Add support for PDFTK

doc/admin/config.rst

@@ -295,5 +295,13 @@ various places like order codes, secrets in the ticket QR codes, etc. Example::
     ; Voucher code needs to be < 255 characters, default is 16
     voucher_code=16
 
+External tools
+--------------
+
+pretix can make use of some external tools if they are installed. Currently, they are all optional. Example::
+
+    [tools]
+    pdftk=/usr/bin/pdftk
+
 .. _Python documentation: https://docs.python.org/3/library/configparser.html?highlight=configparser#supported-ini-file-structure
 .. _Celery documentation: http://docs.celeryproject.org/en/latest/userguide/configuration.html

src/pretix/base/pdf.py

@@ -1,11 +1,15 @@
 import copy
 import logging
+import os
 import re
+import subprocess
+import tempfile
 import uuid
 from collections import OrderedDict
 from io import BytesIO
 
 import bleach
+from django.conf import settings
 from django.contrib.staticfiles import finders
 from django.utils.formats import date_format
 from django.utils.translation import ugettext_lazy as _
@@ -222,6 +226,7 @@ class Renderer:
         self.layout = layout
         self.background_file = background_file
         self.variables = get_variables(event)
+        if not settings.PDFTK:
             if self.background_file:
                 self.bg_pdf = PdfFileReader(BytesIO(self.background_file.read()), strict=False)
             else:
@@ -340,6 +345,25 @@ class Renderer:
         canvas.showPage()
 
     def render_background(self, buffer, title=_('Ticket')):
+        if settings.PDFTK:
+            buffer.seek(0)
+            with tempfile.TemporaryDirectory() as d:
+                with open(os.path.join(d, 'back.pdf'), 'wb') as f:
+                    f.write(self.background_file.read())
+                with open(os.path.join(d, 'front.pdf'), 'wb') as f:
+                    f.write(buffer.read())
+                subprocess.run([
+                    settings.PDFTK,
+                    os.path.join(d, 'front.pdf'),
+                    'multistamp',
+                    os.path.join(d, 'back.pdf'),
+                    'output',
+                    os.path.join(d, 'out.pdf'),
+                    'compress'
+                ], check=True)
+                with open(os.path.join(d, 'out.pdf'), 'rb') as f:
+                    return BytesIO(f.read())
+        else:
             from PyPDF2 import PdfFileWriter, PdfFileReader
             buffer.seek(0)
             new_pdf = PdfFileReader(buffer)

src/pretix/settings.py

@@ -57,6 +57,8 @@ else:
 debug_fallback = "runserver" in sys.argv
 DEBUG = config.getboolean('django', 'debug', fallback=debug_fallback)
 
+PDFTK = config.get('tools', 'pdftk', fallback=None)
+
 db_backend = config.get('database', 'backend', fallback='sqlite3')
 if db_backend == 'postgresql_psycopg2':
     db_backend = 'postgresql'