Hi,
Am 11.03.22 um 21:49 schrieb Ryan Jackson:
Dear Apache Devs:
I believe that I have identified a bug in the creation of the
(begin/end)bfrange operator used when embedding fonts with the
PDCIDFontType2Embedder class.
The bug exists (as best I can tell) in both the main trunk and in the 2.0
branch. The code in question may be found here
<https://github.com/ryanjackson-wf/pdfbox/blob/trunk/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/font/ToUnicodeWriter.java#L133-L136>.
The portion of the PDF specification (version 1.7) that bears upon this
code is Section 5.9, Example 5.16.
The existing code attempts to limit the range logic to changes less than or
equal to 255 code points, but it fails to account for at least the
following situation by allowing this (for example):
[srcCode1 srcCode2 dstString]
03FF 0400 0036
The overflow between srcCode1 and srcCode2 is not allowed by the
specification and any text extraction will fail. The glyphs themselves
render fine so it is not immediately obvious there is a problem until one
tries to examine the text by using the Content Panel or by copy/pasting
from Acrobat (Pro) to some other document. By contrast the following
bfrange operator does allow the text extraction to work as intended:
[srcCode1 srcCode2 dstString]
03FE 03FF 0035
Notice that no overflow exists, and as such the requirements of the
specification are met.
I'm afraid you are right, good catch.
I've looked briefly at the PDFBOX project in Jira and have found the
following tickets that may be caused by this same problem:
PDFBOX-4785 <https://issues.apache.org/jira/browse/PDFBOX-4785>
PDFBOX-5350 <https://issues.apache.org/jira/browse/PDFBOX-5350>
Yes, somehow. Those are about reading malformed pdfs containing the very same
issue your have described above.
Fun fact: we are complaining about other pdf writers not following the spec and
are doing the very same: I never came up with the idea to check our own code :-(
I have put together a proposed solution here
<https://github.com/ryanjackson-wf/pdfbox/pull/1> in my fork of the PDFBox
GH mirror. With your permission I'd like to open a new Jira ticket for this
and collaborate with whomever would like to help drive this work to get it
reviewed and merged. I do have some open questions about how surrogates are
to be handled. I'm also open to changes in the proposed code.
You don't have to wait for permission. Please create a JIRA ticket including a
link to you PR
Thank you for your time.
Thanks for you time and the proposed solution.
Andreas
Sincerely,
Ryan Jackson
Senior Software Engineer
Workiva Inc.
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