Small, command-line tool only enhancements to do soon ===================================================== * Handle input file = output file as a special case. See issue 29. Behavior: detect if output file is the same as one of the input files. If so, refuse to operate unless --allow-overwrite is specified. In that case, write to a temporary file and, if there are no errors or warnings, rename the temporary output file over the input file. If rename fails, delete the temporary file. * Consider providing alternative methods for specifying passwords. The methods should be general enough to use for both encryption and decryption passwords. Example methods could be reading the password from a file, a file descriptor, or prompting. Prompting should never be done with being specifically requested though; we don't want to create a situation where running qpdf might block waiting for input where it previously did not. Test case: encrypt an encrypted file with the output file having different user/owner passwords. Make sure we have a predictable way to read all three passwords (input, output user, output owner). Maybe we have something like --password-source=:,... where method could be file=/path, fd=n, or prompt and which could be one of input, user, owner. If a password source is provided for input, it takes precedence over --password if specified later on the command line. If a password source is specified for output passwords, the corresponding passwords must be '-'. If more than one password is read from the same source, passwords are newline separated. Trailing newlines are ignored. Example: qpdf --password-source=fd=3:input,owner a.pdf b.pdf would read two lines from file descriptor 3. The first would the password for reading a.pdf, and the second would be the owner password for b.pdf. The encryption arguments would specify the actual user password for b.pdf and - as the owner password. qpdf --password-source=file=/tmp/a:input --password=source=prompt:user,owner would read the input file from /tmp/a and would prompt twice: one for the user password and once for the owner password. * 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). Next ABI change =============== Remove private methods that are there only for ABI compatibility including extra QPDFWriter writeTrailer, writeXRefTable, writeXRefStream. 5.2.0 ===== * Before release: remember to bump minor shared library version since new methods were added (even though private). * Figure out what about a3576a73593987b26cd3eff346f8f7c11f713cbd broke binary compatibility. * Implement automated testing for binary compatibility and add to release checklist. * 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. * Provide an option for QPDFWriter to preserve unreferenced objects when writing out a file. * Look at all the exceptions and error conditions in QPDF_stream and figure out which ones should be converted to warnings and treating the stream as not filterable. * 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 fitlers 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 RLE, 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 lack %%EOF at the end but otherwise have a valid startxref near the end - Files that have no whitespace token after "endobj" such that endobj collides with the start of the next object - Files with individual corrupted streams. Just leave the streams unfiltered after giving a warning, or maybe do something else like applying as many of the filters as possible, etc. QPDFWriter can have some kind of retry mechanism on streams where filtering fails after filterable returns true. - Files whose PDF header is malformed, perhaps with no version number (as literally %PDF-a.b). Maybe keep track of features to try to infer a version based on encryption formats and object streams. - For really hard errors like corrupted streams where there is virtually guaranteed to be loss, maybe require an additional option to tell qpdf that it's okay to continue and treat those as warnings. Probably need separate options for each type of error plus a generic tryReallyHard kind of method that enables them all. Then the qpdf command-line tool can have a single flag that enables all supported aggressive recovery techniques. - See ../misc/broken-files General ======= * 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. * Consider impact of article threads on page splitting/merging. Subramanyam provided a test file; see ../misc/article-threads.pdf. Email Q-Count: 431864 from 2009-11-03. Other things to consider: outlines, page labels, thumbnails, zones. There are probably others. * See if we can avoid preserving unreferenced objects in object streams even when preserving the object streams. * For debugging linearization bugs, consider adding an option to save pass 1 of linearization. This code is sufficient. Change the interface to allow specification of a pass1 file, which would change the behavior as in this patch. ------------------------------ Index: QPDFWriter.cc =================================================================== --- QPDFWriter.cc (revision 932) +++ QPDFWriter.cc (working copy) @@ -1965,11 +1965,15 @@ // Write file in two passes. Part numbers refer to PDF spec 1.4. + FILE* XXX = 0; for (int pass = 1; pass <= 2; ++pass) { if (pass == 1) { - pushDiscardFilter(); +// pushDiscardFilter(); + XXX = QUtil::safe_fopen("/tmp/pass1.pdf", "w"); + pushPipeline(new Pl_StdioFile("pass1", XXX)); + activatePipelineStack(); } // Part 1: header @@ -2204,6 +2208,8 @@ // Restore hint offset this->xref[hint_id] = QPDFXRefEntry(1, hint_offset, 0); + fclose(XXX); + XXX = 0; } } } ------------------------------ * 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. * Pl_PNGFilter is only partially implemented. If we ever decoded images, we'd have to finish implementing it along with the other filter decode parameters and types. For just handling xref streams, there's really no need as it wouldn't make sense to use any kind of predictor other than 12 (PNG UP filter). * 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.