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Tidy Objects::read
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6408c5c364
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@ -1489,15 +1489,17 @@ Objects::read(
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}
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QPDFObjectHandle oh = read_object(description, og);
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if (!unresolved(og)) {
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return oh;
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}
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if (unresolved(og)) {
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// Store the object in the cache here so it gets cached whether we first know the offset or
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// whether we first know the object ID and generation (in which we case we would get here
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// through resolve).
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// Determine the end offset of this object before and after white space. We use these
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// numbers to validate linearization hint tables. Offsets and lengths of objects may imply
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// the end of an object to be anywhere between these values.
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// Determine the end offset of this object before and after white space. We use these numbers
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// to validate linearization hint tables. Offsets and lengths of objects may imply the end of
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// an object to be anywhere between these values.
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qpdf_offset_t end_before_space = m->file->tell();
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// skip over spaces
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@ -1514,39 +1516,36 @@ Objects::read(
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}
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qpdf_offset_t end_after_space = m->file->tell();
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if (skip_cache_if_in_xref && xref.type(og)) {
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// Ordinarily, an object gets read here when resolved through xref table or stream. In
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// the special case of the xref stream and linearization hint tables, the offset comes
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// from another source. For the specific case of xref streams, the xref stream is read
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// and loaded into the object cache very early in parsing. Ordinarily, when a file is
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// updated by appending, items inserted into the xref table in later updates take
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// precedence over earlier items. In the special case of reusing the object number
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// previously used as the xref stream, we have the following order of events:
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// Ordinarily, an object gets read here when resolved through xref table or stream. In the
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// special case of the xref stream and linearization hint tables, the offset comes from
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// another source. For the specific case of xref streams, the xref stream is read and loaded
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// into the object cache very early in parsing. Ordinarily, when a file is updated by
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// appending, items inserted into the xref table in later updates take precedence over
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// earlier items. In the special case of reusing the object number previously used as the
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// xref stream, we have the following order of events:
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//
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// * reused object gets loaded into the xref table
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// * old object is read here while reading xref streams
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// * original xref entry is ignored (since already in xref table)
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//
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// It is the second step that causes a problem. Even though the xref table is correct in
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// this case, the old object is already in the cache and so effectively prevails over
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// the reused object. To work around this issue, we have a special case for the xref
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// stream (via the skip_cache_if_in_xref): if the object is already in the xref stream,
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// don't cache what we read here.
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// this case, the old object is already in the cache and so effectively prevails over the
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// reused object. To work around this issue, we have a special case for the xref stream (via
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// the skip_cache_if_in_xref): if the object is already in the xref stream, don't cache what
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// we read here.
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//
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// It is likely that the same bug may exist for linearization hint tables, but the
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// existing code uses end_before_space and end_after_space from the cache, so fixing
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// that would require more significant rework. The chances of a linearization hint
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// stream being reused seems smaller because the xref stream is probably the highest
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// object in the file and the linearization hint stream would be some random place in
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// the middle, so I'm leaving that bug unfixed for now. If the bug were to be fixed, we
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// could use !check_og in place of skip_cache_if_in_xref.
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// It is likely that the same bug may exist for linearization hint tables, but the existing
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// code uses end_before_space and end_after_space from the cache, so fixing that would
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// require more significant rework. The chances of a linearization hint stream being reused
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// seems smaller because the xref stream is probably the highest object in the file and the
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// linearization hint stream would be some random place in the middle, so I'm leaving that
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// bug unfixed for now. If the bug were to be fixed, we could use !check_og in place of
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// skip_cache_if_in_xref.
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QTC::TC("qpdf", "QPDF skipping cache for known unchecked object");
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} else {
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xref.linearization_offsets(toS(og.getObj()), end_before_space, end_after_space);
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update_table(og.getObj(), og.getGen(), oh.getObj());
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}
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}
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return oh;
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}
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xref.linearization_offsets(toS(og.getObj()), end_before_space, end_after_space);
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return {update_table(og.getObj(), og.getGen(), oh.getObj())};
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}
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QPDFObject*
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