Database result backend now works with Python 3

Author: ask

djcelery/models.py

@@ -31,8 +31,10 @@ class TaskMeta(models.Model):
     date_done = models.DateTimeField(_('done at'), auto_now=True)
     traceback = models.TextField(_('traceback'), blank=True, null=True)
     hidden = models.BooleanField(editable=False, default=False, db_index=True)
+    # TODO compression was enabled by mistake, we need to disable it
+    # but this is a backwards incompatible change that needs planning.
     meta = PickledObjectField(
-        _('meta'), null=True, default=None, editable=False,
+        compress=True, null=True, default=None, editable=False,
     )
 
     objects = managers.TaskManager()

djcelery/picklefield.py

@@ -14,10 +14,14 @@
 """
 from __future__ import absolute_import, unicode_literals
 
+import django
+
 from base64 import b64encode, b64decode
 from zlib import compress, decompress
 
+from celery.five import with_metaclass
 from celery.utils.serialization import pickle
+from kombu.utils.encoding import bytes_to_str, str_to_bytes
 
 from django.db import models
 
@@ -28,35 +32,45 @@
 
 DEFAULT_PROTOCOL = 2
 
+NO_DECOMPRESS_HEADER = b'\x1e\x00r8d9qwwerwhA@'
+
+
+if django.VERSION < (1, 3):
+    BaseField = models.Field
+else:
+    @with_metaclass(models.SubfieldBase)
+    class BaseField(models.Field):
+        pass
+
 
 class PickledObject(str):
     pass
 
 
 def maybe_compress(value, do_compress=False):
     if do_compress:
-        return compress(value)
+        return compress(str_to_bytes(value))
     return value
 
 
 def maybe_decompress(value, do_decompress=False):
     if do_decompress:
-        return decompress(value)
+        if str_to_bytes(value[:15]) != NO_DECOMPRESS_HEADER:
+            return decompress(str_to_bytes(value))
     return value
 
 
 def encode(value, compress_object=False, pickle_protocol=DEFAULT_PROTOCOL):
-    return b64encode(maybe_compress(
+    return bytes_to_str(b64encode(maybe_compress(
         pickle.dumps(value, pickle_protocol), compress_object),
-    )
+    ))
 
 
 def decode(value, compress_object=False):
     return pickle.loads(maybe_decompress(b64decode(value), compress_object))
 
 
-class PickledObjectField(models.Field):
-    __metaclass__ = models.SubfieldBase
+class PickledObjectField(BaseField):
 
     def __init__(self, compress=False, protocol=DEFAULT_PROTOCOL,
                  *args, **kwargs):