我正在尝试编写一个示例原始套接字程序来清除我对原始套接字的理解。我创建了一个原始 UDP 套接字，然后调用 sendto。我的 sendto 成功了，但我从来没有看到对方收到的数据包。我没有运行任何接收端，因此我依赖于在发送方和接收方上运行的 Wireshark。我在这里粘贴代码片段。请指出任何错误。
#include<stdio.h>
#include<stdlib.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<string.h>
#include "protHeaders.x"
#include "gen.h"
U16 csum(U16* buf, S32 nwords)
{
U32 sum;
for (sum = 0; nwords > 0; nwords--)
sum += *buf++;
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
return ~sum;
}/*csum*/
int main(int argc,char** argv)
{
U8 datagram[MAX_IPPACKET];
U8 udpPayLoad[MAX_UDPPAYLOAD];
CustIpHeader* ipH;
CustUdpHeader* udpH;
struct sockaddr_in sin;
S32 sockFd;
S32 one = 1;
const S32* val = &one;
ipH = (CustIpHeader *)datagram;
udpH = (CustUdpHeader *)(datagram + sizeof(CustIpHeader));
memset(datagram,0,sizeof(datagram));
memset(udpPayLoad,0,sizeof(udpPayLoad));
memset(&sin,0,sizeof(struct sockaddr_in));
strcpy(udpPayLoad,"<<<<Aditya>>>>");
sin.sin_family = AF_INET;
sin.sin_port = htons(atoi(argv[4]));
/* fill the Ip header */
ipH->ip_hl = 5;
ipH->ip_v = 4;
ipH->ip_tos = 0;
ipH->ip_len = sizeof(CustIpHeader) + sizeof(CustUdpHeader) + strlen(udpPayLoad);
ipH->ip_id = htonl(54321);
ipH->ip_off = 0;
ipH->ip_p = 17;
ipH->ip_ttl = 65;
ipH->ip_sum = 0;
ipH->ip_src.s_addr = inet_addr(argv[1]);
ipH->ip_dst.s_addr = inet_addr(argv[3]);
/* fill the Udp header */
udpH->uh_sport = htons(atoi(argv[2]));
udpH->uh_dport = htons(atoi(argv[4]));
udpH->uh_len = sizeof(CustUdpHeader) + strlen(udpPayLoad);
udpH->uh_check = 0;
printf("Checksum = %u\n",udpH->uh_check);
/* copy udpPayLoad */
strcpy(datagram+sizeof(CustIpHeader)+sizeof(CustUdpHeader),udpPayLoad);
#if 1
printf("Datagram %p,UdpPayload %p\n",(void *)datagram,(void *)datagram+sizeof(CustIpHeader)+sizeof(CustUdpHeader));
printf("IpHeader %p, UdpHeader %p\n",(void *)ipH,udpH);
#endif
/* fill in the checksum */
ipH->ip_sum = csum((U16 *)datagram,ipH->ip_len >> 1);
printf("Checksum = %u\n",ipH->ip_sum);
if ((sockFd = socket(PF_INET,SOCK_RAW,IPPROTO_UDP)) < 0)
{
perror("socket:create");
RETURN(RFAILED);
}
/* doing the IP_HDRINCL call */
if (setsockopt(sockFd,IPPROTO_IP,IP_HDRINCL,val,sizeof(one)) < 0)
{
perror("Client:setsockopt");
}
while(1)
{
if ( sendto(sockFd,
datagram,
ipH->ip_len,
0,
(struct sockaddr *)&sin,
sizeof (sin)) < 0)
{ perror("Client:sendto"); }
else
printf(".");
}
RETURN(ROK);
}
IP 和 UDP 标头是：
typedef struct _ipheader
{
U8 ip_hl:4,ip_v:4; /* ip_hl: the ip header length in 32bit octets.
* ip_v : ip version (always 4 for our case).
*/
U8 ip_tos; /* reliability of the service. 0x00 is Normal */
U16 ip_len; /* totoal length including ip header,icmp/tcp/udp header
* and payload size in bytes
*/
U16 ip_id; /* sequence no. used for reassembly of fragmented IP packets */
U16 ip_off; /* the fragment offset used for reassembly of fragmented packets */
U16 ip_p; /* the transport layer protocol. can be tcp (6), udp(17) */
U8 ip_ttl; /* time to live */
U16 ip_sum; /* the datagram checksum for the whole IP packet */
struct in_addr ip_src; /* the source IP address, converted to a long format */
struct in_addr ip_dst; /* the desitnation IP address, converted to a long format */
}CustIpHeader; /* total ip header length: 20 bytes */
typedef struct _udpheader
{
U16 uh_sport; /* The source port that a client bind()s to */
U16 uh_dport; /* The desination port that a server bind()s to*/
U16 uh_len; /* The length of udp header and payload data in bytes */
U16 uh_check; /* The checksum of header and data */
}CustUdpHeader; /* total udp header length: 8 bytes (=64 bits) */
我以 root 用户身份运行，所以权限不是问题。
语言：C
操作系统：Linux