Cache downloaded data in zc/buildout/buildout.py:_open() in memory to accelerate remote extends.

src/zc/buildout/buildout.py

@@ -28,6 +28,7 @@ except ImportError:
     from collections import MutableMapping as DictMixin
 
 import zc.buildout.configparser
+from cStringIO import StringIO
 import copy
 import datetime
 import distutils.errors
@@ -1586,6 +1587,7 @@ def _default_globals():
 
     return globals_defs
 
+_open_download_cache = {}
 def _open(base, filename, seen, dl_options, override, downloaded):
     """Open a configuration file and return the result as a dictionary,
 
@@ -1615,8 +1617,14 @@ def _open(base, filename, seen, dl_options, override, downloaded):
             base = os.path.dirname(filename)
         else:
             filename = base + '/' + filename
-            downloaded_filename, is_temp = download(filename)
-            fp = open(downloaded_filename)
+            data = _open_download_cache.get(filename)
+            if data is None:
+                downloaded_filename, is_temp = download(filename)
+                data = file(downloaded_filename).read()
+                _open_download_cache[filename] = data
+            else:
+                is_temp = False
+            fp = StringIO(data)
             base = filename[:filename.rfind('/')]
     else:
         filename = os.path.join(base, filename)