Solaris 10 -- 从 recvmsg() 的 UDP 多播数据包中获取 IP 源地址

Question

我有创建 UDP 套接字来接收多播数据包的项目代码。该代码可移植到 Linux 和 Solaris 操作系统。我的项目的一个扩展是在使用 recvmsg() 函数时检索 UDP 数据包的源 IP 地址。我曾就此事询问过一位专家，她提到 Linux 似乎能够提供源 IP 地址，但 Solaris 在使用 recvmsg() 函数时可能无法提供。所以我在这里提出问题，我能否在 Solaris 10 上使用 recvmsg() 检索源 IP 地址？

操作系统：Solaris 10、Sunstudio 12 cc（无 U1 或 U2）。 代码库：C/C++

//Socket initially opened with the following options from a different function.
// This connects the socket to receive multicast:
setsockopt(data->fd, IPPROTO_IP, IP_ADD_SOURCE_MEMBERSHIP,
    (char *)&mregs, sizeof(mregs) ) < 0)

//A different function performs an infinite loop reading from the socket:

struct iovec vector;
vector.iov_base = buf;     //passed in param
vector.iov_len = len;      //passed in param
struct msghdr msg;
char    caddr[100] ;
msg.msg_name =  caddr;
msg.msg_namelen = 100;
msg.msg_iov = &vector;
msg.msg_iovlen = 1;
int flags = 0;

char controlBuffer[1024];
msg.msg_control = controlBuffer;
msg.msg_controllen = 1024;

bytes = ::recvmsg(data->fd, &msg, flags);

//removed error checking    

struct cmsghdr *cmsg;
struct in_pktinfo *dest_ip_ptr;
rrcp_u32_t dest_ip = 0;
cmsg = CMSG_FIRSTHDR(&msg);
for ( cmsg = CMSG_FIRSTHDR(&msg);
    cmsg != NULL;
    cmsg = CMSG_NXTHDR( &msg, cmsg ) )
{
    //if ( cmsg->cmsg_type == IPPROTO_IP && cmsg->cmsg_level == IP_PKTINFO )
    {
#ifdef Linux
        struct in_pktinfo *dest_ip_ptr = (struct in_pktinfo*)CMSG_DATA(cmsg);
        dest_ip = dest_ip_ptr->ipi_addr.s_addr;
#else
        //in_addr only has 1 address
        struct in_addr * dest_ip_ptr = (struct in_addr *)CMSG_DATA(cmsg);
        dest_ip = dest_ip_ptr->_S_un._S_addr;
#endif
    }
}
if( ipaddr ) 
    ipaddr->IP = dest_ip;

//according to the Linux article mentioned below, the caddr should have the source
//socket address.  In my case, the caddr field is not filled with any coherent data,
//so this does not seem to be the source address.  Then again, "source socket" could
//be the interface IP on the local machine, which isn't what I need.

我还看到了以下文章，但它们似乎没有回答我的问题： Get destination address of a received UDP packet，解决方法：Get destination address of a received UDP packet

Answer 1

有两个问题：一是你没有在任何地方使用caddr，而且你没有说它是什么，所以很难帮助你；另一个（可能是您遇到的问题）是您从recvmsg 获得的地址不是字符串。

msg.msg_name 应该指向 struct sockaddr_in，msg.msg_namelen 应该指向 sizeof(struct sockaddr_in)。然后，您可以从中获取地址。