implemented the basic usage of select method.

slapos/libnetworkcache/__init__.py

@@ -129,6 +129,23 @@ class NetworkcacheClient(object):
       raise FileNotFound(result.read())
     return result
 
+  def select(self, directory_key=None):
+    '''Download a file from shacache by selecting the entry in shadir
+    Raise DirectoryNotFound if multiple files are found.
+    '''
+    path_info = self.shadir_path
+    if directory_key is not None
+      path_info = os.path.join(self.shadir_path, directory_key)
+
+    self.shadir_connection = httplib.HTTPConnection(self.shadir_host)
+    self.shadir_connection.request('GET', path_info, headers=self.shadir_header_dict)
+    result = self.shadir_connection.getresponse()
+    if result.status != 200:
+      raise DirectoryNotFound(result.read())
+    data = json.loads(result.read())
+    self.close()
+    return data
+
   def close(self):
     ''' It must be called to close the HTTP Connection. '''
     if hasattr(self, 'shacache_connection'):
@@ -137,5 +154,10 @@ class NetworkcacheClient(object):
     if hasattr(self, 'shadir_connection'):
       self.shadir_connection.close()
 
+
 class FileNotFound(Exception):
   pass
+
+
+class DirectoryNotFound(Exception):
+  pass