首页 > 代码库 > ping的实现（原始套接字系列三）
ping的实现（原始套接字系列三）
使用Raw Socket实现Ping
仅仅采用ICMP.DLL并不能完全实现ICMP灵活多变的各类报文，只有使用Raw Socket才是ICMP的终极解决之道。
使用Raw Socket发送ICMP报文前，我们要完全依靠自己的代码组装报文：
| //功能：初始化ICMP的报头, 给data部分填充数据, 计算校验和 void init_ping_packet(ICMPHeader *icmp_hdr, int packet_size, int seq_no) { //设置ICMP报头字段 icmp_hdr->type = ICMP_ECHO_REQUEST; icmp_hdr->code = 0; icmp_hdr->checksum = 0; icmp_hdr->id = (unsigned short)GetCurrentProcessId(); icmp_hdr->seq = seq_no; icmp_hdr->timestamp = GetTickCount(); // 填充data域 const unsigned long int deadmeat = 0xDEADBEEF; char *datapart = (char*)icmp_hdr + sizeof(ICMPHeader); int bytes_left = packet_size - sizeof(ICMPHeader); while (bytes_left > 0) { memcpy(datapart, &deadmeat, min(int(sizeof(deadmeat)), bytes_left)); bytes_left -= sizeof(deadmeat); datapart += sizeof(deadmeat); } // 计算校验和 icmp_hdr->checksum = ip_checksum((unsigned short*)icmp_hdr, packet_size); } |
计算校验和（Checksum）的函数为：
| //功能：计算ICMP包的校验和 unsigned short ip_checksum(unsigned short *buffer, int size) { unsigned long cksum = 0; // 将所有的16数相加 while (size > 1) { cksum += *buffer++; size -= sizeof(unsigned short); } if (size) //加上最后一个BYTE { cksum += *(unsigned char*)buffer; } //和的前16位和后16位相加 cksum = (cksum >> 16) + (cksum &0xffff); cksum += (cksum >> 16); return (unsigned short)(~cksum); } |
在真正发送Ping报文前，需要先初始化Raw Socket：
| // 功能：初始化RAW Socket, 设置ttl, 初始化目标地址 // 返回值：<0 失败 int setup_for_ping(char *host, int ttl, SOCKET &sd, sockaddr_in &dest) { // 创建原始套接字 sd = WSASocket(AF_INET, SOCK_RAW, IPPROTO_ICMP, 0, 0, 0); if (sd == INVALID_SOCKET) { cerr << "Failed to create raw socket: " << WSAGetLastError() << endl; return - 1; } if (setsockopt(sd, IPPROTO_IP, IP_TTL, (const char*) &ttl, sizeof(ttl)) ==SOCKET_ERROR) { cerr << "TTL setsockopt failed: " << WSAGetLastError() << endl; return - 1; } // 初始化目标主机信息块 memset(&dest, 0, sizeof(dest)); // 将第1个参数转换为目标IP地址 unsigned int addr = inet_addr(host); if (addr != INADDR_NONE) { // 为IP地址 dest.sin_addr.s_addr = addr; dest.sin_family = AF_INET; } else { // 非IP地址，进行主机名和IP地址的转换 hostent *hp = gethostbyname(host); if (hp != 0) { // 查找主机名对应的IP地址 memcpy(&(dest.sin_addr), hp->h_addr, hp->h_length); dest.sin_family = hp->h_addrtype; } else { // 不能识别的主机名 cerr << "Failed to resolve " << host << endl; return - 1; } } return 0; } |
下面可以利用Raw Socket发送生成的ICMP报文：
| //功能：发送生成的ICMP包 //返回值：<0 发送失败 int send_ping(SOCKET sd, const sockaddr_in &dest, ICMPHeader *send_buf, int packet_size) { // 发送send_buf缓冲区中的报文 cout << "Sending " << packet_size << " bytes to " << inet_ntoa(dest.sin_addr) << "..." << flush; int bwrote = sendto(sd, (char*)send_buf, packet_size, 0, (sockaddr*) &dest,sizeof(dest)); if (bwrote == SOCKET_ERROR) { cerr << "send failed: " << WSAGetLastError() << endl; return - 1; } else if (bwrote < packet_size) { cout << "sent " << bwrote << " bytes..." << flush; } return 0; } |
发送Ping报文后，我们需要接收Ping回复ICMP报文：
| //功能：接收Ping回复 //返回值： <0 接收失败 int recv_ping(SOCKET sd, sockaddr_in &source, IPHeader *recv_buf, int packet_size) { // 等待Ping回复 int fromlen = sizeof(source); int bread = recvfrom(sd, (char*)recv_buf, packet_size + sizeof(IPHeader), 0,(sockaddr*) &source, &fromlen); if (bread == SOCKET_ERROR) { cerr << "read failed: "; if (WSAGetLastError() == WSAEMSGSIZE) { cerr << "buffer too small" << endl; } else { cerr << "error #" << WSAGetLastError() << endl; } return - 1; } return 0; } |
并使用如下函数对接收到的报文进行解析：
| // 功能：解析接收到的ICMP报文 // 返回值： -2忽略, -1失败, 0 成功 int decode_reply(IPHeader *reply, int bytes, sockaddr_in *from) { // 偏移到ICMP报头 unsigned short header_len = reply->h_len *4; ICMPHeader *icmphdr = (ICMPHeader*)((char*)reply + header_len); // 报文太短 if (bytes < header_len + ICMP_MIN) { cerr << "too few bytes from " << inet_ntoa(from->sin_addr) << endl; return - 1; } // 解析回复报文类型 else if (icmphdr->type != ICMP_ECHO_REPLY) { //非正常回复 if (icmphdr->type != ICMP_TTL_EXPIRE) { //ttl减为零 if (icmphdr->type == ICMP_DEST_UNREACH) { //主机不可达 cerr << "Destination unreachable" << endl; } else { //非法的ICMP包类型 cerr << "Unknown ICMP packet type " << int(icmphdr->type) <<" received" << endl; } return - 1; } } else if (icmphdr->id != (unsigned short)GetCurrentProcessId()) { //不是本进程发的包, 可能是同机的其它ping进程发的 return - 2; } // 指出往返时间TTL int nHops = int(256-reply->ttl); if (nHops == 192) { // TTL came back 64, so ping was probably to a host on the // LAN -- call it a single hop. nHops = 1; } else if (nHops == 128) { // Probably localhost nHops = 0; } // 输出信息 cout << endl << bytes << " bytes from " << inet_ntoa(from->sin_addr) <<", icmp_seq " << icmphdr->seq << ", "; if (icmphdr->type == ICMP_TTL_EXPIRE) { cout << "TTL expired." << endl; } else { cout << nHops << " hop" << (nHops == 1 ? "" : "s"); cout << ", time: " << (GetTickCount() - icmphdr->timestamp) << " ms." <<endl; } return 0; } |
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