Minimise memory footprint during download.

There is no need to read and store downloaded file. Returning the location is
good enough.

CHANGES.txt

 0.2 (unreleased)
 ================
 
+ * Incompatible change: NetworkcacheClient.download returns downloaded
+   location instead of content in order to minimise memory footprint. [Łukasz
+   Nowak]
  * Minimise memory footprint during upload. [Łukasz Nowak]
  * Use PUT instead of POST during upload. [Lucas Carvalho]
 

slapos/libnetworkcache.py

@@ -18,7 +18,6 @@ import hashlib
 import httplib
 import json
 import os
-import tempfile
 from urllib import urlretrieve
 from urlparse import urlparse
 
@@ -130,16 +129,11 @@ class NetworkcacheClient(object):
   def download(self, sha512sum):
     ''' Download the file.
     It uses http GET request method.
+    Returns downloaded file absolute location
     '''
     sha_cache_url = os.path.join(self.shacache_url, sha512sum)
-    path, headers = urlretrieve(sha_cache_url, tempfile.mktemp())
-    f = open(path)
-    try:
-      file_content = f.read()
-    finally:
-      f.close()
-
-    return file_content
+    path, headers = urlretrieve(sha_cache_url)
+    return path
 
   def select(self, directory_key=None):
     ''' Download a file from shacache by selecting the entry in shadir