Cluster: nodes re-addition blacklist API.

src/cluster.c

@@ -622,6 +622,75 @@ void clusterRenameNode(clusterNode *node, char *newname) {
     clusterAddNode(node);
 }
 
+/* -----------------------------------------------------------------------------
+ * CLUSTER nodes blacklist
+ *
+ * The nodes blacklist is just a way to ensure that a given node with a given
+ * Node ID is not readded before some time elapsed (this time is specified
+ * in seconds in REDIS_CLUSTER_BLACKLIST_TTL).
+ *
+ * This is useful when we want to remove a node from the cluster completely:
+ * when CLUSTER FORGET is called, it also puts the node into the blacklist so
+ * that even if we receive gossip messages from other nodes that still remember
+ * about the node we want to remove, we don't re-add it before some time.
+ *
+ * Currently the REDIS_CLUSTER_BLACKLIST_TTL is set to 1 minute, this means
+ * that redis-trib has 60 seconds to send CLUSTER FORGET messages to nodes
+ * in the cluster without dealing with the problem if other nodes re-adding
+ * back the node to nodes we already sent the FORGET command to.
+ *
+ * The data structure used is an hash table with an sds string representing
+ * the node ID as key, and the time when it is ok to re-add the node as
+ * value.
+ * -------------------------------------------------------------------------- */
+
+#define REDIS_CLUSTER_BLACKLIST_TTL 60      /* 1 minute. */
+
+
+/* Before of the addNode() or Exists() operations we always remove expired
+ * entries from the black list. This is an O(N) operation but it is not a
+ * problem since add / exists operations are called very infrequently and
+ * the hash table is supposed to contain very little elements at max.
+ * However without the cleanup during long uptimes and with some automated
+ * node add/removal procedures, entries could accumulate. */
+void clusterBlacklistCleanup(void) {
+    dictIterator *di;
+    dictEntry *de;
+
+    di = dictGetSafeIterator(server.cluster->nodes_black_list);
+    while((de = dictNext(di)) != NULL) {
+        int64_t expire = dictGetUnsignedIntegerVal(de);
+
+        if (expire < server.unixtime)
+            dictDelete(server.cluster->nodes_black_list,dictGetKey(de));
+    }
+    dictReleaseIterator(di);
+}
+
+/* Cleanup the blacklist and add a new node ID to the black list. */
+void clusterBlacklistAddNode(clusterNode *node) {
+    dictEntry *de;
+    sds id = sdsnewlen(node->name,REDIS_CLUSTER_NAMELEN);
+
+    clusterBlacklistCleanup();
+    if (dictAdd(server.cluster->nodes_black_list,id,NULL) == DICT_ERR)
+        sdsfree(id); /* Key was already there. */
+    de = dictFind(server.cluster->nodes_black_list,node->name);
+    dictSetUnsignedIntegerVal(de,time(NULL));
+}
+
+/* Return non-zero if the specified node ID exists in the blacklist.
+ * You don't need to pass an sds string here, any pointer to 40 bytes
+ * will work. */
+int clusterBlacklistExists(char *nodeid) {
+    sds id = sdsnewlen(nodeid,REDIS_CLUSTER_NAMELEN);
+    int retval;
+
+    retval = dictFind(server.cluster->nodes_black_list,id) != NULL;
+    sdsfree(id);
+    return retval;
+}
+
 /* -----------------------------------------------------------------------------
  * CLUSTER messages exchange - PING/PONG and gossip
  * -------------------------------------------------------------------------- */