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qpdf/libqpdf/QPDF_objects.cc

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#include <qpdf/qpdf-config.h> // include first for large file support
#include <qpdf/QPDF_private.hh>
#include <array>
#include <cstring>
#include <limits>
#include <map>
#include <vector>
#include <qpdf/BufferInputSource.hh>
#include <qpdf/OffsetInputSource.hh>
#include <qpdf/Pipeline.hh>
#include <qpdf/QPDFExc.hh>
#include <qpdf/QPDFLogger.hh>
#include <qpdf/QPDFObject_private.hh>
#include <qpdf/QPDFParser.hh>
#include <qpdf/QPDF_Array.hh>
#include <qpdf/QPDF_Dictionary.hh>
#include <qpdf/QPDF_Null.hh>
#include <qpdf/QPDF_Reserved.hh>
#include <qpdf/QPDF_Stream.hh>
#include <qpdf/QPDF_Unresolved.hh>
#include <qpdf/QTC.hh>
#include <qpdf/QUtil.hh>
using Objects = QPDF::Objects;
using Xref_table = Objects::Xref_table;
namespace
{
class InvalidInputSource final: public InputSource
{
public:
InvalidInputSource(std::string const& name) :
name(name)
{
}
~InvalidInputSource() final = default;
qpdf_offset_t
findAndSkipNextEOL() final
{
throwException();
return 0;
}
std::string const&
getName() const final
{
return name;
}
qpdf_offset_t
tell() final
{
throwException();
return 0;
}
void
seek(qpdf_offset_t offset, int whence) final
{
throwException();
}
void
rewind() final
{
throwException();
}
size_t
read(char* buffer, size_t length) final
{
throwException();
return 0;
}
void
unreadCh(char ch) final
{
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");
}
std::string const& name;
};
} // namespace
bool
QPDF::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
Xref_table::initialize_empty()
{
initialized_ = true;
trailer_ = QPDFObjectHandle::newDictionary();
auto rt = qpdf.makeIndirectObject(QPDFObjectHandle::newDictionary());
auto pgs = qpdf.makeIndirectObject(QPDFObjectHandle::newDictionary());
pgs.replaceKey("/Type", QPDFObjectHandle::newName("/Pages"));
pgs.replaceKey("/Kids", QPDFObjectHandle::newArray());
pgs.replaceKey("/Count", QPDFObjectHandle::newInteger(0));
rt.replaceKey("/Type", QPDFObjectHandle::newName("/Catalog"));
rt.replaceKey("/Pages", pgs);
trailer_.replaceKey("/Root", rt);
trailer_.replaceKey("/Size", QPDFObjectHandle::newInteger(3));
}
void
Xref_table::initialize_json()
{
initialized_ = true;
table.resize(1);
trailer_ = QPDFObjectHandle::newDictionary();
trailer_.replaceKey("/Size", QPDFObjectHandle::newInteger(1));
}
void
Xref_table::initialize()
{
// 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.
file->seek(0, SEEK_END);
qpdf_offset_t end_offset = file->tell();
// Sanity check on object ids. All objects must appear in xref table / stream. In all realistic
// scenarios at least 3 bytes are required.
if (max_id_ > end_offset / 3) {
max_id_ = static_cast<int>(end_offset / 3);
}
qpdf_offset_t start_offset = (end_offset > 1054 ? end_offset - 1054 : 0);
PatternFinder sf(qpdf, &QPDF::findStartxref);
qpdf_offset_t xref_offset = 0;
if (file->findLast("startxref", start_offset, 0, sf)) {
xref_offset = QUtil::string_to_ll(read_token().getValue().c_str());
}
try {
if (xref_offset == 0) {
QTC::TC("qpdf", "QPDF can't find startxref");
throw damaged_pdf("can't find startxref");
}
try {
read(xref_offset);
} catch (QPDFExc&) {
throw;
} catch (std::exception& e) {
throw damaged_pdf(std::string("error reading xref: ") + e.what());
}
} catch (QPDFExc& e) {
if (attempt_recovery_) {
reconstruct(e);
QTC::TC("qpdf", "QPDF reconstructed xref table");
} else {
throw;
}
}
initialized_ = true;
}
void
Xref_table::reconstruct(QPDFExc& e)
{
if (reconstructed_) {
// 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 = qpdf.m->warnings.size() + 1000U;
auto check_warnings = [this, max_warnings]() {
if (qpdf.m->warnings.size() > max_warnings) {
throw damaged_pdf("too many errors while reconstructing cross-reference table");
}
};
reconstructed_ = true;
// We may find more objects, which may contain dangling references.
qpdf.m->fixed_dangling_refs = false;
warn_damaged("file is damaged");
qpdf.warn(e);
warn_damaged("Attempting to reconstruct cross-reference table");
// Delete all references to type 1 (uncompressed) objects
for (auto& iter: table) {
if (iter.type() == 1) {
iter = {};
}
}
std::vector<std::tuple<int, int, qpdf_offset_t>> objects;
std::vector<qpdf_offset_t> trailers;
int max_found = 0;
file->seek(0, SEEK_END);
qpdf_offset_t eof = file->tell();
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 (file->tell() < eof) {
QPDFTokenizer::Token t1 = read_token(MAX_LEN);
qpdf_offset_t token_start = file->tell() - toO(t1.getValue().length());
if (t1.isInteger()) {
auto pos = file->tell();
QPDFTokenizer::Token t2 = read_token(MAX_LEN);
if (t2.isInteger() && read_token(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 <= max_id_) {
objects.emplace_back(obj, gen, token_start);
if (obj > max_found) {
max_found = obj;
}
} else {
warn_damaged("ignoring object with impossibly large id " + std::to_string(obj));
}
}
file->seek(pos, SEEK_SET);
} else if (!trailer_ && t1.isWord("trailer")) {
trailers.emplace_back(file->tell());
}
file->findAndSkipNextEOL();
}
table.resize(toS(max_found) + 1);
for (auto tr: trailers) {
file->seek(tr, SEEK_SET);
auto t = read_trailer();
if (!t.isDictionary()) {
// Oh well. It was worth a try.
} else {
trailer_ = t;
break;
}
check_warnings();
}
auto rend = objects.rend();
for (auto it = objects.rbegin(); it != rend; it++) {
auto [obj, gen, token_start] = *it;
insert(obj, 1, token_start, gen);
check_warnings();
}
if (!trailer_) {
qpdf_offset_t max_offset{0};
// If there are any xref streams, take the last one to appear.
int i = -1;
for (auto const& item: table) {
++i;
if (item.type() != 1) {
continue;
}
auto oh = qpdf.getObject(i, item.gen());
try {
if (!oh.isStreamOfType("/XRef")) {
continue;
}
} catch (std::exception&) {
continue;
}
auto offset = item.offset();
if (offset > max_offset) {
max_offset = offset;
trailer_ = oh.getDict();
}
check_warnings();
}
if (max_offset > 0) {
try {
read(max_offset);
} catch (std::exception&) {
throw damaged_pdf(
"error decoding candidate xref stream while recovering damaged file");
}
QTC::TC("qpdf", "QPDF recover xref stream");
}
}
if (!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 damaged_pdf("unable to find trailer dictionary while recovering damaged file");
}
if (table.empty()) {
// We cannot check for an empty xref table in parse because empty tables are valid when
// creating QPDF objects from JSON.
throw damaged_pdf("unable to find objects while recovering damaged file");
}
check_warnings();
if (!initialized_) {
initialized_ = true;
qpdf.getAllPages();
check_warnings();
if (qpdf.m->all_pages.empty()) {
initialized_ = false;
throw damaged_pdf("unable to find any pages while recovering damaged file");
}
}
// 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
Xref_table::read(qpdf_offset_t xref_offset)
{
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));
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 == file->read(&ch, 1)) {
if (QUtil::is_space(ch)) {
skipped_space = true;
} else {
file->unreadCh(ch);
done = true;
}
} else {
QTC::TC("qpdf", "QPDF eof skipping spaces before xref", skipped_space ? 0 : 1);
done = true;
}
}
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) && QUtil::is_space(buf[4])) {
if (skipped_space) {
QTC::TC("qpdf", "QPDF xref skipped space");
warn_damaged("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 QUtil::is_space('\0') is false, so this won't overrun.
while (QUtil::is_space(buf[skip])) {
++skip;
}
xref_offset = process_section(xref_offset + skip);
} else {
xref_offset = read_stream(xref_offset);
}
if (visited.count(xref_offset) != 0) {
QTC::TC("qpdf", "QPDF xref loop");
throw damaged_pdf("loop detected following xref tables");
}
}
if (!trailer_) {
throw damaged_pdf("unable to find trailer while reading xref");
}
int size = trailer_.getKey("/Size").getIntValueAsInt();
if (size < 3) {
throw damaged_pdf("too few objects - file can't have a page tree");
}
// We are no longer reporting what the highest id in the xref table is. I don't think it adds
// anything. If we want to report more detail, we should report the total number of missing
// entries, including missing entries before the last actual entry.
}
Xref_table::Subsection
Xref_table::subsection(std::string const& line)
{
auto terminate = [this]() -> void {
QTC::TC("qpdf", "QPDF invalid xref");
throw damaged_table("xref syntax invalid");
};
// 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 (QUtil::is_space(*p)) {
++p;
}
// Require digit
if (!QUtil::is_digit(*p)) {
terminate();
}
// Gather digits
std::string obj_str;
while (QUtil::is_digit(*p)) {
obj_str.append(1, *p++);
}
// Require space
if (!QUtil::is_space(*p)) {
terminate();
}
// Skip spaces
while (QUtil::is_space(*p)) {
++p;
}
// Require digit
if (!QUtil::is_digit(*p)) {
terminate();
}
// Gather digits
std::string num_str;
while (QUtil::is_digit(*p)) {
num_str.append(1, *p++);
}
// Skip any space including line terminators
while (QUtil::is_space(*p)) {
++p;
}
auto obj = QUtil::string_to_int(obj_str.c_str());
auto count = QUtil::string_to_int(num_str.c_str());
if (obj > max_id() || count > max_id() || (obj + count) > max_id()) {
throw damaged_table("xref table subsection header contains impossibly large entry");
}
return {obj, count, file->getLastOffset() + toI(p - start)};
}
std::vector<Xref_table::Subsection>
Xref_table::bad_subsections(std::string& line, qpdf_offset_t start)
{
std::vector<Xref_table::Subsection> result;
file->seek(start, SEEK_SET);
while (true) {
line.assign(50, '\0');
file->read(line.data(), line.size());
auto [obj, num, offset] = result.emplace_back(subsection(line));
file->seek(offset, SEEK_SET);
for (qpdf_offset_t i = obj; i - num < obj; ++i) {
if (!std::get<0>(read_entry())) {
QTC::TC("qpdf", "QPDF invalid xref entry");
throw damaged_table("invalid xref entry (obj=" + std::to_string(i) + ")");
}
}
qpdf_offset_t pos = file->tell();
if (read_token().isWord("trailer")) {
return result;
} else {
file->seek(pos, SEEK_SET);
}
}
}
// Optimistically read and parse all subsection headers. If an error is encountered return the
// result of bad_subsections.
std::vector<Xref_table::Subsection>
Xref_table::subsections(std::string& line)
{
auto recovery_offset = file->tell();
try {
std::vector<Xref_table::Subsection> result;
while (true) {
line.assign(50, '\0');
file->read(line.data(), line.size());
auto& sub = result.emplace_back(subsection(line));
auto count = std::get<1>(sub);
auto offset = std::get<2>(sub);
file->seek(offset + 20 * toO(count) - 1, SEEK_SET);
file->read(line.data(), 1);
if (!(line[0] == '\n' || line[0] == '\n')) {
return bad_subsections(line, recovery_offset);
}
qpdf_offset_t pos = file->tell();
if (read_token().isWord("trailer")) {
return result;
} else {
file->seek(pos, SEEK_SET);
}
}
} catch (...) {
return bad_subsections(line, recovery_offset);
}
}
// Returns (success, f1, f2, type).
std::tuple<bool, qpdf_offset_t, int, char>
Xref_table::read_bad_entry()
{
qpdf_offset_t f1{0};
int f2{0};
char type{'\0'};
// Reposition after initial read attempt and reread.
file->seek(file->getLastOffset(), SEEK_SET);
auto line = 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 (QUtil::is_space(*p)) {
++p;
QTC::TC("qpdf", "QPDF ignore first space in xref entry");
invalid = true;
}
// Require digit
if (!QUtil::is_digit(*p)) {
return {false, 0, 0, '\0'};
}
// Gather digits
std::string f1_str;
while (QUtil::is_digit(*p)) {
f1_str.append(1, *p++);
}
// Require space
if (!QUtil::is_space(*p)) {
return {false, 0, 0, '\0'};
}
if (QUtil::is_space(*(p + 1))) {
QTC::TC("qpdf", "QPDF ignore first extra space in xref entry");
invalid = true;
}
// Skip spaces
while (QUtil::is_space(*p)) {
++p;
}
// Require digit
if (!QUtil::is_digit(*p)) {
return {false, 0, 0, '\0'};
}
// Gather digits
std::string f2_str;
while (QUtil::is_digit(*p)) {
f2_str.append(1, *p++);
}
// Require space
if (!QUtil::is_space(*p)) {
return {false, 0, 0, '\0'};
}
if (QUtil::is_space(*(p + 1))) {
QTC::TC("qpdf", "QPDF ignore second extra space in xref entry");
invalid = true;
}
// Skip spaces
while (QUtil::is_space(*p)) {
++p;
}
if ((*p == 'f') || (*p == 'n')) {
type = *p;
} else {
return {false, 0, 0, '\0'};
}
if ((f1_str.length() != 10) || (f2_str.length() != 5)) {
QTC::TC("qpdf", "QPDF ignore length error xref entry");
invalid = true;
}
if (invalid) {
qpdf.warn(damaged_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, f1, f2, type};
}
// Optimistically read and parse xref entry. If entry is bad, call read_bad_xrefEntry and return
// result. Returns (success, f1, f2, type).
std::tuple<bool, qpdf_offset_t, int, char>
Xref_table::read_entry()
{
qpdf_offset_t f1{0};
int f2{0};
char type{'\0'};
std::array<char, 21> line;
f1 = 0;
f2 = 0;
if (file->read(line.data(), 20) != 20) {
// C++20: [[unlikely]]
return {false, 0, 0, '\0'};
}
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 (QUtil::is_digit(*p) && f1_len++ < 10) {
f1 *= 10;
f1 += *p++ - '0';
}
// Require space
if (!QUtil::is_space(*p++)) {
// Entry doesn't start with space or digit.
// C++20: [[unlikely]]
return {false, 0, 0, '\0'};
}
// Gather digits. NB No risk of overflow as 99'999 < max int.
while (*p == '0') {
++f2_len;
++p;
}
while (QUtil::is_digit(*p) && f2_len++ < 5) {
f2 *= 10;
f2 += static_cast<int>(*p++ - '0');
}
if (QUtil::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, f1, f2, type};
}
}
return read_bad_entry();
}
// Read a single cross-reference table section and associated trailer.
qpdf_offset_t
Xref_table::process_section(qpdf_offset_t xref_offset)
{
file->seek(xref_offset, SEEK_SET);
std::string line;
auto subs = subsections(line);
auto cur_trailer_offset = file->tell();
auto cur_trailer = read_trailer();
if (!cur_trailer.isDictionary()) {
QTC::TC("qpdf", "QPDF missing trailer");
throw qpdf.damagedPDF("", "expected trailer dictionary");
}
if (!trailer_) {
unsigned int sz;
trailer_ = cur_trailer;
if (!trailer_.hasKey("/Size")) {
QTC::TC("qpdf", "QPDF trailer lacks size");
throw qpdf.damagedPDF("trailer", "trailer dictionary lacks /Size key");
}
if (!trailer_.getKey("/Size").getValueAsUInt(sz)) {
QTC::TC("qpdf", "QPDF trailer size not integer");
throw qpdf.damagedPDF("trailer", "/Size key in trailer dictionary is not an integer");
}
if (sz >= static_cast<unsigned int>(max_id_)) {
QTC::TC("qpdf", "QPDF trailer size impossibly large");
throw qpdf.damagedPDF("trailer", "/Size key in trailer dictionary is impossibly large");
}
table.resize(sz);
}
for (auto [obj, num, offset]: subs) {
file->seek(offset, SEEK_SET);
for (qpdf_offset_t i = obj; i - num < obj; ++i) {
if (i == 0) {
// This is needed by checkLinearization()
first_item_offset_ = file->tell();
}
// For xref_table, these will always be small enough to be ints
auto [success, f1, f2, type] = read_entry();
if (!success) {
throw damaged_table("invalid xref entry (obj=" + std::to_string(i) + ")");
}
if (type == 'f') {
insert_free(QPDFObjGen(toI(i), f2));
} else {
insert(toI(i), 1, f1, f2);
}
}
qpdf_offset_t pos = file->tell();
if (read_token().isWord("trailer")) {
break;
} else {
file->seek(pos, SEEK_SET);
}
}
if (cur_trailer.hasKey("/XRefStm")) {
if (ignore_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_stream(cur_trailer.getKey("/XRefStm").getIntValue());
} else {
throw qpdf.damagedPDF("xref stream", cur_trailer_offset, "invalid /XRefStm");
}
}
}
if (cur_trailer.hasKey("/Prev")) {
if (!cur_trailer.getKey("/Prev").isInteger()) {
QTC::TC("qpdf", "QPDF trailer prev not integer");
throw qpdf.damagedPDF(
"trailer", cur_trailer_offset, "/Prev key in trailer dictionary is not an integer");
}
QTC::TC("qpdf", "QPDF prev key in trailer dictionary");
return cur_trailer.getKey("/Prev").getIntValue();
}
return 0;
}
// Read a single cross-reference stream.
qpdf_offset_t
Xref_table::read_stream(qpdf_offset_t xref_offset)
{
if (!ignore_streams_) {
QPDFObjGen x_og;
QPDFObjectHandle xref_obj;
try {
xref_obj = qpdf.objects().read(
false, xref_offset, "xref stream", QPDFObjGen(0, 0), x_og, true);
} catch (QPDFExc&) {
// ignore -- report error below
}
if (xref_obj.isStreamOfType("/XRef")) {
QTC::TC("qpdf", "QPDF found xref stream");
return process_stream(xref_offset, xref_obj);
}
}
QTC::TC("qpdf", "QPDF can't find xref");
throw qpdf.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>>
Xref_table::process_W(QPDFObjectHandle& dict, std::function<QPDFExc(std::string_view)> damaged)
{
auto W_obj = dict.getKey("/W");
if (!(W_obj.isArray() && W_obj.getArrayNItems() >= 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 entry and return the maximum number of entries that the xref stream can contain and
// the value of the Size entry.
std::pair<int, size_t>
Xref_table::process_Size(
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, toS(size)};
}
// Return the number of entries of the xref stream and the processed Index array.
std::pair<int, std::vector<std::pair<int, int>>>
Xref_table::process_Index(
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.isNull()) {
QTC::TC("qpdf", "QPDF xref /Index is null");
return {size, {{0, size}}};
} else {
throw damaged("Cross-reference stream does not have a proper /Index key");
}
}
qpdf_offset_t
Xref_table::process_stream(qpdf_offset_t xref_offset, QPDFObjectHandle& xref_obj)
{
auto damaged = [this, xref_offset](std::string_view msg) -> QPDFExc {
return qpdf.damagedPDF("xref stream", xref_offset, msg.data());
};
auto dict = xref_obj.getDict();
auto [entry_size, W] = process_W(dict, damaged);
auto [max_num_entries, size] = process_Size(dict, entry_size, damaged);
auto [num_entries, indx] = process_Index(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 {
qpdf.warn(x);
}
}
if (!trailer_) {
trailer_ = dict;
if (size > toS(max_id_)) {
throw damaged("Cross-reference stream /Size entry is impossibly large");
}
table.resize(size);
}
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) {
QTC::TC("qpdf", "QPDF default for xref stream field 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_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.
insert_free(QPDFObjGen(obj, 0));
} else {
insert(obj, toI(fields[0]), fields[1], toI(fields[2]));
}
++obj;
}
}
if (dict.hasKey("/Prev")) {
if (!dict.getKey("/Prev").isInteger()) {
throw qpdf.damagedPDF(
"xref stream", "/Prev key in xref stream dictionary is not an integer");
}
QTC::TC("qpdf", "QPDF prev key in xref stream dictionary");
return dict.getKey("/Prev").getIntValue();
} else {
return 0;
}
}
void
Xref_table::insert(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 (!(obj > 0 && static_cast<size_t>(obj) < table.size() && 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.
QTC::TC("qpdf", "QPDF xref overwrite invalid objgen");
return;
}
auto& entry = table[static_cast<size_t>(obj)];
auto old_type = entry.type();
if (!old_type && entry.gen() > 0) {
// At the moment we are processing the updates last to first and therefore the gen doesn't
// matter as long as it > 0 to distinguish it from an uninitialized entry. This will need
// to be revisited when we want to support incremental updates or more comprehensive
// checking.
QTC::TC("qpdf", "QPDF xref deleted object");
return;
}
if (f0 == 2 && static_cast<int>(f1) == obj) {
qpdf.warn(qpdf.damagedPDF(
"xref stream", "self-referential object stream " + std::to_string(obj)));
return;
}
if (old_type && entry.gen() >= new_gen) {
QTC::TC("qpdf", "QPDF xref reused object");
return;
}
switch (f0) {
case 1:
// f2 is generation
QTC::TC("qpdf", "QPDF xref gen > 0", (f2 > 0) ? 1 : 0);
entry = {f2, Uncompressed(f1)};
break;
case 2:
entry = {0, Compressed(toI(f1), f2)};
object_streams_ = true;
break;
default:
throw qpdf.damagedPDF(
"xref stream", "unknown xref stream entry type " + std::to_string(f0));
break;
}
}
void
Xref_table::insert_free(QPDFObjGen og)
{
// At the moment we are processing the updates last to first and therefore the gen doesn't
// matter as long as it > 0 to distinguish it from an uninitialized entry. This will need to be
// revisited when we want to support incremental updates or more comprehensive checking.
if (og.getObj() < 1) {
return;
}
size_t id = static_cast<size_t>(og.getObj());
if (id < table.size() && !type(id)) {
table[id] = {1, {}};
}
}
QPDFObjGen
Xref_table::at_offset(qpdf_offset_t offset) const noexcept
{
int id = 0;
int gen = 0;
qpdf_offset_t start = 0;
int i = 0;
for (auto const& item: table) {
auto o = item.offset();
if (start < o && o <= offset) {
start = o;
id = i;
gen = item.gen();
}
++i;
}
return QPDFObjGen(id, gen);
}
std::map<QPDFObjGen, QPDFXRefEntry>
Xref_table::as_map() const
{
std::map<QPDFObjGen, QPDFXRefEntry> result;
int i{0};
for (auto const& item: table) {
switch (item.type()) {
case 0:
break;
case 1:
result.emplace(QPDFObjGen(i, item.gen()), item.offset());
break;
case 2:
result.emplace(
QPDFObjGen(i, 0), QPDFXRefEntry(item.stream_number(), item.stream_index()));
break;
default:
throw std::logic_error("Xref_table: invalid entry type");
}
++i;
}
return result;
}
void
Xref_table::show()
{
auto& cout = *qpdf.m->log->getInfo();
int i = -1;
for (auto const& item: table) {
++i;
if (item.type()) {
cout << std::to_string(i) << "/" << std::to_string(item.gen()) << ": ";
switch (item.type()) {
case 1:
cout << "uncompressed; offset = " << item.offset() << "\n";
break;
case 2:
cout << "compressed; stream = " << item.stream_number()
<< ", index = " << item.stream_index() << "\n";
break;
default:
throw std::logic_error(
"unknown cross-reference table type while showing xref_table");
}
}
}
}
// Resolve all objects in the xref table. If this triggers a xref table reconstruction abort and
// return false. Otherwise return true.
bool
Xref_table::resolve()
{
bool may_change = !reconstructed_;
int i = -1;
for (auto& item: table) {
++i;
if (item.type()) {
if (objects.unresolved(QPDFObjGen(i, item.gen()))) {
objects.resolve(QPDFObjGen(i, item.gen()));
if (may_change && reconstructed_) {
return false;
}
}
}
}
return true;
}
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->objects.obj_cache) {
result.push_back(newIndirect(iter.first, iter.second.object));
}
return result;
}
QPDFObjectHandle
Xref_table::read_trailer()
{
qpdf_offset_t offset = file->tell();
bool empty = false;
auto object = QPDFParser(*file, "trailer", tokenizer, nullptr, &qpdf, true).parse(empty, false);
if (empty) {
// Nothing in the PDF spec appears to allow empty objects, but they have been encountered in
// actual PDF files and Adobe Reader appears to ignore them.
qpdf.warn(qpdf.damagedPDF("trailer", "empty object treated as null"));
} else if (object.isDictionary() && read_token().isWord("stream")) {
qpdf.warn(qpdf.damagedPDF("trailer", file->tell(), "stream keyword found in trailer"));
}
// Override last_offset so that it points to the beginning of the object we just read
file->setLastOffset(offset);
return object;
}
QPDFObjectHandle
Objects::read_object(std::string const& description, QPDFObjGen og)
{
qpdf.setLastObjectDescription(description, og);
qpdf_offset_t offset = m->file->tell();
bool empty = false;
StringDecrypter decrypter{&qpdf, og};
StringDecrypter* decrypter_ptr = m->encp->encrypted ? &decrypter : nullptr;
auto object =
QPDFParser(*m->file, m->last_object_description, m->tokenizer, decrypter_ptr, &qpdf, true)
.parse(empty, false);
if (empty) {
// Nothing in the PDF spec appears to allow empty objects, but they have been encountered in
// actual PDF files and Adobe Reader appears to ignore them.
qpdf.warn(
qpdf.damagedPDF(*m->file, m->file->getLastOffset(), "empty object treated as null"));
return object;
}
auto token = qpdf.readToken(*m->file);
if (object.isDictionary() && token.isWord("stream")) {
read_stream(object, og, offset);
token = qpdf.readToken(*m->file);
}
if (!token.isWord("endobj")) {
QTC::TC("qpdf", "QPDF err expected endobj");
qpdf.warn(qpdf.damagedPDF("expected endobj"));
}
return object;
}
// After reading stream dictionary and stream keyword, read rest of stream.
void
Objects::read_stream(QPDFObjectHandle& object, QPDFObjGen og, qpdf_offset_t offset)
{
validate_stream_line_end(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.isNull()) {
QTC::TC("qpdf", "QPDF stream without length");
throw qpdf.damagedPDF(offset, "stream dictionary lacks /Length key");
}
QTC::TC("qpdf", "QPDF stream length not integer");
throw qpdf.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 (!qpdf.readToken(*m->file).isWord("endstream")) {
QTC::TC("qpdf", "QPDF missing endstream");
throw qpdf.damagedPDF("expected endstream");
}
} catch (QPDFExc& e) {
if (m->attempt_recovery) {
qpdf.warn(e);
length = recover_stream_length(m->file_sp, og, stream_offset);
} else {
throw;
}
}
object = {QPDF_Stream::create(&qpdf, og, object, stream_offset, length)};
}
void
Objects::validate_stream_line_end(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
QTC::TC("qpdf", "QPDF stream with NL only");
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.
QTC::TC("qpdf", "QPDF stream with CR only");
m->file->unreadCh(ch);
qpdf.warn(qpdf.damagedPDF(
m->file->tell(), "stream keyword followed by carriage return only"));
}
}
return;
}
if (!QUtil::is_space(ch)) {
QTC::TC("qpdf", "QPDF stream without newline");
m->file->unreadCh(ch);
qpdf.warn(qpdf.damagedPDF(
m->file->tell(), "stream keyword not followed by proper line terminator"));
return;
}
qpdf.warn(
qpdf.damagedPDF(m->file->tell(), "stream keyword followed by extraneous whitespace"));
}
}
QPDFObjectHandle
Objects::readObjectInStream(std::shared_ptr<InputSource>& input, int obj)
{
m->last_object_description.erase(7); // last_object_description starts with "object "
m->last_object_description += std::to_string(obj);
m->last_object_description += " 0";
bool empty = false;
auto object = QPDFParser(*input, m->last_object_description, m->tokenizer, nullptr, &qpdf, true)
.parse(empty, false);
if (empty) {
// Nothing in the PDF spec appears to allow empty objects, but they have been encountered in
// actual PDF files and Adobe Reader appears to ignore them.
qpdf.warn(qpdf.damagedPDF(*input, input->getLastOffset(), "empty object treated as null"));
}
return object;
}
bool
QPDF::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::recover_stream_length(
std::shared_ptr<InputSource> input, QPDFObjGen og, qpdf_offset_t stream_offset)
{
// Try to reconstruct stream length by looking for endstream or endobj
qpdf.warn(qpdf.damagedPDF(*input, stream_offset, "attempting to recover stream length"));
PatternFinder ef(qpdf, &QPDF::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 = qpdf.readToken(*m->file);
if (t.getValue() == "endobj") {
m->file->seek(m->file->getLastOffset(), SEEK_SET);
}
}
if (length) {
// Make sure this is inside this object
auto found = xref.at_offset(stream_offset + toO(length));
if (found == QPDFObjGen() || found == 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\endobj within the space allowed for this object, so we're probably
// in good shape.
} else {
QTC::TC("qpdf", "QPDF found wrong endstream in recovery");
length = 0;
}
}
if (length == 0) {
qpdf.warn(qpdf.damagedPDF(
*input, stream_offset, "unable to recover stream data; treating stream as empty"));
} else {
qpdf.warn(qpdf.damagedPDF(
*input, stream_offset, "recovered stream length: " + std::to_string(length)));
}
QTC::TC("qpdf", "QPDF recovered stream length");
return length;
}
QPDFObjectHandle
Objects::read(
bool try_recovery,
qpdf_offset_t offset,
std::string const& description,
QPDFObjGen exp_og,
QPDFObjGen& og,
bool skip_cache_if_in_xref)
{
bool check_og = true;
if (exp_og.getObj() == 0) {
// This method uses an expect object ID of 0 to indicate that we don't know or don't care
// what the actual object ID is at this offset. This is true when we read the xref stream
// and linearization hint streams. In this case, we don't verify the expect object
// ID/generation against what was read from the file. There is also no reason to attempt
// xref recovery if we get a failure in this case since the read attempt was not triggered
// by an xref lookup.
check_og = false;
try_recovery = false;
}
qpdf.setLastObjectDescription(description, exp_og);
if (!m->attempt_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) {
QTC::TC("qpdf", "QPDF bogus 0 offset", 0);
qpdf.warn(qpdf.damagedPDF(0, "object has offset 0"));
return QPDFObjectHandle::newNull();
}
m->file->seek(offset, SEEK_SET);
try {
QPDFTokenizer::Token tobjid = qpdf.readToken(*m->file);
bool objidok = tobjid.isInteger();
QTC::TC("qpdf", "QPDF check objid", objidok ? 1 : 0);
if (!objidok) {
QTC::TC("qpdf", "QPDF expected n n obj");
throw qpdf.damagedPDF(offset, "expected n n obj");
}
QPDFTokenizer::Token tgen = qpdf.readToken(*m->file);
bool genok = tgen.isInteger();
QTC::TC("qpdf", "QPDF check generation", genok ? 1 : 0);
if (!genok) {
throw qpdf.damagedPDF(offset, "expected n n obj");
}
QPDFTokenizer::Token tobj = qpdf.readToken(*m->file);
bool objok = tobj.isWord("obj");
QTC::TC("qpdf", "QPDF check obj", objok ? 1 : 0);
if (!objok) {
throw qpdf.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());
og = QPDFObjGen(objid, generation);
if (objid == 0) {
QTC::TC("qpdf", "QPDF object id 0");
throw qpdf.damagedPDF(offset, "object with ID 0");
}
if (check_og && (exp_og != og)) {
QTC::TC("qpdf", "QPDF err wrong objid/generation");
QPDFExc e = qpdf.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.
qpdf.warn(e);
}
}
} catch (QPDFExc& e) {
if (try_recovery) {
// Try again after reconstructing xref table
xref.reconstruct(e);
if (xref.type(exp_og) == 1) {
QTC::TC("qpdf", "QPDF recovered in readObjectAtOffset");
return read(false, xref.offset(exp_og), description, exp_og, og, false);
} else {
QTC::TC("qpdf", "QPDF object gone after xref reconstruction");
qpdf.warn(qpdf.damagedPDF(
"",
0,
("object " + exp_og.unparse(' ') +
" not found in file after regenerating cross reference table")));
return QPDFObjectHandle::newNull();
}
} else {
throw;
}
}
QPDFObjectHandle oh = read_object(description, og);
if (unresolved(og)) {
// Store the object in the cache here so it gets cached whether we first know the offset or
// whether we first know the object ID and generation (in which we case we would get here
// through resolve).
// 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)) {
if (!isspace(static_cast<unsigned char>(ch))) {
m->file->seek(-1, SEEK_CUR);
break;
}
} else {
throw qpdf.damagedPDF(m->file->tell(), "EOF after endobj");
}
}
qpdf_offset_t end_after_space = m->file->tell();
if (skip_cache_if_in_xref && xref.type(og)) {
// Ordinarily, an object gets read here when resolved through xref table or stream. 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");
} else {
xref.linearization_offsets(toS(og.getObj()), end_before_space, end_after_space);
update_table(og, oh.getObj());
}
}
return oh;
}
QPDFObject*
Objects::resolve(QPDFObjGen og)
{
if (!unresolved(og)) {
return obj_cache[og].object.get();
}
if (m->resolving.count(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.
QTC::TC("qpdf", "QPDF recursion loop in resolve");
qpdf.warn(qpdf.damagedPDF("", "loop detected resolving object " + og.unparse(' ')));
update_table(og, QPDF_Null::create());
return obj_cache[og].object.get();
}
ResolveRecorder rr(&qpdf, og);
try {
switch (xref.type(og)) {
case 0:
break;
case 1:
{
// Object stored in cache by readObjectAtOffset
QPDFObjGen a_og;
QPDFObjectHandle oh = read(true, xref.offset(og), "", og, a_og, false);
}
break;
case 2:
resolveObjectsInStream(xref.stream_number(og.getObj()));
break;
default:
throw qpdf.damagedPDF(
"", 0, ("object " + og.unparse('/') + " has unexpected xref entry type"));
}
} catch (QPDFExc& e) {
qpdf.warn(e);
} catch (std::exception& e) {
qpdf.warn(qpdf.damagedPDF(
"", 0, ("object " + og.unparse('/') + ": error reading object: " + e.what())));
}
if (unresolved(og)) {
// PDF spec says unknown objects resolve to the null object.
QTC::TC("qpdf", "QPDF resolve failure to null");
update_table(og, QPDF_Null::create());
}
auto result(obj_cache[og].object);
result->setDefaultDescription(&qpdf, og);
return result.get();
}
void
Objects::resolveObjectsInStream(int obj_stream_number)
{
if (m->resolved_object_streams.count(obj_stream_number)) {
return;
}
m->resolved_object_streams.insert(obj_stream_number);
// Force resolution of object stream
QPDFObjectHandle obj_stream = qpdf.getObject(obj_stream_number, 0);
if (!obj_stream.isStream()) {
throw qpdf.damagedPDF(
"supposed object stream " + std::to_string(obj_stream_number) + " is not a stream");
}
QPDFObjectHandle dict = obj_stream.getDict();
if (!dict.isDictionaryOfType("/ObjStm")) {
QTC::TC("qpdf", "QPDF ERR object stream with wrong type");
qpdf.warn(qpdf.damagedPDF(
"supposed object stream " + std::to_string(obj_stream_number) + " has wrong type"));
}
if (!(dict.getKey("/N").isInteger() && dict.getKey("/First").isInteger())) {
throw qpdf.damagedPDF(
("object stream " + std::to_string(obj_stream_number) + " has incorrect keys"));
}
int n = dict.getKey("/N").getIntValueAsInt();
int first = dict.getKey("/First").getIntValueAsInt();
std::map<int, int> offsets;
std::shared_ptr<Buffer> bp = obj_stream.getStreamData(qpdf_dl_specialized);
auto input = std::shared_ptr<InputSource>(
// line-break
new BufferInputSource(
(m->file->getName() + " object stream " + std::to_string(obj_stream_number)),
bp.get()));
qpdf_offset_t last_offset = -1;
for (int i = 0; i < n; ++i) {
QPDFTokenizer::Token tnum = qpdf.readToken(*input);
QPDFTokenizer::Token toffset = qpdf.readToken(*input);
if (!(tnum.isInteger() && toffset.isInteger())) {
throw damagedPDF(
*input,
m->last_object_description,
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 > xref.max_id()) {
continue;
}
if (num == obj_stream_number) {
QTC::TC("qpdf", "QPDF ignore self-referential object stream");
qpdf.warn(damagedPDF(
*input,
m->last_object_description,
input->getLastOffset(),
"object stream claims to contain itself"));
continue;
}
if (offset <= last_offset) {
throw damagedPDF(
*input,
m->last_object_description,
input->getLastOffset(),
"expected offsets in object stream to be increasing");
}
last_offset = offset;
offsets[num] = toI(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.
m->last_object_description.clear();
m->last_object_description += "object ";
for (auto const& iter: offsets) {
QPDFObjGen og(iter.first, 0);
if (xref.type(og) == 2 && xref.stream_number(og.getObj()) == obj_stream_number) {
int offset = iter.second;
input->seek(offset, SEEK_SET);
QPDFObjectHandle oh = readObjectInStream(input, iter.first);
update_table(og, oh.getObj());
} else {
QTC::TC("qpdf", "QPDF not caching overridden objstm object");
}
}
}
void
Objects::update_table(QPDFObjGen og, const std::shared_ptr<QPDFObject>& object)
{
object->setObjGen(&qpdf, og);
if (cached(og)) {
auto& cache = obj_cache[og];
cache.object->assign(object);
} else {
obj_cache[og] = ObjCache(object);
}
}
bool
Objects::cached(QPDFObjGen og)
{
return obj_cache.count(og) != 0;
}
bool
Objects::unresolved(QPDFObjGen og)
{
return !cached(og) || obj_cache[og].object->isUnresolved();
}
QPDFObjGen
Objects::next_id()
{
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 QPDFObjGen(max_objid + 1, 0);
}
QPDFObjectHandle
Objects::make_indirect(std::shared_ptr<QPDFObject> const& obj)
{
QPDFObjGen next{next_id()};
obj_cache[next] = ObjCache(obj);
return qpdf.newIndirect(next, obj_cache[next].object);
}
std::shared_ptr<QPDFObject>
Objects::get_for_parser(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 = obj_cache.find(og); iter != obj_cache.end()) {
return iter->second.object;
}
if (xref.type(og) || !xref.initialized()) {
return obj_cache.insert({og, QPDF_Unresolved::create(&qpdf, og)}).first->second.object;
}
if (parse_pdf) {
return QPDF_Null::create();
}
return obj_cache.insert({og, QPDF_Null::create(&qpdf, og)}).first->second.object;
}
std::shared_ptr<QPDFObject>
Objects::get_for_json(int id, int gen)
{
auto og = QPDFObjGen(id, gen);
auto [it, inserted] = obj_cache.try_emplace(og);
auto& obj = it->second.object;
if (inserted) {
obj = (xref.initialized() && !xref.type(og)) ? QPDF_Null::create(&qpdf, og)
: QPDF_Unresolved::create(&qpdf, og);
}
return obj;
}
void
QPDF::replaceObject(QPDFObjGen const& og, QPDFObjectHandle oh)
{
if (!oh || (oh.isIndirect() && !(oh.isStream() && oh.getObjGen() == og))) {
QTC::TC("qpdf", "QPDF replaceObject called with indirect object");
throw std::logic_error("QPDF::replaceObject called with indirect object handle");
}
objects().update_table(og, oh.getObj());
}
void
Objects::erase(QPDFObjGen og)
{
if (auto cached = obj_cache.find(og); cached != obj_cache.end()) {
// Take care of any object handles that may be floating around.
cached->second.object->assign(QPDF_Null::create());
cached->second.object->setObjGen(nullptr, QPDFObjGen());
obj_cache.erase(cached);
}
}
void
QPDF::swapObjects(QPDFObjGen const& og1, QPDFObjGen const& 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->objects.obj_cache[og1].object->swapWith(m->objects.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 = toI(xref.size());
if (max_xref > 0) {
--max_xref;
}
auto max_obj = obj_cache.size() ? 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
qpdf.stopOnError("Impossibly large object id encountered.");
}
if (max_obj < 1.1 * std::max(toI(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 = 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(trailer());
std::vector<T> result;
if constexpr (std::is_same_v<T, QPDFObjGen>) {
result.reserve(obj_cache.size());
} else if constexpr (std::is_same_v<T, bool>) {
result.resize(max_obj + 1U, false);
} else {
throw std::logic_error("Unsupported type in QPDF::getCompressibleObjGens");
}
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]) {
QTC::TC("qpdf", "QPDF loop detected traversing objects");
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 = obj_cache.upper_bound(og);
if (upper != obj_cache.end() && upper->first.getObj() == og.getObj()) {
erase(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()) {
QPDFObjectHandle dict = obj.getDict();
std::set<std::string> keys = dict.getKeys();
for (auto iter = keys.rbegin(); iter != keys.rend(); ++iter) {
std::string const& key = *iter;
QPDFObjectHandle value = dict.getKey(key);
if (key == "/Length") {
// omit stream lengths
if (value.isIndirect()) {
QTC::TC("qpdf", "QPDF exclude indirect length");
}
} else {
queue.push_back(value);
}
}
} else if (obj.isDictionary()) {
std::set<std::string> keys = obj.getKeys();
for (auto iter = keys.rbegin(); iter != keys.rend(); ++iter) {
queue.push_back(obj.getKey(*iter));
}
} else if (obj.isArray()) {
int n = obj.getArrayNItems();
for (int i = 1; i <= n; ++i) {
queue.push_back(obj.getArrayItem(n - i));
}
}
}
return result;
}
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