收到UDP數(shù)據(jù)包后，我需要用他用來向其發(fā)送數(shù)據(jù)包的地址來響應(yīng)發(fā)送方。該recvfrom調(diào)用使我可以獲取發(fā)送方的地址，但是如何獲取接收到的數(shù)據(jù)包的目標(biāo)地址，該地址應(yīng)與本地主機接口之一的地址匹配？
3 回答
BIG陽
TA貢獻1859條經(jīng)驗 獲得超6個贊
我構(gòu)建了一個示例，該示例提取了源地址，目標(biāo)地址和接口地址。為簡便起見，沒有提供錯誤檢查。
// sock is bound AF_INET socket, usually SOCK_DGRAM
// include struct in_pktinfo in the message "ancilliary" control data
setsockopt(sock, IPPROTO_IP, IP_PKTINFO, &opt, sizeof(opt));
// the control data is dumped here
char cmbuf[0x100];
// the remote/source sockaddr is put here
struct sockaddr_in peeraddr;
// if you want access to the data you need to init the msg_iovec fields
struct msghdr mh = {
.msg_name = &peeraddr,
.msg_namelen = sizeof(peeraddr),
.msg_control = cmbuf,
.msg_controllen = sizeof(cmbuf),
};
recvmsg(sock, &mh, 0);
for ( // iterate through all the control headers
struct cmsghdr *cmsg = CMSG_FIRSTHDR(&mh);
cmsg != NULL;
cmsg = CMSG_NXTHDR(&mh, cmsg))
{
// ignore the control headers that don't match what we want
if (cmsg->cmsg_level != IPPROTO_IP ||
cmsg->cmsg_type != IP_PKTINFO)
{
continue;
}
struct in_pktinfo *pi = CMSG_DATA(cmsg);
// at this point, peeraddr is the source sockaddr
// pi->ipi_spec_dst is the destination in_addr
// pi->ipi_addr is the receiving interface in_addr
}
守著一只汪
TA貢獻1872條經(jīng)驗 獲得超4個贊
為了提供O（1）查找，您需要將輔助控制結(jié)構(gòu)打包到提供O（1）查找的數(shù)據(jù)容器中。填充該結(jié)構(gòu)的數(shù)量至少為輔助控制消息的O（n）。您不必?fù)?dān)心要查找的控制消息的復(fù)雜性：總是只有少數(shù)幾個，并且只有您請求的那些。代您還需要零內(nèi)存管理。這是微不足道的開銷。
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