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Data extraction from /Filter /FlateDecode PDF stream in PHP

Posted by: admin April 23, 2020 Leave a comment

Questions:

I can not decrypt the data from the stream like:

    56 0 obj 
    << /Length 1242 /Filter /FlateDecode >>
    stream
    x]êΩnƒ Ñ{ûbÀKq¬æ\âê¢....(whole binary is omitted)
    endstream
    endobj

I tried isolate the binary content (x]êΩnƒ Ñ{ûbÀKq¬æ\âê¢....) in a file and in a binary string. Decoding function gzinflate($encripted_data) sends me error of decoding, and I think it happens because encoded content in not “deflated” or so.

In PDF Reference v 1.7, (six edition), on a page 67, I found the description of /FlateDecode filter as: …Decompresses data encoded using the zlib/deflate compression method, reproducing the original text or binary data

I need real raw solution, aka php function or/and algorithm what to do with this “\FlateDecoded” stream.

Thank You!

How to&Answers:

Since you didn’t tell if you need to access one decompressed stream only or if you need all streams decompressed, I’ll suggest you a simple commandline tool which does it in one go for the complete PDF: Jay Berkenbilt’s qpdf.

Example commandline:

 qpdf --qdf --object-streams=disable in.pdf out.pdf

out.pdf can then be inspected in a text editor (only embedded ICC profiles, images and fonts could still be binary).

qpdf will also automatically re-order the objects and display the PDF syntax in a normalized way (and telling you in a comment what the original object ID of the de-compressed object was).

Should you require to re-compress the file again (maybe after you edited it), just run this command:

 qpdf out-edited.pdf out-recompressed.pdf

(You may see some warning message, telling that the utility was attempting to repair a damaged file….)

qpdf is multi-platform and available from Sourceforge.

Answer:

header('Content-Type: text');           // I going to download the result of decoding
$n = "binary_file.bin";                 // decoded part in file in a directory
$f = @fopen($n, "rb");                  // now file is mine
$c = fread($f, filesize($n));           // now I know all about it 
$u = @gzuncompress($c);                 // function, exactly fits for this /FlateDecode filter
$out = fopen("php://output", "wb");     // ready to output anywhere
fwrite($out, $u);                       // output to downloadable file

Jingle bells! Jingle bells!…

gzuncompress() – the solution

Answer:

Long overdue, but someone might find it helpful. In this case:
<< /Length 1242 /Filter /FlateDecode >> all you need is to pass the isolated binary string (so basically everything between “stream” and “endstream”) to zlib.decompress:

import zlib
stream = b"êΩnƒ Ñ{ûbÀKq¬æ\âê"  # binary stream here
data = zlib.decompress(stream) # Here you have your clean decompressed stream

However, if you have/DecodeParms in your PDF object thing become complicated. You will need the /Predictor value and columns number. Better use PyPDF2 for this.

Answer:

i just used

import de.intarsys.pdf.filter.FlateFilter;

from jpod / source forge
and it works well

FlateFilter filter = new FlateFilter(null);
byte[] decoded = filter.decode(bytes, start, end - start);

the bytes are straight from the pdf file