Allow ticket output providers to handle downloads externally (#1402)

* TicketOutput-Providers: Make preview optional; download/attachable optional; optional specific target; update doc

* Spelling fixes in doc

* Changes after code-review

* Changes after code-review

* Commit missing template file

* Allow for redirects instead of files

* Return HTTPResponse with Content-Type text/uri-list on API

* Update API-doc

* Add viewable to spellinglist, fixing doc-test

doc/api/resources/orders.rst

@@ -219,6 +219,11 @@ pdf_data                              object                     Data object req
 
   The value ``auto_checked_in`` has been added to the ``checkins``-attribute.
 
+.. versionchanged:: 3.3
+
+  The ``url`` of a ticket ``download`` can now also return a ``text/uri-list`` instead of a file. See
+  :ref:`order-position-ticket-download` for details.
+
 .. _order-payment-resource:
 
 Order payment resource
@@ -1483,6 +1488,8 @@ Fetching individual positions
    :statuscode 403: The requested organizer/event does not exist **or** you have no permission to view this resource.
    :statuscode 404: The requested order position does not exist.
 
+.. _`order-position-ticket-download`:
+
 Order position ticket download
 ------------------------------
 
@@ -1492,6 +1499,11 @@ Order position ticket download
    Depending on the chosen output, the response might be a ZIP file, PDF file or something else. The order details
    response contains a list of output options for this particular order position.
 
+   Be aware that the output does not have to be a file, but can also be a regular HTTP response with a ``Content-Type``
+   set to ``text/uri-list``. In this case, the user is expected to navigate to that URL in order to access their ticket.
+   The referenced URL can provide a download or a regular, human-viewable website - so it is advised to open this URL
+   in a webbrowser and leave it up to the user to handle the result.
+
    Tickets can be only downloaded if the order is paid and if ticket downloads are active. Also, depending on event
    configuration downloads might be only unavailable for add-on products or non-admission products.
    Note that in some cases the ticket file might not yet have been created. In that case, you will receive a status

doc/development/api/ticketoutput.rst

@@ -69,3 +69,9 @@ The output class
    .. automethod:: generate_order
 
    .. autoattribute:: download_button_text
+
+   .. autoattribute:: download_button_icon
+
+   .. autoattribute:: preview_allowed
+
+   .. autoattribute:: javascript_required

doc/spelling_wordlist.txt

@@ -31,6 +31,7 @@ deprovision
 discoverable
 django
 dockerfile
+downloadable
 durations
 eu
 filename
@@ -140,6 +141,7 @@ username
 url
 versa
 versioning
+viewable
 viewset
 viewsets
 waitinglist

src/pretix/api/views/order.py

@@ -6,7 +6,7 @@ import pytz
 from django.db import transaction
 from django.db.models import F, Prefetch, Q
 from django.db.models.functions import Coalesce, Concat
-from django.http import FileResponse
+from django.http import FileResponse, HttpResponse
 from django.shortcuts import get_object_or_404
 from django.utils.timezone import make_aware, now
 from django.utils.translation import ugettext as _
@@ -148,12 +148,16 @@ class OrderViewSet(viewsets.ModelViewSet):
             generate.apply_async(args=('order', order.pk, provider.identifier))
             raise RetryException()
         else:
-            resp = FileResponse(ct.file.file, content_type=ct.type)
+            if ct.type == 'text/uri-list':
-            resp['Content-Disposition'] = 'attachment; filename="{}-{}-{}{}"'.format(
+                resp = HttpResponse(ct.file.file.read(), content_type='text/uri-list')
-                self.request.event.slug.upper(), order.code,
+                return resp
-                provider.identifier, ct.extension
+            else:
-            )
+                resp = FileResponse(ct.file.file, content_type=ct.type)
-            return resp
+                resp['Content-Disposition'] = 'attachment; filename="{}-{}-{}{}"'.format(
+                    self.request.event.slug.upper(), order.code,
+                    provider.identifier, ct.extension
+                )
+                return resp
 
     @action(detail=True, methods=['POST'])
     def mark_paid(self, request, **kwargs):
@@ -759,12 +763,16 @@ class OrderPositionViewSet(mixins.DestroyModelMixin, viewsets.ReadOnlyModelViewS
             generate.apply_async(args=('orderposition', pos.pk, provider.identifier))
             raise RetryException()
         else:
-            resp = FileResponse(ct.file.file, content_type=ct.type)
+            if ct.type == 'text/uri-list':
-            resp['Content-Disposition'] = 'attachment; filename="{}-{}-{}-{}{}"'.format(
+                resp = HttpResponse(ct.file.file.read(), content_type='text/uri-list')
-                self.request.event.slug.upper(), pos.order.code, pos.positionid,
+                return resp
-                provider.identifier, ct.extension
+            else:
-            )
+                resp = FileResponse(ct.file.file, content_type=ct.type)
-            return resp
+                resp['Content-Disposition'] = 'attachment; filename="{}-{}-{}-{}{}"'.format(
+                    self.request.event.slug.upper(), pos.order.code, pos.positionid,
+                    provider.identifier, ct.extension
+                )
+                return resp
 
     def perform_destroy(self, instance):
         try:

src/pretix/base/services/tickets.py

@@ -47,6 +47,9 @@ def generate_order(order: int, provider: str):
             prov = response(order.event)
             if prov.identifier == provider:
                 filename, ttype, data = prov.generate_order(order)
+                if ttype == 'text/uri-list':
+                    continue
+
                 path, ext = os.path.splitext(filename)
                 for ct in CachedCombinedTicket.objects.filter(order=order, provider=provider):
                     ct.delete()
@@ -124,6 +127,9 @@ def get_tickets_for_order(order, base_position=None):
         if not p.is_enabled:
             continue
 
+        if p.download_handled_by_frontend:
+            continue
+
         if p.multi_download_enabled and not base_position:
             try:
                 if len(positions) == 0:

src/pretix/base/ticketoutput.py

@@ -46,12 +46,19 @@ class BaseTicketOutput:
         filename, a file type and file content. The extension will be taken from the filename
         which is otherwise ignored.
 
+        Alternatively, you can pass a tuple consisting of an arbitrary string, ``text/uri-list``
+        and a single URL. In this case, the user will be redirected to this link instead of
+        being asked to download a generated file.
+
         .. note:: If the event uses the event series feature (internally called subevents)
                   and your generated ticket contains information like the event name or date,
                   you probably want to display the properties of the subevent. A common pattern
                   to do this would be a declaration ``ev = position.subevent or position.order.event``
                   and then access properties that are present on both classes like ``ev.name`` or
                   ``ev.date_from``.
+
+        .. note:: Should you elect to use the URI redirection feature instead of offering downloads,
+                  you should also set the ``multi_download_enabled``-property to ``False``.
         """
         raise NotImplementedError()
 
@@ -161,3 +168,21 @@ class BaseTicketOutput:
         The Font Awesome icon on the download button in the frontend.
         """
         return 'fa-download'
+
+    @property
+    def preview_allowed(self) -> bool:
+        """
+        By default, the ``generate()`` method is called for generating a preview in the pretix backend.
+        In case your plugin cannot generate previews for any reason, you can manually disable it here.
+        """
+        return True
+
+    @property
+    def javascript_required(self) -> bool:
+        """
+        If this property is set to true, the download-button for this ticket-type will not be displayed
+        when the user's browser has JavaScript disabled.
+
+        Defaults to ``False``
+        """
+        return False

src/pretix/control/templates/pretixcontrol/event/tickets.html

@@ -29,7 +29,7 @@
                     <div class="panel panel-default ticketoutput-panel">
                         <div class="panel-heading">
                             <a href="{% url "control:event.settings.tickets.preview" event=request.event.slug organizer=request.organizer.slug output=provider.identifier %}"
-                                    class="btn btn-default btn-sm pull-right flip {% if not provider.preview_allowed %}disabled{% endif %}"
+                                    class="btn btn-default btn-sm pull-right flip {% if not provider.evaluated_preview_allowed %}disabled{% endif %}"
                                     target="_blank">
                                 {% trans "Preview" %}
                             </a>

src/pretix/control/templates/pretixcontrol/order/index.html

@@ -287,7 +287,7 @@
                                             {% for b in download_buttons %}
                                                 <form action="{% url "control:event.order.download.ticket" code=order.code event=request.event.slug organizer=request.event.organizer.slug position=line.pk output=b.identifier %}"
                                                         method="post" data-asynctask data-asynctask-download
-                                                        class="form-inline helper-display-inline">
+                                                        class="form-inline helper-display-inline{% if b.javascript_required %} requirejs{% endif %}">
                                                     {% csrf_token %}
                                                     <button type="submit"
                                                             class="btn btn-xs btn-default">

src/pretix/control/views/event.py

@@ -736,11 +736,14 @@ class TicketSettings(EventSettingsViewMixin, EventPermissionRequiredMixin, FormV
             provider.settings_content = provider.settings_content_render(self.request)
             provider.form.prepare_fields()
 
-            provider.preview_allowed = True
+            provider.evaluated_preview_allowed = True
-            for k, v in provider.settings_form_fields.items():
+            if not provider.preview_allowed:
-                if v.required and not self.request.event.settings.get('ticketoutput_%s_%s' % (provider.identifier, k)):
+                provider.evaluated_preview_allowed = False
-                    provider.preview_allowed = False
+            else:
-                    break
+                for k, v in provider.settings_form_fields.items():
+                    if v.required and not self.request.event.settings.get('ticketoutput_%s_%s' % (provider.identifier, k)):
+                        provider.evaluated_preview_allowed = False
+                        break
 
             providers.append(provider)
         return providers

src/pretix/control/views/orders.py

@@ -16,7 +16,8 @@ from django.db.models import (
 )
 from django.forms import formset_factory
 from django.http import (
-    FileResponse, Http404, HttpResponseNotAllowed, JsonResponse,
+    FileResponse, Http404, HttpResponseNotAllowed, HttpResponseRedirect,
+    JsonResponse,
 )
 from django.shortcuts import get_object_or_404, redirect, render
 from django.urls import reverse
@@ -225,7 +226,8 @@ class OrderDetail(OrderView):
                 'text': provider.download_button_text or 'Ticket',
                 'icon': provider.download_button_icon or 'fa-download',
                 'identifier': provider.identifier,
-                'multi': provider.multi_download_enabled
+                'multi': provider.multi_download_enabled,
+                'javascript_required': provider.javascript_required
             })
         return buttons
 
@@ -340,12 +342,16 @@ class OrderDownload(AsyncAction, OrderView):
                 'message': str(self.get_success_message(value))
             })
         if isinstance(value, CachedTicket):
-            resp = FileResponse(value.file.file, content_type=value.type)
+            if value.type == 'text/uri-list':
-            resp['Content-Disposition'] = 'attachment; filename="{}-{}-{}-{}{}"'.format(
+                resp = HttpResponseRedirect(value.file.file.read())
-                self.request.event.slug.upper(), self.order.code, self.order_position.positionid,
+                return resp
-                self.output.identifier, value.extension
+            else:
-            )
+                resp = FileResponse(value.file.file, content_type=value.type)
-            return resp
+                resp['Content-Disposition'] = 'attachment; filename="{}-{}-{}-{}{}"'.format(
+                    self.request.event.slug.upper(), self.order.code, self.order_position.positionid,
+                    self.output.identifier, value.extension
+                )
+                return resp
         elif isinstance(value, CachedCombinedTicket):
             resp = FileResponse(value.file.file, content_type=value.type)
             resp['Content-Disposition'] = 'attachment; filename="{}-{}-{}{}"'.format(

src/pretix/presale/templates/pretixpresale/event/fragment_cart.html

@@ -81,7 +81,7 @@
             {% if line.generate_ticket %}
                 {% for b in download_buttons %}
                     <form action="{% if position_page and line.addon_to %}{% eventurl event "presale:event.order.position.download" secret=line.addon_to.web_secret order=order.code output=b.identifier pid=line.pk position=line.addon_to.positionid %}{% elif position_page %}{% eventurl event "presale:event.order.position.download" secret=line.web_secret order=order.code output=b.identifier pid=line.pk position=line.positionid %}{% else %}{% eventurl event "presale:event.order.download" secret=order.secret order=order.code output=b.identifier position=line.pk %}{% endif %}"
-                            method="post" data-asynctask data-asynctask-download class="download-btn-form">
+                            method="post" data-asynctask data-asynctask-download class="download-btn-form{% if b.javascript_required %} requirejs{% endif %}">
                         {% csrf_token %}
                         <button type="submit"
                                 class="btn btn-sm {% if b.identifier == "pdf" %}btn-primary{% else %}btn-default{% endif %}">

src/pretix/presale/views/order.py

@@ -8,7 +8,9 @@ from django.contrib import messages
 from django.core.files import File
 from django.db import transaction
 from django.db.models import Exists, OuterRef, Q, Sum
-from django.http import FileResponse, Http404, JsonResponse
+from django.http import (
+    FileResponse, Http404, HttpResponseRedirect, JsonResponse,
+)
 from django.shortcuts import get_object_or_404, redirect
 from django.utils.decorators import method_decorator
 from django.utils.functional import cached_property
@@ -155,7 +157,8 @@ class OrderDetails(EventViewMixin, OrderDetailMixin, CartMixin, TicketPageMixin,
                 'text': provider.download_button_text or 'Download',
                 'icon': provider.download_button_icon or 'fa-download',
                 'identifier': provider.identifier,
-                'multi': provider.multi_download_enabled
+                'multi': provider.multi_download_enabled,
+                'javascript_required': provider.javascript_required
             })
         return buttons
 
@@ -249,7 +252,8 @@ class OrderPositionDetails(EventViewMixin, OrderPositionDetailMixin, CartMixin,
                 'text': provider.download_button_text or 'Download',
                 'icon': provider.download_button_icon or 'fa-download',
                 'identifier': provider.identifier,
-                'multi': provider.multi_download_enabled
+                'multi': provider.multi_download_enabled,
+                'javascript_required': provider.javascript_required
             })
         return buttons
 
@@ -793,12 +797,16 @@ class OrderDownloadMixin:
                 'message': str(self.get_success_message(value))
             })
         if isinstance(value, CachedTicket):
-            resp = FileResponse(value.file.file, content_type=value.type)
+            if value.type == 'text/uri-list':
-            resp['Content-Disposition'] = 'attachment; filename="{}-{}-{}-{}{}"'.format(
+                resp = HttpResponseRedirect(value.file.file.read())
-                self.request.event.slug.upper(), self.order.code, self.order_position.positionid,
+                return resp
-                self.output.identifier, value.extension
+            else:
-            )
+                resp = FileResponse(value.file.file, content_type=value.type)
-            return resp
+                resp['Content-Disposition'] = 'attachment; filename="{}-{}-{}-{}{}"'.format(
+                    self.request.event.slug.upper(), self.order.code, self.order_position.positionid,
+                    self.output.identifier, value.extension
+                )
+                return resp
         elif isinstance(value, CachedCombinedTicket):
             resp = FileResponse(value.file.file, content_type=value.type)
             resp['Content-Disposition'] = 'attachment; filename="{}-{}-{}{}"'.format(

src/pretix/static/pretixcontrol/scss/main.scss

@@ -667,6 +667,10 @@ h1 .label {
     }
 }
 
+.nojs .requirejs {
+    display: none !important;
+}
+
 @import "../../pretixbase/scss/_rtl.scss";
 @import "../../bootstrap/scss/_rtl.scss";
-@import "_rtl.scss";
+@import "_rtl.scss";

src/pretix/static/pretixpresale/scss/main.scss

@@ -288,6 +288,10 @@ h2 .label {
     display: inline-block;
 }
 
+.nojs .requirejs {
+    display: none !important;
+}
+
 @import "_iframe.scss";
 @import "_a11y.scss";
 @import "_print.scss";