Support PDF generation without available request object

aleksis/core/preferences.py

 from django.conf import settings
+from django.core.validators import URLValidator
 from django.forms import EmailField, ImageField, URLField
 from django.forms.widgets import SelectMultiple
 from django.utils.translation import gettext_lazy as _
@@ -52,6 +53,20 @@ class SiteDescription(StringPreference):
     verbose_name = _("Site description")
 
 
+@site_preferences_registry.register
+class PDFURL(StringPreference):
+    """URL which should be used as base for PDF printing."""
+
+    section = general
+    name = "pdf_url"
+    default = ""
+    required = False
+    verbose_name = _("PDF URL")
+    help_text = _("This URL is used for PDF printing.")
+
+    field_kwargs = {"validators": [URLValidator()]}
+
+
 @site_preferences_registry.register
 class ColourPrimary(StringPreference):
     """Primary colour in AlekSIS frontend."""

aleksis/core/util/pdf.py

 import os
 import subprocess  # noqa
 from tempfile import TemporaryDirectory
-from typing import Optional
+from typing import Optional, Tuple
+from urllib.parse import urljoin
 
 from django.core.files import File
 from django.core.files.base import ContentFile
@@ -14,11 +15,13 @@ from django.utils import timezone
 from django.utils.translation import get_language
 from django.utils.translation import gettext as _
 
+from celery.result import AsyncResult
 from celery_progress.backend import ProgressRecorder
 
 from aleksis.core.celery import app
 from aleksis.core.models import PDFFile
 from aleksis.core.util.celery_progress import recorded_task, render_progress_page
+from aleksis.core.util.core_helpers import get_site_preferences
 
 
 @recorded_task
@@ -64,6 +67,27 @@ def generate_pdf(
     recorder.set_progress(1, 1)
 
 
+def generate_pdf_from_template(
+    template_name: str, context: Optional[dict] = None, request: Optional[HttpRequest] = None
+) -> Tuple[PDFFile, AsyncResult]:
+    """Start a PDF generation task and return the matching file object and Celery result."""
+    html_template = render_to_string(template_name, context, request)
+
+    file_object = PDFFile.objects.create(html_file=ContentFile(html_template, name="source.html"))
+
+    # As this method may be run in background and there is no request available,
+    # we have to use a predefined URL from preferences then
+    if request:
+        html_url = request.build_absolute_uri(file_object.html_file.url)
+    else:
+        pdf_base_url = get_site_preferences()["general__pdf_url"]
+        html_url = urljoin(pdf_base_url, file_object.html_file.url)
+
+    result = generate_pdf.delay(file_object.pk, html_url, lang=get_language())
+
+    return file_object, result
+
+
 def render_pdf(request: HttpRequest, template_name: str, context: dict = None) -> HttpResponse:
     """Start PDF generation and show progress page.
 
@@ -72,14 +96,7 @@ def render_pdf(request: HttpRequest, template_name: str, context: dict = None) -
     if not context:
         context = {}
 
-    html_template = render_to_string(template_name, context, request)
-
-    file_object = PDFFile.objects.create(
-        person=request.user.person, html_file=ContentFile(html_template, name="source.html")
-    )
-    html_url = request.build_absolute_uri(file_object.html_file.url)
-
-    result = generate_pdf.delay(file_object.pk, html_url, lang=get_language())
+    file_object, result = generate_pdf_from_template(template_name, context, request)
 
     redirect_url = reverse("redirect_to_pdf_file", args=[file_object.pk])