Fixes #9670. If `qpdf` fails to decrypt a PDF, try `gs`.

Documentation/Manual.rst

@@ -52,6 +52,7 @@ The following features are only tested / supported on linux hosts:
 * HTML to PDF conversion - command `wkhtmltopdf`.
 * Concatenation of PDF files - command `pdfunite`.
 * PDF decrypt (used for merge with pdfunite) - command `qpdf`.
+* PDF decrypt (used for merge with pdfunite) - command `gs` - in case `qpdf` is not successful.
 * Mime type detection for uploads - command `file`.
 
 
@@ -67,12 +68,12 @@ To normalize UTF8 input, *php-intl* package is needed by
 
 * normalizer::normalize()
 
-For the `download`_ function, the programs `pdfunite`, `qpdf` and `file` are necessary to concatenate PDF files.
+For the `download`_ function, the programs `pdfunite`, `qpdf`, `gs` and `file` are necessary to concatenate PDF files.
 
 Preparation for Ubuntu::
 
   sudo apt install php-intl
-  sudo apt install poppler-utils libxrender1 file pdf2svg pdfunite qpdf # for file upload, PDF and 'HTML to PDF' (wkhtmltopdf), PDF split
+  sudo apt install poppler-utils libxrender1 file pdf2svg pdfunite qpdf ghostscript # for file upload, PDF and 'HTML to PDF' (wkhtmltopdf), PDF split
   sudo apt install inkscape imagemagick            # to render thumbnails
 
 .. _wkhtml:

extension/Classes/Core/Report/Download.php

@@ -174,12 +174,12 @@ class Download {
         $last = '';
         $rcOutput = '-';
 
-        // Try to merge the PDFs as long as a problematic PDF has been repaired.
+        // Try to merge the PDFs as long as a problematic PDF has been repaired. Check this by comparing the last and the current output.
         while ($last != $rcOutput) {
 
             $last = $rcOutput; // Remember last
 
-            // Merge
+            // Merge:
             exec($cmd, $rcOutput, $rc);
 
             if ($rc == 0) {
@@ -200,15 +200,24 @@ class Download {
                         HelperFile::copy($file, $backup);
                     }
 
+                    // Try 1: via 'qpdf --decrypt'
                     $cmdQpdf = "qpdf --decrypt '$backup' '$file' 2>&1"; // Try to decrypt file
                     exec($cmdQpdf, $outputQpdf, $rcQpdf);
 
                     if ($rcQpdf != 0) {
-                        // qpdf failed: restore origfile in case the $file has been destroyed.
-                        HelperFile::copy($backup, $file);
-                        throw new \DownloadException (json_encode([ERROR_MESSAGE_TO_USER => "Failed to decrypt PDF",
-                                ERROR_MESSAGE_TO_DEVELOPER => "CMD: " . $cmdQpdf . "<br>RC: $rc<br>Output: " . implode("<br>", $outputQpdf)])
-                            , ERROR_DOWNLOAD_MERGE_FAILED);
+
+                        // Try 2: via 'gs -sDEVICE=pdfwrite'
+                        $cmdGs = "gs -sDEVICE=pdfwrite -dNOPAUSE -sOutputFile=\"$file\" -- \"$backup\"";
+                        exec($cmdGs, $outputGs, $rcGs);
+
+                        if ($rcGs != 0) {
+                            // qpdf failed: restore origfile in case the $file has been destroyed.
+                            HelperFile::copy($backup, $file);
+                            throw new \DownloadException (json_encode([ERROR_MESSAGE_TO_USER => "Failed to decrypt PDF",
+                                    ERROR_MESSAGE_TO_DEVELOPER => "CMD1: " . $cmdQpdf . "<br>RC: $rcQpdf<br>Output: " . implode("<br>", $outputQpdf) . '<br>' .
+                                        "CMD2: " . $cmdGs . "<br>RC: $rcGs<br>Output: " . implode("<br>", $outputGs)])
+                                , ERROR_DOWNLOAD_MERGE_FAILED);
+                        }
                     }
                 }
             } else {
@@ -217,6 +226,7 @@ class Download {
                     , ERROR_DOWNLOAD_MERGE_FAILED);
             }
         }
+
         return $rc;
     }