Candidates for upcoming release =============================== * Open "next" issues * bugs * #473: zsh completion with directories * Non-bugs * #446: recognize edited QDF files * #436: parsing of document with form xobject * See if we can work in Windows Build/External Libraries (below) * Remember to check work `qpdf` project for private issues * file with very slow page extraction * big page even with --remove-unreferenced-resources=yes, even with --empty * optimize image failure because of colorspace * Make it possible for StreamDataProvider to modify the stream dictionary in addition to the stream data so it can calculate things about the dictionary at runtime. Will require a small change to QPDFWriter. * Take flattenRotation code from pdf-split and do something with it, maybe adding it to the library. Once there, call it from pdf-split and bump up the required version of qpdf. * Externalize inline images doesn't walk into form XObjects. In general: * Check QPDFPageObjectHelper and see what can be applied to form XObjects. Maybe think about generalizing it to work with form XObjects. * There is an increasing amount of logic in qpdf.cc that should probably move into the library. This includes externalizing inline images and page splitting as those operations become more elaborate, particularly with handling of form XObjects. * Flattening of form XObjects seems like something that would be useful in the library. We are seeing more cases of completely valid PDF files with form XObjects that cause problems in other software. Flattening of form XObjects could be a useful way to work around those issues or to prepare files for additional processing, making it possible for users of the qpdf library to not be concerned about form XObjects. This could be done recursively; i.e., we could have a method to embed a form XObject into whatever contains it, whether that is a form XObject or a page. This would require more significant interpretation of the content stream. We would need a test file in which the placement of the form XObject has to be in the right place, e.g., the form XObject partially obscures earlier code and is partially obscured by later code. * See if the tokenizer is a performance bottleneck and, if so, optimize it. We might end up with a high-performance tokenizer that has a different interface but still ultimately creates the same tokens. Fuzz Errors =========== * https://bugs.chromium.org/p/oss-fuzz/issues/detail?id= * Ignoring these: * Problems inside the jpeg library: 15470, 15751, 18633, 18732, 18745, 20391, 23581 * Timeout: 15471, 17630 GitHub Actions ============== * Actions are triggered on push to main and master. When we eventually rename master to main, make sure the reference to master is removed from .github/workflows/*.yml. * At the time of migrating from Azure Pipelines to GitHub Actions (2020-10), there was no standard test result publisher (to replace the PublishTestResults@2 task). There are some third-party actions, but I'd rather not depend on them. Keep an eye open for this coming to GitHub Actions. Windows Build/External Libraries ================================ * Migrate external library build code to a separate repository. * Automate downloading and building latest versions of external libraries. Add openssl. * Build external libraries on a schedule and create releases periodically or when they change. See if we can get rid of the external-libs branch in qpdf/qpdf. * Update the Windows build so that it uses current versions of external libraries and openssl as its crypto provider. ABI Changes =========== This is a list of changes to make next time there is an ABI change. Comments appear in the code prefixed by "ABI" * Consider removing InputSource::unreadCh. Maybe we can declare it final and delete so it will be forced to be removed from derived classes. C++-11 ====== * Search for ::iterator and ::const_iterator and replace with either auto or foreach-style iteration. * There may be some places where std::function and lambdas can simplify handlers rather than using classes with apply methods. * My c++11 branch adds re-implements PointerHolder so that it is interchangeable with std::shared_ptr. We may not actually want to ever do this because it turns out PointerHolder is slightly more performant than std::shared_ptr, at least as of g++ 9.2.1. It is not actually possible to just replace PointerHolder with std::shared_ptr for two reasons: there is no automatic creation of std::shared_ptr from T* like there is for PointerHolder, which breaks some code, and also there is no automatic conversion from something like std::vector> to std::vector>. It may be a good idea to replace PointerHolder with std::shared_ptr in the API even if it requires some work for the developer, but even if that isn't worth it, we should find all occurrences of PointerHolder within the code and replace with std::shared_ptr or std::unique_ptr as needed. This will definitely break binary compatibility as the PointerHolder pattern is part of the ABI for almost every class. Page splitting/merging ====================== * Update page splitting and merging to handle document-level constructs with page impact such as interactive forms and article threading. Check keys in the document catalog for others, such as outlines, page labels, thumbnails, and zones. For threads, Subramanyam provided a test file; see ../misc/article-threads.pdf. Email Q-Count: 431864 from 2009-11-03. * bookmarks (outlines) 12.3.3 * support bookmarks when merging * prune bookmarks that don't point to a surviving page when merging or splitting * make sure conflicting named destinations work possibly test by including the same file by two paths in a merge * see also comments in issue 343 Note: original implementation of bookmark preservation for split pages caused a very high performance hit. The problem was introduced in 313ba081265f69ac9a0324f9fe87087c72918191 and reverted in the commit that adds this paragraph. The revert includes marking a few tests cases as $td->EXPECT_FAILURE. When properly coded, the test cases will need to be adjusted to only include the parts of the outlines that are actually copied. The tests in question are "split page with outlines". When implementing properly, ensure that the performance is not adversely affected by timing split-pages on a large file with complex outlines such as the PDF specification. When pruning outlines, keep all outlines in the hierarchy that are above an outline for a page we care about. If one of the ancestor outlines points to a non-existent page, clear its dest. If an outline does not have any children that point to pages in the document, just omit it. Possible strategy: * resolve all named destinations to explicit destinations * concatenate top-level outlines * prune outlines whose dests don't point to a valid page * recompute all /Count fields Test files * page-labels-and-outlines.pdf: old file with both page labels and outlines. All destinations are explicit destinations. Each page has Potato and a number. All titles are feline names. * outlines-with-actions.pdf: mixture of explicit destinations, named destinations, goto actions with explicit destinations, and goto actions with named destinations; uses /Dests key in names dictionary. Each page has Salad and a number. All titles are silly words. One destination is an indirect object. * outlines-with-old-root-dests.pdf: like outlines-with-actions except it uses the PDF-1.1 /Dests dictionary for named destinations, and each page has Soup and a number. Also pages are numbered with upper-case Roman numerals starting with 0. All titles are silly words preceded by a bullet. If outline handling is significantly improved, see ../misc/bad-outlines/bad-outlines.pdf and email: https://mail.google.com/mail/u/0/#search/rfc822msgid%3A02aa01d3d013%249f766990%24de633cb0%24%40mono.hr) * Form fields: should be similar to outlines. Performance =========== As described in https://github.com/qpdf/qpdf/issues/401, there was great performance degradation between qpdf 7.1.1 and 9.1.1. Doing a bisect between dac65a21fb4fa5f871e31c314280b75adde89a6c and release-qpdf-7.1.1, I found several commits that damaged performance. I fixed some of them to improve performance by about 70% (as measured by saying that old times were 170% of new times). The remaining commits that broke performance either can't be correct because they would re-introduce an old bug or aren't worth correcting because of the high value they offer relative to a relatively low penalty. For historical reference, here are the commits. The numbers are the time in seconds on the machine I happened to be using of splitting the first 100 pages of PDF32000_2008.pdf 20 times and taking an average duration. Commits that broke performance: * d0e99f195a987c483bbb6c5449cf39bee34e08a1 -- object description and context: 0.39 -> 0.45 * a01359189b32c60c2d55b039f7aefd6c3ce0ebde (minus 313ba08) -- fix dangling references: 0.55 -> 0.6 * e5f504b6c5dc34337cc0b316b4a7b1fca7e614b1 -- sparse array: 0.6 -> 0.62 Other intermediate steps that were previously fixed: * 313ba081265f69ac9a0324f9fe87087c72918191 -- copy outlines into split: 0.55 -> 4.0 * a01359189b32c60c2d55b039f7aefd6c3ce0ebde -- fix dangling references: 4.0 -> 9.0 This commit fixed the awful problem introduced in 313ba081: * a5a016cdd26a8e5c99e5f019bc30d1bdf6c050a2 -- revert outline preservation: 9.0 -> 0.6 Note that the fix dangling references commit had a much worse impact prior to removing the outline preservation, so I also measured its impact in isolation. A few important lessons: * Indirection through PointerHolder is expensive, and should not be used for things that are created and destroyed frequently such as QPDFObjectHandle and QPDFObject. * Traversal of objects is expensive and should be avoided where possible. Future ideas: * Look at places in the code where object traversal is being done and, where possible, try to avoid it entirely or at least avoid ever traversing the same objects multiple times. * Avoid attaching too much metadata to objects and object handles since those have to get copied around a lot. Also, it turns out that PointerHolder is more performant than std::shared_ptr. Analytics ========= Consider features that make it easier to detect certain patterns in PDF files. The information below could be computed using an external program that reads the existing json, but if it's useful enough, we could add it directly to the json output. * Add to "pages" in the json: * "inheritsresources": bool; whether there are any inherited attributes from ancestor page tree nodes * "sharedresources": a list of indirect objects that are "/Resources" dictionaries or "XObject" resource dictionary subkeys of either the page itself or of any form XObject referenced by the page. * Add to "objectinfo" in json: "directpagerefcount": the number of pages that directly reference this object (i.e., you can find an indirect reference to the object in the page dictionary without traversing over any indirect objects) General ======= NOTE: Some items in this list refer to files in my personal home directory or that are otherwise not publicly accessible. This includes things sent to me by email that are specifically not public. Even so, I find it useful to make reference to them in this list * Add support for writing name and number trees * Figure out how to render Gajić correctly in the PDF version of the qpdf manual. * Investigate whether there is a way to automate the memory checker tests for Windows. * Part of closed_file_input_source.cc is disabled on Windows because of odd failures. It might be worth investigating so we can fully exercise this in the test suite. That said, ClosedFileInputSource is exercised elsewhere in qpdf's test suite, so this is not that pressing. * Support user-pluggable stream filters. This would enable external code to provide interpretation for filters that are missing from qpdf. Make it possible for user-provided filters to override built-in filters. Make sure that the pluggable filters can be prioritized so that we can poll all registered filters to see whether they are capable of filtering a particular stream. * If possible, consider adding CCITT3, CCITT4, or any other easy filters. For some reference code that we probably can't use but may be handy anyway, see http://partners.adobe.com/public/developer/ps/sdk/index_archive.html * If possible, support the following types of broken files: - Files that have no whitespace token after "endobj" such that endobj collides with the start of the next object - See ../misc/broken-files * Additional form features * set value from CLI? Specify title, and provide way to disambiguate, probably by giving objgen of field * replace mode: --replace-object, --replace-stream-raw, --replace-stream-filtered * update first paragraph of QPDF JSON in the manual to mention this * object numbers are not preserved by write, so object ID lookup has to be done separately for each invocation * you don't have to specify length for streams * you only have to specify filtering for streams if providing raw data * Pl_TIFFPredictor is pretty slow. * Support for handling file names with Unicode characters in Windows is incomplete. qpdf seems to support them okay from a functionality standpoint, and the right thing happens if you pass in UTF-8 encoded filenames to QPDF library routines in Windows (they are converted internally to wchar_t*), but file names are encoded in UTF-8 on output, which doesn't produce nice error messages or output on Windows in some cases. * If we ever wanted to do anything more with character encoding, see ../misc/character-encoding/, which includes machine-readable dump of table D.2 in the ISO-32000 PDF spec. This shows the mapping between Unicode, StandardEncoding, WinAnsiEncoding, MacRomanEncoding, and PDFDocEncoding. * Some test cases on bad files fail because qpdf is unable to find the root dictionary when it fails to read the trailer. Recovery could find the root dictionary and even the info dictionary in other ways. In particular, issue-202.pdf can be opened by evince, and there's no real reason that qpdf couldn't be made to be able to recover that file as well. * Audit every place where qpdf allocates memory to see whether there are cases where malicious inputs could cause qpdf to attempt to grab very large amounts of memory. Certainly there are cases like this, such as if a very highly compressed, very large image stream is requested in a buffer. Hopefully normal input to output filtering doesn't ever try to do this. QPDFWriter should be checked carefully too. See also bugs/private/from-email-663916/ * Interactive form modification: https://github.com/qpdf/qpdf/issues/213 contains a good discussion of some ideas for adding methods to modify annotations and form fields if we want to make it easier to support modifications to interactive forms. Some of the ideas have been implemented, and some of the probably never will be implemented, but it's worth a read if there is an intention to work on this. In the issue, search for "Regarding write functionality", and read that comment and the responses to it. * Look at ~/Q/pdf-collection/forms-from-appian/ * Consider adding "uninstall" target to makefile. It should only uninstall what it installed, which means that you must run uninstall from the version you ran install with. It would only be supported for the toolchains that support the install target (libtool). * Provide support in QPDFWriter for writing incremental updates. Provide support in qpdf for preserving incremental updates. The goal should be that QDF mode should be fully functional for files with incremental updates including fix_qdf. Note that there's nothing that says an indirect object in one update can't refer to an object that doesn't appear until a later update. This means that QPDF has to treat indirect null objects differently from how it does now. QPDF drops indirect null objects that appear as members of arrays or dictionaries. For arrays, it's handled in QPDFWriter where we make indirect nulls direct. This is in a single if block, and nothing else in the code cares about it. We could just remove that if block and not break anything except a few test cases that exercise the current behavior. For dictionaries, it's more complicated. In this case, QPDF_Dictionary::getKeys() ignores all keys with null values, and hasKey() returns false for keys that have null values. We would probably want to make QPDF_Dictionary able to handle the special case of keys that are indirect nulls and basically never have it drop any keys that are indirect objects. If we make a change to have qpdf preserve indirect references to null objects, we have to note this in ChangeLog and in the release notes since this will change output files. We did this before when we stopped flattening scalar references, so this is probably not a big deal. We also have to make sure that the testing for this handles non-trivial cases of the targets of indirect nulls being replaced by real objects in an update. I'm not sure how this plays with linearization, if at all. For cases where incremental updates are not being preserved as incremental updates and where the data is being folded in (as is always the case with qpdf now), none of this should make any difference in the actual semantics of the files. * When decrypting files with /R=6, hash_V5 is called more than once with the same inputs. Caching the results or refactoring to reduce the number of identical calls could improve performance for workloads that involve processing large numbers of small files. * Consider adding a method to balance the pages tree. It would call pushInheritedAttributesToPage, construct a pages tree from scratch, and replace the /Pages key of the root dictionary with the new tree. * Secure random number generation could be made more efficient by using a local static to ensure a single random device or crypt provider as long as this can be done in a thread-safe fashion. In the initial implementation, this is being skipped to avoid having to add any dependencies on threading libraries. * Study what's required to support savable forms that can be saved by Adobe Reader. Does this require actually signing the document with an Adobe private key? Search for "Digital signatures" in the PDF spec, and look at ~/Q/pdf-collection/form-with-full-save.pdf, which came from Adobe's example site. See also ../misc/digital-sign-from-trueroad/. If digital signatures are implemented, update the docs on crypto providers, which mention that this may happen in the future. * See if we can avoid preserving unreferenced objects in object streams even when preserving the object streams. * Provide APIs for embedded files. See *attachments*.pdf in test suite. The private method findAttachmentStreams finds at least cases for modern versions of Adobe Reader (>= 1.7, maybe earlier). PDF Reference 1.7 section 3.10, "File Specifications", discusses this. A sourceforge user asks if qpdf can handle extracting and embedded resources and references these tools, which may be useful as a reference. http://multivalent.sourceforge.net/Tools/pdf/Extract.html http://multivalent.sourceforge.net/Tools/pdf/Embed.html * The description of Crypt filters is unclear with respect to how to use them to override /StmF for specific streams. I'm not sure whether qpdf will do the right thing for any specific individual streams that might have crypt filters, but I believe it does based on my testing of a limited subset. The specification seems to imply that only embedded file streams and metadata streams can have crypt filters, and there are already special cases in the code to handle those. Most likely, it won't be a problem, but someday someone may find a file that qpdf doesn't work on because of crypt filters. There is an example in the spec of using a crypt filter on a metadata stream. For now, we notice /Crypt filters and decode parameters consistent with the example in the PDF specification, and the right thing happens for metadata filters that happen to be uncompressed or otherwise compressed in a way we can filter. This should handle all normal cases, but it's more or less just a guess since I don't have any test files that actually use stream-specific crypt filters in them. * The second xref stream for linearized files has to be padded only because we need file_size as computed in pass 1 to be accurate. If we were not allowing writing to a pipe, we could seek back to the beginning and fill in the value of /L in the linearization dictionary as an optimization to alleviate the need for this padding. Doing so would require us to pad the /L value individually and also to save the file descriptor and determine whether it's seekable. This is probably not worth bothering with. * The whole xref handling code in the QPDF object allows the same object with more than one generation to coexist, but a lot of logic assumes this isn't the case. Anything that creates mappings only with the object number and not the generation is this way, including most of the interaction between QPDFWriter and QPDF. If we wanted to allow the same object with more than one generation to coexist, which I'm not sure is allowed, we could fix this by changing xref_table. Alternatively, we could detect and disallow that case. In fact, it appears that Adobe reader and other PDF viewing software silently ignores objects of this type, so this is probably not a big deal. * Based on an idea suggested by user "Atom Smasher", consider providing some mechanism to recover earlier versions of a file embedded prior to appended sections. * From a suggestion in bug 3152169, consider having an option to re-encode inline images with an ASCII encoding. * From github issue 2, provide more in-depth output for examining hint stream contents. Consider adding on option to provide a human-readable dump of linearization hint tables. This should include improving the 'overflow reading bit stream' message as reported in issue #2. There are multiple calls to stopOnError in the linearization checking code. Ideally, these should not terminate checking. It would require re-acquiring an understanding of all that code to make the checks more robust. In particular, it's hard to look at the code and quickly determine what is a true logic error and what could happen because of malformed user input. See also ../misc/linearization-errors. * If I ever decide to make appearance stream-generation aware of fonts or font metrics, see email from Tobias with Message-ID <5C3C9C6C.8000102@thax.hardliners.org> dated 2019-01-14. * Consider creating a sanitizer to make it easier for people to send broken files. Now that we have json mode, this is probably no longer worth doing. Here is the previous idea, possibly implemented by making it possible to run the lexer (tokenizer) over a whole file. Make it possible to replace all strings in a file lexically even on badly broken files. Ideally this should work files that are lacking xref, have broken links, etc., and ideally it should work with encrypted files if possible. This should go through the streams and strings and replace them with fixed or random characters, preferably, but not necessarily, in a manner that works with fonts. One possibility would be to detect whether a string contains characters with normal encoding, and if so, use 0x41. If the string uses character maps, use 0x01. The output should otherwise be unrelated to the input. This could be built after the filtering and tokenizer rewrite and should be done in a manner that takes advantage of the other lexical features. This sanitizer should also clear metadata and replace images.