Added deserializer for Bytes field

Author: jtc42

labthings/server/fields.py

@@ -1,5 +1,8 @@
 # Marshmallow fields
 from marshmallow import ValidationError
+
+from base64 import b64decode
+
 from marshmallow.fields import (
     Field,
     Raw,
@@ -75,3 +78,11 @@ def _validate(self, value):
 
         if value is None or value == b"":
             raise ValidationError("Invalid value")
+
+    def _deserialize(self, value, attr, data, **kwargs):
+        if isinstance(value, bytes):
+            return value
+        if isinstance(value, str):
+            return b64decode(value)
+        else:
+            raise self.make_error("invalid", input=value)