OpenSystemsDevelopment / qpdf

Also removes preclusion of stream references in stream parameters of
filterable streams and reduces write times by about 8% by eliminating
an extra traversal of the objects.

* Return rather than exiting from realmain in qpdf.cc
* Remove extraneous blank line
* Don't assign temporary to const reference

fix-qdf assumes there is exactly one XRef stream and that it is at the
end of the file.

Even though this is disallowed by the spec, files like this have been
encountered in the wild.

Various PDF digital signing tools do not encrypt /Contents value in
signature dictionary. Adobe Acrobat Reader DC can handle a PDF with
the /Contents value not encrypted.

Write Contents in signature dictionary without encryption

Tests ensure that string /Contents are not handled specially when not
found in sig dicts.

Table 8.93 "Entries in a signature dictionary" in PDF 1.5 reference
describes that the value of Contents entry is a hexadecimal string
representation when ByteRange is specified.

This commit makes QPDF always uses hexadecimal strings representation
instead of literal strings for it.

Ordinarily the trailer doesn't contain any strings, so this is usually
a non-issue, but if the trailer contains strings, linearizing and
encrypting with object streams would include encrypted strings in the
trailer, which would blow out the padding because encrypted strings
are longer than their cleartext counterparts.

It's detected in QPDFWriter instead of at parse time because I can't
figure out how to construct a test case in a reasonable time. This
commit moves the fuzz file into the regular test suite for a QTC
coverage case.

Use destructors to pop the pipeline stack, and ensure that code that
pops the stack is actually popping the intended thing.

For some reason, qpdf from the beginning was replacing indirect
references to null with literal null in arrays even after removing the
old behavior of flattening scalar references. This seems like a bad
idea.

Use PointerHolder in several places where manually memory allocation
and deallocation were being used. This helps to protect against memory
leaks when exceptions are thrown in surprising places.

In a small number of cases, it makes sense to replace an overloaded
function with a function that takes a default argument. We can do this
now because we've already broken binary compatibility since the last
release.

* Several assertions in linearization were not always true; change
  them to run time errors
* Handle a few cases of uninitialized objects
* Handle pages with no contents when doing form operations
* Handle invalid page tree nodes when traversing pages

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.

On read, ignore /DecodeParms when empty list; on write, delete it.
Some files have been found that include an empty list for
/DecodeParms, but this is not technically compliant with the spec, and
the only sensible interpretation is to treat it as if there are no
decode parameters.

Setting encryption permissions for R >= 3 set permission bits in
groups corresponding to menu options in Acrobat 5. The new API allows
the bits to be set individually.

On certain operations, such as iterating through all objects and
adding new indirect objects, walk through the entire object structure
and explicitly resolve any indirect references to non-existent
objects. That prevents new objects from springing into existence and
causing the previously dangling references to point to them.

There were a few places in the code that were checking that a pointer
wasn't null before deleting it, even though C++ has always allowed
delete 0. Most of the code did not perform these checks.

Turns out you can keep adding zero to a number over and over again and
it just doesn't get any bigger. Who would have known?

Implement a TokenFilter class and refactor Pl_QPDFTokenizer to use a
TokenFilter class called ContentNormalizer. Pl_QPDFTokenizer is now a
general filter that passes data through a TokenFilter.

This is useful only for debugging the linearization code.

Tweak the message so that we inform the user that we are mitigating
data loss.