通过扩展redis-cli来实现在redis集群中移动槽位

下面的扩展代码基于redis 5.0.2进行扩展， 对于其他的redis版本， 我没有进行相关的测试。考虑到redis集群的修改频率，这段代码应该同时适用于其他的redis版本。

下面为修改的代码：

static clusterManagerNode *clusterManagerByIpPort(const char* ip, int port);
static int clusterManagerCommandMoveSlot(int argc, char **argv);

{"move-slot", clusterManagerCommandMoveSlot, 3,
"from-host:from-port to-host:to-port slotNo", NULL},

// 根据ip和端口号来获取对应的redis集群节点
clusterManagerNode *clusterManagerByIpPort(const char* ip, int port)
{
    if (cluster_manager.nodes == NULL) return NULL;
    clusterManagerNode *found = NULL;
    sds lcip = sdsempty();
    lcip = sdscpy(lcip, ip);
    sdstolower(lcip);
    listIter li;
    listNode *ln;
    listRewind(cluster_manager.nodes, &li);
    while ((ln = listNext(&li)) != NULL) {
        clusterManagerNode *n = ln->value;
        if (n->ip && !sdscmp(n->ip, lcip) && (n->port == port)) {
            found = n;
            break;
        }
    }
    sdsfree(lcip);
    return found;
}

// 在redis集群中实现移动槽位功能
static int clusterManagerCommandMoveSlot(int argc, char **argv) {
    assert(argc == 3);

    char *to_ip = NULL, *from_ip = NULL;
    int to_port = 0, from_port = 0;
    if (!getClusterHostFromCmdArgs(1, argv + 1, &to_ip, &to_port))
        goto invalid_args;
    if (!getClusterHostFromCmdArgs(1, argv, &from_ip, &from_port))
        goto invalid_args;
    char *end = NULL;
    char *slotStr = argv[2];
    int slotNo = strtol(slotStr, &end, 10);
    if ((size_t)(end - slotStr) != strlen(slotStr)) {
        clusterManagerLogErr("*** the slotNo should be number.
");
        return 0;
    }
    clusterManagerLogInfo("Moving slot number: %d from node %s:%d to node %s:%d
", 
            slotNo, from_ip, from_port, to_ip, to_port);

    clusterManagerNode *tonode = clusterManagerNewNode(to_ip, to_port);
    if (!clusterManagerLoadInfoFromNode(tonode, 0)) return 0;

    clusterManagerCheckCluster(0);
    if (cluster_manager.errors && listLength(cluster_manager.errors) > 0) {
        fflush(stdout);
        fprintf(stderr,
                "*** Please fix your cluster problems before moving slot
");
        return 0;
    }

    clusterManagerNode *fromnode = clusterManagerByIpPort(from_ip, from_port);
    // check fromnode and tonode is valid
    const char *invalid_node_msg = "*** The specified node (%s:%d) is not known "
                                   "or not a master, please retry.
";

    if (!fromnode || (fromnode->flags & CLUSTER_MANAGER_FLAG_SLAVE)) {
        clusterManagerLogErr(invalid_node_msg, from_ip, from_port);
        return 0;
    } else if (!tonode || (tonode->flags & CLUSTER_MANAGER_FLAG_SLAVE)) {
        clusterManagerLogErr(invalid_node_msg, to_ip, to_port);
        return 0;
    } else if (!strcmp(fromnode->name, tonode->name) && (fromnode->port == tonode->port)){
            clusterManagerLogErr( "*** It is not possible to use "
                                  "the target node as "
                                  "source node.
");
            return 0;
    }

    // check fromnode has the slot
    if (slotNo < 0 || slotNo >= CLUSTER_MANAGER_SLOTS) {
        // Don't give a range hint for using it when someone is familiar with redis
        clusterManagerLogErr("*** The slotNo is invalid, slotNo: %d
", slotNo);
        return 0;
    } else if (fromnode->slots[slotNo] == (uint8_t)(0)) {
        clusterManagerLogErr("*** From node don't have the slot: %d
", slotNo);
        return 0;
    }

    int opts = CLUSTER_MANAGER_OPT_VERBOSE | CLUSTER_MANAGER_OPT_UPDATE;
    char *err = NULL;
    int result = clusterManagerMoveSlot(fromnode, tonode, slotNo,
                                    opts, &err);
    if (!result) {
        if (err != NULL) {
            //clusterManagerLogErr("
%s
", err);
            zfree(err);
        }
    } else {
        clusterManagerLogInfo("Moving finished with success.
");
    }
    

    return result;

invalid_args:
    fprintf(stderr, CLUSTER_MANAGER_INVALID_HOST_ARG);
    return 0;
}

上述代码， 就是新增的在集群中移动槽位的功能， 使用方法如下：

（1）在redis-cli.c文件中添加上述代码

（2）在redis根目录调用make命令， 编译代码

（3）对编译生成的redis-cli执行如下的命令：

　　$ src/redis-cli --cluster help

其中的move-slot from-host:from-port to-host:to-port slotNo就是新增的子命令。假设192.168.5.1:6379分配了槽位0-5460，192.168.5.2:6379分配了槽位5461-10922,192.168.5.3:6379分配了槽位10923-16383， 通过调用src/redis-cli --cluster move-slot 192.168.5.1:6379 192.168.5.2:6379 10，这样192.168.5.1:6379当前拥有槽位0-9,11-5460,而192.168.5.2:6379拥有槽位10,5461-10922。

对于redis5.0.2的redis-cli.c文件的修改后的文件可以参考：

https://github.com/ss-torres/redis-cli-addition.git

如果有什么好的建议或者提议，欢迎提出。