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#include <qpdf/InputSource.hh>
#include <qpdf/QIntC.hh>
#include <qpdf/QTC.hh>
#include <cstring>
#include <stdexcept>
void
InputSource::setLastOffset(qpdf_offset_t offset)
{
this->last_offset = offset;
}
qpdf_offset_t
InputSource::getLastOffset() const
{
return this->last_offset;
}
std::string
InputSource::readLine(size_t max_line_length)
{
// Return at most max_line_length characters from the next line. Lines are terminated by one or
// more \r or \n characters. Consume the trailing newline characters but don't return them.
// After this is called, the file will be positioned after a line terminator or at the end of
// the file, and last_offset will point to position the file had when this method was called.
qpdf_offset_t offset = this->tell();
auto bp = std::make_unique<char[]>(max_line_length + 1);
char* buf = bp.get();
memset(buf, '\0', max_line_length + 1);
this->read(buf, max_line_length);
this->seek(offset, SEEK_SET);
qpdf_offset_t eol = this->findAndSkipNextEOL();
this->last_offset = offset;
size_t line_length = QIntC::to_size(eol - offset);
if (line_length < max_line_length) {
buf[line_length] = '\0';
}
return {buf};
}
bool
InputSource::findFirst(char const* start_chars, qpdf_offset_t offset, size_t len, Finder& finder)
{
// Basic approach: search for the first character of start_chars starting from offset but not
// going past len (if len != 0). Once the first character is found, see if it is the beginning
// of a sequence of characters matching start_chars. If so, call finder.check() to do
// caller-specific additional checks. If not, keep searching.
// This code is tricky and highly subject to off-by-one or other edge case logic errors. See
// comments throughout that explain how we're not missing any edge cases. There are also tests
// specifically constructed to make sure we caught the edge cases in testing.
char buf[1025]; // size known to input_source.cc in libtests
// To enable us to guarantee null-termination, save an extra byte so that buf[size] is valid
// memory.
size_t size = sizeof(buf) - 1;
if ((strlen(start_chars) < 1) || (strlen(start_chars) > size)) {
throw std::logic_error(
"InputSource::findSource called with"
" too small or too large of a character sequence");
}
char* p = nullptr;
qpdf_offset_t buf_offset = offset;
size_t bytes_read = 0;
// Guarantee that we return from this loop. Each time through, we either return, advance p, or
// restart the loop with a condition that will cause return on the next pass. Eventually we will
// either be out of range or hit EOF, either of which forces us to return.
while (true) {
// Do we need to read more data? Pretend size = 5, buf starts at 0, and start_chars has 3
// characters. buf[5] is valid and null. If p == 2, start_chars could be buf[2] through
// buf[4], so p + strlen(start_chars) == buf + size is okay. If p points to buf[size], since
// strlen(start_chars) is always >= 1, this overflow test will be correct for that case
// regardless of start_chars.
if ((p == nullptr) || ((p + strlen(start_chars)) > (buf + bytes_read))) {
if (p) {
QTC::TC(
"libtests", "InputSource read next block", ((p == buf + bytes_read) ? 0 : 1));
buf_offset += (p - buf);
}
this->seek(buf_offset, SEEK_SET);
// Read into buffer and zero out the rest of the buffer including buf[size]. We
// allocated an extra byte so that we could guarantee null termination as an extra
// protection against overrun when using string functions.
bytes_read = this->read(buf, size);
if (bytes_read < strlen(start_chars)) {
QTC::TC("libtests", "InputSource find EOF", bytes_read == 0 ? 0 : 1);
return false;
}
memset(buf + bytes_read, '\0', 1 + (size - bytes_read));
p = buf;
}
// Search for the first character.
if ((p = static_cast<char*>(
// line-break
memchr(p, start_chars[0], bytes_read - QIntC::to_size(p - buf)))) != nullptr) {
if (p == buf) {
QTC::TC("libtests", "InputSource found match at buf[0]");
}
// Found first letter.
if (len != 0) {
// Make sure it's in range.
size_t p_relative_offset = QIntC::to_size((p - buf) + (buf_offset - offset));
if (p_relative_offset >= len) {
// out of range
QTC::TC("libtests", "InputSource out of range");
return false;
}
}
if ((p + strlen(start_chars)) > (buf + bytes_read)) {
// If there are not enough bytes left in the file for start_chars, we will detect
// this on the next pass as EOF and return.
QTC::TC("libtests", "InputSource not enough bytes");
continue;
}
// See if p points to a sequence matching start_chars. We already checked above to make
// sure we are not going to overrun memory.
if (strncmp(p, start_chars, strlen(start_chars)) == 0) {
// Call finder.check() with the input source positioned to the point of the match.
this->seek(buf_offset + (p - buf), SEEK_SET);
if (finder.check()) {
return true;
} else {
QTC::TC("libtests", "InputSource start_chars matched but not check");
}
} else {
QTC::TC("libtests", "InputSource first char matched but not string");
}
// This occurrence of the first character wasn't a match. Skip over it and keep
// searching.
++p;
} else {
// Trigger reading the next block
p = buf + bytes_read;
}
}
throw std::logic_error("InputSource after while (true)");
}
bool
InputSource::findLast(char const* start_chars, qpdf_offset_t offset, size_t len, Finder& finder)
{
bool found = false;
qpdf_offset_t after_found_offset = 0;
qpdf_offset_t cur_offset = offset;
size_t cur_len = len;
while (this->findFirst(start_chars, cur_offset, cur_len, finder)) {
if (found) {
QTC::TC("libtests", "InputSource findLast found more than one");
} else {
found = true;
}
after_found_offset = this->tell();
cur_offset = after_found_offset;
cur_len = len - QIntC::to_size((cur_offset - offset));
}
if (found) {
this->seek(after_found_offset, SEEK_SET);
}
return found;
}