Length-0 streams are read incorrectly, which breaks some PDFs

[benrg]

DictionaryObject.read_from_stream contains this code:

            if length is None:  # if the PDF is damaged
                length = -1
            pstart = stream.tell()
            if length > 0:
                data["__streamdata__"] = stream.read(length)
            else:
                data["__streamdata__"] = read_until_regex(
                    stream, re.compile(b"endstream")
                )

Since read_until_regex doesn't strip the trailing newline, this will read almost all length-0 streams as b"\n" or b"\r\n" instead of b"".

I have some PDFs with creator PFU ScanSnap Manager 5.1.30 #S1500 that contain JBIG2-encoded pages with /JBIG2Globals pointing to an empty stream object. After loading and saving them with pypdf, the /JBIG2Globals stream is invalid, and some (not all) PDF viewers fail to render the pages.

Suggested fix:

• If there exist broken PDFs in the wild with /Length 0 followed by a stream of nonzero length that pypdf needs to support, check for stream\r?\n\r?\n?endstream as a special case first before falling back to read_until_regex, to ensure that valid PDFs with length-0 streams are always read correctly.
• Or, if there are no such PDFs, and length > 0 was just meant to catch the -1 case, change the test to length >= 0.
• In the read_until_regex case, if endstream is preceded by \r then strip it, or if it's preceded by \r\n then strip the \n, and strip the \r also iff stream was followed by \r. That isn't guaranteed to work, but it's probably the best one can do.

[stefan6419846]

Thanks for the report. You are invited to propose a corresponding PR including tests of course.

For the future, please report bugs with the actual bug template to not omit relevant aspects for reproduction.

[benrg]

Here's a pair of PDFs showing the problem. correct.pdf should display the text "Hello, World!" in any PDF reader (such as Acrobat Reader). broken.pdf fails to display the text in Acrobat Reader (with the message "Insufficient data for an image"), though some other readers such as SumatraPDF display it. The only difference between them is that the JBIG2Globals stream is empty in correct.pdf and contains a single 0A byte in broken.pdf. The latter is obtained from the former by

>>> import pypdf
>>> r = pypdf.PdfReader("correct.pdf")
>>> w = pypdf.PdfWriter(r)
>>> w.write("broken.pdf")

jbig2_with_0_length_symbols.zip