用raw socket实现一个ICMP_ECHO的功能，出错了！

[zhoufanking]

下面这段代码是发送一个ICMP_ECHO然后等待对方的ICMP_REPLY,我在本机测试时可以ping通，能接收到ICMP_REPLY，但ping其他主机时，就会一直死等在recvfrom上，请大家帮忙看看是什么问题阿！另外我想问问，在自己构造ip头，icmp头时哪些字段需要进行字节顺序转换？

／*                 main.c                         */
#include "errexit.h"
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <string.h>
#include <errno.h>
#include <linux/icmp.h>
#include <linux/ip.h>
#include <unistd.h>

#define BUFFLENGTH    4096

void Usage()__attribute__((noreturn));
unsigned short in_cksum(unsigned short *addr, int len);

char *ProgName = "rping";
char *myip = "192.168.1.3";


int main( int argc, char * argv[])
{
    if( argc != 2 )
        Usage();
   
    struct sockaddr_in to, from;
    char *buffer[BUFFLENGTH];
    char *recvbuffer[BUFFLENGTH];
    struct icmphdr *icmphd;
    struct iphdr *iphd;
    int res;
    int tosock;
    int fromlen = sizeof(struct sockaddr);
    int one = 1;
    int *ptr_one = &one;
   
    to.sin_family = AF_INET;
    res = inet_aton(argv[1],&to.sin_addr);
    if( res < 0 )
        errexit("invalid address!\n%s\n",strerror(errno));
   
    memset(buffer,0x00,BUFFLENGTH);
    memset(recvbuffer,0x00,BUFFLENGTH);
   
    /*
     * create a socket to send out the icmp echo message
     */
    tosock = socket(AF_INET,SOCK_RAW,IPPROTO_ICMP);
    if(tosock<0)
        errexit("create socket failed!\n%s\n",strerror(errno));
   
    res = setsockopt(tosock, IPPROTO_IP, IP_HDRINCL,ptr_one, sizeof(one));
    if(res < 0)
        errexit("setsockopt failed!\n%s\n",strerror(errno));
    /*
     * construct the ip header
     */
    iphd = ( struct iphdr *)buffer;
    iphd->version = 4;
    iphd->ihl = 5;
    iphd->tos = 0;
    iphd->tot_len = 84;
    iphd->id = getpid() & 0xffff;
    iphd->frag_off =0;
    iphd->ttl = 32;
    iphd->protocol =IPPROTO_ICMP;
    iphd->check = 0;
    iphd->saddr = inet_addr(myip);
    iphd->daddr = to.sin_addr.s_addr;
        
    /*
     * construct the icmp header
     */
    icmphd = (struct icmphdr *)(iphd+1);
    icmphd->type = ICMP_ECHO;
    icmphd->code = 5;
    icmphd->checksum = in_cksum((unsigned short *)icmphd,64);
    icmphd->un.echo.id = (short)(getpid()&0xffff);
    icmphd->un.echo.sequence = 1;

    while(1)
    {
        res = sendto(tosock,(void *)buffer,84,0,(struct sockaddr*)&to,sizeof(struct sockaddr));
        if(res == -1)
            errexit("rping error occured!\n%s\n",strerror(errno));
        else if(res == 84)
            break;
        else if (errno == EINTR)
            continue;
    }
   
    printf("done,%d bytes sent.\n",res);
   
    char *addr = (char *)&(iphd->saddr);        
    printf("src ip address is :%d.%d.%d.%d\n",
                    addr[0]&0xff,addr[1]&0xff,addr[2]&0xff,addr[3]&0xff);
   
    while(1)
    {
        res = recvfrom(tosock,recvbuffer,BUFFLENGTH,0,(struct sockaddr*)&from,(socklen_t *)&fromlen);
        if(res == -1)
            errexit("rping recv failed!\n%s\n",strerror(errno));
        else if( errno == EINTR)
            continue;
        
        iphd = (struct iphdr *)recvbuffer;
   
        char *saddr = (char *)&(iphd->saddr);
        
        icmphd = (struct icmphdr*)(iphd+1);
        if(icmphd->type == ICMP_ECHO)
            continue;
        if(icmphd->type == ICMP_ECHOREPLY)
        {
            printf("ping %d bytes received,seq = %d,code = %d\n",
                    res,
                    icmphd->un.echo.sequence & 0xffff,
                    icmphd->code & 0xff);
            printf("src ip address is :%d.%d.%d.%d\n",
                    saddr[0]&0xff,saddr[1]&0xff,saddr[2]&0xff,saddr[3]&0xff);
            break;
        
        }
    }
    return 0;
}

void Usage()
{
    printf("%s dstIPaddress\n",ProgName);
    exit(-1);
}

unsigned short in_cksum(unsigned short *addr, int len)
{
    register int nleft = len;
    register unsigned short *w = addr;
    register unsigned short answer;
    register int sum = 0;
   
    while(nleft > 1)
    {
        sum+=*w++;
        nleft -= 2;
    }
    /* mop up and odd byte, if necessary */
    if(nleft == 1)
    {
        unsigned short u = 0;
        
        *(unsigned short *)(&u) = *(unsigned short *)w;
        sum +=u;
    }
   
    sum = ( sum >> 16 ) + (sum & 0xffff)
    sum +=(sum>>16);
    answer = ~sum;     
    return ( answer );
   
}
/*                      errexit.h            */
#ifndef ERREXIT_H
#define ERREXIT_H

#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>

extern void errexit(const char *fmt,...)__attribute__((format(printf,1,2)));

#endif
/*                        errexit.c             */
#include "errexit.h"

void errexit(const char * fmt,...){
    va_list vp;
    va_start(vp,fmt);
    vfprintf(stderr,fmt,vp);
    va_end(vp);
   
    exit(-1);
}

[zhoufanking]

我用TCPDUMP看了一下，对方收到了我发送的echo request但没有发出echo reply.这是怎么回事呢，怎么解决阿？

[zhoufanking]

终于通拉！感谢两位！尤其是blackbillow！
定义buffer时笔误了，checksum放错了地方！顺便再问一下，这两个错误未更正之前为什么也能ping通自己呢？
另：icmp->code不会被检查到，所以任何值都无所谓，这个字段可以用来做些非法的事：）

[快乐田伯光]

你测试的另外一台机器是否允许ping?

[快乐田伯光]

你直接用系统自带的ping工具测试一下是你程序的问题还是你程序的问题先

[zhoufanking]

我用系统自带的ping能ping通对方，但用我的就不行。我在对发机子上用tcpdump也抓到了我发的ECHO,为什么它不给我回呢？

[快乐田伯光]

那就比较一下系统自带工具发的ping包跟你发的ping包有什么不同

[zhoufanking]

我把用自己写的一个程序将抓出来的包比较了一下，我发出的包，和系统自带的ping发出的包好像没什么区别阿。我等下再对比一下。感谢楼上，我试完了再把结果贴上。

[blackbillow]

/*
     * construct the icmp header
     */
    icmphd = (struct icmphdr *)(iphd+1);
    icmphd->type = ICMP_ECHO;
    icmphd->code = 5;
    icmphd->checksum = in_cksum((unsigned short *)icmphd,64);
    icmphd->un.echo.id = (short)(getpid()&0xffff);
    icmphd->un.echo.sequence = 1;

这里有两个错误：
1 icmphd->code = 5; 这里应该为0，echo request类型只有code 0

2 应该在最后计算checksum
正确的应该是这样：

/*
     * construct the icmp header
     */
    icmphd = (struct icmphdr *)(iphd+1);
    icmphd->type = ICMP_ECHO;
    icmphd->code = 0;
    icmphd->un.echo.id = (short)(getpid()&0xffff);
    icmphd->un.echo.sequence = 1;
    icmphd->checksum = in_cksum((unsigned short *)icmphd,64);

还有
char *buffer[BUFFLENGTH];
char *recvbuffer[BUFFLENGTH];
应该是
char buffer[BUFFLENGTH];
char recvbuffer[BUFFLENGTH];
才对把