Currently image resources, as opposed to e.g. font resources, are handled exclusively on a page-specific basis. Generally speaking this makes sense, since pages are separate from each other, however there's PDF documents where many (or even all) pages actually references exactly the same image resources (through the XRef table). Hence, in some cases, we're decoding the *same* images over and over for every page which is obviously slow and wasting both CPU and memory resources better used elsewhere.[1]
Obviously we cannot simply treat all image resources as-if they're used throughout the entire PDF document, since that would end up increasing memory usage too much.[2]
However, by introducing a `GlobalImageCache` in the worker we can track image resources that appear on more than one page. Hence we can switch image resources from being page-specific to being document-specific, once the image resource has been seen on more than a certain number of pages.
In many cases, such as e.g. the referenced issue, this patch will thus lead to reduced memory usage for image resources. Scrolling through all pages of the document, there's now only a few main-thread copies of the same image data, as opposed to one for each rendered page (i.e. there could theoretically be *twenty* copies of the image data).
While this obviously benefit both CPU and memory usage in this case, for *very* large image data this patch *may* possibly increase persistent main-thread memory usage a tiny bit. Thus to avoid negatively affecting memory usage too much in general, particularly on the main-thread, the `GlobalImageCache` will *only* cache a certain number of image resources at the document level and simply fallback to the default behaviour.
Unfortunately the asynchronous nature of the code, with ranged/streamed loading of data, actually makes all of this much more complicated than if all data could be assumed to be immediately available.[3]
*Please note:* The patch will lead to *small* movement in some existing test-cases, since we're now using the built-in PDF.js JPEG decoder more. This was done in order to simplify the overall implementation, especially on the main-thread, by limiting it to only the `OPS.paintImageXObject` operator.
---
[1] There's e.g. PDF documents that use the same image as background on all pages.
[2] Given that data stored in the `commonObjs`, on the main-thread, are only cleared manually through `PDFDocumentProxy.cleanup`. This as opposed to data stored in the `objs` of each page, which is automatically removed when the page is cleaned-up e.g. by being evicted from the cache in the default viewer.
[3] If the latter case were true, we could simply check for repeat images *before* parsing started and thus avoid handling *any* duplicate image resources.
This should ensure that a page will always render successfully, even if there's errors during the Annotation fetching/parsing.
Additionally the `OperatorList.addOpList` method is also adjusted to ignore invalid data, to make it slightly more robust.
- Add a reduced test-case for issue 11768, to prevent future regressions.
(Given that PR 11769 is only a work-around, rather than a proper solution, it may not be entirely accurate for the issue to be closed as fixed.)
- Add more validation of the charCode, as found by the heuristics, in `PartialEvaluator._buildSimpleFontToUnicode` to prevent future issues.
At this point in time, compared to when the "ignore single-char" code was added, we *should* generally be doing a much better job of combining text into as few chunks as possible.
However, there's still bad cases where we're not able to combine text as much as one would like, which is why I'm *not* proposing to simply measure/scale all text. Instead this patch will to only measure/scale single-char text in cases where the horizontal/vertical scale is off significantly, since that's were you'd expect bad text-selection behaviour otherwise.
Note that most of the movement caused by this patch is with Type3 fonts, which is a somewhat special font type and one where our current text-selection behaviour is probably the least good.
Fixes#11718 in which the `ff` ligature glyph is at index zero in a CFF font. Beacuse this is a CIDFont, glyph names are CIDs, which are integers. Thus the string `".notdef"` is not correct. The rest of the charset data is already parsed correctly as integers when the boolean argument `cid` is true.
The /Differences array of the problematic font contains a `/c.1` entry, which is consequently detected as a *possible* Cdd{d}/cdd{d} glyphName by the existing heuristics.
Because of how the base 10 conversion is implemented, which is necessary for the base 16 special case, the parsed charCode becomes `0.1` thus causing `String.fromCodePoint` to throw since that obviously isn't a valid code point.
To fix the referenced issue, and to hopefully prevent similar ones in the future, the patch adds *additional* validation of the charCode found by the heuristics.
The PDF document in question is *corrupt*, since it contains an XObject with a truncated dictionary and where the stream contents start without a "stream" operator.
Fixes#11477
The PDF draws many space characters but the embedded fonts don't have a glyph named `space`, so `.notdef` should be drawn instead. PDF.js assumed that Type1 fonts define `.notdef` as the first glyph (index 0). However, now the fonts have the glyph `A` at index 0 and `.notdef` is the last one, so `A` appears where spaces are expected.
Because the rest of the font machinery in `core/fonts.js` assumes `.notdef` is at index zero, it's easiest to modify `core/type1_parser.js` so that it "repairs" fonts and makes sure `.notdef` is at index 0.
The PDF document in question is *corrupt*, since it contains multiple instances of incorrect operators.
We obviously don't want to slow down parsing of *all* documents (since most are valid), just to accommodate a particular bad PDF generator, hence the reason for the inline check before calling the `ensureStateFont` method.
*This whole patch feels somewhat arbitrary, and I'd be slightly worried about possibly breaking something else.*
To limit the impact of these changes, we only re-parse JPEG images using a reduced `scanLines` value if and only if: An unexpected EOI (End of Image) marker was encountered during decoding of Scan data *and* the "actual" `scanLines` value is at least one order of magnitude smaller than expected.
While it would be nice to change the `PDFFormatVersion` property, as returned through `PDFDocumentProxy.getMetadata`, to a number (rather than a string) that would unfortunately be a breaking API change.
However, it does seem like a good idea to at least *validate* the PDF header version on the worker-thread, rather than potentially returning an arbitrary string.
In the current `AnnotationLayer` implementation, Popup annotations require that the parent annotation have already been rendered (otherwise they're simply ignored).
Usually the annotations are ordered, in the `/Annots` array, in such a way that this isn't a problem, however there's obviously no guarantee that all PDF generators actually do so. Hence we simply ensure, when rendering the `AnnotationLayer`, that the Popup annotations are handled last.
- Re-factor the "incorrect encoding" check, since this can be easily achieved using the general `findNextFileMarker` helper function (with a suitable `startPos` argument).
- Tweak a condition, to make it easier to see that the end of the data has been reached.
- Add a reference test for issue 1877, since it's what prompted the "incorrect encoding" check.
Fixes#11403
The PDF uses the non-embedded Type1 font Helvetica. Character codes 194 and 160 (`Â` and `NBSP`) are encoded as `.notdef`. We shouldn't show those glyphs because it seems that Acrobat Reader doesn't draw glyphs that are named `.notdef` in fonts like this.
In addition to testing `glyphName === ".notdef"`, we must test also `glyphName === ""` because the name `""` is used in `core/encodings.js` for undefined glyphs in encodings like `WinAnsiEncoding`.
The solution above hides the `Â` characters but now the replacement character (space) appears to be too wide. I found out that PDF.js ignores font's `Widths` array if the font has no `FontDescriptor` entry. That happens in #11403, so the default widths of Helvetica were used as specified in `core/metrics.js` and `.nodef` got a width of 333. The correct width is 0 as specified by the `Widths` array in the PDF. Thus we must never ignore `Widths`.
The original issue did not contain a (reduced) test case that we could
include and linked test cases are not ideal for unit tests, so the
original PR could only be verified manually.
I found this a bit unfortunate considering that the print data is
exposed through the API, so I thought about how we could have an
automated test and managed to create a reduced test case with the
OpenAction dictionary from the file in the original issue.
Therefore, this commit includes a unit test for parsing OpenAction
dictionaries without `Type` entries. I verified that this PDF file
behaves the same as the original one, i.e., no print dialog is shown for
older viewers and the print dialog is shown for the most recent viewer.
In the PDF document in question, there's an ASCII85Decode inline image where the '>' part of EOD (end-of-data) marker is missing; hence the PDF document is corrupt.
For documents with a Linearization dictionary the computed `startXRef` position will be relative to the raw file, rather than the actual PDF document itself (which begins with `%PDF-`).
Hence it's necessary to subtract `stream.start` in this case, since otherwise the `XRef.readXRef` method will increment the position too far resulting in parsing errors.
This will allow us to attempt to recover as much as possible of a page, rather than immediately failing, when a broken/unsupported ColorSpace is encountered. This patch thus extends the framework added in PRs such as e.g. 8240 and 8922, to also cover parsing of ColorSpaces.
Obviously this won't look exactly right, but considering that the PDF file doesn't bother embedding non-standard fonts this is the best that we can do here.
This patch is making me somewhat worried about future regressions, since it's certainly easy to imagine this completely breaking certain kinds of corrupt/edited PDF documents while fixing others.[1]
Obviously it passes all existing reference tests (and even improves one), however compared to many other patches there's no telling how much it could break.
The only reason that I'm even submitting this patch, is because of the number of open issues that it would address.
Generally speaking though, the best course of action would probably be if `XRef.indexObjects` was re-written to be much more robust (since it currently feels somewhat hand-wavy in parts). E.g. by actually checking/validating more of the objects before committing to them.
---
[1] Especially given that it's reverting part of PR 5910, however in the case of issue 5909 it seems that other (more recent) changes have actually made that PR redundant.
As part of attempting to fix a number issues containing PDF documents with corrupt XRef tables, I'd like to improve the reference test-coverage slightly *first*.
Obviously this will increase the runtime of the tests a bit, however I'd rather "waste" resources on the bots instead of developer time fixing regressions which could have been avoided.
*Please note:* I've been thinking about possible ways of addressing this issue for a while now, but all of the solutions I came up with became too complicated and thus hurt readability of the code.
However, it occured to me that we're essentially trying to add a heuristic *on top* of another heuristic, and that it shouldn't matter how efficient the code is as long as it works.
In the PDF file in the issue the Encoding contains glyphNames of the `Cdd` format, which our existing heuristics will treat as base 10 values. However, in this particular file they actually contain base 16 values, which we thus attempt to detect and fix such that text-selection works.
Hopefully this patch makes sense, and in order to reduce the regression risk the implementation ensures that only completely missing widths are being replaced.
This is based on a real-world PDF file I encountered very recently[1], although I'm currently unable to recall where I saw it.
Note that different PDF viewers handle these sort of errors differently, with Adobe Reader outright failing to render the attached PDF file whereas PDFium mostly handles it "correctly".
The patch makes the following notable changes:
- Refactor the `cropBox` and `mediaBox` getters, on the `Page`, to reduce unnecessary duplication. (This will also help in the future, if support for extracting additional page bounding boxes are added to the API.)
- Ensure that the page bounding boxes, i.e. `cropBox` and `mediaBox`, are never empty to prevent issues/weirdness in the viewer.
- Ensure that the `view` getter on the `Page` will never return an empty intersection of the `cropBox` and `mediaBox`.
- Add an *optional* parameter to `Util.intersect`, to allow checking that the computed intersection isn't actually empty.
- Change `Util.intersect` to have consistent return types, since Arrays are of type `Object` and falling back to returning a `Boolean` thus seem strange.
---
[1] In that case I believe that only the `cropBox` was empty, but it seemed like a good idea to attempt to fix a bunch of related cases all at once.
This patch will not incur any (measurable) overhead, since the glyphlist is already quite long and one more entry won't really matter, which is important given that this sort of PDF corruption ought to be very rare.
Furthermore, this patch purposely does *not* add a bunch of similarly modified ligature names on pure speculation. Any similar additions, for other ligatures, should only be made if there's real-world examples of PDF files where that's actually necessary.
