Adapt the s3 key object to the python stream file interface, one that is compatible with tarfile.

storage/s3.py

@@ -1,6 +1,6 @@
-
 import cStringIO as StringIO
 import os
+import logging
 
 import boto.s3.connection
 import boto.s3.key
@@ -8,6 +8,30 @@ import boto.s3.key
 from . import Storage
 
 
+logger = logging.getLogger(__name__)
+
+
+class StreamReadKeyAsFile(object):
+    def __init__(self, key):
+        self._key = key
+        self._finished = False
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type, value, tb):
+        self._key.close(fast=True)
+
+    def read(self, amt=None):
+        if self._finished:
+            return None
+
+        resp = self._key.read(amt)
+        if not resp:
+            self._finished = True
+        return resp
+
+
 class S3Storage(Storage):
 
     def __init__(self, storage_path, s3_access_key, s3_secret_key, s3_bucket):
@@ -65,7 +89,7 @@ class S3Storage(Storage):
         key = boto.s3.key.Key(self._s3_bucket, path)
         if not key.exists():
             raise IOError('No such key: \'{0}\''.format(path))
-        return key
+        return StreamReadKeyAsFile(key)
 
     def stream_write(self, path, fp):
         # Minimum size of upload part size on S3 is 5MB