简单实现traceroute功能

原理：

  程序利用增加存活时间（TTL）值来实现其功能的。每当数据包经过一个路由器，其存活时间就会减1。当其存活时间是0时，主机便取消数据包，并传送一个ICMP TTL数据包给原数据包的发出者。程序发出的首3个数据包TTL值是1，之后3个是2，如此类推，它便得到一连串数据包路径。注意IP不保证每个数据包走的路径都一样。
  以下代码简单实现了traceroute的基本功能，可能会有些bug，没细测。

#include<stdio.h>#include<stdlib.h>#include<signal.h>#include<unistd.h>#include<netinet/ip_icmp.h>#include<netdb.h>#include<string.h>#include<sys/types.h>#include<sys/socket.h>#include<sys/time.h>#include<netinet/in.h>#include<arpa/inet.h>#include<pthread.h>struct sockaddr_in dst_addr;struct sockaddr_in recv_addr;char icmp_pkt[1024] = {0};char recv_pkt[1024] = {0};int bytes = 56, nsend_pkt = 0, nrecv_pkt = 0;int in_chksum(unsigned short *buf, int size);int pack(int send_pkt, pid_t pid);void send_traceroute(int sockfd, pid_t pid);int unpack(int sockfd, char *recv_pkt, struct sockaddr_in *src_addr, int size, pid_t pid);int recv_traceroutes(int sockfd, pid_t pid);void tv_sub(struct timeval *out,struct timeval *in);int main(int argc, char **argv){int size = 50 * 1024;int errno = -1;int tried_times = 30, i = 0;int ttl = 0, ret = 0;int sockfd = 0;struct in_addr ipv4_addr;struct hostent *ipv4_host;struct protoent *protocol = NULL;pid_t pid;if (argc < 2){printf("usage: ./ping <host>\n");return -1;}if ((protocol = getprotobyname("icmp")) == NULL){printf("unkown protocol\n");return -1;}pid = getpid();for(i = 0; i < tried_times; i++){ttl = i + 1;if ((sockfd = socket(AF_INET, SOCK_RAW, protocol->p_proto)) < 0){printf("socket fail, need root\n");return -1;}setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));setsockopt(sockfd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));setsockopt(sockfd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));memset(&dst_addr, 0, sizeof(dst_addr));dst_addr.sin_family = AF_INET;errno = inet_aton(argv[1], &ipv4_addr);if (errno == 0){ipv4_host = gethostbyname(argv[1]);if (NULL == ipv4_host){printf("connect: Invalid argument\n");return -1;}memcpy(&(dst_addr.sin_addr), ipv4_host->h_addr, sizeof(struct in_addr));}else{memcpy(&(dst_addr.sin_addr), &(ipv4_addr.s_addr), sizeof(struct in_addr));}printf("%d", i + 1);send_traceroute(sockfd, pid);ret = recv_traceroutes(sockfd, pid);close(sockfd);if(ret == 1){break;}}return 0;}int in_chksum(unsigned short *buf, int size){int nleft = size;int sum = 0;unsigned short *w = buf;unsigned short ans = 0;while(nleft > 1){sum += *w++;nleft -= 2;}if (nleft == 1){*(unsigned char *) (&ans) = *(unsigned char *)w;sum += ans;}sum = (sum >> 16) + (sum & 0xFFFF);sum += (sum >> 16);ans = ~sum;return ans;}int pack(int send_pkt, pid_t pid){struct icmp *pkt = (struct icmp *)icmp_pkt;pkt->icmp_type = ICMP_ECHO;pkt->icmp_cksum = 0;pkt->icmp_seq = htons(nsend_pkt);pkt->icmp_id = pid;pkt->icmp_cksum = in_chksum((unsigned short *)pkt, bytes + 8);return bytes + 8;}void send_traceroute(int sockfd, pid_t pid){int send_bytes = 0;int ret = -1;nsend_pkt++;send_bytes = pack(nsend_pkt, pid);ret = sendto(sockfd, icmp_pkt, send_bytes, 0, (struct sockaddr *)&dst_addr, sizeof(dst_addr));if (ret == -1){printf("send fail\n");sleep(1);return ;}}int unpack(int sockfd, char *recv_pkt, struct sockaddr_in *src_addr, int size, pid_t pid){struct iphdr *ip = NULL;int iphdrlen;struct icmp *icmp;struct timeval *tvsend;double rtt;struct sockaddr peer_addr;struct sockaddr_in *tmp_addr = NULL;size_t len = 0;memset(&peer_addr, 0, sizeof(struct sockaddr));ip = (struct iphdr *)recv_pkt;iphdrlen = ip->ihl<<2;icmp = (struct icmp *)(recv_pkt + iphdrlen);size -= iphdrlen;if (size < 8){printf("ICMP size is less than 8\n");return -1;}len = sizeof(peer_addr);if ((icmp->icmp_type == ICMP_TIME_EXCEEDED)){tmp_addr = (struct sockaddr_in *)src_addr;printf("%s\n", inet_ntoa(tmp_addr->sin_addr));}else if((icmp->icmp_type == ICMP_ECHOREPLY) && (icmp->icmp_id == pid)){tmp_addr = (struct sockaddr_in *)src_addr;printf("%s\n", inet_ntoa(tmp_addr->sin_addr));return 1;}return 0;}int recv_traceroutes(int sockfd, pid_t pid){fd_set rd_set;struct timeval time;time.tv_sec = 5;time.tv_usec = 0;int ret = 0, nread = 0,recv_len = 0;recv_len = sizeof(recv_addr);FD_ZERO(&rd_set);FD_SET(sockfd, &rd_set);ret = select(sockfd + 1, &rd_set, NULL, NULL, &time);if (ret <= 0){return -1;}else if (FD_ISSET(sockfd, &rd_set)){nread = recvfrom(sockfd, recv_pkt, sizeof(recv_pkt), 0, (struct sockaddr *)&recv_addr,(socklen_t *) &recv_len);if (nread < 0){return -1;}ret = unpack(sockfd, recv_pkt, &recv_addr, nread, pid);return ret;}}