src/waiter/models.py

   1 # This file is part of Wolnelektury, licensed under GNU Affero GPLv3 or later.
   2 # Copyright © Fundacja Nowoczesna Polska. See NOTICE for more information.
   3 #
   4 from os.path import join, isfile
   5 from django.urls import reverse
   6 from django.db import models
   7 from waiter.settings import WAITER_URL, WAITER_MAX_QUEUE
   8 from waiter.utils import check_abspath
   9 from picklefield import PickledObjectField
  10
  11
  12 class WaitedFile(models.Model):
  13     path = models.CharField(max_length=255, unique=True, db_index=True)
  14     task_id = models.CharField(max_length=128, db_index=True, null=True, blank=True)
  15     task = PickledObjectField(null=True, editable=False)
  16     description = models.CharField(max_length=255, null=True, blank=True)
  17
  18     @classmethod
  19     def exists(cls, path):
  20         """Returns opened file or None.
  21
  22         `path` is relative to WAITER_ROOT.
  23         Won't open a path leading outside of WAITER_ROOT.
  24         """
  25         abs_path = check_abspath(path)
  26         # Pre-fetch objects for deletion to avoid minor race condition
  27         relevant = [o.id for o in cls.objects.filter(path=path)]
  28         if isfile(abs_path):
  29             cls.objects.filter(id__in=relevant).delete()
  30             return True
  31         else:
  32             return False
  33
  34     @classmethod
  35     def can_order(cls, path):
  36         return (cls.objects.filter(path=path).exists() or
  37                 cls.exists(path) or
  38                 cls.objects.count() < WAITER_MAX_QUEUE
  39                 )
  40
  41     @classmethod
  42     def order(cls, path, task_creator, description=None):
  43         """
  44         Returns an URL for the user to follow.
  45         If the file is ready, returns download URL.
  46         If not, starts preparing it and returns waiting URL.
  47
  48         task_creator: function taking a path and generating the file;
  49         description: a string or string proxy with a description for user;
  50         """
  51         already = cls.exists(path)
  52         if not already:
  53             waited, created = cls.objects.get_or_create(path=path)
  54             if created:
  55                 waited.task = task_creator(check_abspath(path), waited.pk)
  56                 waited.task_id = waited.task.task_id
  57                 waited.description = description
  58                 waited.save()
  59             return reverse("waiter", args=[path])
  60         return join(WAITER_URL, path)