icmp的程序（ping的实现）

code来源于《网络编程与分层协议设计》 chap7 ICMP协议程序设计

----没有理解，没有编译，只是敲了出来

ping.h

#define ICMP_ECHOREPLY 0
#define ICMP_ECHO 8

#define BUFSIZE 1500
#define DEFAULT_LEN 56

typedef unsigned char u8;
typedef unsigned short u16;
typedef unsigned int u32;

struct icmphdr{
u8 type;
u8 code;
u16 checksum;
union{
struct {
u16 id;
u16 sequence;
}echo;
u32 gateway;
struct
{
u16 unused;
u16 mtu;
}frag;
}un;
u8 data[0];
#define icmp_id un.echo.id
#define icmp_seq un.echo.sequence
};
#define ICMP_HSIZE sizeof(struct icmphdr)

struct iphdr{
u8 hlen:4, ver:4;
u8 tos;
u16 tot_len;
u16 id;
u16 frag_off;
u8 ttl;
u8 protocol;
u16 check;
u32 saddr;
u32 daddr;
};

char *hostname;
int datalen = DEFAULT_LEN;
char sendbuf[BUFSIZE];
char recvbuf[BUFSIZE];
int nsent;
int nrecv;
pid_t pid;
struct timeval recvtime;
int sockfd;
struct sockaddr_in dest;
struct sockaddr_in from;
struct sigaction act_alarm;
struct sigaction act_int;

void alarm_handler(int);
void int_handler(int);
void set_sighandler();
void send_ping();
void recv_reply();
u16 checksum(u8 *buf, int len);
int handle_pkt();
void get_statistics(int, int);
void bail(const char *)

ping.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netdb.h>
#include <errno.h>
#include <arpa/inet.h>
#include <signal.h>
#include <netinet/in.h>

#include "ping.h"

struct itimerval val_alarm={.it_interval.tv_sec = 1,
.it_interval.tv_usec = 0,
.it_value.tv_sec = 0,
.it_value.tv_usec = 1
};

int main(int argc, char **argv)
{
struct hostent *host;

if (argc < 2){
printf("Usuage: %s hostname ", argv[0]);
exit(1);
}

if (host = gethostbyname(argv[1]) == NULL){
perror("can not understand the host name");
exit(1);
}

hostname = argv[1];

memset(&dest, 0, sizeof(dest));
dest.sin_family = PF_INET;
dest.sin_port = ntohs(0);
dest.sin_addr = *(struct in_addr *)host->h_addr_list[0];

if ((sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP)) < 0){
perror("raw socket created error");
exit(1);
}

setuid(getuid());
pid = getpid();

set_sighandler();
printf("Ping %s(%s): %d bytes data in ICMP packets. ",
argv[1], inet_ntoa(dest.sin_addr), datalen);

if ((setitimer(ITIMER_REAL, &val_alarm, NULL)) == -1)
bail("setitimer fails.");

recv_reply();

return 0;
}

void send_ping(void)
{
struct icmphdr *icmp_hdr;
int len;

icmp_hdr = (struct icmphdr *)sendbuf;
icmp_hdr->type = ICMP_ECHO;
icmp_hdr->code = 0;
icmp_hdr->icmp_id = pid;
icmp_hdr->icmp_seq = nsent++;
memset(icmp_hdr->data, 0xff, datalen);

gettimeofday((struct timeval *)icmp_hdr->data, NULL);

len = ICMP_HSIZE + datalen;
icmp_hdr->checksum = 0;
icmp_hdr->checksum = checksum((u8 *)icmp_hdr, len);

sendto(sockfd, sendbuf, len, 0, (struct sockaddr *)&dest, sizeof(dest));
}

void recv_reply()
{
int n, len;
int errno;

n = nrecv = 0;
len = sizeof(from);

while (nrecv < 3){
if ((n = recvfrom(sockfd, recvbuf, sizeof(recvbuf), 0, (struct sockaddr *)&from, &len)) < 0){
if (errno == EINTR)
continue;
bail("recvfrom error");
}

gettimeofday(&recvtime, NULL);

if (handle_pkt())

continue;
nrecv++;
}

get_statistics(nsent, nrecv);
}

u16 checksum(u8 *buf, int len)
{
u32 sum = 0;
u16 *cbuf;

cbuf = (u16 *)buf;

while (len > 1){
sum += *cbuf++;
len -= 2;
}

if(len)
sum += *(u8 *)cbuf;

sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);

return -sum;
}

int handle_pkt()
{
struct iphdr *ip;
struct icmphdr *icmp;

int ip_hlen;
u16 ip_datalen;
double rtt;
struct timeval *sendtime;

ip = (struct iphdr *)recvbuf;

ip_hlen = ip->hlen << 2;
ip_datalen = ntohs(ip->tot_len) - ip_hlen;

icmp = (struct icmphdr *)(recvbuf + ip_hlen);

if (checksum(u8 *)icmp, ip_datalen)
return -1;

if(icmp->icmp_id != pid)
return -1;

sendtime = (struct timeval *)icmp->data;
rtt = ((&recvtime)->tv_sec - sendtime->tv_sec)*1000 + ((&recvtime)->tv_usec - sendtime->tv_usec)/1000.0;

printf("%d bytes from %s: icmp_seq = %u ttl=%d rtt=%.3f ms ",
ip_datalen,
inet_ntoa(from.sin_addr),
icmp->icmp_seq,
ip->ttl,
rtt);

return 0;
}

void set_sighandler()
{
act_alarm.sa_handler = alarm_handler;
if (sigaction(SIGALRM, &act_alarm, NULL) == -1)
bail("SIGALRM handler setting fails.");

act_int.sa_handler = int_handler;
if (sigaction(SIGINT, &act_int, NULL) == -1)
bail("SIGINT handler setting fails.");
}

void get_statistics(int nsent, int nrecv)
{
printf("---%s ping statistics --- ", inet_ntoa(dest.sin_addr));
printf("%d packets transmitted, %d received, %0.0f%%" "packet loss ",
nsent, nrecv, 1.0*(nsent - nrecv)/nsent*100);
}

void bail(const char *on_what)
{
fputs(strerror(errno), stderr);
fputs(":", stderr);
fputs(on_what, stderr);
fputc(' ', stderr);
exit(1);
}

void int_handler(int sig)
{
get_statistics(nsent, nrecv);
close(sockfd);
exit(1);
}

void alarm_handler(int signo)
{
send_ping();
}