Fix #122 -- Allow users to re-send order links (#197)

If the provided mail address has not ordered anything, there will still
be a mail generated and sent to an invalid mail address, to avoid
obvious timing attacks to determine active users.

src/pretix/presale/views/user.py

@@ -0,0 +1,73 @@
+import logging
+
+from django.conf import settings
+from django.contrib import messages
+from django.shortcuts import redirect
+from django.utils.functional import cached_property
+from django.utils.translation import ugettext_lazy as _
+from django.views.generic import TemplateView
+
+from pretix.base.services.mail import INVALID_ADDRESS, SendMailException, mail
+from pretix.multidomain.urlreverse import build_absolute_uri, eventreverse
+from pretix.presale.forms.user import ResendLinkForm
+from pretix.presale.views import EventViewMixin
+
+
+class ResendLinkView(EventViewMixin, TemplateView):
+    template_name = 'pretixpresale/event/resend_link.html'
+
+    @cached_property
+    def link_form(self):
+        return ResendLinkForm(data=self.request.POST if self.request.method == 'POST' else None)
+
+    def post(self, request, *args, **kwargs):
+        if not self.link_form.is_valid():
+            messages.error(self.request, _('We had difficulties processing your input.'))
+            return self.get(request, *args, **kwargs)
+
+        user = self.link_form.cleaned_data.get('email')
+
+        if settings.HAS_REDIS:
+            from django_redis import get_redis_connection
+            rc = get_redis_connection("redis")
+            if rc.exists('pretix_resend_{}'.format(user)):
+                messages.error(request, _('We already sent you an email in the last 24 hours.'))
+                return redirect('presale:user.resend')
+            else:
+                rc.setex('pretix_resend_{}'.format(user), 3600 * 24, '1')
+
+        orders = self.request.event.orders.filter(email=user)
+        order_context = []
+
+        for order in orders:
+            url = build_absolute_uri(
+                self.request.event,
+                'presale:event.order',
+                kwargs={'order': order.code, 'secret': order.secret}
+            )
+            order_context.append(' - {} - {}'.format(order, url))
+
+        if not orders:
+            user = INVALID_ADDRESS
+
+        subject = _('Your orders for {}'.format(self.request.event))
+        template = self.request.event.settings.mail_text_resend_all_links
+        context = {
+            'orders': '\n'.join(order_context),
+            'event': self.request.event,
+        }
+        try:
+            mail(user, subject, template, context, event=self.request.event, locale=self.request.LANGUAGE_CODE)
+        except SendMailException:
+            logger = logging.getLogger('pretix.presale.user')
+            logger.exception('A mail resending order links to {} could not be sent.'.format(user))
+            messages.error(self.request, _('We have trouble sending emails right now, please check back later.'))
+            return self.get(request, *args, **kwargs)
+
+        messages.success(self.request, _('If there were any orders by this user, they will receive an email with their order codes.'))
+        return redirect(eventreverse(self.request.event, 'presale:event.index'))
+
+    def get_context_data(self, **kwargs):
+        context = super().get_context_data(**kwargs)
+        context['form'] = self.link_form
+        return context