+/* This is the semantic of this command:
+ * LPOPPUSH srclist dstlist:
+ * IF LLEN(srclist) > 0
+ * element = RPOP srclist
+ * LPUSH dstlist element
+ * RETURN element
+ * ELSE
+ * RETURN nil
+ * END
+ * END
+ *
+ * The idea is to be able to get an element from a list in a reliable way
+ * since the element is not just returned but pushed against another list
+ * as well. This command was originally proposed by Ezra Zygmuntowicz.
+ */
+static void lpoppushCommand(redisClient *c) {
+ robj *sobj;
+
+ sobj = lookupKeyWrite(c->db,c->argv[1]);
+ if (sobj == NULL) {
+ addReply(c,shared.nullbulk);
+ } else {
+ if (sobj->type != REDIS_LIST) {
+ addReply(c,shared.wrongtypeerr);
+ } else {
+ list *srclist = sobj->ptr;
+ listNode *ln = listLast(srclist);
+
+ if (ln == NULL) {
+ addReply(c,shared.nullbulk);
+ } else {
+ robj *dobj = lookupKeyWrite(c->db,c->argv[2]);
+ robj *ele = listNodeValue(ln);
+ list *dstlist;
+
+ if (dobj == NULL) {
+
+ /* Create the list if the key does not exist */
+ dobj = createListObject();
+ dictAdd(c->db->dict,c->argv[2],dobj);
+ incrRefCount(c->argv[2]);
+ } else if (dobj->type != REDIS_LIST) {
+ addReply(c,shared.wrongtypeerr);
+ return;
+ }
+ /* Add the element to the target list */
+ dstlist = dobj->ptr;
+ listAddNodeHead(dstlist,ele);
+ incrRefCount(ele);
+
+ /* Send the element to the client as reply as well */
+ addReplyBulkLen(c,ele);
+ addReply(c,ele);
+ addReply(c,shared.crlf);
+
+ /* Finally remove the element from the source list */
+ listDelNode(srclist,ln);
+ server.dirty++;
+ }
+ }
+ }
+}
+
+