Function migrateGetSocket

app/redis-6.2.6/src/cluster.c:5242–5287

Return a migrateCachedSocket containing a TCP socket 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 a

 * should be called so that the connection will be created from scratch
 * the next time. */
migrateCachedSocket* migrateGetSocket(client *c, robj *host, robj *port, long timeout) {
    connection *conn;
    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;
    }

    /* 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);
        connClose(cs->conn);
        zfree(cs);
        dictDelete(server.migrate_cached_sockets,dictGetKey(de));
    }

    /* Create the socket */
    conn = server.tls_cluster ? connCreateTLS() : connCreateSocket();
    if (connBlockingConnect(conn, c->argv[1]->ptr, atoi(c->argv[2]->ptr), timeout)
            != C_OK) {
        addReplyError(c,"-IOERR error or timeout connecting to the client");
        connClose(conn);
        sdsfree(name);
        return NULL;
    }
    connEnableTcpNoDelay(conn);

    /* Add to the cache and return it to the caller. */
    cs = zmalloc(sizeof(*cs));
    cs->conn = conn;

    cs->last_dbid = -1;
    cs->last_use_time = server.unixtime;
    dictAdd(server.migrate_cached_sockets,name,cs);
    return cs;
}

/* Free a migrate cached connection. */
void migrateCloseSocket(robj *host, robj *port) {