apps/waiter/models.py

   1 from os.path import join, abspath, exists
   2 from django.core.urlresolvers import reverse
   3 from django.db import models
   4 from waiter.settings import WAITER_ROOT, WAITER_URL
   5 from djcelery.models import TaskMeta
   6
   7
   8 class WaitedFile(models.Model):
   9     path = models.CharField(max_length=255, unique=True, db_index=True)
  10     task = models.CharField(max_length=64, null=True, editable=False)
  11     description = models.CharField(max_length=255, null=True, blank=True)
  12
  13     @staticmethod
  14     def abspath(path):
  15         abs_path = abspath(join(WAITER_ROOT, path))
  16         if not abs_path.startswith(WAITER_ROOT):
  17             raise ValueError('Path not inside WAITER_ROOT.')
  18         return abs_path
  19
  20     @classmethod
  21     def exists(cls, path):
  22         """Returns opened file or None.
  23
  24         `path` is relative to WAITER_ROOT.
  25         Won't open a path leading outside of WAITER_ROOT.
  26         """
  27         abs_path = cls.abspath(path)
  28         # Pre-fetch objects for deletion to avoid minor race condition
  29         relevant = [o.id for o in cls.objects.filter(path=path)]
  30         if exists(abs_path):
  31             cls.objects.filter(id__in=relevant).delete()
  32             return True
  33         else:
  34             return False
  35
  36     def is_stale(self):
  37         if self.task is None:
  38             # Race; just let the other task roll.
  39             return False
  40         try:
  41             meta = TaskMeta.objects.get(task_id=self.task)
  42             assert meta.status in (u'PENDING', u'STARTED', u'SUCCESS', u'RETRY')
  43         except TaskMeta.DoesNotExist:
  44             # Might happen it's not yet there.
  45             pass
  46         except AssertionError:
  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(cls.abspath(path))
  65                 waited.description = description
  66                 waited.save()
  67             return reverse("waiter", args=[path])
  68         return join(WAITER_URL, path)