我使用BSD套接字构建不需要root权限(如tracepath的)一个先进的路由跟踪程序。 使用UDP和绑定套接字,我呼吁:
recvmsg(socket, header, MSG_ERRQUEUE)
我收到关于先前发送的数据包触发了所谓ICMP通知的信息。 你知道,如果有可能访问ICMP有效载荷(这应该是先前发送的数据包)?
我从recvmsg手册页阅读:
[..] The payload of the original packet that caused the error
is passed as normal data via msg_iovec. [..]
但我无法找到任何有用那里,它只是似乎随机数据(我使用Wireshark的交叉检查数据)。
您可以使用此示例代码来检查你有哪些ICMP错误和处理它(样品含有一些评论和链接):
#define BUFFER_MAX_SIZE 1024
int on = 1;
/* Set the option, so we can receive errors */
setsockopt(socket, SOL_IP, IP_RECVERR,(char*)&on, sizeof(on));
/* Other code here */
/* .... */
/* Handle receving ICMP Errors */
int return_status;
char buffer[BUFFER_MAX_SIZE];
struct iovec iov; /* Data array */
struct msghdr msg; /* Message header */
struct cmsghdr *cmsg; /* Control related data */
struct sock_extended_err *sock_err; /* Struct describing the error */
struct icmphdr icmph; /* ICMP header */
struct sockaddr_in remote; /* Our socket */
for (;;)
{
iov.iov_base = &icmph;
iov.iov_len = sizeof(icmph);
msg.msg_name = (void*)&remote;
msg.msg_namelen = sizeof(remote);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_flags = 0;
msg.msg_control = buffer;
msg.msg_controllen = sizeof(buffer);
/* Receiving errors flog is set */
return_status = recvmsg(socket, &msg, MSG_ERRQUEUE);
if (return_status < 0)
continue;
/* Control messages are always accessed via some macros
* http://www.kernel.org/doc/man-pages/online/pages/man3/cmsg.3.html
*/
for (cmsg = CMSG_FIRSTHDR(&msg);cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg))
{
/* Ip level */
if (cmsg->cmsg_level == SOL_IP)
{
/* We received an error */
if (cmsg->cmsg_type == IP_RECVERR)
{
fprintf(stderror, "We got IP_RECVERR message\n");
sock_err = (struct sock_extended_err*)CMSG_DATA(cmsg);
if (sock_err)
{
/* We are intrested in ICMP errors */
if (sock_err->ee_origin == SO_EE_ORIGIN_ICMP)
{
/* Handle ICMP errors types */
switch (sock_err->ee_type)
{
case ICMP_NET_UNREACH:
/* Hendle this error */
fprintf(stderror, "Network Unreachable Error\n");
break;
case ICMP_HOST_UNREACH:
/* Hendle this error */
fprintf(stderror, "Host Unreachable Error\n");
break;
/* Handle all other cases. Find more errors :
* http://lxr.linux.no/linux+v3.5/include/linux/icmp.h#L39
*/
}
}
}
}
}
}
}