Redis Cluster 的实现 - cluster 消息的接收和分包
/* 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;
ssize_t nread;
clusterMsg *hdr;
clusterLink *link = (clusterLink*) privdata;
int readlen, rcvbuflen;
REDIS_NOTUSED(el);
REDIS_NOTUSED(mask);
while(1) { /* Read as long as there is data to read. */
rcvbuflen = sdslen(link->rcvbuf);
if (rcvbuflen < 8) {
/* First, obtain the first 8 bytes to get the full message
* length. */
readlen = 8 - rcvbuflen;
} else {
// 已经知道了本条消息的长度
// 本块代码主要计算剩余还需读入的字节数(readlen)才是完整的消息
/* Finally read the full message. */
hdr = (clusterMsg*) link->rcvbuf;
if (rcvbuflen == 8) {
/* Perform some sanity check on the message signature
* and length. */
if (memcmp(hdr->sig,"RCmb",4) != 0 ||
ntohl(hdr->totlen) < CLUSTERMSG_MIN_LEN)
{
redisLog(REDIS_WARNING,
"Bad message length or signature received "
"from Cluster bus.");
handleLinkIOError(link);
return;
}
}
readlen = ntohl(hdr->totlen) - rcvbuflen;
if (readlen > sizeof(buf)) readlen = sizeof(buf);
}
// 读入本条消息记录的剩余 readlen 个字节的数据
// 因为这里的 fd 是非阻塞的，所以需要判断 EAGAIN
nread = read(fd,buf,readlen);
if (nread == -1 && errno == EAGAIN) return; /* No more data ready. */
if (nread rcvbuf = sdscatlen(link->rcvbuf,buf,nread);
hdr = (clusterMsg*) link->rcvbuf;
rcvbuflen += nread;
}
/* Total length obtained? Process this packet. */
if (rcvbuflen >= 8 && rcvbuflen == ntohl(hdr->totlen)) {
// 表明 link 上的 rcvbuf 已经是一个完整的 cluster 消息
// 下面开始处理此消息
if (clusterProcessPacket(link)) {
sdsfree(link->rcvbuf);
link->rcvbuf = sdsempty();
} else {
return; /* Link no longer valid. */
}
}
}
}
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