[19].
        if (*(++p) && *(++p) && (*p == '\n' || *p == '\r') && f1_len == 10 && f2_len == 5) {
            // C++20: [[likely]]
            return true;
        }
    }
    return read_bad_xrefEntry(f1, f2, type);
}

// Read a single cross-reference table section and associated trailer.
qpdf_offset_t
Objects::read_xrefTable(qpdf_offset_t xref_offset)
{
    m->file->seek(xref_offset, SEEK_SET);
    std::string line;
    while (true) {
        line.assign(50, '\0');
        m->file->read(line.data(), line.size());
        int obj = 0;
        int num = 0;
        int bytes = 0;
        if (!parse_xrefFirst(line, obj, num, bytes)) {
            throw damagedPDF("xref table", "xref syntax invalid");
        }
        m->file->seek(m->file->getLastOffset() + bytes, SEEK_SET);
        for (qpdf_offset_t i = obj; i - num < obj; ++i) {
            if (i == 0) {
                // This is needed by checkLinearization()
                first_xref_item_offset_ = m->file->tell();
            }
            // For xref_table, these will always be small enough to be ints
            qpdf_offset_t f1 = 0;
            int f2 = 0;
            char type = '\0';
            if (!read_xrefEntry(f1, f2, type)) {
                throw damagedPDF(
                    "xref table", "invalid xref entry (obj=" + std::to_string(i) + ")");
            }
            if (type == 'f') {
                insertFreeXrefEntry(QPDFObjGen(toI(i), f2));
            } else {
                insertXrefEntry(toI(i), 1, f1, f2);
            }
        }
        qpdf_offset_t pos = m->file->tell();
        if (readToken(*m->file).isWord("trailer")) {
            break;
        } else {
            m->file->seek(pos, SEEK_SET);
        }
    }

    // Set offset to previous xref table if any
    QPDFObjectHandle cur_trailer = m->objects.readTrailer();
    if (!cur_trailer.isDictionary()) {
        throw damagedPDF("", "expected trailer dictionary");
    }

    if (!m->trailer) {
        setTrailer(cur_trailer);

        if (!m->trailer.hasKey("/Size")) {
            throw damagedPDF("trailer", "trailer dictionary lacks /Size key");
        }
        if (!m->trailer.getKey("/Size").isInteger()) {
            throw damagedPDF("trailer", "/Size key in trailer dictionary is not an integer");
        }
    }

    if (cur_trailer.hasKey("/XRefStm")) {
        if (cf.ignore_xref_streams()) {
            QTC::TC("qpdf", "QPDF ignoring XRefStm in trailer");
        } else {
            if (cur_trailer.getKey("/XRefStm").isInteger()) {
                // Read the xref stream but disregard any return value -- we'll use our trailer's
                // /Prev key instead of the xref stream's.
                (void)read_xrefStream(cur_trailer.getKey("/XRefStm").getIntValue());
            } else {
                throw damagedPDF("xref stream", xref_offset, "invalid /XRefStm");
            }
        }
    }

    if (cur_trailer.hasKey("/Prev")) {
        if (!cur_trailer.getKey("/Prev").isInteger()) {
            throw damagedPDF("trailer", "/Prev key in trailer dictionary is not an integer");
        }
        return cur_trailer.getKey("/Prev").getIntValue();
    }

    return 0;
}

// Read a single cross-reference stream.
qpdf_offset_t
Objects::read_xrefStream(qpdf_offset_t xref_offset, bool in_stream_recovery)
{
    if (!cf.ignore_xref_streams()) {
        QPDFObjectHandle xref_obj;
        try {
            m->in_read_xref_stream = true;
            xref_obj = readObjectAtOffset(xref_offset, "xref stream", true);
        } catch (QPDFExc&) {
            // ignore -- report error below
        }
        m->in_read_xref_stream = false;
        if (xref_obj.isStreamOfType("/XRef")) {
            return processXRefStream(xref_offset, xref_obj, in_stream_recovery);
        }
    }

    throw damagedPDF("", xref_offset, "xref not found");
    return 0; // unreachable
}

// Return the entry size of the xref stream and the processed W array.
std::pair<int, std::array<int, 3>>
Objects::processXRefW(QPDFObjectHandle& dict, std::function<QPDFExc(std::string_view)> damaged)
{
    auto W_obj = dict.getKey("/W");
    if (!(W_obj.size() >= 3 && W_obj.getArrayItem(0).isInteger() &&
          W_obj.getArrayItem(1).isInteger() && W_obj.getArrayItem(2).isInteger())) {
        throw damaged("Cross-reference stream does not have a proper /W key");
    }

    std::array<int, 3> W;
    int entry_size = 0;
    auto w_vector = W_obj.getArrayAsVector();
    int max_bytes = sizeof(qpdf_offset_t);
    for (size_t i = 0; i < 3; ++i) {
        W[i] = w_vector[i].getIntValueAsInt();
        if (W[i] > max_bytes) {
            throw damaged("Cross-reference stream's /W contains impossibly large values");
        }
        if (W[i] < 0) {
            throw damaged("Cross-reference stream's /W contains negative values");
        }
        entry_size += W[i];
    }
    if (entry_size == 0) {
        throw damaged("Cross-reference stream's /W indicates entry size of 0");
    }
    return {entry_size, W};
}

// Validate Size key and return the maximum number of entries that the xref stream can contain.
int
Objects::processXRefSize(
    QPDFObjectHandle& dict, int entry_size, std::function<QPDFExc(std::string_view)> damaged)
{
    // Number of entries is limited by the highest possible object id and stream size.
    auto max_num_entries = std::numeric_limits<int>::max();
    if (max_num_entries > (std::numeric_limits<qpdf_offset_t>::max() / entry_size)) {
        max_num_entries = toI(std::numeric_limits<qpdf_offset_t>::max() / entry_size);
    }

    auto Size_obj = dict.getKey("/Size");
    long long size;
    if (!dict.getKey("/Size").getValueAsInt(size)) {
        throw damaged("Cross-reference stream does not have a proper /Size key");
    } else if (size < 0) {
        throw damaged("Cross-reference stream has a negative /Size key");
    } else if (size >= max_num_entries) {
        throw damaged("Cross-reference stream has an impossibly large /Size key");
    }
    // We are not validating that Size <= (Size key of parent xref / trailer).
    return max_num_entries;
}

// Return the number of entries of the xref stream and the processed Index array.
std::pair<int, std::vector<std::pair<int, int>>>
Objects::processXRefIndex(
    QPDFObjectHandle& dict, int max_num_entries, std::function<QPDFExc(std::string_view)> damaged)
{
    auto size = dict.getKey("/Size").getIntValueAsInt();
    auto Index_obj = dict.getKey("/Index");

    if (Index_obj.isArray()) {
        std::vector<std::pair<int, int>> indx;
        int num_entries = 0;
        auto index_vec = Index_obj.getArrayAsVector();
        if ((index_vec.size() % 2) || index_vec.size() < 2) {
            throw damaged("Cross-reference stream's /Index has an invalid number of values");
        }

        int i = 0;
        long long first = 0;
        for (auto& val: index_vec) {
            if (val.isInteger()) {
                if (i % 2) {
                    auto count = val.getIntValue();
                    if (count <= 0) {
                        throw damaged(
                            "Cross-reference stream section claims to contain " +
                            std::to_string(count) + " entries");
                    }
                    // We are guarding against the possibility of num_entries * entry_size
                    // overflowing. We are not checking that entries are in ascending order as
                    // required by the spec, which probably should generate a warning. We are also
                    // not checking that for each subsection first object number + number of entries
                    // <= /Size. The spec requires us to ignore object number > /Size.
                    if (first > (max_num_entries - count) ||
                        count > (max_num_entries - num_entries)) {
                        throw damaged(
                            "Cross-reference stream claims to contain too many entries: " +
                            std::to_string(first) + " " + std::to_string(max_num_entries) + " " +
                            std::to_string(num_entries));
                    }
                    indx.emplace_back(static_cast<int>(first), static_cast<int>(count));
                    num_entries += static_cast<int>(count);
                } else {
                    first = val.getIntValue();
                    if (first < 0) {
                        throw damaged(
                            "Cross-reference stream's /Index contains a negative object id");
                    } else if (first > max_num_entries) {
                        throw damaged(
                            "Cross-reference stream's /Index contains an impossibly "
                            "large object id");
                    }
                }
            } else {
                throw damaged(
                    "Cross-reference stream's /Index's item " + std::to_string(i) +
                    " is not an integer");
            }
            i++;
        }
        QTC::TC("qpdf", "QPDF xref /Index is array", index_vec.size() == 2 ? 0 : 1);
        return {num_entries, indx};
    } else if (Index_obj.null()) {
        return {size, {{0, size}}};
    } else {
        throw damaged("Cross-reference stream does not have a proper /Index key");
    }
}

qpdf_offset_t
Objects::processXRefStream(
    qpdf_offset_t xref_offset, QPDFObjectHandle& xref_obj, bool in_stream_recovery)
{
    auto damaged = [this, xref_offset](std::string_view msg) -> QPDFExc {
        return damagedPDF("xref stream", xref_offset, msg.data());
    };

    auto dict = xref_obj.getDict();

    auto [entry_size, W] = processXRefW(dict, damaged);
    int max_num_entries = processXRefSize(dict, entry_size, damaged);
    auto [num_entries, indx] = processXRefIndex(dict, max_num_entries, damaged);

    std::shared_ptr<Buffer> bp = xref_obj.getStreamData(qpdf_dl_specialized);
    size_t actual_size = bp->getSize();
    auto expected_size = toS(entry_size) * toS(num_entries);

    if (expected_size != actual_size) {
        QPDFExc x = damaged(
            "Cross-reference stream data has the wrong size; expected = " +
            std::to_string(expected_size) + "; actual = " + std::to_string(actual_size));
        if (expected_size > actual_size) {
            throw x;
        } else {
            warn(x);
        }
    }

    bool saw_first_compressed_object = false;

    // Actual size vs. expected size check above ensures that we will not overflow any buffers here.
    // We know that entry_size * num_entries is less or equal to the size of the buffer.
    auto p = bp->getBuffer();
    for (auto [obj, sec_entries]: indx) {
        // Process a subsection.
        for (int i = 0; i < sec_entries; ++i) {
            // Read this entry
            std::array<qpdf_offset_t, 3> fields{};
            if (W[0] == 0) {
                fields[0] = 1;
            }
            for (size_t j = 0; j < 3; ++j) {
                for (int k = 0; k < W[j]; ++k) {
                    fields[j] <<= 8;
                    fields[j] |= *p++;
                }
            }

            // Get the generation number.  The generation number is 0 unless this is an uncompressed
            // object record, in which case the generation number appears as the third field.
            if (saw_first_compressed_object) {
                if (fields[0] != 2) {
                    uncompressed_after_compressed_ = true;
                }
            } else if (fields[0] == 2) {
                saw_first_compressed_object = true;
            }
            if (obj == 0) {
                // This is needed by checkLinearization()
                first_xref_item_offset_ = xref_offset;
            } else if (fields[0] == 0) {
                // Ignore fields[2], which we don't care about in this case. This works around the
                // issue of some PDF files that put invalid values, like -1, here for deleted
                // objects.
                insertFreeXrefEntry(QPDFObjGen(obj, 0));
            } else {
                auto typ = toI(fields[0]);
                if (!in_stream_recovery || typ == 2) {
                    // If we are in xref stream recovery all actual uncompressed objects have
                    // already been inserted into the xref table. Avoid adding junk data into the
                    // xref table.
                    insertXrefEntry(obj, toI(fields[0]), fields[1], toI(fields[2]));
                }
            }
            ++obj;
        }
    }

    if (!m->trailer) {
        setTrailer(dict);
    }

    if (dict.hasKey("/Prev")) {
        if (!dict.getKey("/Prev").isInteger()) {
            throw damagedPDF(
                "xref stream", "/Prev key in xref stream dictionary is not an integer");
        }
        return dict.getKey("/Prev").getIntValue();
    } else {
        return 0;
    }
}

void
Objects::insertXrefEntry(int obj, int f0, qpdf_offset_t f1, int f2)
{
    // Populate the xref table in such a way that the first reference to an object that we see,
    // which is the one in the latest xref table in which it appears, is the one that gets stored.
    // This works because we are reading more recent appends before older ones.

    // If there is already an entry for this object and generation in the table, it means that a
    // later xref table has registered this object.  Disregard this one.
    int new_gen = f0 == 2 ? 0 : f2;

    if (!(f0 == 1 || f0 == 2)) {
        return;
    }

    if (!(obj > 0 && obj <= m->xref_table_max_id && 0 <= f2 && new_gen < 65535)) {
        // We are ignoring invalid objgens. Most will arrive here from xref reconstruction. There
        // is probably no point having another warning but we could count invalid items in order to
        // decide when to give up.
        // ignore impossibly large object ids or object ids > Size.
        return;
    }

    if (m->deleted_objects.contains(obj)) {
        return;
    }

    if (f0 == 2) {
        if (f1 == obj) {
            warn(
                damagedPDF("xref stream", "self-referential object stream " + std::to_string(obj)));
            return;
        }
        if (f1 > m->xref_table_max_id) {
            // ignore impossibly large object stream ids
            warn(damagedPDF(
                "xref stream",
                "object stream id " + std::to_string(f1) + " for object " + std::to_string(obj) +
                    " is impossibly large"));
            return;
        }
    }

    auto [iter, created] = m->xref_table.try_emplace(QPDFObjGen(obj, (f0 == 2 ? 0 : f2)));
    if (!created) {
        return;
    }

    switch (f0) {
    case 1:
        // f2 is generation
        QTC::TC("qpdf", "QPDF xref gen > 0", ((f2 > 0) ? 1 : 0));
        iter->second = QPDFXRefEntry(f1);
        break;

    case 2:
        iter->second = QPDFXRefEntry(toI(f1), f2);
        break;

    default:
        throw damagedPDF("xref stream", "unknown xref stream entry type " + std::to_string(f0));
        break;
    }
}

void
Objects::insertFreeXrefEntry(QPDFObjGen og)
{
    if (!m->xref_table.contains(og) && og.getObj() <= m->xref_table_max_id) {
        m->deleted_objects.insert(og.getObj());
    }
}

void
QPDF::showXRefTable()
{
    auto& cout = *m->cf.log()->getInfo();
    for (auto const& iter: m->xref_table) {
        QPDFObjGen const& og = iter.first;
        QPDFXRefEntry const& entry = iter.second;
        cout << og.unparse('/') << ": ";
        switch (entry.getType()) {
        case 1:
            cout << "uncompressed; offset = " << entry.getOffset();
            break;

        case 2:
            *m->cf.log()->getInfo() << "compressed; stream = " << entry.getObjStreamNumber()
                                    << ", index = " << entry.getObjStreamIndex();
            break;

        default:
            throw std::logic_error("unknown cross-reference table type while showing xref_table");
            break;
        }
        m->cf.log()->info("\n");
    }
}

// Resolve all objects in the xref table. If this triggers a xref table reconstruction abort and
// return false. Otherwise return true.
bool
Objects::resolveXRefTable()
{
    bool may_change = !m->reconstructed_xref;
    for (auto& iter: m->xref_table) {
        if (isUnresolved(iter.first)) {
            resolve(iter.first);
            if (may_change && m->reconstructed_xref) {
                return false;
            }
        }
    }
    return true;
}

// Ensure all objects in the pdf file, including those in indirect references, appear in the object
// cache.
void
QPDF::fixDanglingReferences(bool force)
{
    if (m->fixed_dangling_refs) {
        return;
    }
    if (!m->objects.resolveXRefTable()) {
        m->objects.resolveXRefTable();
    }
    m->fixed_dangling_refs = true;
}

size_t
QPDF::getObjectCount()
{
    // This method returns the next available indirect object number. makeIndirectObject uses it for
    // this purpose. After fixDanglingReferences is called, all objects in the xref table will also
    // be in obj_cache.
    fixDanglingReferences();
    QPDFObjGen og;
    if (!m->obj_cache.empty()) {
        og = (*(m->obj_cache.rbegin())).first;
    }
    return QIntC::to_size(og.getObj());
}

std::vector<QPDFObjectHandle>
QPDF::getAllObjects()
{
    // After fixDanglingReferences is called, all objects are in the object cache.
    fixDanglingReferences();
    std::vector<QPDFObjectHandle> result;
    for (auto const& iter: m->obj_cache) {
        result.emplace_back(m->objects.newIndirect(iter.first, iter.second.object));
    }
    return result;
}

void
Objects::setLastObjectDescription(std::string const& description, QPDFObjGen og)
{
    m->last_object_description.clear();
    if (!description.empty()) {
        m->last_object_description += description;
        if (og.isIndirect()) {
            m->last_object_description += ": ";
        }
    }
    if (og.isIndirect()) {
        m->last_object_description += "object " + og.unparse(' ');
    }
}

QPDFObjectHandle
Objects::readTrailer()
{
    qpdf_offset_t offset = m->file->tell();
    auto object =
        Parser::parse(*m->file, "trailer", m->tokenizer, nullptr, qpdf, m->reconstructed_xref);
    if (object.isDictionary() && m->objects.readToken(*m->file).isWord("stream")) {
        warn(damagedPDF("trailer", m->file->tell(), "stream keyword found in trailer"));
    }
    // Override last_offset so that it points to the beginning of the object we just read
    m->file->setLastOffset(offset);
    return object;
}

QPDFObjectHandle
Objects::readObject(std::string const& description, QPDFObjGen og)
{
    setLastObjectDescription(description, og);
    qpdf_offset_t offset = m->file->tell();

    StringDecrypter decrypter{&qpdf, og};
    StringDecrypter* decrypter_ptr = m->encp->encrypted ? &decrypter : nullptr;
    auto object = Parser::parse(
        *m->file,
        m->last_object_description,
        m->tokenizer,
        decrypter_ptr,
        qpdf,
        m->reconstructed_xref || m->in_read_xref_stream);
    if (!object) {
        return {};
    }
    auto token = readToken(*m->file);
    if (object.isDictionary() && token.isWord("stream")) {
        readStream(object, og, offset);
        token = readToken(*m->file);
    }
    if (!token.isWord("endobj")) {
        warn(damagedPDF("expected endobj"));
    }
    return object;
}

// After reading stream dictionary and stream keyword, read rest of stream.
void
Objects::readStream(QPDFObjectHandle& object, QPDFObjGen og, qpdf_offset_t offset)
{
    validateStreamLineEnd(object, og, offset);

    // Must get offset before accessing any additional objects since resolving a previously
    // unresolved indirect object will change file position.
    qpdf_offset_t stream_offset = m->file->tell();
    size_t length = 0;

    try {
        auto length_obj = object.getKey("/Length");

        if (!length_obj.isInteger()) {
            if (length_obj.null()) {
                throw damagedPDF(offset, "stream dictionary lacks /Length key");
            }
            throw damagedPDF(offset, "/Length key in stream dictionary is not an integer");
        }

        length = toS(length_obj.getUIntValue());
        // Seek in two steps to avoid potential integer overflow
        m->file->seek(stream_offset, SEEK_SET);
        m->file->seek(toO(length), SEEK_CUR);
        if (!readToken(*m->file).isWord("endstream")) {
            throw damagedPDF("expected endstream");
        }
    } catch (QPDFExc& e) {
        if (!cf.surpress_recovery()) {
            warn(e);
            length = recoverStreamLength(m->file, og, stream_offset);
        } else {
            throw;
        }
    }
    object = QPDFObjectHandle(qpdf::Stream(qpdf, og, object, stream_offset, length));
}

void
Objects::validateStreamLineEnd(QPDFObjectHandle& object, QPDFObjGen og, qpdf_offset_t offset)
{
    // The PDF specification states that the word "stream" should be followed by either a carriage
    // return and a newline or by a newline alone.  It specifically disallowed following it by a
    // carriage return alone since, in that case, there would be no way to tell whether the NL in a
    // CR NL sequence was part of the stream data.  However, some readers, including Adobe reader,
    // accept a carriage return by itself when followed by a non-newline character, so that's what
    // we do here. We have also seen files that have extraneous whitespace between the stream
    // keyword and the newline.
    while (true) {
        char ch;
        if (m->file->read(&ch, 1) == 0) {
            // A premature EOF here will result in some other problem that will get reported at
            // another time.
            return;
        }
        if (ch == '\n') {
            // ready to read stream data
            return;
        }
        if (ch == '\r') {
            // Read another character
            if (m->file->read(&ch, 1) != 0) {
                if (ch == '\n') {
                    // Ready to read stream data
                    QTC::TC("qpdf", "QPDF stream with CRNL");
                } else {
                    // Treat the \r by itself as the whitespace after endstream and start reading
                    // stream data in spite of not having seen a newline.
                    m->file->unreadCh(ch);
                    warn(damagedPDF(
                        m->file->tell(), "stream keyword followed by carriage return only"));
                }
            }
            return;
        }
        if (!util::is_space(ch)) {
            m->file->unreadCh(ch);
            warn(damagedPDF(
                m->file->tell(), "stream keyword not followed by proper line terminator"));
            return;
        }
        warn(damagedPDF(m->file->tell(), "stream keyword followed by extraneous whitespace"));
    }
}

bool
Objects::findEndstream()
{
    // Find endstream or endobj. Position the input at that token.
    auto t = readToken(*m->file, 20);
    if (t.isWord("endobj") || t.isWord("endstream")) {
        m->file->seek(m->file->getLastOffset(), SEEK_SET);
        return true;
    }
    return false;
}

size_t
Objects::recoverStreamLength(
    std::shared_ptr<InputSource> input, QPDFObjGen og, qpdf_offset_t stream_offset)
{
    // Try to reconstruct stream length by looking for endstream or endobj
    warn(damagedPDF(*input, stream_offset, "attempting to recover stream length"));

    PatternFinder ef(*this, &Objects::findEndstream);
    size_t length = 0;
    if (m->file->findFirst("end", stream_offset, 0, ef)) {
        length = toS(m->file->tell() - stream_offset);
        // Reread endstream but, if it was endobj, don't skip that.
        QPDFTokenizer::Token t = readToken(*m->file);
        if (t.getValue() == "endobj") {
            m->file->seek(m->file->getLastOffset(), SEEK_SET);
        }
    }

    if (length) {
        auto end = stream_offset + toO(length);
        qpdf_offset_t found_offset = 0;
        QPDFObjGen found_og;

        // Make sure this is inside this object
        for (auto const& [current_og, entry]: m->xref_table) {
            if (entry.getType() == 1) {
                qpdf_offset_t obj_offset = entry.getOffset();
                if (found_offset < obj_offset && obj_offset < end) {
                    found_offset = obj_offset;
                    found_og = current_og;
                }
            }
        }
        if (!found_offset || found_og == og) {
            // If we are trying to recover an XRef stream the xref table will not contain and
            // won't contain any entries, therefore we cannot check the found length. Otherwise we
            // found endstream\nendobj within the space allowed for this object, so we're probably
            // in good shape.
        } else {
            length = 0;
        }
    }

    if (length == 0) {
        warn(damagedPDF(
            *input, stream_offset, "unable to recover stream data; treating stream as empty"));
    } else {
        warn(damagedPDF(
            *input, stream_offset, "recovered stream length: " + std::to_string(length)));
    }

    return length;
}

QPDFTokenizer::Token
Objects::readToken(InputSource& input, size_t max_len)
{
    return m->tokenizer.readToken(input, m->last_object_description, true, max_len);
}

QPDFObjGen
Objects::read_object_start(qpdf_offset_t offset)
{
    m->file->seek(offset, SEEK_SET);
    QPDFTokenizer::Token tobjid = readToken(*m->file);
    bool objidok = tobjid.isInteger();
    if (!objidok) {
        throw damagedPDF(offset, "expected n n obj");
    }
    QPDFTokenizer::Token tgen = readToken(*m->file);
    bool genok = tgen.isInteger();
    if (!genok) {
        throw damagedPDF(offset, "expected n n obj");
    }
    QPDFTokenizer::Token tobj = readToken(*m->file);

    bool objok = tobj.isWord("obj");

    if (!objok) {
        throw damagedPDF(offset, "expected n n obj");
    }
    int objid = QUtil::string_to_int(tobjid.getValue().c_str());
    int generation = QUtil::string_to_int(tgen.getValue().c_str());
    if (objid == 0) {
        throw damagedPDF(offset, "object with ID 0");
    }
    return {objid, generation};
}

void
Objects::readObjectAtOffset(
    bool try_recovery, qpdf_offset_t offset, std::string const& description, QPDFObjGen exp_og)
{
    QPDFObjGen og;
    setLastObjectDescription(description, exp_og);

    if (cf.surpress_recovery()) {
        try_recovery = false;
    }

    // Special case: if offset is 0, just return null.  Some PDF writers, in particular
    // "Mac OS X 10.7.5 Quartz PDFContext", may store deleted objects in the xref table as
    // "0000000000 00000 n", which is not correct, but it won't hurt anything for us to ignore
    // these.
    if (offset == 0) {
        warn(damagedPDF(
            -1,
            "object has offset 0 - a common error handled correctly by qpdf and most other "
            "applications"));
        return;
    }

    try {
        og = read_object_start(offset);
        if (exp_og != og) {
            QPDFExc e = damagedPDF(offset, "expected " + exp_og.unparse(' ') + " obj");
            if (try_recovery) {
                // Will be retried below
                throw e;
            } else {
                // We can try reading the object anyway even if the ID doesn't match.
                warn(e);
            }
        }
    } catch (QPDFExc& e) {
        if (!try_recovery) {
            throw;
        }
        // Try again after reconstructing xref table
        reconstruct_xref(e);
        if (m->xref_table.contains(exp_og) && m->xref_table[exp_og].getType() == 1) {
            qpdf_offset_t new_offset = m->xref_table[exp_og].getOffset();
            readObjectAtOffset(false, new_offset, description, exp_og);
            return;
        }
        warn(damagedPDF(
            "",
            -1,
            ("object " + exp_og.unparse(' ') +
             " not found in file after regenerating cross reference table")));
        return;
    }

    if (auto oh = readObject(description, og)) {
        // Determine the end offset of this object before and after white space.  We use these
        // numbers to validate linearization hint tables.  Offsets and lengths of objects may imply
        // the end of an object to be anywhere between these values.
        qpdf_offset_t end_before_space = m->file->tell();

        // skip over spaces
        while (true) {
            char ch;
            if (!m->file->read(&ch, 1)) {
                throw damagedPDF(m->file->tell(), "EOF after endobj");
            }
            if (!isspace(static_cast<unsigned char>(ch))) {
                m->file->seek(-1, SEEK_CUR);
                break;
            }
        }
        m->objects.updateCache(og, oh.obj_sp(), end_before_space, m->file->tell());
    }
}

QPDFObjectHandle
Objects::readObjectAtOffset(
    qpdf_offset_t offset, std::string const& description, bool skip_cache_if_in_xref)
{
    auto og = read_object_start(offset);
    auto oh = readObject(description, og);

    if (!oh || !m->objects.isUnresolved(og)) {
        return oh;
    }

    if (skip_cache_if_in_xref && m->xref_table.contains(og)) {
        // In the special case of the xref stream and linearization hint tables, the offset comes
        // from another source. For the specific case of xref streams, the xref stream is read and
        // loaded into the object cache very early in parsing. Ordinarily, when a file is updated by
        // appending, items inserted into the xref table in later updates take precedence over
        // earlier items. In the special case of reusing the object number previously used as the
        // xref stream, we have the following order of events:
        //
        // * reused object gets loaded into the xref table
        // * old object is read here while reading xref streams
        // * original xref entry is ignored (since already in xref table)
        //
        // It is the second step that causes a problem. Even though the xref table is correct in
        // this case, the old object is already in the cache and so effectively prevails over the
        // reused object. To work around this issue, we have a special case for the xref stream (via
        // the skip_cache_if_in_xref): if the object is already in the xref stream, don't cache what
        // we read here.
        //
        // It is likely that the same bug may exist for linearization hint tables, but the existing
        // code uses end_before_space and end_after_space from the cache, so fixing that would
        // require more significant rework. The chances of a linearization hint stream being reused
        // seems smaller because the xref stream is probably the highest object in the file and the
        // linearization hint stream would be some random place in the middle, so I'm leaving that
        // bug unfixed for now. If the bug were to be fixed, we could use !check_og in place of
        // skip_cache_if_in_xref.
        QTC::TC("qpdf", "QPDF skipping cache for known unchecked object");
        return oh;
    }

    // Determine the end offset of this object before and after white space.  We use these
    // numbers to validate linearization hint tables.  Offsets and lengths of objects may imply
    // the end of an object to be anywhere between these values.
    qpdf_offset_t end_before_space = m->file->tell();

    // skip over spaces
    while (true) {
        char ch;
        if (!m->file->read(&ch, 1)) {
            throw damagedPDF(m->file->tell(), "EOF after endobj");
        }
        if (!isspace(static_cast<unsigned char>(ch))) {
            m->file->seek(-1, SEEK_CUR);
            break;
        }
    }
    m->objects.updateCache(og, oh.obj_sp(), end_before_space, m->file->tell());

    return oh;
}

std::shared_ptr<QPDFObject> const&
Objects::resolve(QPDFObjGen og)
{
    if (!isUnresolved(og)) {
        return m->obj_cache[og].object;
    }

    if (m->resolving.contains(og)) {
        // This can happen if an object references itself directly or indirectly in some key that
        // has to be resolved during object parsing, such as stream length.
        warn(damagedPDF("", "loop detected resolving object " + og.unparse(' ')));
        updateCache(og, QPDFObject::create<QPDF_Null>(), -1, -1);
        return m->obj_cache[og].object;
    }
    ResolveRecorder rr(qpdf, og);

    if (m->xref_table.contains(og)) {
        QPDFXRefEntry const& entry = m->xref_table[og];
        try {
            switch (entry.getType()) {
            case 1:
                // Object stored in cache by readObjectAtOffset
                readObjectAtOffset(true, entry.getOffset(), "", og);
                break;

            case 2:
                resolveObjectsInStream(entry.getObjStreamNumber());
                break;

            default:
                throw damagedPDF(
                    "", -1, ("object " + og.unparse('/') + " has unexpected xref entry type"));
            }
        } catch (QPDFExc& e) {
            warn(e);
        } catch (std::exception& e) {
            warn(damagedPDF(
                "", -1, ("object " + og.unparse('/') + ": error reading object: " + e.what())));
        }
    }

    if (isUnresolved(og)) {
        // PDF spec says unknown objects resolve to the null object.
        updateCache(og, QPDFObject::create<QPDF_Null>(), -1, -1);
    }

    auto& result(m->obj_cache[og].object);
    result->setDefaultDescription(&qpdf, og);
    return result;
}

void
Objects::resolveObjectsInStream(int obj_stream_number)
{
    auto damaged =
        [this, obj_stream_number](int id, qpdf_offset_t offset, std::string const& msg) -> QPDFExc {
        return {
            qpdf_e_damaged_pdf,
            m->file->getName() + " object stream " + std::to_string(obj_stream_number),
            +"object " + std::to_string(id) + " 0",
            offset,
            msg,
            true};
    };

    if (m->resolved_object_streams.contains(obj_stream_number)) {
        return;
    }
    m->resolved_object_streams.insert(obj_stream_number);
    // Force resolution of object stream
    Stream obj_stream = qpdf.getObject(obj_stream_number, 0);
    if (!obj_stream) {
        throw damagedPDF(
            "object " + std::to_string(obj_stream_number) + " 0",
            "supposed object stream " + std::to_string(obj_stream_number) + " is not a stream");
    }

    // For linearization data in the object, use the data from the object stream for the objects in
    // the stream.
    QPDFObjGen stream_og(obj_stream_number, 0);
    qpdf_offset_t end_before_space = m->obj_cache[stream_og].end_before_space;
    qpdf_offset_t end_after_space = m->obj_cache[stream_og].end_after_space;

    QPDFObjectHandle dict = obj_stream.getDict();
    if (!dict.isDictionaryOfType("/ObjStm")) {
        warn(damagedPDF(
            "object " + std::to_string(obj_stream_number) + " 0",
            "supposed object stream " + std::to_string(obj_stream_number) + " has wrong type"));
    }

    unsigned int n{0};
    int first{0};
    if (!(dict.getKey("/N").getValueAsUInt(n) && dict.getKey("/First").getValueAsInt(first))) {
        throw damagedPDF(
            "object " + std::to_string(obj_stream_number) + " 0",
            "object stream " + std::to_string(obj_stream_number) + " has incorrect keys");
    }

    // id, offset, size
    std::vector<std::tuple<int, qpdf_offset_t, size_t>> offsets;

    auto stream_data = obj_stream.getStreamData(qpdf_dl_specialized);

    is::OffsetBuffer input("", stream_data);

    const auto b_size = stream_data.size();
    const auto end_offset = static_cast<qpdf_offset_t>(b_size);
    auto b_start = stream_data.data();

    if (first >= end_offset) {
        throw damagedPDF(
            "object " + std::to_string(obj_stream_number) + " 0",
            "object stream " + std::to_string(obj_stream_number) + " has invalid /First entry");
    }

    int id = 0;
    long long last_offset = -1;
    bool is_first = true;
    for (unsigned int i = 0; i < n; ++i) {
        auto tnum = readToken(input);
        auto id_offset = input.getLastOffset();
        auto toffset = readToken(input);
        if (!(tnum.isInteger() && toffset.isInteger())) {
            throw damaged(0, input.getLastOffset(), "expected integer in object stream header");
        }

        int num = QUtil::string_to_int(tnum.getValue().c_str());
        long long offset = QUtil::string_to_int(toffset.getValue().c_str());

        if (num == obj_stream_number) {
            warn(damaged(num, id_offset, "object stream claims to contain itself"));
            continue;
        }

        if (num < 1) {
            warn(damaged(num, id_offset, "object id is invalid"s));
            continue;
        }

        if (offset <= last_offset) {
            warn(damaged(
                num,
                input.getLastOffset(),
                "offset " + std::to_string(offset) +
                    " is invalid (must be larger than previous offset " +
                    std::to_string(last_offset) + ")"));
            continue;
        }

        if (num > m->xref_table_max_id) {
            continue;
        }

        if (first + offset >= end_offset) {
            warn(damaged(
                num, input.getLastOffset(), "offset " + std::to_string(offset) + " is too large"));
            continue;
        }

        if (is_first) {
            is_first = false;
        } else {
            offsets.emplace_back(
                id, last_offset + first, static_cast<size_t>(offset - last_offset));
        }

        last_offset = offset;
        id = num;
    }

    if (!is_first) {
        // We found at least one valid entry.
        offsets.emplace_back(
            id, last_offset + first, b_size - static_cast<size_t>(last_offset + first));
    }

    // To avoid having to read the object stream multiple times, store all objects that would be
    // found here in the cache.  Remember that some objects stored here might have been overridden
    // by new objects appended to the file, so it is necessary to recheck the xref table and only
    // cache what would actually be resolved here.
    for (auto const& [obj_id, obj_offset, obj_size]: offsets) {
        QPDFObjGen og(obj_id, 0);
        auto entry = m->xref_table.find(og);
        if (entry != m->xref_table.end() && entry->second.getType() == 2 &&
            entry->second.getObjStreamNumber() == obj_stream_number) {
            is::OffsetBuffer in("", {b_start + obj_offset, obj_size}, obj_offset);
            if (auto oh = Parser::parse(in, obj_stream_number, obj_id, m->tokenizer, qpdf)) {
                updateCache(og, oh.obj_sp(), end_before_space, end_after_space);
            }
        } else {
            QTC::TC("qpdf", "QPDF not caching overridden objstm object");
        }
    }
}

QPDFObjectHandle
Objects::newIndirect(QPDFObjGen og, std::shared_ptr<QPDFObject> const& obj)
{
    obj->setDefaultDescription(&qpdf, og);
    return {obj};
}

void
Objects::updateCache(
    QPDFObjGen og,
    std::shared_ptr<QPDFObject> const& object,
    qpdf_offset_t end_before_space,
    qpdf_offset_t end_after_space,
    bool destroy)
{
    object->setObjGen(&qpdf, og);
    if (isCached(og)) {
        auto& cache = m->obj_cache[og];
        object->move_to(cache.object, destroy);
        cache.end_before_space = end_before_space;
        cache.end_after_space = end_after_space;
    } else {
        m->obj_cache[og] = ObjCache(object, end_before_space, end_after_space);
    }
}

bool
Objects::isCached(QPDFObjGen og)
{
    return m->obj_cache.contains(og);
}

bool
Objects::isUnresolved(QPDFObjGen og)
{
    return !isCached(og) || m->obj_cache[og].object->isUnresolved();
}

QPDFObjGen
Objects::nextObjGen()
{
    int max_objid = toI(qpdf.getObjectCount());
    if (max_objid == std::numeric_limits<int>::max()) {
        throw std::range_error("max object id is too high to create new objects");
    }
    return {max_objid + 1, 0};
}

QPDFObjectHandle
Objects::makeIndirectFromQPDFObject(std::shared_ptr<QPDFObject> const& obj)
{
    QPDFObjGen next{nextObjGen()};
    m->obj_cache[next] = ObjCache(obj, -1, -1);
    return newIndirect(next, m->obj_cache[next].object);
}

QPDFObjectHandle
QPDF::makeIndirectObject(QPDFObjectHandle oh)
{
    if (!oh) {
        throw std::logic_error("attempted to make an uninitialized QPDFObjectHandle indirect");
    }
    return m->objects.makeIndirectFromQPDFObject(oh.obj_sp());
}

std::shared_ptr<QPDFObject>
Objects::getObjectForParser(int id, int gen, bool parse_pdf)
{
    // This method is called by the parser and therefore must not resolve any objects.
    auto og = QPDFObjGen(id, gen);
    if (auto iter = m->obj_cache.find(og); iter != m->obj_cache.end()) {
        return iter->second.object;
    }
    if (m->xref_table.contains(og) || (!m->parsed && og.getObj() < m->xref_table_max_id)) {
        return m->obj_cache.insert({og, QPDFObject::create<QPDF_Unresolved>(&qpdf, og)})
            .first->second.object;
    }
    if (parse_pdf) {
        return QPDFObject::create<QPDF_Null>();
    }
    return m->obj_cache.insert({og, QPDFObject::create<QPDF_Null>(&qpdf, og)}).first->second.object;
}

std::shared_ptr<QPDFObject>
Objects::getObjectForJSON(int id, int gen)
{
    auto og = QPDFObjGen(id, gen);
    auto [it, inserted] = m->obj_cache.try_emplace(og);
    auto& obj = it->second.object;
    if (inserted) {
        obj = (m->parsed && !m->xref_table.contains(og))
            ? QPDFObject::create<QPDF_Null>(&qpdf, og)
            : QPDFObject::create<QPDF_Unresolved>(&qpdf, og);
    }
    return obj;
}

QPDFObjectHandle
QPDF::getObject(QPDFObjGen og)
{
    if (auto it = m->obj_cache.find(og); it != m->obj_cache.end()) {
        return {it->second.object};
    } else if (m->parsed && !m->xref_table.contains(og)) {
        return QPDFObject::create<QPDF_Null>();
    } else {
        auto result =
            m->obj_cache.try_emplace(og, QPDFObject::create<QPDF_Unresolved>(this, og), -1, -1);
        return {result.first->second.object};
    }
}

void
QPDF::replaceObject(int objid, int generation, QPDFObjectHandle oh)
{
    replaceObject(QPDFObjGen(objid, generation), oh);
}

void
QPDF::replaceObject(QPDFObjGen og, QPDFObjectHandle oh)
{
    if (!oh || (oh.isIndirect() && !(oh.isStream() && oh.getObjGen() == og))) {
        throw std::logic_error("QPDF::replaceObject called with indirect object handle");
    }
    m->objects.updateCache(og, oh.obj_sp(), -1, -1, false);
}

void
QPDF::removeObject(QPDFObjGen og)
{
    m->xref_table.erase(og);
    if (auto cached = m->obj_cache.find(og); cached != m->obj_cache.end()) {
        // Take care of any object handles that may be floating around.
        cached->second.object->assign_null();
        cached->second.object->setObjGen(nullptr, QPDFObjGen());
        m->obj_cache.erase(cached);
    }
}

void
QPDF::replaceReserved(QPDFObjectHandle reserved, QPDFObjectHandle replacement)
{
    QTC::TC("qpdf", "QPDF replaceReserved");
    auto tc = reserved.getTypeCode();
    if (!(tc == ::ot_reserved || tc == ::ot_null)) {
        throw std::logic_error("replaceReserved called with non-reserved object");
    }
    replaceObject(reserved.getObjGen(), replacement);
}

void
QPDF::swapObjects(int objid1, int generation1, int objid2, int generation2)
{
    swapObjects(QPDFObjGen(objid1, generation1), QPDFObjGen(objid2, generation2));
}

void
QPDF::swapObjects(QPDFObjGen og1, QPDFObjGen og2)
{
    // Force objects to be read from the input source if needed, then swap them in the cache.
    m->objects.resolve(og1);
    m->objects.resolve(og2);
    m->obj_cache[og1].object->swapWith(m->obj_cache[og2].object);
}

size_t
Objects::table_size()
{
    // If obj_cache is dense, accommodate all object in tables,else accommodate only original
    // objects.
    auto max_xref = !m->xref_table.empty() ? m->xref_table.crbegin()->first.getObj() : 0;
    auto max_obj = !m->obj_cache.empty() ? m->obj_cache.crbegin()->first.getObj() : 0;
    auto max_id = std::numeric_limits<int>::max() - 1;
    if (max_obj >= max_id || max_xref >= max_id) {
        // Temporary fix. Long-term solution is
        // - QPDFObjGen to enforce objgens are valid and sensible
        // - xref table and obj cache to protect against insertion of impossibly large obj ids
        stopOnError("Impossibly large object id encountered.");
    }
    if (max_obj < 1.1 * std::max(toI(m->obj_cache.size()), max_xref)) {
        return toS(++max_obj);
    }
    return toS(++max_xref);
}

std::vector<QPDFObjGen>
Objects::compressible_vector()
{
    return compressible<QPDFObjGen>();
}

std::vector<bool>
Objects::compressible_set()
{
    return compressible<bool>();
}

template <typename T>
std::vector<T>
Objects::compressible()
{
    // Return a list of objects that are allowed to be in object streams.  Walk through the objects
    // by traversing the document from the root, including a traversal of the pages tree.  This
    // makes that objects that are on the same page are more likely to be in the same object stream,
    // which is slightly more efficient, particularly with linearized files.  This is better than
    // iterating through the xref table since it avoids preserving orphaned items.

    // Exclude encryption dictionary, if any
    QPDFObjectHandle encryption_dict = m->trailer.getKey("/Encrypt");
    QPDFObjGen encryption_dict_og = encryption_dict.getObjGen();

    const size_t max_obj = qpdf.getObjectCount();
    std::vector<bool> visited(max_obj, false);
    std::vector<QPDFObjectHandle> queue;
    queue.reserve(512);
    queue.emplace_back(m->trailer);
    std::vector<T> result;
    if constexpr (std::is_same_v<T, QPDFObjGen>) {
        result.reserve(m->obj_cache.size());
    } else {
        qpdf_static_expect(std::is_same_v<T, bool>);
        result.resize(max_obj + 1U, false);
    }
    while (!queue.empty()) {
        auto obj = queue.back();
        queue.pop_back();
        if (obj.getObjectID() > 0) {
            QPDFObjGen og = obj.getObjGen();
            const size_t id = toS(og.getObj() - 1);
            if (id >= max_obj) {
                throw std::logic_error(
                    "unexpected object id encountered in getCompressibleObjGens");
            }
            if (visited[id]) {
                continue;
            }

            // Check whether this is the current object. If not, remove it (which changes it into a
            // direct null and therefore stops us from revisiting it) and move on to the next object
            // in the queue.
            auto upper = m->obj_cache.upper_bound(og);
            if (upper != m->obj_cache.end() && upper->first.getObj() == og.getObj()) {
                qpdf.removeObject(og);
                continue;
            }

            visited[id] = true;

            if (og == encryption_dict_og) {
                QTC::TC("qpdf", "QPDF exclude encryption dictionary");
            } else if (!(obj.isStream() ||
                         (obj.isDictionaryOfType("/Sig") && obj.hasKey("/ByteRange") &&
                          obj.hasKey("/Contents")))) {
                if constexpr (std::is_same_v<T, QPDFObjGen>) {
                    result.push_back(og);
                } else if constexpr (std::is_same_v<T, bool>) {
                    result[id + 1U] = true;
                }
            }
        }
        if (obj.isStream()) {
            auto dict = obj.getDict().as_dictionary();
            auto end = dict.crend();
            for (auto iter = dict.crbegin(); iter != end; ++iter) {
                std::string const& key = iter->first;
                QPDFObjectHandle const& value = iter->second;
                if (!value.null()) {
                    if (key == "/Length") {
                        // omit stream lengths
                        if (value.isIndirect()) {
                            QTC::TC("qpdf", "QPDF exclude indirect length");
                        }
                    } else {
                        queue.emplace_back(value);
                    }
                }
            }
        } else if (obj.isDictionary()) {
            auto dict = obj.as_dictionary();
            auto end = dict.crend();
            for (auto iter = dict.crbegin(); iter != end; ++iter) {
                if (!iter->second.null()) {
                    queue.emplace_back(iter->second);
                }
            }
        } else if (auto items = obj.as_array()) {
            queue.insert(queue.end(), items.crbegin(), items.crend());
        }
    }

    return result;
}

Coverage Report

Created: 2026-06-09 07:01