Implement getting the cluster nodes list from nodes

Periodically call a user-defined Lua function on a node to obtain or
refresh the full cluster nodes list.

Resolves: #134

Author: msiomkin

tarantool/const.py

@@ -86,3 +86,5 @@
 RECONNECT_MAX_ATTEMPTS = 10
 # Default delay between attempts to reconnect (seconds)
 RECONNECT_DELAY = 0.1
+# Default cluster nodes list refresh interval (seconds)
+NODES_REFRESH_INTERVAL = 300

tarantool/mesh_connection.py

@@ -4,13 +4,15 @@
 between tarantool instances and basic Round-Robin strategy.
 '''
 
+import time
 from tarantool.connection import Connection
 from tarantool.error import NetworkError
 from tarantool.utils import ENCODING_DEFAULT
 from tarantool.const import (
     SOCKET_TIMEOUT,
     RECONNECT_MAX_ATTEMPTS,
-    RECONNECT_DELAY
+    RECONNECT_DELAY,
+    NODES_REFRESH_INTERVAL
 )
 
 
@@ -34,12 +36,15 @@ def __init__(self, addrs,
                  reconnect_delay=RECONNECT_DELAY,
                  connect_now=True,
                  encoding=ENCODING_DEFAULT,
-                 strategy_class=RoundRobinStrategy):
+                 strategy_class=RoundRobinStrategy,
+                 nodes_refresh_interval=NODES_REFRESH_INTERVAL):
         self.nattempts = 2 * len(addrs) + 1
         self.strategy = strategy_class(addrs)
         addr = self.strategy.getnext()
         host = addr['host']
         port = addr['port']
+        self.nodes_refresh_interval = nodes_refresh_interval
+        self.last_nodes_refresh = 0
         super(MeshConnection, self).__init__(host=host,
                                              port=port,
                                              user=user,
@@ -63,3 +68,11 @@ def _opt_reconnect(self):
                 self.port = addr['port']
         else:
             raise NetworkError
+
+        now = time.time()
+        if now - self.last_nodes_refresh > self.nodes_refresh_interval:
+            addrs = super(MeshConnection, self).call('get_nodes')
+            if addrs and type(addrs) is list:
+                self.addrs = addrs
+                self.pos = 0
+                self.last_nodes_refresh = now