apps/waiter/models.py

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