cluster.c

/* Redis Cluster implementation.
 *
 * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "redis.h"
#include "endianconv.h"

#include <arpa/inet.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/socket.h>

void clusterAcceptHandler(aeEventLoop *el, int fd, void *privdata, int mask);
void clusterReadHandler(aeEventLoop *el, int fd, void *privdata, int mask);
void clusterSendPing(clusterLink *link, int type);
void clusterSendFail(char *nodename);
void clusterUpdateState(void);
int clusterNodeGetSlotBit(clusterNode *n, int slot);
sds clusterGenNodesDescription(void);
clusterNode *clusterLookupNode(char *name);
int clusterNodeAddSlave(clusterNode *master, clusterNode *slave);
int clusterAddSlot(clusterNode *n, int slot);
int clusterDelSlot(int slot);

/* -----------------------------------------------------------------------------
 * Initialization
 * -------------------------------------------------------------------------- */

int clusterLoadConfig(char *filename) {
    FILE *fp = fopen(filename,"r");
    char *line;
    int maxline, j;
   
    if (fp == NULL) return REDIS_ERR;

    /* Parse the file. Note that single liens of the cluster config file can
     * be really long as they include all the hash slots of the node.
     * This means in the worst possible case REDIS_CLUSTER_SLOTS/2 integers.
     * To simplify we allocate 1024+REDIS_CLUSTER_SLOTS*16 bytes per line. */
    maxline = 1024+REDIS_CLUSTER_SLOTS*16;
    line = zmalloc(maxline);
    while(fgets(line,maxline,fp) != NULL) {
        int argc;
        sds *argv = sdssplitargs(line,&argc);
        clusterNode *n, *master;
        char *p, *s;

        /* Create this node if it does not exist */
        n = clusterLookupNode(argv[0]);
        if (!n) {
            n = createClusterNode(argv[0],0);
            clusterAddNode(n);
        }
        /* Address and port */
        if ((p = strchr(argv[1],':')) == NULL) goto fmterr;
        *p = '\0';
        memcpy(n->ip,argv[1],strlen(argv[1])+1);
        n->port = atoi(p+1);

        /* Parse flags */
        p = s = argv[2];
        while(p) {
            p = strchr(s,',');
            if (p) *p = '\0';
            if (!strcasecmp(s,"myself")) {
                redisAssert(server.cluster->myself == NULL);
                server.cluster->myself = n;
                n->flags |= REDIS_NODE_MYSELF;
            } else if (!strcasecmp(s,"master")) {
                n->flags |= REDIS_NODE_MASTER;
            } else if (!strcasecmp(s,"slave")) {
                n->flags |= REDIS_NODE_SLAVE;
            } else if (!strcasecmp(s,"fail?")) {
                n->flags |= REDIS_NODE_PFAIL;
            } else if (!strcasecmp(s,"fail")) {
                n->flags |= REDIS_NODE_FAIL;
            } else if (!strcasecmp(s,"handshake")) {
                n->flags |= REDIS_NODE_HANDSHAKE;
            } else if (!strcasecmp(s,"noaddr")) {
                n->flags |= REDIS_NODE_NOADDR;
            } else if (!strcasecmp(s,"noflags")) {
                /* nothing to do */
            } else {
                redisPanic("Unknown flag in redis cluster config file");
            }
            if (p) s = p+1;
        }

        /* Get master if any. Set the master and populate master's
         * slave list. */
        if (argv[3][0] != '-') {
            master = clusterLookupNode(argv[3]);
            if (!master) {
                master = createClusterNode(argv[3],0);
                clusterAddNode(master);
            }
            n->slaveof = master;
            clusterNodeAddSlave(master,n);
        }

        /* Set ping sent / pong received timestamps */
        if (atoi(argv[4])) n->ping_sent = time(NULL);
        if (atoi(argv[5])) n->pong_received = time(NULL);

        /* Populate hash slots served by this instance. */
        for (j = 7; j < argc; j++) {
            int start, stop;

            if (argv[j][0] == '[') {
                /* Here we handle migrating / importing slots */
                int slot;
                char direction;
                clusterNode *cn;

                p = strchr(argv[j],'-');
                redisAssert(p != NULL);
                *p = '\0';
                direction = p[1]; /* Either '>' or '<' */
                slot = atoi(argv[j]+1);
                p += 3;
                cn = clusterLookupNode(p);
                if (!cn) {
                    cn = createClusterNode(p,0);
                    clusterAddNode(cn);
                }
                if (direction == '>') {
                    server.cluster->migrating_slots_to[slot] = cn;
                } else {
                    server.cluster->importing_slots_from[slot] = cn;
                }
                continue;
            } else if ((p = strchr(argv[j],'-')) != NULL) {
                *p = '\0';
                start = atoi(argv[j]);
                stop = atoi(p+1);
            } else {
                start = stop = atoi(argv[j]);
            }
            while(start <= stop) clusterAddSlot(n, start++);
        }

        sdssplitargs_free(argv,argc);
    }
    zfree(line);
    fclose(fp);

    /* Config sanity check */
    redisAssert(server.cluster->myself != NULL);
    redisLog(REDIS_NOTICE,"Node configuration loaded, I'm %.40s",
        server.cluster->myself->name);
    clusterUpdateState();
    return REDIS_OK;

fmterr:
    redisLog(REDIS_WARNING,"Unrecoverable error: corrupted cluster config file.");
    fclose(fp);
    exit(1);
}

/* Cluster node configuration is exactly the same as CLUSTER NODES output.
 *
 * This function writes the node config and returns 0, on error -1
 * is returned. */
int clusterSaveConfig(void) {
    sds ci = clusterGenNodesDescription();
    int fd;
    
    if ((fd = open(server.cluster_configfile,O_WRONLY|O_CREAT|O_TRUNC,0644))
        == -1) goto err;
    if (write(fd,ci,sdslen(ci)) != (ssize_t)sdslen(ci)) goto err;
    close(fd);
    sdsfree(ci);
    return 0;

err:
    sdsfree(ci);
    return -1;
}

void clusterSaveConfigOrDie(void) {
    if (clusterSaveConfig() == -1) {
        redisLog(REDIS_WARNING,"Fatal: can't update cluster config file.");
        exit(1);
    }
}

void clusterInit(void) {
    int saveconf = 0;

    server.cluster = zmalloc(sizeof(clusterState));
    server.cluster->myself = NULL;
    server.cluster->state = REDIS_CLUSTER_FAIL;
    server.cluster->nodes = dictCreate(&clusterNodesDictType,NULL);
    server.cluster->node_timeout = 15;
    memset(server.cluster->migrating_slots_to,0,
        sizeof(server.cluster->migrating_slots_to));
    memset(server.cluster->importing_slots_from,0,
        sizeof(server.cluster->importing_slots_from));
    memset(server.cluster->slots,0,
        sizeof(server.cluster->slots));
    if (clusterLoadConfig(server.cluster_configfile) == REDIS_ERR) {
        /* No configuration found. We will just use the random name provided
         * by the createClusterNode() function. */
        server.cluster->myself = createClusterNode(NULL,REDIS_NODE_MYSELF);
        redisLog(REDIS_NOTICE,"No cluster configuration found, I'm %.40s",
            server.cluster->myself->name);
        clusterAddNode(server.cluster->myself);
        saveconf = 1;
    }
    if (saveconf) clusterSaveConfigOrDie();
    /* We need a listening TCP port for our cluster messaging needs */
    server.cfd = anetTcpServer(server.neterr,
            server.port+REDIS_CLUSTER_PORT_INCR, server.bindaddr);
    if (server.cfd == -1) {
        redisLog(REDIS_WARNING, "Opening cluster TCP port: %s", server.neterr);
        exit(1);
    }
    if (aeCreateFileEvent(server.el, server.cfd, AE_READABLE,
        clusterAcceptHandler, NULL) == AE_ERR) redisPanic("Unrecoverable error creating Redis Cluster file event.");
    server.cluster->slots_to_keys = zslCreate();
}

/* -----------------------------------------------------------------------------
 * CLUSTER communication link
 * -------------------------------------------------------------------------- */

clusterLink *createClusterLink(clusterNode *node) {
    clusterLink *link = zmalloc(sizeof(*link));
    link->sndbuf = sdsempty();
    link->rcvbuf = sdsempty();
    link->node = node;
    link->fd = -1;
    return link;
}

/* Free a cluster link, but does not free the associated node of course.
 * Just this function will make sure that the original node associated
 * with this link will have the 'link' field set to NULL. */
void freeClusterLink(clusterLink *link) {
    if (link->fd != -1) {
        aeDeleteFileEvent(server.el, link->fd, AE_WRITABLE);
        aeDeleteFileEvent(server.el, link->fd, AE_READABLE);
    }
    sdsfree(link->sndbuf);
    sdsfree(link->rcvbuf);
    if (link->node)
        link->node->link = NULL;
    close(link->fd);
    zfree(link);
}

void clusterAcceptHandler(aeEventLoop *el, int fd, void *privdata, int mask) {
    int cport, cfd;
    char cip[128];
    clusterLink *link;
    REDIS_NOTUSED(el);
    REDIS_NOTUSED(mask);
    REDIS_NOTUSED(privdata);

    cfd = anetTcpAccept(server.neterr, fd, cip, &cport);
    if (cfd == AE_ERR) {
        redisLog(REDIS_VERBOSE,"Accepting cluster node: %s", server.neterr);
        return;
    }
    redisLog(REDIS_VERBOSE,"Accepted cluster node %s:%d", cip, cport);
    /* We need to create a temporary node in order to read the incoming
     * packet in a valid contest. This node will be released once we
     * read the packet and reply. */
    link = createClusterLink(NULL);
    link->fd = cfd;
    aeCreateFileEvent(server.el,cfd,AE_READABLE,clusterReadHandler,link);
}

/* -----------------------------------------------------------------------------
 * Key space handling
 * -------------------------------------------------------------------------- */

/* We have 16384 hash slots. The hash slot of a given key is obtained
 * as the least significant 14 bits of the crc16 of the key. */
unsigned int keyHashSlot(char *key, int keylen) {
    return crc16(key,keylen) & 0x3FFF;
}

/* -----------------------------------------------------------------------------
 * CLUSTER node API
 * -------------------------------------------------------------------------- */

/* Create a new cluster node, with the specified flags.
 * If "nodename" is NULL this is considered a first handshake and a random
 * node name is assigned to this node (it will be fixed later when we'll
 * receive the first pong).
 *
 * The node is created and returned to the user, but it is not automatically
 * added to the nodes hash table. */
clusterNode *createClusterNode(char *nodename, int flags) {
    clusterNode *node = zmalloc(sizeof(*node));

    if (nodename)
        memcpy(node->name, nodename, REDIS_CLUSTER_NAMELEN);
    else
        getRandomHexChars(node->name, REDIS_CLUSTER_NAMELEN);
    node->flags = flags;
    memset(node->slots,0,sizeof(node->slots));
    node->numslaves = 0;
    node->slaves = NULL;
    node->slaveof = NULL;
    node->ping_sent = node->pong_received = 0;
    node->configdigest = NULL;
    node->configdigest_ts = 0;
    node->link = NULL;
    memset(node->ip,0,sizeof(node->ip));
    node->port = 0;
    return node;
}

int clusterNodeRemoveSlave(clusterNode *master, clusterNode *slave) {
    int j;

    for (j = 0; j < master->numslaves; j++) {
        if (master->slaves[j] == slave) {
            memmove(master->slaves+j,master->slaves+(j+1),
                (master->numslaves-1)-j);
            master->numslaves--;
            return REDIS_OK;
        }
    }
    return REDIS_ERR;
}

int clusterNodeAddSlave(clusterNode *master, clusterNode *slave) {
    int j;

    /* If it's already a slave, don't add it again. */
    for (j = 0; j < master->numslaves; j++)
        if (master->slaves[j] == slave) return REDIS_ERR;
    master->slaves = zrealloc(master->slaves,
        sizeof(clusterNode*)*(master->numslaves+1));
    master->slaves[master->numslaves] = slave;
    master->numslaves++;
    return REDIS_OK;
}

void clusterNodeResetSlaves(clusterNode *n) {
    zfree(n->slaves);
    n->numslaves = 0;
}

void freeClusterNode(clusterNode *n) {
    sds nodename;
    
    nodename = sdsnewlen(n->name, REDIS_CLUSTER_NAMELEN);
    redisAssert(dictDelete(server.cluster->nodes,nodename) == DICT_OK);
    sdsfree(nodename);
    if (n->slaveof) clusterNodeRemoveSlave(n->slaveof, n);
    if (n->link) freeClusterLink(n->link);
    zfree(n);
}

/* Add a node to the nodes hash table */
int clusterAddNode(clusterNode *node) {
    int retval;
    
    retval = dictAdd(server.cluster->nodes,
            sdsnewlen(node->name,REDIS_CLUSTER_NAMELEN), node);
    return (retval == DICT_OK) ? REDIS_OK : REDIS_ERR;
}

/* Node lookup by name */
clusterNode *clusterLookupNode(char *name) {
    sds s = sdsnewlen(name, REDIS_CLUSTER_NAMELEN);
    struct dictEntry *de;

    de = dictFind(server.cluster->nodes,s);
    sdsfree(s);
    if (de == NULL) return NULL;
    return dictGetVal(de);
}

/* This is only used after the handshake. When we connect a given IP/PORT
 * as a result of CLUSTER MEET we don't have the node name yet, so we
 * pick a random one, and will fix it when we receive the PONG request using
 * this function. */
void clusterRenameNode(clusterNode *node, char *newname) {
    int retval;
    sds s = sdsnewlen(node->name, REDIS_CLUSTER_NAMELEN);
   
    redisLog(REDIS_DEBUG,"Renaming node %.40s into %.40s",
        node->name, newname);
    retval = dictDelete(server.cluster->nodes, s);
    sdsfree(s);
    redisAssert(retval == DICT_OK);
    memcpy(node->name, newname, REDIS_CLUSTER_NAMELEN);
    clusterAddNode(node);
}

/* -----------------------------------------------------------------------------
 * CLUSTER messages exchange - PING/PONG and gossip
 * -------------------------------------------------------------------------- */

/* Process the gossip section of PING or PONG packets.
 * Note that this function assumes that the packet is already sanity-checked
 * by the caller, not in the content of the gossip section, but in the
 * length. */
void clusterProcessGossipSection(clusterMsg *hdr, clusterLink *link) {
    uint16_t count = ntohs(hdr->count);
    clusterMsgDataGossip *g = (clusterMsgDataGossip*) hdr->data.ping.gossip;
    clusterNode *sender = link->node ? link->node : clusterLookupNode(hdr->sender);

    while(count--) {
        sds ci = sdsempty();
        uint16_t flags = ntohs(g->flags);
        clusterNode *node;

        if (flags == 0) ci = sdscat(ci,"noflags,");
        if (flags & REDIS_NODE_MYSELF) ci = sdscat(ci,"myself,");
        if (flags & REDIS_NODE_MASTER) ci = sdscat(ci,"master,");
        if (flags & REDIS_NODE_SLAVE) ci = sdscat(ci,"slave,");
        if (flags & REDIS_NODE_PFAIL) ci = sdscat(ci,"fail?,");
        if (flags & REDIS_NODE_FAIL) ci = sdscat(ci,"fail,");
        if (flags & REDIS_NODE_HANDSHAKE) ci = sdscat(ci,"handshake,");
        if (flags & REDIS_NODE_NOADDR) ci = sdscat(ci,"noaddr,");
        if (ci[sdslen(ci)-1] == ',') ci[sdslen(ci)-1] = ' ';

        redisLog(REDIS_DEBUG,"GOSSIP %.40s %s:%d %s",
            g->nodename,
            g->ip,
            ntohs(g->port),
            ci);
        sdsfree(ci);

        /* Update our state accordingly to the gossip sections */
        node = clusterLookupNode(g->nodename);
        if (node != NULL) {
            /* We already know this node. Let's start updating the last
             * time PONG figure if it is newer than our figure.
             * Note that it's not a problem if we have a PING already 
             * in progress against this node. */
            if (node->pong_received < (signed) ntohl(g->pong_received)) {
                 redisLog(REDIS_DEBUG,"Node pong_received updated by gossip");
                node->pong_received = ntohl(g->pong_received);
            }
            /* Mark this node as FAILED if we think it is possibly failing
             * and another node also thinks it's failing. */
            if (node->flags & REDIS_NODE_PFAIL &&
                (flags & (REDIS_NODE_FAIL|REDIS_NODE_PFAIL)))
            {
                redisLog(REDIS_NOTICE,"Received a PFAIL acknowledge from node %.40s, marking node %.40s as FAIL!", hdr->sender, node->name);
                node->flags &= ~REDIS_NODE_PFAIL;
                node->flags |= REDIS_NODE_FAIL;
                /* Broadcast the failing node name to everybody */
                clusterSendFail(node->name);
                clusterUpdateState();
                clusterSaveConfigOrDie();
            }
        } else {
            /* If it's not in NOADDR state and we don't have it, we
             * start an handshake process against this IP/PORT pairs.
             *
             * Note that we require that the sender of this gossip message
             * is a well known node in our cluster, otherwise we risk
             * joining another cluster. */
            if (sender && !(flags & REDIS_NODE_NOADDR)) {
                clusterNode *newnode;

                redisLog(REDIS_DEBUG,"Adding the new node");
                newnode = createClusterNode(NULL,REDIS_NODE_HANDSHAKE);
                memcpy(newnode->ip,g->ip,sizeof(g->ip));
                newnode->port = ntohs(g->port);
                clusterAddNode(newnode);
            }
        }

        /* Next node */
        g++;
    }
}

/* IP -> string conversion. 'buf' is supposed to at least be 16 bytes. */
void nodeIp2String(char *buf, clusterLink *link) {
    struct sockaddr_in sa;
    socklen_t salen = sizeof(sa);

    if (getpeername(link->fd, (struct sockaddr*) &sa, &salen) == -1)
        redisPanic("getpeername() failed.");
    strncpy(buf,inet_ntoa(sa.sin_addr),sizeof(link->node->ip));
}


/* Update the node address to the IP address that can be extracted
 * from link->fd, and at the specified port. */
void nodeUpdateAddress(clusterNode *node, clusterLink *link, int port) {
    /* TODO */
}

/* When this function is called, there is a packet to process starting
 * at node->rcvbuf. Releasing the buffer is up to the caller, so this
 * function should just handle the higher level stuff of processing the
 * packet, modifying the cluster state if needed.
 *
 * The function returns 1 if the link is still valid after the packet
 * was processed, otherwise 0 if the link was freed since the packet
 * processing lead to some inconsistency error (for instance a PONG
 * received from the wrong sender ID). */
int clusterProcessPacket(clusterLink *link) {
    clusterMsg *hdr = (clusterMsg*) link->rcvbuf;
    uint32_t totlen = ntohl(hdr->totlen);
    uint16_t type = ntohs(hdr->type);
    clusterNode *sender;

    redisLog(REDIS_DEBUG,"--- Processing packet of type %d, %lu bytes",
        type, (unsigned long) totlen);

    /* Perform sanity checks */
    if (totlen < 8) return 1;
    if (totlen > sdslen(link->rcvbuf)) return 1;
    if (type == CLUSTERMSG_TYPE_PING || type == CLUSTERMSG_TYPE_PONG ||
        type == CLUSTERMSG_TYPE_MEET)
    {
        uint16_t count = ntohs(hdr->count);
        uint32_t explen; /* expected length of this packet */

        explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
        explen += (sizeof(clusterMsgDataGossip)*count);
        if (totlen != explen) return 1;
    }
    if (type == CLUSTERMSG_TYPE_FAIL) {
        uint32_t explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);

        explen += sizeof(clusterMsgDataFail);
        if (totlen != explen) return 1;
    }
    if (type == CLUSTERMSG_TYPE_PUBLISH) {
        uint32_t explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);

        explen += sizeof(clusterMsgDataPublish) +
                ntohl(hdr->data.publish.msg.channel_len) +
                ntohl(hdr->data.publish.msg.message_len);
        if (totlen != explen) return 1;
    }

    /* Ready to process the packet. Dispatch by type. */
    sender = clusterLookupNode(hdr->sender);
    if (type == CLUSTERMSG_TYPE_PING || type == CLUSTERMSG_TYPE_MEET) {
        int update_config = 0;
        redisLog(REDIS_DEBUG,"Ping packet received: %p", link->node);

        /* Add this node if it is new for us and the msg type is MEET.
         * In this stage we don't try to add the node with the right
         * flags, slaveof pointer, and so forth, as this details will be
         * resolved when we'll receive PONGs from the server. */
        if (!sender && type == CLUSTERMSG_TYPE_MEET) {
            clusterNode *node;

            node = createClusterNode(NULL,REDIS_NODE_HANDSHAKE);
            nodeIp2String(node->ip,link);
            node->port = ntohs(hdr->port);
            clusterAddNode(node);
            update_config = 1;
        }

        /* Get info from the gossip section */
        clusterProcessGossipSection(hdr,link);

        /* Anyway reply with a PONG */
        clusterSendPing(link,CLUSTERMSG_TYPE_PONG);

        /* Update config if needed */
        if (update_config) clusterSaveConfigOrDie();
    } else if (type == CLUSTERMSG_TYPE_PONG) {
        int update_state = 0;
        int update_config = 0;

        redisLog(REDIS_DEBUG,"Pong packet received: %p", link->node);
        if (link->node) {
            if (link->node->flags & REDIS_NODE_HANDSHAKE) {
                /* If we already have this node, try to change the
                 * IP/port of the node with the new one. */
                if (sender) {
                    redisLog(REDIS_WARNING,
                        "Handshake error: we already know node %.40s, updating the address if needed.", sender->name);
                    nodeUpdateAddress(sender,link,ntohs(hdr->port));
                    freeClusterNode(link->node); /* will free the link too */
                    return 0;
                }

                /* First thing to do is replacing the random name with the
                 * right node name if this was an handshake stage. */
                clusterRenameNode(link->node, hdr->sender);
                redisLog(REDIS_DEBUG,"Handshake with node %.40s completed.",
                    link->node->name);
                link->node->flags &= ~REDIS_NODE_HANDSHAKE;
                update_config = 1;
            } else if (memcmp(link->node->name,hdr->sender,
                        REDIS_CLUSTER_NAMELEN) != 0)
            {
                /* If the reply has a non matching node ID we
                 * disconnect this node and set it as not having an associated
                 * address. */
                redisLog(REDIS_DEBUG,"PONG contains mismatching sender ID");
                link->node->flags |= REDIS_NODE_NOADDR;
                freeClusterLink(link);
                update_config = 1;
                /* FIXME: remove this node if we already have it.
                 *
                 * If we already have it but the IP is different, use
                 * the new one if the old node is in FAIL, PFAIL, or NOADDR
                 * status... */
                return 0;
            }
        }
        /* Update our info about the node */
        if (link->node) link->node->pong_received = time(NULL);

        /* Update master/slave info */
        if (sender) {
            if (!memcmp(hdr->slaveof,REDIS_NODE_NULL_NAME,
                sizeof(hdr->slaveof)))
            {
                sender->flags &= ~REDIS_NODE_SLAVE;
                sender->flags |= REDIS_NODE_MASTER;
                sender->slaveof = NULL;
            } else {
                clusterNode *master = clusterLookupNode(hdr->slaveof);

                sender->flags &= ~REDIS_NODE_MASTER;
                sender->flags |= REDIS_NODE_SLAVE;
                if (sender->numslaves) clusterNodeResetSlaves(sender);
                if (master) clusterNodeAddSlave(master,sender);
            }
        }

        /* Update our info about served slots if this new node is serving
         * slots that are not served from our point of view. */
        if (sender && sender->flags & REDIS_NODE_MASTER) {
            int newslots, j;

            newslots =
                memcmp(sender->slots,hdr->myslots,sizeof(hdr->myslots)) != 0;
            memcpy(sender->slots,hdr->myslots,sizeof(hdr->myslots));
            if (newslots) {
                for (j = 0; j < REDIS_CLUSTER_SLOTS; j++) {
                    if (clusterNodeGetSlotBit(sender,j)) {
                        if (server.cluster->slots[j] == sender) continue;
                        if (server.cluster->slots[j] == NULL ||
                            server.cluster->slots[j]->flags & REDIS_NODE_FAIL)
                        {
                            clusterDelSlot(j);
                            clusterAddSlot(sender,j);
                            update_state = update_config = 1;
                        }
                    }
                }
            }
        }

        /* Get info from the gossip section */
        clusterProcessGossipSection(hdr,link);

        /* Update the cluster state if needed */
        if (update_state) clusterUpdateState();
        if (update_config) clusterSaveConfigOrDie();
    } else if (type == CLUSTERMSG_TYPE_FAIL && sender) {
        clusterNode *failing;

        failing = clusterLookupNode(hdr->data.fail.about.nodename);
        if (failing && !(failing->flags & (REDIS_NODE_FAIL|REDIS_NODE_MYSELF)))
        {
            redisLog(REDIS_NOTICE,
                "FAIL message received from %.40s about %.40s",
                hdr->sender, hdr->data.fail.about.nodename);
            failing->flags |= REDIS_NODE_FAIL;
            failing->flags &= ~REDIS_NODE_PFAIL;
            clusterUpdateState();
            clusterSaveConfigOrDie();
        }
    } else if (type == CLUSTERMSG_TYPE_PUBLISH) {
        robj *channel, *message;
        uint32_t channel_len, message_len;

        /* Don't bother creating useless objects if there are no Pub/Sub subscribers. */
        if (dictSize(server.pubsub_channels) || listLength(server.pubsub_patterns)) {
            channel_len = ntohl(hdr->data.publish.msg.channel_len);
            message_len = ntohl(hdr->data.publish.msg.message_len);
            channel = createStringObject(
                        (char*)hdr->data.publish.msg.bulk_data,channel_len);
            message = createStringObject(
                        (char*)hdr->data.publish.msg.bulk_data+channel_len, message_len);
            pubsubPublishMessage(channel,message);
            decrRefCount(channel);
            decrRefCount(message);
        }
    } else {
        redisLog(REDIS_WARNING,"Received unknown packet type: %d", type);
    }
    return 1;
}

/* This function is called when we detect the link with this node is lost.
   We set the node as no longer connected. The Cluster Cron will detect
   this connection and will try to get it connected again.
   
   Instead if the node is a temporary node used to accept a query, we
   completely free the node on error. */
void handleLinkIOError(clusterLink *link) {
    freeClusterLink(link);
}

/* Send data. This is handled using a trivial send buffer that gets
 * consumed by write(). We don't try to optimize this for speed too much
 * as this is a very low traffic channel. */
void clusterWriteHandler(aeEventLoop *el, int fd, void *privdata, int mask) {
    clusterLink *link = (clusterLink*) privdata;
    ssize_t nwritten;
    REDIS_NOTUSED(el);
    REDIS_NOTUSED(mask);

    nwritten = write(fd, link->sndbuf, sdslen(link->sndbuf));
    if (nwritten <= 0) {
        redisLog(REDIS_DEBUG,"I/O error writing to node link: %s",
            strerror(errno));
        handleLinkIOError(link);
        return;
    }
    link->sndbuf = sdsrange(link->sndbuf,nwritten,-1);
    if (sdslen(link->sndbuf) == 0)
        aeDeleteFileEvent(server.el, link->fd, AE_WRITABLE);
}

/* Read data. Try to read the first field of the header first to check the
 * full length of the packet. When a whole packet is in memory this function
 * will call the function to process the packet. And so forth. */
void clusterReadHandler(aeEventLoop *el, int fd, void *privdata, int mask) {
    char buf[4096];
    ssize_t nread;
    clusterMsg *hdr;
    clusterLink *link = (clusterLink*) privdata;
    int readlen, rcvbuflen;
    REDIS_NOTUSED(el);
    REDIS_NOTUSED(mask);

again:
    rcvbuflen = sdslen(link->rcvbuf);
    if (rcvbuflen < 4) {
        /* First, obtain the first four bytes to get the full message
         * length. */
        readlen = 4 - rcvbuflen;
    } else {
        /* Finally read the full message. */
        hdr = (clusterMsg*) link->rcvbuf;
        if (rcvbuflen == 4) {
            /* Perform some sanity check on the message length. */
            if (ntohl(hdr->totlen) < CLUSTERMSG_MIN_LEN) {
                redisLog(REDIS_WARNING,
                    "Bad message length received from Cluster bus.");
                handleLinkIOError(link);
                return;
            }
        }
        readlen = ntohl(hdr->totlen) - rcvbuflen;
    }

    nread = read(fd,buf,readlen);
    if (nread == -1 && errno == EAGAIN) return; /* No more data ready. */

    if (nread <= 0) {
        /* I/O error... */
        redisLog(REDIS_DEBUG,"I/O error reading from node link: %s",
            (nread == 0) ? "connection closed" : strerror(errno));
        handleLinkIOError(link);
        return;
    } else {
        /* Read data and recast the pointer to the new buffer. */
        link->rcvbuf = sdscatlen(link->rcvbuf,buf,nread);
        hdr = (clusterMsg*) link->rcvbuf;
        rcvbuflen += nread;
    }

    /* Total length obtained? read the payload now instead of burning
     * cycles waiting for a new event to fire. */
    if (rcvbuflen == 4) goto again;

    /* Whole packet in memory? We can process it. */
    if (rcvbuflen == ntohl(hdr->totlen)) {
        if (clusterProcessPacket(link)) {
            sdsfree(link->rcvbuf);
            link->rcvbuf = sdsempty();
            rcvbuflen = 0; /* Useless line of code currently... defensive. */
        }
    }
}

/* Put stuff into the send buffer. */
void clusterSendMessage(clusterLink *link, unsigned char *msg, size_t msglen) {
    if (sdslen(link->sndbuf) == 0 && msglen != 0)
        aeCreateFileEvent(server.el,link->fd,AE_WRITABLE,
                    clusterWriteHandler,link);

    link->sndbuf = sdscatlen(link->sndbuf, msg, msglen);
}

/* Send a message to all the nodes with a reliable link */
void clusterBroadcastMessage(void *buf, size_t len) {
    dictIterator *di;
    dictEntry *de;

    di = dictGetIterator(server.cluster->nodes);
    while((de = dictNext(di)) != NULL) {
        clusterNode *node = dictGetVal(de);

        if (!node->link) continue;
        if (node->flags & (REDIS_NODE_MYSELF|REDIS_NODE_NOADDR)) continue;
        clusterSendMessage(node->link,buf,len);
    }
    dictReleaseIterator(di);
}

/* Build the message header */
void clusterBuildMessageHdr(clusterMsg *hdr, int type) {
    int totlen = 0;

    memset(hdr,0,sizeof(*hdr));
    hdr->type = htons(type);
    memcpy(hdr->sender,server.cluster->myself->name,REDIS_CLUSTER_NAMELEN);
    memcpy(hdr->myslots,server.cluster->myself->slots,
        sizeof(hdr->myslots));
    memset(hdr->slaveof,0,REDIS_CLUSTER_NAMELEN);
    if (server.cluster->myself->slaveof != NULL) {
        memcpy(hdr->slaveof,server.cluster->myself->slaveof->name,
                                    REDIS_CLUSTER_NAMELEN);
    }
    hdr->port = htons(server.port);
    hdr->state = server.cluster->state;
    memset(hdr->configdigest,0,32); /* FIXME: set config digest */

    if (type == CLUSTERMSG_TYPE_FAIL) {
        totlen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
        totlen += sizeof(clusterMsgDataFail);
    }
    hdr->totlen = htonl(totlen);
    /* For PING, PONG, and MEET, fixing the totlen field is up to the caller */
}

/* Send a PING or PONG packet to the specified node, making sure to add enough
 * gossip informations. */
void clusterSendPing(clusterLink *link, int type) {
    unsigned char buf[4096];
    clusterMsg *hdr = (clusterMsg*) buf;
    int gossipcount = 0, totlen;
    /* freshnodes is the number of nodes we can still use to populate the
     * gossip section of the ping packet. Basically we start with the nodes
     * we have in memory minus two (ourself and the node we are sending the
     * message to). Every time we add a node we decrement the counter, so when
     * it will drop to <= zero we know there is no more gossip info we can
     * send. */
    int freshnodes = dictSize(server.cluster->nodes)-2;

    if (link->node && type == CLUSTERMSG_TYPE_PING)
        link->node->ping_sent = time(NULL);
    clusterBuildMessageHdr(hdr,type);
        
    /* Populate the gossip fields */
    while(freshnodes > 0 && gossipcount < 3) {
        struct dictEntry *de = dictGetRandomKey(server.cluster->nodes);
        clusterNode *this = dictGetVal(de);
        clusterMsgDataGossip *gossip;
        int j;

        /* Not interesting to gossip about ourself.
         * Nor to send gossip info about HANDSHAKE state nodes (zero info). */
        if (this == server.cluster->myself ||
            this->flags & REDIS_NODE_HANDSHAKE) {
                freshnodes--; /* otherwise we may loop forever. */
                continue;
        }

        /* Check if we already added this node */
        for (j = 0; j < gossipcount; j++) {
            if (memcmp(hdr->data.ping.gossip[j].nodename,this->name,
                    REDIS_CLUSTER_NAMELEN) == 0) break;
        }
        if (j != gossipcount) continue;

        /* Add it */
        freshnodes--;
        gossip = &(hdr->data.ping.gossip[gossipcount]);
        memcpy(gossip->nodename,this->name,REDIS_CLUSTER_NAMELEN);
        gossip->ping_sent = htonl(this->ping_sent);
        gossip->pong_received = htonl(this->pong_received);
        memcpy(gossip->ip,this->ip,sizeof(this->ip));
        gossip->port = htons(this->port);
        gossip->flags = htons(this->flags);
        gossipcount++;
    }
    totlen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
    totlen += (sizeof(clusterMsgDataGossip)*gossipcount);
    hdr->count = htons(gossipcount);
    hdr->totlen = htonl(totlen);
    clusterSendMessage(link,buf,totlen);
}

/* Send a PUBLISH message.
 *
 * If link is NULL, then the message is broadcasted to the whole cluster. */
void clusterSendPublish(clusterLink *link, robj *channel, robj *message) {
    unsigned char buf[4096], *payload;
    clusterMsg *hdr = (clusterMsg*) buf;
    uint32_t totlen;
    uint32_t channel_len, message_len;

    channel = getDecodedObject(channel);
    message = getDecodedObject(message);
    channel_len = sdslen(channel->ptr);
    message_len = sdslen(message->ptr);

    clusterBuildMessageHdr(hdr,CLUSTERMSG_TYPE_PUBLISH);
    totlen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
    totlen += sizeof(clusterMsgDataPublish) + channel_len + message_len;

    hdr->data.publish.msg.channel_len = htonl(channel_len);
    hdr->data.publish.msg.message_len = htonl(message_len);
    hdr->totlen = htonl(totlen);

    /* Try to use the local buffer if possible */
    if (totlen < sizeof(buf)) {
        payload = buf;
    } else {
        payload = zmalloc(totlen);
        hdr = (clusterMsg*) payload;
        memcpy(payload,hdr,sizeof(*hdr));
    }
    memcpy(hdr->data.publish.msg.bulk_data,channel->ptr,sdslen(channel->ptr));
    memcpy(hdr->data.publish.msg.bulk_data+sdslen(channel->ptr),
        message->ptr,sdslen(message->ptr));

    if (link)
        clusterSendMessage(link,payload,totlen);
    else
        clusterBroadcastMessage(payload,totlen);

    decrRefCount(channel);
    decrRefCount(message);
    if (payload != buf) zfree(payload);
}

/* Send a FAIL message to all the nodes we are able to contact.
 * The FAIL message is sent when we detect that a node is failing
 * (REDIS_NODE_PFAIL) and we also receive a gossip confirmation of this:
 * we switch the node state to REDIS_NODE_FAIL and ask all the other
 * nodes to do the same ASAP. */
void clusterSendFail(char *nodename) {
    unsigned char buf[4096];
    clusterMsg *hdr = (clusterMsg*) buf;

    clusterBuildMessageHdr(hdr,CLUSTERMSG_TYPE_FAIL);
    memcpy(hdr->data.fail.about.nodename,nodename,REDIS_CLUSTER_NAMELEN);
    clusterBroadcastMessage(buf,ntohl(hdr->totlen));
}

/* -----------------------------------------------------------------------------
 * CLUSTER Pub/Sub support
 *
 * For now we do very little, just propagating PUBLISH messages across the whole
 * cluster. In the future we'll try to get smarter and avoiding propagating those
 * messages to hosts without receives for a given channel.
 * -------------------------------------------------------------------------- */
void clusterPropagatePublish(robj *channel, robj *message) {
    clusterSendPublish(NULL, channel, message);
}

/* -----------------------------------------------------------------------------
 * CLUSTER cron job
 * -------------------------------------------------------------------------- */

/* This is executed 1 time every second */
void clusterCron(void) {
    dictIterator *di;
    dictEntry *de;
    int j;
    time_t min_ping_sent = 0;
    clusterNode *min_ping_node = NULL;

    /* Check if we have disconnected nodes and re-establish the connection. */
    di = dictGetIterator(server.cluster->nodes);
    while((de = dictNext(di)) != NULL) {
        clusterNode *node = dictGetVal(de);

        if (node->flags & (REDIS_NODE_MYSELF|REDIS_NODE_NOADDR)) continue;
        if (node->link == NULL) {
            int fd;
            clusterLink *link;

            fd = anetTcpNonBlockConnect(server.neterr, node->ip,
                node->port+REDIS_CLUSTER_PORT_INCR);
            if (fd == -1) continue;
            link = createClusterLink(node);
            link->fd = fd;
            node->link = link;
            aeCreateFileEvent(server.el,link->fd,AE_READABLE,clusterReadHandler,link);
            /* If the node is flagged as MEET, we send a MEET message instead
             * of a PING one, to force the receiver to add us in its node
             * table. */
            clusterSendPing(link, node->flags & REDIS_NODE_MEET ?
                    CLUSTERMSG_TYPE_MEET : CLUSTERMSG_TYPE_PING);
            /* We can clear the flag after the first packet is sent.
             * If we'll never receive a PONG, we'll never send new packets
             * to this node. Instead after the PONG is received and we
             * are no longer in meet/handshake status, we want to send
             * normal PING packets. */
            node->flags &= ~REDIS_NODE_MEET;

            redisLog(REDIS_DEBUG,"Connecting with Node %.40s at %s:%d", node->name, node->ip, node->port+REDIS_CLUSTER_PORT_INCR);
        }
    }
    dictReleaseIterator(di);

    /* Ping some random node. Check a few random nodes and ping the one with
     * the oldest ping_sent time */
    for (j = 0; j < 5; j++) {
        de = dictGetRandomKey(server.cluster->nodes);
        clusterNode *this = dictGetVal(de);

        if (this->link == NULL) continue;
        if (this->flags & (REDIS_NODE_MYSELF|REDIS_NODE_HANDSHAKE)) continue;
        if (min_ping_node == NULL || min_ping_sent > this->ping_sent) {
            min_ping_node = this;
            min_ping_sent = this->ping_sent;
        }
    }
    if (min_ping_node) {
        redisLog(REDIS_DEBUG,"Pinging node %40s", min_ping_node->name);
        clusterSendPing(min_ping_node->link, CLUSTERMSG_TYPE_PING);
    }

    /* Iterate nodes to check if we need to flag something as failing */
    di = dictGetIterator(server.cluster->nodes);
    while((de = dictNext(di)) != NULL) {
        clusterNode *node = dictGetVal(de);
        int delay;

        if (node->flags &
            (REDIS_NODE_MYSELF|REDIS_NODE_NOADDR|REDIS_NODE_HANDSHAKE))
                continue;
        /* Check only if we already sent a ping and did not received
         * a reply yet. */
        if (node->ping_sent == 0 ||
            node->ping_sent <= node->pong_received) continue;

        delay = time(NULL) - node->pong_received;
        if (delay < server.cluster->node_timeout) {
            /* The PFAIL condition can be reversed without external
             * help if it is not transitive (that is, if it does not
             * turn into a FAIL state).
             *
             * The FAIL condition is also reversible if there are no slaves
             * for this host, so no slave election should be in progress.
             *
             * TODO: consider all the implications of resurrecting a
             * FAIL node. */
            if (node->flags & REDIS_NODE_PFAIL) {
                node->flags &= ~REDIS_NODE_PFAIL;
            } else if (node->flags & REDIS_NODE_FAIL && !node->numslaves) {
                node->flags &= ~REDIS_NODE_FAIL;
                clusterUpdateState();
            }
        } else {
            /* Timeout reached. Set the node as possibly failing if it is
             * not already in this state. */
            if (!(node->flags & (REDIS_NODE_PFAIL|REDIS_NODE_FAIL))) {
                redisLog(REDIS_DEBUG,"*** NODE %.40s possibly failing",
                    node->name);
                node->flags |= REDIS_NODE_PFAIL;
            }
        }
    }
    dictReleaseIterator(di);
}

/* -----------------------------------------------------------------------------
 * Slots management
 * -------------------------------------------------------------------------- */

/* Set the slot bit and return the old value. */
int clusterNodeSetSlotBit(clusterNode *n, int slot) {
    off_t byte = slot/8;
    int bit = slot&7;
    int old = (n->slots[byte] & (1<<bit)) != 0;
    n->slots[byte] |= 1<<bit;
    return old;
}

/* Clear the slot bit and return the old value. */
int clusterNodeClearSlotBit(clusterNode *n, int slot) {
    off_t byte = slot/8;
    int bit = slot&7;
    int old = (n->slots[byte] & (1<<bit)) != 0;
    n->slots[byte] &= ~(1<<bit);
    return old;
}

/* Return the slot bit from the cluster node structure. */
int clusterNodeGetSlotBit(clusterNode *n, int slot) {
    off_t byte = slot/8;
    int bit = slot&7;
    return (n->slots[byte] & (1<<bit)) != 0;
}

/* Add the specified slot to the list of slots that node 'n' will
 * serve. Return REDIS_OK if the operation ended with success.
 * If the slot is already assigned to another instance this is considered
 * an error and REDIS_ERR is returned. */
int clusterAddSlot(clusterNode *n, int slot) {
    if (clusterNodeSetSlotBit(n,slot) != 0)
        return REDIS_ERR;
    server.cluster->slots[slot] = n;
    return REDIS_OK;
}

/* Delete the specified slot marking it as unassigned.
 * Returns REDIS_OK if the slot was assigned, otherwise if the slot was
 * already unassigned REDIS_ERR is returned. */
int clusterDelSlot(int slot) {
    clusterNode *n = server.cluster->slots[slot];

    if (!n) return REDIS_ERR;
    redisAssert(clusterNodeClearSlotBit(n,slot) == 1);
    server.cluster->slots[slot] = NULL;
    return REDIS_OK;
}

/* -----------------------------------------------------------------------------
 * Cluster state evaluation function
 * -------------------------------------------------------------------------- */
void clusterUpdateState(void) {
    int ok = 1;
    int j;

    for (j = 0; j < REDIS_CLUSTER_SLOTS; j++) {
        if (server.cluster->slots[j] == NULL ||
            server.cluster->slots[j]->flags & (REDIS_NODE_FAIL))
        {
            ok = 0;
            break;
        }
    }
    if (ok) {
        if (server.cluster->state == REDIS_CLUSTER_NEEDHELP) {
            server.cluster->state = REDIS_CLUSTER_NEEDHELP;
        } else {
            server.cluster->state = REDIS_CLUSTER_OK;
        }
    } else {
        server.cluster->state = REDIS_CLUSTER_FAIL;
    }
}

/* -----------------------------------------------------------------------------
 * CLUSTER command
 * -------------------------------------------------------------------------- */

sds clusterGenNodesDescription(void) {
    sds ci = sdsempty();
    dictIterator *di;
    dictEntry *de;
    int j, start;

    di = dictGetIterator(server.cluster->nodes);
    while((de = dictNext(di)) != NULL) {
        clusterNode *node = dictGetVal(de);

        /* Node coordinates */
        ci = sdscatprintf(ci,"%.40s %s:%d ",
            node->name,
            node->ip,
            node->port);

        /* Flags */
        if (node->flags == 0) ci = sdscat(ci,"noflags,");
        if (node->flags & REDIS_NODE_MYSELF) ci = sdscat(ci,"myself,");
        if (node->flags & REDIS_NODE_MASTER) ci = sdscat(ci,"master,");
        if (node->flags & REDIS_NODE_SLAVE) ci = sdscat(ci,"slave,");
        if (node->flags & REDIS_NODE_PFAIL) ci = sdscat(ci,"fail?,");
        if (node->flags & REDIS_NODE_FAIL) ci = sdscat(ci,"fail,");
        if (node->flags & REDIS_NODE_HANDSHAKE) ci =sdscat(ci,"handshake,");
        if (node->flags & REDIS_NODE_NOADDR) ci = sdscat(ci,"noaddr,");
        if (ci[sdslen(ci)-1] == ',') ci[sdslen(ci)-1] = ' ';

        /* Slave of... or just "-" */
        if (node->slaveof)
            ci = sdscatprintf(ci,"%.40s ",node->slaveof->name);
        else
            ci = sdscatprintf(ci,"- ");

        /* Latency from the POV of this node, link status */
        ci = sdscatprintf(ci,"%ld %ld %s",
            (long) node->ping_sent,
            (long) node->pong_received,
            (node->link || node->flags & REDIS_NODE_MYSELF) ?
                        "connected" : "disconnected");

        /* Slots served by this instance */
        start = -1;
        for (j = 0; j < REDIS_CLUSTER_SLOTS; j++) {
            int bit;

            if ((bit = clusterNodeGetSlotBit(node,j)) != 0) {
                if (start == -1) start = j;
            }
            if (start != -1 && (!bit || j == REDIS_CLUSTER_SLOTS-1)) {
                if (j == REDIS_CLUSTER_SLOTS-1) j++;

                if (start == j-1) {
                    ci = sdscatprintf(ci," %d",start);
                } else {
                    ci = sdscatprintf(ci," %d-%d",start,j-1);
                }
                start = -1;
            }
        }

        /* Just for MYSELF node we also dump info about slots that
         * we are migrating to other instances or importing from other
         * instances. */
        if (node->flags & REDIS_NODE_MYSELF) {
            for (j = 0; j < REDIS_CLUSTER_SLOTS; j++) {
                if (server.cluster->migrating_slots_to[j]) {
                    ci = sdscatprintf(ci," [%d->-%.40s]",j,
                        server.cluster->migrating_slots_to[j]->name);
                } else if (server.cluster->importing_slots_from[j]) {
                    ci = sdscatprintf(ci," [%d-<-%.40s]",j,
                        server.cluster->importing_slots_from[j]->name);
                }
            }
        }
        ci = sdscatlen(ci,"\n",1);
    }
    dictReleaseIterator(di);
    return ci;
}

int getSlotOrReply(redisClient *c, robj *o) {
    long long slot;

    if (getLongLongFromObject(o,&slot) != REDIS_OK ||
        slot < 0 || slot > REDIS_CLUSTER_SLOTS)
    {
        addReplyError(c,"Invalid or out of range slot");
        return -1;
    }
    return (int) slot;
}

void clusterCommand(redisClient *c) {
    if (server.cluster_enabled == 0) {
        addReplyError(c,"This instance has cluster support disabled");
        return;
    }

    if (!strcasecmp(c->argv[1]->ptr,"meet") && c->argc == 4) {
        clusterNode *n;
        struct sockaddr_in sa;
        long port;

        /* Perform sanity checks on IP/port */
        if (inet_aton(c->argv[2]->ptr,&sa.sin_addr) == 0) {
            addReplyError(c,"Invalid IP address in MEET");
            return;
        }
        if (getLongFromObjectOrReply(c, c->argv[3], &port, NULL) != REDIS_OK ||
                    port < 0 || port > (65535-REDIS_CLUSTER_PORT_INCR))
        {
            addReplyError(c,"Invalid TCP port specified");
            return;
        }

        /* Finally add the node to the cluster with a random name, this 
         * will get fixed in the first handshake (ping/pong). */
        n = createClusterNode(NULL,REDIS_NODE_HANDSHAKE|REDIS_NODE_MEET);
        strncpy(n->ip,inet_ntoa(sa.sin_addr),sizeof(n->ip));
        n->port = port;
        clusterAddNode(n);
        addReply(c,shared.ok);
    } else if (!strcasecmp(c->argv[1]->ptr,"nodes") && c->argc == 2) {
        robj *o;
        sds ci = clusterGenNodesDescription();

        o = createObject(REDIS_STRING,ci);
        addReplyBulk(c,o);
        decrRefCount(o);
    } else if ((!strcasecmp(c->argv[1]->ptr,"addslots") ||
               !strcasecmp(c->argv[1]->ptr,"delslots")) && c->argc >= 3)
    {
        /* CLUSTER ADDSLOTS <slot> [slot] ... */
        /* CLUSTER DELSLOTS <slot> [slot] ... */
        int j, slot;
        unsigned char *slots = zmalloc(REDIS_CLUSTER_SLOTS);
        int del = !strcasecmp(c->argv[1]->ptr,"delslots");

        memset(slots,0,REDIS_CLUSTER_SLOTS);
        /* Check that all the arguments are parsable and that all the
         * slots are not already busy. */
        for (j = 2; j < c->argc; j++) {
            if ((slot = getSlotOrReply(c,c->argv[j])) == -1) {
                zfree(slots);
                return;
            }
            if (del && server.cluster->slots[slot] == NULL) {
                addReplyErrorFormat(c,"Slot %d is already unassigned", slot);
                zfree(slots);
                return;
            } else if (!del && server.cluster->slots[slot]) {
                addReplyErrorFormat(c,"Slot %d is already busy", slot);
                zfree(slots);
                return;
            }
            if (slots[slot]++ == 1) {
                addReplyErrorFormat(c,"Slot %d specified multiple times",
                    (int)slot);
                zfree(slots);
                return;
            }
        }
        for (j = 0; j < REDIS_CLUSTER_SLOTS; j++) {
            if (slots[j]) {
                int retval;

                /* If this slot was set as importing we can clear this 
                 * state as now we are the real owner of the slot. */
                if (server.cluster->importing_slots_from[j])
                    server.cluster->importing_slots_from[j] = NULL;

                retval = del ? clusterDelSlot(j) :
                               clusterAddSlot(server.cluster->myself,j);
                redisAssertWithInfo(c,NULL,retval == REDIS_OK);
            }
        }
        zfree(slots);
        clusterUpdateState();
        clusterSaveConfigOrDie();
        addReply(c,shared.ok);
    } else if (!strcasecmp(c->argv[1]->ptr,"setslot") && c->argc >= 4) {
        /* SETSLOT 10 MIGRATING <node ID> */
        /* SETSLOT 10 IMPORTING <node ID> */
        /* SETSLOT 10 STABLE */
        /* SETSLOT 10 NODE <node ID> */
        int slot;
        clusterNode *n;

        if ((slot = getSlotOrReply(c,c->argv[2])) == -1) return;

        if (!strcasecmp(c->argv[3]->ptr,"migrating") && c->argc == 5) {
            if (server.cluster->slots[slot] != server.cluster->myself) {
                addReplyErrorFormat(c,"I'm not the owner of hash slot %u",slot);
                return;
            }
            if ((n = clusterLookupNode(c->argv[4]->ptr)) == NULL) {
                addReplyErrorFormat(c,"I don't know about node %s",
                    (char*)c->argv[4]->ptr);
                return;
            }
            server.cluster->migrating_slots_to[slot] = n;
        } else if (!strcasecmp(c->argv[3]->ptr,"importing") && c->argc == 5) {
            if (server.cluster->slots[slot] == server.cluster->myself) {
                addReplyErrorFormat(c,
                    "I'm already the owner of hash slot %u",slot);
                return;
            }
            if ((n = clusterLookupNode(c->argv[4]->ptr)) == NULL) {
                addReplyErrorFormat(c,"I don't know about node %s",
                    (char*)c->argv[3]->ptr);
                return;
            }
            server.cluster->importing_slots_from[slot] = n;
        } else if (!strcasecmp(c->argv[3]->ptr,"stable") && c->argc == 4) {
            /* CLUSTER SETSLOT <SLOT> STABLE */
            server.cluster->importing_slots_from[slot] = NULL;
            server.cluster->migrating_slots_to[slot] = NULL;
        } else if (!strcasecmp(c->argv[3]->ptr,"node") && c->argc == 5) {
            /* CLUSTER SETSLOT <SLOT> NODE <NODE ID> */
            clusterNode *n = clusterLookupNode(c->argv[4]->ptr);

            if (!n) addReplyErrorFormat(c,"Unknown node %s",
                (char*)c->argv[4]->ptr);
            /* If this hash slot was served by 'myself' before to switch
             * make sure there are no longer local keys for this hash slot. */
            if (server.cluster->slots[slot] == server.cluster->myself &&
                n != server.cluster->myself)
            {
                int numkeys;
                robj **keys;

                keys = zmalloc(sizeof(robj*)*1);
                numkeys = GetKeysInSlot(slot, keys, 1);
                zfree(keys);
                if (numkeys != 0) {
                    addReplyErrorFormat(c, "Can't assign hashslot %d to a different node while I still hold keys for this hash slot.", slot);
                    return;
                }
            }
            /* If this node was the slot owner and the slot was marked as
             * migrating, assigning the slot to another node will clear
             * the migratig status. */
            if (server.cluster->slots[slot] == server.cluster->myself &&
                server.cluster->migrating_slots_to[slot])
                server.cluster->migrating_slots_to[slot] = NULL;

            /* If this node was importing this slot, assigning the slot to
             * itself also clears the importing status. */
            if (n == server.cluster->myself && server.cluster->importing_slots_from[slot])
                server.cluster->importing_slots_from[slot] = NULL;

            clusterDelSlot(slot);
            clusterAddSlot(n,slot);
        } else {
            addReplyError(c,"Invalid CLUSTER SETSLOT action or number of arguments");
            return;
        }
        clusterSaveConfigOrDie();
        addReply(c,shared.ok);
    } else if (!strcasecmp(c->argv[1]->ptr,"info") && c->argc == 2) {
        char *statestr[] = {"ok","fail","needhelp"};
        int slots_assigned = 0, slots_ok = 0, slots_pfail = 0, slots_fail = 0;
        int j;

        for (j = 0; j < REDIS_CLUSTER_SLOTS; j++) {
            clusterNode *n = server.cluster->slots[j];

            if (n == NULL) continue;
            slots_assigned++;
            if (n->flags & REDIS_NODE_FAIL) {
                slots_fail++;
            } else if (n->flags & REDIS_NODE_PFAIL) {
                slots_pfail++;
            } else {
                slots_ok++;
            }
        }

        sds info = sdscatprintf(sdsempty(),
            "cluster_state:%s\r\n"
            "cluster_slots_assigned:%d\r\n"
            "cluster_slots_ok:%d\r\n"
            "cluster_slots_pfail:%d\r\n"
            "cluster_slots_fail:%d\r\n"
            "cluster_known_nodes:%lu\r\n"
            , statestr[server.cluster->state],
            slots_assigned,
            slots_ok,
            slots_pfail,
            slots_fail,
            dictSize(server.cluster->nodes)
        );
        addReplySds(c,sdscatprintf(sdsempty(),"$%lu\r\n",
            (unsigned long)sdslen(info)));
        addReplySds(c,info);
        addReply(c,shared.crlf);
    } else if (!strcasecmp(c->argv[1]->ptr,"keyslot") && c->argc == 3) {
        sds key = c->argv[2]->ptr;

        addReplyLongLong(c,keyHashSlot(key,sdslen(key)));
    } else if (!strcasecmp(c->argv[1]->ptr,"getkeysinslot") && c->argc == 4) {
        long long maxkeys, slot;
        unsigned int numkeys, j;
        robj **keys;

        if (getLongLongFromObjectOrReply(c,c->argv[2],&slot,NULL) != REDIS_OK)
            return;
        if (getLongLongFromObjectOrReply(c,c->argv[3],&maxkeys,NULL) != REDIS_OK)
            return;
        if (slot < 0 || slot >= REDIS_CLUSTER_SLOTS || maxkeys < 0 ||
            maxkeys > 1024*1024) {
            addReplyError(c,"Invalid slot or number of keys");
            return;
        }

        keys = zmalloc(sizeof(robj*)*maxkeys);
        numkeys = GetKeysInSlot(slot, keys, maxkeys);
        addReplyMultiBulkLen(c,numkeys);
        for (j = 0; j < numkeys; j++) addReplyBulk(c,keys[j]);
        zfree(keys);
    } else {
        addReplyError(c,"Wrong CLUSTER subcommand or number of arguments");
    }
}

/* -----------------------------------------------------------------------------
 * DUMP, RESTORE and MIGRATE commands
 * -------------------------------------------------------------------------- */

/* Generates a DUMP-format representation of the object 'o', adding it to the
 * io stream pointed by 'rio'. This function can't fail. */
void createDumpPayload(rio *payload, robj *o) {
    unsigned char buf[2];
    uint64_t crc;

    /* Serialize the object in a RDB-like format. It consist of an object type
     * byte followed by the serialized object. This is understood by RESTORE. */
    rioInitWithBuffer(payload,sdsempty());
    redisAssert(rdbSaveObjectType(payload,o));
    redisAssert(rdbSaveObject(payload,o));

    /* Write the footer, this is how it looks like:
     * ----------------+---------------------+---------------+
     * ... RDB payload | 2 bytes RDB version | 8 bytes CRC64 |
     * ----------------+---------------------+---------------+
     * RDB version and CRC are both in little endian.
     */

    /* RDB version */
    buf[0] = REDIS_RDB_VERSION & 0xff;
    buf[1] = (REDIS_RDB_VERSION >> 8) & 0xff;
    payload->io.buffer.ptr = sdscatlen(payload->io.buffer.ptr,buf,2);

    /* CRC64 */
    crc = crc64(0,(unsigned char*)payload->io.buffer.ptr,
                sdslen(payload->io.buffer.ptr));
    memrev64ifbe(&crc);
    payload->io.buffer.ptr = sdscatlen(payload->io.buffer.ptr,&crc,8);
}

/* Verify that the RDB version of the dump payload matches the one of this Redis
 * instance and that the checksum is ok.
 * If the DUMP payload looks valid REDIS_OK is returned, otherwise REDIS_ERR
 * is returned. */
int verifyDumpPayload(unsigned char *p, size_t len) {
    unsigned char *footer;
    uint16_t rdbver;
    uint64_t crc;

    /* At least 2 bytes of RDB version and 8 of CRC64 should be present. */
    if (len < 10) return REDIS_ERR;
    footer = p+(len-10);

    /* Verify RDB version */
    rdbver = (footer[1] << 8) | footer[0];
    if (rdbver != REDIS_RDB_VERSION) return REDIS_ERR;

    /* Verify CRC64 */
    crc = crc64(0,p,len-8);
    memrev64ifbe(&crc);
    return (memcmp(&crc,footer+2,8) == 0) ? REDIS_OK : REDIS_ERR;
}

/* DUMP keyname
 * DUMP is actually not used by Redis Cluster but it is the obvious
 * complement of RESTORE and can be useful for different applications. */
void dumpCommand(redisClient *c) {
    robj *o, *dumpobj;
    rio payload;

    /* Check if the key is here. */
    if ((o = lookupKeyRead(c->db,c->argv[1])) == NULL) {
        addReply(c,shared.nullbulk);
        return;
    }

    /* Create the DUMP encoded representation. */
    createDumpPayload(&payload,o);

    /* Transfer to the client */
    dumpobj = createObject(REDIS_STRING,payload.io.buffer.ptr);
    addReplyBulk(c,dumpobj);
    decrRefCount(dumpobj);
    return;
}

/* RESTORE key ttl serialized-value [REPLACE] */
void restoreCommand(redisClient *c) {
    long ttl;
    rio payload;
    int j, type, replace = 0;
    robj *obj;

    /* Parse additional options */
    for (j = 4; j < c->argc; j++) {
        if (!strcasecmp(c->argv[j]->ptr,"replace")) {
            replace = 1;
        } else {
            addReply(c,shared.syntaxerr);
            return;
        }
    }

    /* Make sure this key does not already exist here... */
    if (!replace && lookupKeyWrite(c->db,c->argv[1]) != NULL) {
        addReplyError(c,"Target key name is busy.");
        return;
    }

    /* Check if the TTL value makes sense */
    if (getLongFromObjectOrReply(c,c->argv[2],&ttl,NULL) != REDIS_OK) {
        return;
    } else if (ttl < 0) {
        addReplyError(c,"Invalid TTL value, must be >= 0");
        return;
    }

    /* Verify RDB version and data checksum. */
    if (verifyDumpPayload(c->argv[3]->ptr,sdslen(c->argv[3]->ptr)) == REDIS_ERR) {
        addReplyError(c,"DUMP payload version or checksum are wrong");
        return;
    }

    rioInitWithBuffer(&payload,c->argv[3]->ptr);
    if (((type = rdbLoadObjectType(&payload)) == -1) ||
        ((obj = rdbLoadObject(type,&payload)) == NULL))
    {
        addReplyError(c,"Bad data format");
        return;
    }

    /* Remove the old key if needed. */
    if (replace) dbDelete(c->db,c->argv[1]);

    /* Create the key and set the TTL if any */
    dbAdd(c->db,c->argv[1],obj);
    if (ttl) setExpire(c->db,c->argv[1],mstime()+ttl);
    signalModifiedKey(c->db,c->argv[1]);
    addReply(c,shared.ok);
    server.dirty++;
}

/* MIGRATE socket cache implementation.
 *
 * We take a map between host:ip and a TCP socket that we used to connect
 * to this instance in recent time.
 * This sockets are closed when the max number we cache is reached, and also
 * in serverCron() when they are around for more than a few seconds. */
#define MIGRATE_SOCKET_CACHE_ITEMS 64 /* max num of items in the cache. */
#define MIGRATE_SOCKET_CACHE_TTL 10 /* close cached socekts after 10 sec. */

typedef struct migrateCachedSocket {
    int fd;
    time_t last_use_time;
} migrateCachedSocket;

/* Return a TCP scoket connected with the target instance, possibly returning
 * a cached one.
 *
 * This function is responsible of sending errors to the client if a
 * connection can't be established. In this case -1 is returned.
 * Otherwise on success the socket is returned, and the caller should not
 * attempt to free it after usage.
 *
 * If the caller detects an error while using the socket, migrateCloseSocket()
 * should be called so that the connection will be craeted from scratch
 * the next time. */
int migrateGetSocket(redisClient *c, robj *host, robj *port, long timeout) {
    int fd;
    sds name = sdsempty();
    migrateCachedSocket *cs;

    /* Check if we have an already cached socket for this ip:port pair. */
    name = sdscatlen(name,host->ptr,sdslen(host->ptr));
    name = sdscatlen(name,":",1);
    name = sdscatlen(name,port->ptr,sdslen(port->ptr));
    cs = dictFetchValue(server.migrate_cached_sockets,name);
    if (cs) {
        sdsfree(name);
        cs->last_use_time = server.unixtime;
        return cs->fd;
    }

    /* No cached socket, create one. */
    if (dictSize(server.migrate_cached_sockets) == MIGRATE_SOCKET_CACHE_ITEMS) {
        /* Too many items, drop one at random. */
        dictEntry *de = dictGetRandomKey(server.migrate_cached_sockets);
        cs = dictGetVal(de);
        close(cs->fd);
        zfree(cs);
        dictDelete(server.migrate_cached_sockets,dictGetKey(de));
    }

    /* Create the socket */
    fd = anetTcpNonBlockConnect(server.neterr,c->argv[1]->ptr,
                atoi(c->argv[2]->ptr));
    if (fd == -1) {
        sdsfree(name);
        addReplyErrorFormat(c,"Can't connect to target node: %s",
            server.neterr);
        return -1;
    }
    anetEnableTcpNoDelay(server.neterr,fd);

    /* Check if it connects within the specified timeout. */
    if ((aeWait(fd,AE_WRITABLE,timeout) & AE_WRITABLE) == 0) {
        sdsfree(name);
        addReplySds(c,sdsnew("-IOERR error or timeout connecting to the client\r\n"));
        close(fd);
        return -1;
    }

    /* Add to the cache and return it to the caller. */
    cs = zmalloc(sizeof(*cs));
    cs->fd = fd;
    cs->last_use_time = server.unixtime;
    dictAdd(server.migrate_cached_sockets,name,cs);
    return fd;
}

/* Free a migrate cached connection. */
void migrateCloseSocket(robj *host, robj *port) {
    sds name = sdsempty();
    migrateCachedSocket *cs;

    name = sdscatlen(name,host->ptr,sdslen(host->ptr));
    name = sdscatlen(name,":",1);
    name = sdscatlen(name,port->ptr,sdslen(port->ptr));
    cs = dictFetchValue(server.migrate_cached_sockets,name);
    if (!cs) {
        sdsfree(name);
        return;
    }

    close(cs->fd);
    zfree(cs);
    dictDelete(server.migrate_cached_sockets,name);
    sdsfree(name);
}

void migrateCloseTimedoutSockets(void) {
    dictIterator *di = dictGetSafeIterator(server.migrate_cached_sockets);
    dictEntry *de;

    while((de = dictNext(di)) != NULL) {
        migrateCachedSocket *cs = dictGetVal(de);

        if ((server.unixtime - cs->last_use_time) > MIGRATE_SOCKET_CACHE_TTL) {
            close(cs->fd);
            zfree(cs);
            dictDelete(server.migrate_cached_sockets,dictGetKey(de));
        }
    }
    dictReleaseIterator(di);
}

/* MIGRATE host port key dbid timeout [COPY | REPLACE] */
void migrateCommand(redisClient *c) {
    int fd, copy, replace, j;
    long timeout;
    long dbid;
    long long ttl, expireat;
    robj *o;
    rio cmd, payload;
    int retry_num = 0;

try_again:
    /* Initialization */
    copy = 0;
    replace = 0;
    ttl = 0;

    /* Parse additional options */
    for (j = 6; j < c->argc; j++) {
        if (!strcasecmp(c->argv[j]->ptr,"copy")) {
            copy = 1;
        } else if (!strcasecmp(c->argv[j]->ptr,"replace")) {
            replace = 1;
        } else {
            addReply(c,shared.syntaxerr);
            return;
        }
    }

    /* Sanity check */
    if (getLongFromObjectOrReply(c,c->argv[5],&timeout,NULL) != REDIS_OK)
        return;
    if (getLongFromObjectOrReply(c,c->argv[4],&dbid,NULL) != REDIS_OK)
        return;
    if (timeout <= 0) timeout = 1000;

    /* Check if the key is here. If not we reply with success as there is
     * nothing to migrate (for instance the key expired in the meantime), but
     * we include such information in the reply string. */
    if ((o = lookupKeyRead(c->db,c->argv[3])) == NULL) {
        addReplySds(c,sdsnew("+NOKEY\r\n"));
        return;
    }
    
    /* Connect */
    fd = migrateGetSocket(c,c->argv[1],c->argv[2],timeout);
    if (fd == -1) return; /* error sent to the client by migrateGetSocket() */

    /* Create RESTORE payload and generate the protocol to call the command. */
    rioInitWithBuffer(&cmd,sdsempty());
    redisAssertWithInfo(c,NULL,rioWriteBulkCount(&cmd,'*',2));
    redisAssertWithInfo(c,NULL,rioWriteBulkString(&cmd,"SELECT",6));
    redisAssertWithInfo(c,NULL,rioWriteBulkLongLong(&cmd,dbid));

    expireat = getExpire(c->db,c->argv[3]);
    if (expireat != -1) {
        ttl = expireat-mstime();
        if (ttl < 1) ttl = 1;
    }
    redisAssertWithInfo(c,NULL,rioWriteBulkCount(&cmd,'*',replace ? 5 : 4));
    if (server.cluster_enabled)
        redisAssertWithInfo(c,NULL,
            rioWriteBulkString(&cmd,"RESTORE-ASKING",14));
    else
        redisAssertWithInfo(c,NULL,rioWriteBulkString(&cmd,"RESTORE",7));
    redisAssertWithInfo(c,NULL,c->argv[3]->encoding == REDIS_ENCODING_RAW);
    redisAssertWithInfo(c,NULL,rioWriteBulkString(&cmd,c->argv[3]->ptr,sdslen(c->argv[3]->ptr)));
    redisAssertWithInfo(c,NULL,rioWriteBulkLongLong(&cmd,ttl));

    /* Emit the payload argument, that is the serialized object using
     * the DUMP format. */
    createDumpPayload(&payload,o);
    redisAssertWithInfo(c,NULL,rioWriteBulkString(&cmd,payload.io.buffer.ptr,
                                sdslen(payload.io.buffer.ptr)));
    sdsfree(payload.io.buffer.ptr);

    /* Add the REPLACE option to the RESTORE command if it was specified
     * as a MIGRATE option. */
    if (replace)
        redisAssertWithInfo(c,NULL,rioWriteBulkString(&cmd,"REPLACE",7));

    /* Transfer the query to the other node in 64K chunks. */
    errno = 0;
    {
        sds buf = cmd.io.buffer.ptr;
        size_t pos = 0, towrite;
        int nwritten = 0;

        while ((towrite = sdslen(buf)-pos) > 0) {
            towrite = (towrite > (64*1024) ? (64*1024) : towrite);
            nwritten = syncWrite(fd,buf+pos,towrite,timeout);
            if (nwritten != (signed)towrite) goto socket_wr_err;
            pos += nwritten;
        }
    }

    /* Read back the reply. */
    {
        char buf1[1024];
        char buf2[1024];

        /* Read the two replies */
        if (syncReadLine(fd, buf1, sizeof(buf1), timeout) <= 0)
            goto socket_rd_err;
        if (syncReadLine(fd, buf2, sizeof(buf2), timeout) <= 0)
            goto socket_rd_err;
        if (buf1[0] == '-' || buf2[0] == '-') {
            addReplyErrorFormat(c,"Target instance replied with error: %s",
                (buf1[0] == '-') ? buf1+1 : buf2+1);
        } else {
            robj *aux;

            if (!copy) {
                /* No COPY option: remove the local key, signal the change. */
                dbDelete(c->db,c->argv[3]);
                signalModifiedKey(c->db,c->argv[3]);
            }
            addReply(c,shared.ok);
            server.dirty++;

            /* Translate MIGRATE as DEL for replication/AOF. */
            aux = createStringObject("DEL",3);
            rewriteClientCommandVector(c,2,aux,c->argv[3]);
            decrRefCount(aux);
        }
    }

    sdsfree(cmd.io.buffer.ptr);
    return;

socket_wr_err:
    sdsfree(cmd.io.buffer.ptr);
    migrateCloseSocket(c->argv[1],c->argv[2]);
    if (errno != ETIMEDOUT && retry_num++ == 0) goto try_again;
    addReplySds(c,
        sdsnew("-IOERR error or timeout writing to target instance\r\n"));
    return;

socket_rd_err:
    sdsfree(cmd.io.buffer.ptr);
    migrateCloseSocket(c->argv[1],c->argv[2]);
    if (errno != ETIMEDOUT && retry_num++ == 0) goto try_again;
    addReplySds(c,
        sdsnew("-IOERR error or timeout reading from target node\r\n"));
    return;
}

/* The ASKING command is required after a -ASK redirection.
 * The client should issue ASKING before to actually send the command to
 * the target instance. See the Redis Cluster specification for more
 * information. */
void askingCommand(redisClient *c) {
    if (server.cluster_enabled == 0) {
        addReplyError(c,"This instance has cluster support disabled");
        return;
    }
    c->flags |= REDIS_ASKING;
    addReply(c,shared.ok);
}

/* -----------------------------------------------------------------------------
 * Cluster functions related to serving / redirecting clients
 * -------------------------------------------------------------------------- */

/* Return the pointer to the cluster node that is able to serve the command.
 * For the function to succeed the command should only target a single
 * key (or the same key multiple times).
 *
 * If the returned node should be used only for this request, the *ask
 * integer is set to '1', otherwise to '0'. This is used in order to
 * let the caller know if we should reply with -MOVED or with -ASK.
 *
 * If the command contains multiple keys, and as a consequence it is not
 * possible to handle the request in Redis Cluster, NULL is returned. */
clusterNode *getNodeByQuery(redisClient *c, struct redisCommand *cmd, robj **argv, int argc, int *hashslot, int *ask) {
    clusterNode *n = NULL;
    robj *firstkey = NULL;
    multiState *ms, _ms;
    multiCmd mc;
    int i, slot = 0;

    /* We handle all the cases as if they were EXEC commands, so we have
     * a common code path for everything */
    if (cmd->proc == execCommand) {
        /* If REDIS_MULTI flag is not set EXEC is just going to return an
         * error. */
        if (!(c->flags & REDIS_MULTI)) return server.cluster->myself;
        ms = &c->mstate;
    } else {
        /* In order to have a single codepath create a fake Multi State
         * structure if the client is not in MULTI/EXEC state, this way
         * we have a single codepath below. */
        ms = &_ms;
        _ms.commands = &mc;
        _ms.count = 1;
        mc.argv = argv;
        mc.argc = argc;
        mc.cmd = cmd;
    }

    /* Check that all the keys are the same key, and get the slot and
     * node for this key. */
    for (i = 0; i < ms->count; i++) {
        struct redisCommand *mcmd;
        robj **margv;
        int margc, *keyindex, numkeys, j;

        mcmd = ms->commands[i].cmd;
        margc = ms->commands[i].argc;
        margv = ms->commands[i].argv;

        keyindex = getKeysFromCommand(mcmd,margv,margc,&numkeys,
                                      REDIS_GETKEYS_ALL);
        for (j = 0; j < numkeys; j++) {
            if (firstkey == NULL) {
                /* This is the first key we see. Check what is the slot
                 * and node. */
                firstkey = margv[keyindex[j]];

                slot = keyHashSlot((char*)firstkey->ptr, sdslen(firstkey->ptr));
                n = server.cluster->slots[slot];
                redisAssertWithInfo(c,firstkey,n != NULL);
            } else {
                /* If it is not the first key, make sure it is exactly
                 * the same key as the first we saw. */
                if (!equalStringObjects(firstkey,margv[keyindex[j]])) {
                    getKeysFreeResult(keyindex);
                    return NULL;
                }
            }
        }
        getKeysFreeResult(keyindex);
    }
    if (ask) *ask = 0; /* This is the default. Set to 1 if needed later. */
    /* No key at all in command? then we can serve the request
     * without redirections. */
    if (n == NULL) return server.cluster->myself;
    if (hashslot) *hashslot = slot;
    /* This request is about a slot we are migrating into another instance?
     * Then we need to check if we have the key. If we have it we can reply.
     * If instead is a new key, we pass the request to the node that is
     * receiving the slot. */
    if (n == server.cluster->myself &&
        server.cluster->migrating_slots_to[slot] != NULL)
    {
        if (lookupKeyRead(&server.db[0],firstkey) == NULL) {
            if (ask) *ask = 1;
            return server.cluster->migrating_slots_to[slot];
        }
    }
    /* Handle the case in which we are receiving this hash slot from
     * another instance, so we'll accept the query even if in the table
     * it is assigned to a different node, but only if the client
     * issued an ASKING command before. */
    if (server.cluster->importing_slots_from[slot] != NULL &&
        (c->flags & REDIS_ASKING || cmd->flags & REDIS_CMD_ASKING)) {
        return server.cluster->myself;
    }
    /* It's not a -ASK case. Base case: just return the right node. */
    return n;
}