Add fix for boto3 file seek error

Fixes error:
```
  File
  "/var/www/mvsim/releases/blue/mvsim/ve/lib/python3.6/site-packages/django/core/files/base.py",
  line 76, in chunks
      self.seek(0)
      ValueError: seek of closed file
      Build step 'Execute shell' marked build as failure
```

jschneier/django-storages#382

CHANGES

@@ -1,4 +1,9 @@
+0.2.1 (2019-06-20)
+==================
+
+* Add boto3 file seek fix
+
 0.2.0 (2019-06-19)
 ==================
 
-* Update to boto3
+* Update to boto3

cacheds3storage/__init__.py

@@ -1,5 +1,6 @@
+import os
 from django.core.files.storage import get_storage_class
-from storages.backends.s3boto3 import S3Boto3Storage
+from storages.backends.s3boto3 import S3Boto3Storage, SpooledTemporaryFile
 from django.conf import settings
 from dateutil import tz
 
@@ -10,6 +11,29 @@ def __init__(self, *args, **kwargs):
         self.local_storage = get_storage_class(
             'compressor.storage.CompressorFileStorage')()
 
+    # Fix for "ValueError: seek of closed file" problem with boto3
+    # https://github.com/jschneier/django-storages/issues/382#issuecomment-377174808
+    def _save_content(self, obj, content, parameters):
+        """
+        We create a clone of the content file as when this is passed to boto3 it wrongly closes
+        the file upon upload where as the storage backend expects it to still be open
+        """
+        # Seek our content back to the start
+        content.seek(0, os.SEEK_SET)
+
+        # Create a temporary file that will write to disk after a specified size
+        content_autoclose = SpooledTemporaryFile()
+
+        # Write our original content into our copy that will be closed by boto3
+        content_autoclose.write(content.read())
+
+        # Upload the object which will auto close the content_autoclose instance
+        super(CachedS3BotoStorage, self)._save_content(obj, content_autoclose, parameters)
+
+        # Cleanup if this is fixed upstream our duplicate should always close
+        if not content_autoclose.closed:
+            content_autoclose.close()
+
     def save(self, name, content):
         name = super(CachedS3BotoStorage, self).save(name, content)
         self.local_storage._save(name, content)

setup.py

@@ -2,7 +2,7 @@
 
 setup(
     name="django-cacheds3storage",
-    version="0.2.0",
+    version="0.2.1",
     author="Anders Pearson",
     author_email="ctl-dev@columbia.edu",
     url="https://github.com/ccnmtl/django-cacheds3storage",