c - 原始套接字不发送

Question

我正在尝试编写一个原始套接字示例程序来澄清我对原始套接字的理解。我创建一个原始 UDP 套接字，然后调用 sendto。我的 sendto 成功了，但我从未看到对方收到的数据包。我没有任何接收方在运行，所以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。有错误请指出。

#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 header 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

Answer 1

我让 wireshark 在一个慢速系统上运行。数据包确实正在发送，但 Wireshark 只能在 6 分钟左右的间隔后显示它们。迁移到更快的系统会有所帮助。因此，我要自己关闭它。