This was originally not public because I wanted to get rid fo the
pages cache, but I recently realized there were deep reasons not to do
that, and the author of pikepdf wanted this, so I decided to make it
public.
Operations that add the same object to multiple places in the pages
tree are throwing exceptions and then later causing assertion
failures. The assert calls shouldn't be there.
This makes all integer type conversions that have potential data loss
explicit with calls that do range checks and raise an exception. After
this commit, qpdf builds with no warnings when -Wsign-conversion
-Wconversion is used with gcc or clang or when -W3 -Wd4800 is used
with MSVC. This significantly reduces the likelihood of potential
crashes from bogus integer values.
There are some parts of the code that take int when they should take
size_t or an offset. Such places would make qpdf not support files
with more than 2^31 of something that usually wouldn't be so large. In
the event that such a file shows up and is valid, at least qpdf would
raise an error in the right spot so the issue could be legitimately
addressed rather than failing in some weird way because of a silent
overflow condition.
When linearizing a file or getting the list of all pages in a file,
detect if the pages tree contains a duplicated page object and, if so,
shallow copy it. This makes it possible to have a one to one mapping
of page positions to page objects.
Remove calls to assertPageObject(). All cases in the library that
called assertPageObject() work fine if you don't call
assertPageObject() because nothing assumes anything that was being
checked by that call. Removing the calls enables more files to be
successfully processed.
Pushing inherited objects to pages and getting all pages were both
prone to stack overflow infinite loops if there were loops in the
Pages dictionary. There is a general weakness in the code in that any
part of the code that traverses the Pages structure would be prone to
this and would have to implement its own loop detection. A more robust
fix may provide some general method for handling the Pages structure,
but it's probably not worth doing.
Note: addition of *Internal2 private functions was done rather than
changing signatures of existing methods to avoid breaking
compatibility.
Original reported here:
https://bugs.launchpad.net/ubuntu/+source/qpdf/+bug/1397413
The PDF specification says that the /Type key for nodes in the pages
dictionary (both /Page and /Pages) is required, but some PDF files
omit them. Use the presence of other keys to determine the type of
pages tree node this is if the type key is not found.
Ideally, the library should never call assert outside of test code,
but it does in several places. For some cases where the assertion
might conceivably fail because of a problem with the input data,
replace assertions with exceptions so that they can be trapped by the
calling application. This commit surely misses some cases and
replaced some cases unnecessarily, but it should still be an
improvement.
Previous versions of qpdf incorrectly passed arbitrary objects from
/Pages objects down to individual pages in direct contradition with
the PDF specification. These are now left in /Pages. When
intermediate /Pages nodes are being discarded as when the /Pages tree
is being flattened, a warning is issued when unknown keys are
encountered.
Jay Berkenbilt
Tobias Hoffmann