Soon ==== * Figure out how to render Gajić correctly in the PDF version of the qpdf manual. * Add method to push inheritable resources to a single page by walking up and copying without overwrite. Above logic will also be sufficient to fix the limitation in QPDFObjectHandle::getPageImages(). Maybe add a method to get the effective resources for a page without modifying the page and then implement both changes in terms of that method. * 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 * Some qpdf --check tests are fragile on Windows. The output gets truncated. This happens in the loop for content preservation tests. Figure out the source of the fragility. Next ABI ======== Do these things next time we have to break binary compatibility * Pl_Buffer's internal structure is not right for what it does. It was modified for greater efficiency, but it was done in a way that preserved binary compatibility, so the implementation is a bit convoluted. Lexical ======= * Make it possible to run the lexer (tokenizer) over a whole file such that the following things would be possible: * Rewrite fix-qdf in C++ so that there is no longer a runtime perl dependency * 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. 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. 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 * Pl_TIFFPredictor is pretty slow. * Some test cases on bad fails 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. * Form flattening: there is on-going work on this topic. The primary tracking issue is https://github.com/qpdf/qpdf/issues/72, and there has also been discussion in private email threads. My notes are summarized in ../misc/form-flattening/README (not publicly accessible), but all important information is in issues in github. The non-public items in my notes are transcripts of discussions with a google summer of code student who was working on the issue. These notes likely have low value at this point, but I have saved them to review in case form flattening ever moves into the qpdf library from external tools where it is currently being implemented. Note that flattening forms with appearance streams is relatively straightforward, but many PDF files don't have appearance streams and leave rendering of the form fields to the viewer. Handling this in the general case is probably out of scope for what will be in qpdf in the foreseeable future, particularly in the area of embedding and subsetting fonts. * Look at ~/Q/pdf-collection/forms-from-appian/ * Look at Travis-CI for qpdf. See email from Travis-CI in pending. * https://github.com/qpdf/qpdf/pull/172 contains information about running through MacPorts's CI. * 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). * Figure out how to find Visual Studio in Windows registry and see if I can get it to work with make so I can simplify creation of Windows releases. * 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 providing a Windows installer for qpdf using NSIS. * 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. * Consider the possibility of doing something locale-aware to support non-ASCII passwords. Update documentation if this is done. Consider implementing full Unicode password algorithms from newer encryption formats. See ../misc/unicode-password*. If code is added to properly encode Unicode passwords, figure out how to deal with backward compatibility. Either require some additional flag to decode the password or provide a `--raw-password` flag to suppress decoding. While automatically encoding breaks backward compatibility, it's probably the right behavior because the current behavior is arguably a bug. Alternatively, if the password doesn't work as a raw password and contains characters outside US-ASCII, try various encoding methods to see if any work. See section 7.6.3.3, algorithms 2 and 2A, in the ISO spec for details. (This is tracked in https://github.com/qpdf/qpdf/issues/215.) * 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. * If we ever want to have check mode check the integrity of the free list, this can be done by looking at the code from prior to the object stream support of 4/5/2008. It's in an if (0) block and there's a comment about it. There's also something about it in qpdf.test -- search for "free table". On the other hand, the value of doing this seems very low since no viewer seems to care, so it's probably not worth it. * QPDFObjectHandle::getPageImages() doesn't notice images in inherited resource dictionaries. See comments in that function. * 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.