/* This file implements keyspace events notification via Pub/Sub and
 * described at https://redis.io/topics/notifications. */
这个文件通过Pub/Sub实现键空消息通知事件，具体的描述可以参见地址https://redis.io/topics/notifications. 
/* Turn a string representing notification classes into an integer
 * representing notification classes flags xored.
将字符串表示的通知类型转化为用整数表示的通知类型 标志的异或
 * The function returns -1 if the input contains characters not mapping to
 * any class. */
函数返回-1，如果输入的字符串中包含找不到映射到任何类型
int keyspaceEventsStringToFlags(char *classes) {
    char *p = classes;
    int c, flags = 0;

    while((c = *p++) != '\0') {
        switch(c) {
        case 'A': flags |= NOTIFY_ALL; break;  全部
        case 'g': flags |= NOTIFY_GENERIC; break; 一般情况
        case '$': flags |= NOTIFY_STRING; break; 字符串
        case 'l': flags |= NOTIFY_LIST; break; 链表
        case 's': flags |= NOTIFY_SET; break; 集合
        case 'h': flags |= NOTIFY_HASH; break; 哈希
        case 'z': flags |= NOTIFY_ZSET; break; 有序集
        case 'x': flags |= NOTIFY_EXPIRED; break; 过期
        case 'e': flags |= NOTIFY_EVICTED; break; 淘汰
        case 'K': flags |= NOTIFY_KEYSPACE; break; 操作键相关事件
        case 'E': flags |= NOTIFY_KEYEVENT; break; 键相关事件
        case 't': flags |= NOTIFY_STREAM; break; 流
        case 'm': flags |= NOTIFY_KEY_MISS; break; 不命中
        default: return -1; 不能识别的情况
        }
    }
    return flags; 返回对应的整数异或表示标志
}

/* This function does exactly the revese of the function above: it gets
 * as input an integer with the xored flags and returns a string representing
 * the selected classes. The string returned is an sds string that needs to
 * be released with sdsfree(). */
这个函数与上面的函数恰好相反：它获取一个带有异或标志的整数作为输入，
并返回一个用用来表示所选类型的字符串。返回的字符串是sds字符串，需要用函数sdsfree释放
sds keyspaceEventsFlagsToString(int flags) {
    sds res;

    res = sdsempty(); 创建新sds字符串
    if ((flags & NOTIFY_ALL) == NOTIFY_ALL) { 全部事件
        res = sdscatlen(res,"A",1);
    } else {
        if (flags & NOTIFY_GENERIC) res = sdscatlen(res,"g",1); 一般
        if (flags & NOTIFY_STRING) res = sdscatlen(res,"$",1);  字符串
        if (flags & NOTIFY_LIST) res = sdscatlen(res,"l",1); 链表
        if (flags & NOTIFY_SET) res = sdscatlen(res,"s",1); 集合
        if (flags & NOTIFY_HASH) res = sdscatlen(res,"h",1); 哈希
        if (flags & NOTIFY_ZSET) res = sdscatlen(res,"z",1); 有序集
        if (flags & NOTIFY_EXPIRED) res = sdscatlen(res,"x",1); 过期
        if (flags & NOTIFY_EVICTED) res = sdscatlen(res,"e",1); 淘汰
        if (flags & NOTIFY_STREAM) res = sdscatlen(res,"t",1); 流
    }
    if (flags & NOTIFY_KEYSPACE) res = sdscatlen(res,"K",1); 操作键事件
    if (flags & NOTIFY_KEYEVENT) res = sdscatlen(res,"E",1); 键本身事件
    if (flags & NOTIFY_KEY_MISS) res = sdscatlen(res,"m",1); 键不命中
    return res;
}

/* The API provided to the rest of the Redis core is a simple function:
提供给redis数据库核心的其余部分是一个简单的函数：
 * notifyKeyspaceEvent(char *event, robj *key, int dbid);
 *
 * 'event' is a C string representing the event name. event是一个C类型的字符串表示事件名
 * 'key' is a Redis object representing the key name. key 是redis对象表示的键名
 * 'dbid' is the database ID where the key lives.  */ dbid是键所在的数据库ID
void notifyKeyspaceEvent(int type, char *event, robj *key, int dbid) {
    sds chan;
    robj *chanobj, *eventobj;
    int len = -1;
    char buf[24];

    /* If any modules are interested in events, notify the module system now.
     * This bypasses the notifications configuration, but the module engine
     * will only call event subscribers if the event type matches the types
     * they are interested in. */
如果任何模块对事件感兴趣，立刻通知模块系统。
这个绕过了通知事件的配置，但是模块的引擎只调用事件订阅者，当事件类型匹配上了他们（模块）感兴趣的类型
     moduleNotifyKeyspaceEvent(type, event, key, dbid); 通知订阅的模块

    /* If notifications for this class of events are off, return ASAP. */
    如果为这类时间的通知已经关闭，尽快返回
    if (!(server.notify_keyspace_events & type)) return;

    eventobj = createStringObject(event,strlen(event)); 为事件创建字符串对象

    /* __keyspace@<db>__:<key> <event> notifications. */  格式
    if (server.notify_keyspace_events & NOTIFY_KEYSPACE) { 操作键事件
        chan = sdsnewlen("__keyspace@",11);
        len = ll2string(buf,sizeof(buf),dbid);
        chan = sdscatlen(chan, buf, len);
        chan = sdscatlen(chan, "__:", 3); 按照上述格式拼接
        chan = sdscatsds(chan, key->ptr); 到<key>位置的字符串
        chanobj = createObject(OBJ_STRING, chan);
        pubsubPublishMessage(chanobj, eventobj); 向订阅的客户端传递消息
        decrRefCount(chanobj);
    }

    /* __keyevent@<db>__:<event> <key> notifications. */ 格式
    if (server.notify_keyspace_events & NOTIFY_KEYEVENT) { 键本身事件
        chan = sdsnewlen("__keyevent@",11);
        if (len == -1) len = ll2string(buf,sizeof(buf),dbid);
        chan = sdscatlen(chan, buf, len);
        chan = sdscatlen(chan, "__:", 3);
        chan = sdscatsds(chan, eventobj->ptr);
        chanobj = createObject(OBJ_STRING, chan);
        pubsubPublishMessage(chanobj, key); 向订阅的客户端传递消息
        decrRefCount(chanobj);
    }
    decrRefCount(eventobj);
}