set 命令主要用来设置key的值，可以增加一些选项，如过期时间，nx/xx/ex/px等。
在上节中，说到setnx已经被废弃，建议使用set中指定nx参数，
SET key value [NX] [XX] [KEEPTTL] [GET] [EX <seconds>] [PX <milliseconds>]
[EXAT <seconds-timestamp>][PXAT <milliseconds-timestamp>]
EXseconds -- 按秒指定过期时间PXmilliseconds -- 按毫秒指定过期时间EXATtimestamp-seconds -- 指定过期的具体时间点，单位秒。正整数PXATtimestamp-milliseconds -- 指定过期的具体时间点，单位毫秒.正整数NX-- 只有key不存在时，才设置值XX-- 只有key存在时，才设置值KEEPTTL-- 获取当前key的过期时间GET-- 返回旧值或是当前key不存在，如果不是字符串类型，会返回异常。
来看下相应的源码，setcommand 内部也会调用setGenericCommand
void setCommand(client *c) {robj *expire = NULL;// 默认是秒为单位int unit = UNIT_SECONDS;int flags = OBJ_NO_FLAGS;// 解析命令的参数flag、过期时间的单位、过期时间if (parseExtendedStringArgumentsOrReply(c,&flags,&unit,&expire,COMMAND_SET) != C_OK) {return;}// key的值c->argv[2] = tryObjectEncoding(c->argv[2]);// 调用通用方法setGenericCommand(c,flags,c->argv[1],c->argv[2],expire,unit,NULL,NULL);
}这里会调用parseExtendedStringArgumentsOrReply进行参数解析
int parseExtendedStringArgumentsOrReply(client *c, int *flags, int *unit, robj **expire, int command_type) {int j = command_type == COMMAND_GET ? 2 : 3;// 分析命令的参数for (; j < c->argc; j++) {char *opt = c->argv[j]->ptr;robj *next = (j == c->argc-1) ? NULL : c->argv[j+1];// 如果命令中包含选项nx,则增加OBJ_SET_NX标识，但要确认是非OBJ_SET_XX// 以下是处理相关的选项、并增加标识// 如ex\pxif ((opt[0] == 'n' || opt[0] == 'N') &&(opt[1] == 'x' || opt[1] == 'X') && opt[2] == '\0' &&!(*flags & OBJ_SET_XX) && (command_type == COMMAND_SET)){*flags |= OBJ_SET_NX;// 处理xx} else if ((opt[0] == 'x' || opt[0] == 'X') &&(opt[1] == 'x' || opt[1] == 'X') && opt[2] == '\0' &&!(*flags & OBJ_SET_NX) && (command_type == COMMAND_SET)){*flags |= OBJ_SET_XX;// 处理get} else if ((opt[0] == 'g' || opt[0] == 'G') &&(opt[1] == 'e' || opt[1] == 'E') &&(opt[2] == 't' || opt[2] == 'T') && opt[3] == '\0' &&(command_type == COMMAND_SET)){*flags |= OBJ_SET_GET;} else if (!strcasecmp(opt, "KEEPTTL") && !(*flags & OBJ_PERSIST) &&!(*flags & OBJ_EX) && !(*flags & OBJ_EXAT) &&!(*flags & OBJ_PX) && !(*flags & OBJ_PXAT) && (command_type == COMMAND_SET)){*flags |= OBJ_KEEPTTL;} else if (!strcasecmp(opt,"PERSIST") && (command_type == COMMAND_GET) &&!(*flags & OBJ_EX) && !(*flags & OBJ_EXAT) &&!(*flags & OBJ_PX) && !(*flags & OBJ_PXAT) &&!(*flags & OBJ_KEEPTTL)){*flags |= OBJ_PERSIST;} else if ((opt[0] == 'e' || opt[0] == 'E') &&(opt[1] == 'x' || opt[1] == 'X') && opt[2] == '\0' &&!(*flags & OBJ_KEEPTTL) && !(*flags & OBJ_PERSIST) &&!(*flags & OBJ_EXAT) && !(*flags & OBJ_PX) &&!(*flags & OBJ_PXAT) && next){*flags |= OBJ_EX;*expire = next;j++;} else if ((opt[0] == 'p' || opt[0] == 'P') &&(opt[1] == 'x' || opt[1] == 'X') && opt[2] == '\0' &&!(*flags & OBJ_KEEPTTL) && !(*flags & OBJ_PERSIST) &&!(*flags & OBJ_EX) && !(*flags & OBJ_EXAT) &&!(*flags & OBJ_PXAT) && next){*flags |= OBJ_PX;*unit = UNIT_MILLISECONDS;*expire = next;j++;} else if ((opt[0] == 'e' || opt[0] == 'E') &&(opt[1] == 'x' || opt[1] == 'X') &&(opt[2] == 'a' || opt[2] == 'A') &&(opt[3] == 't' || opt[3] == 'T') && opt[4] == '\0' &&!(*flags & OBJ_KEEPTTL) && !(*flags & OBJ_PERSIST) &&!(*flags & OBJ_EX) && !(*flags & OBJ_PX) &&!(*flags & OBJ_PXAT) && next){*flags |= OBJ_EXAT;*expire = next;j++;} else if ((opt[0] == 'p' || opt[0] == 'P') &&(opt[1] == 'x' || opt[1] == 'X') &&(opt[2] == 'a' || opt[2] == 'A') &&(opt[3] == 't' || opt[3] == 'T') && opt[4] == '\0' &&!(*flags & OBJ_KEEPTTL) && !(*flags & OBJ_PERSIST) &&!(*flags & OBJ_EX) && !(*flags & OBJ_EXAT) &&!(*flags & OBJ_PX) && next){*flags |= OBJ_PXAT;*unit = UNIT_MILLISECONDS;*expire = next;j++;} else {// 不支持的参数，直接返回异常addReplyErrorObject(c,shared.syntaxerr);return C_ERR;}}return C_OK;
}该函数主要解析以下几个参数：标识、过期时间单位、过期时间。
void setGenericCommand(client *c, int flags, robj *key, robj *val, robj *expire, int unit, robj *ok_reply, robj *abort_reply) {long long milliseconds = 0; /* initialized to avoid any harmness warning */int found = 0;int setkey_flags = 0;// if (expire && getExpireMillisecondsOrReply(c, expire, flags, unit, &milliseconds) != C_OK) {return;}// set 之前获取 key对应的旧值if (flags & OBJ_SET_GET) {if (getGenericCommand(c) == C_ERR) return;}// 按key进行查询found = (lookupKeyWrite(c->db,key) != NULL);// 如果是SetNx命令，并且找到，则直接返回if ((flags & OBJ_SET_NX && found) ||(flags & OBJ_SET_XX && !found)){if (!(flags & OBJ_SET_GET)) {addReply(c, abort_reply ? abort_reply : shared.null[c->resp]);}return;}setkey_flags |= (flags & OBJ_KEEPTTL) ? SETKEY_KEEPTTL : 0;setkey_flags |= found ? SETKEY_ALREADY_EXIST : SETKEY_DOESNT_EXIST;// 设置key的值setKey(c,c->db,key,val,setkey_flags);server.dirty++;// 空间占用事件notifyKeyspaceEvent(NOTIFY_STRING,"set",key,c->db->id);// 如果有设置过期时间if (expire) {// 将key加入到过期列表setExpire(c,c->db,key,milliseconds);/* Propagate as SET Key Value PXAT millisecond-timestamp if there is* EX/PX/EXAT/PXAT flag. */robj *milliseconds_obj = createStringObjectFromLongLong(milliseconds);rewriteClientCommandVector(c, 5, shared.set, key, val, shared.pxat, milliseconds_obj);decrRefCount(milliseconds_obj);notifyKeyspaceEvent(NOTIFY_GENERIC,"expire",key,c->db->id);}if (!(flags & OBJ_SET_GET)) {addReply(c, ok_reply ? ok_reply : shared.ok);}/* Propagate without the GET argument (Isn't needed if we had expire since in that case we completely re-written the command argv) */if ((flags & OBJ_SET_GET) && !expire) {int argc = 0;int j;robj **argv = zmalloc((c->argc-1)*sizeof(robj*));for (j=0; j < c->argc; j++) {char *a = c->argv[j]->ptr;/* Skip GET which may be repeated multiple times. */if (j >= 3 &&(a[0] == 'g' || a[0] == 'G') &&(a[1] == 'e' || a[1] == 'E') &&(a[2] == 't' || a[2] == 'T') && a[3] == '\0')continue;argv[argc++] = c->argv[j];incrRefCount(c->argv[j]);}replaceClientCommandVector(c, argc, argv);}
}setGenericCommand在前面的章节也有提到过，这里会处理的内容：过期时间的设置，key的value设置、内存的占用计算等。
