透析ICMP协议(四): 牛刀初试之二 应用篇ping(RAW Socket) (转)

透析ICMP协议(四): 牛刀初试之二 应用篇ping(RAW Socket) (转)[@more@]

透析ICMP协议(四): 牛刀初试之二
 应用篇ping(RAW Socket)
===============================
这篇文章出自bugfree/CSDN
平台: VC6 windows XP

今晚一杯茶水之后, 让我们继续我们的ICMP讨论, 今晚介绍的是用RAW Socket 实现的ping程序.

原理简介:
-------- 
 用RAW Socket实现的ping可能比上一节的应用ICMP.DLL的程序庞大些, 但是这才是我们需要关注的东西, 我的观点真正想做网络开发的程序员应该静下心来读读这篇文章, 相信你会从中获益颇多. 中间我也会讲解一些东西为后一章的路由追踪做一些铺垫.
 另一个重要的要讲的东西, 微软宣布随时不支持上节讲的ping用到的开发接口, 但是本节的讲的是更一般的东西. 所以它不会过时, 甚至做很小的改动就可以移植到别的系统上去. 系统移植不是我们的讲的重点. 但是微软的长期支持足以引起我们充分的重视.
 如何少作变动来使的这个程序实现追踪路由的功能, 这里只是抛砖引玉. 将ICMP包中IP包的包头该为特定的值就能得到那个路由器的IP(要求到达目的地的跳数大于你设的特定值).
 这个程序需要windows2k/WindowsXP/WindowsNT平台和系统管理员的权限.

具体实现:
--------
这段源代码大部分来自:
  .NET/wskfaq/examples/rawping.html">http://tangentsoft.net/wskfaq/examples/rawping.html
[bugfree]只做了少量修改,给出了大量的注释, 最后结合经验给出了自己的建议.

----------

/*
 * 程序名: rawping_driver.cpp
 * 说明: 
 *  驱动程序,也是主函数
 */
#include  
#include

#include "rawping.h"

#define DEFAULT_PACKET_SIZE 32  // 默认ICMP包字节数
#define DEFAULT_TTL 30  // 默认TTL值
#define MAX_PING_DATA_SIZE 1024  // 最大数据块
#define MAX_PING_PACKET_SIZE (MAX_PING_DATA_SIZE + sizeof(IPHeader)) //最大ICMP包长度

/* 为 send_buf 和 recv_buf 分配内存
 * send_buf大小为 packet_size
 * recv_buf大小为 MAX_PING_PACKET_SIZE, 保证大于send_buf
 */
int allocate_buffers(ICMPHeader*& send_buf, IPHeader*& recv_buf,
  int packet_size);

///////////////////////////////////////////////////////////////////////
// Program entry point

int main(int argc, char* argv[])
{
 
  int seq_no = 0;  //用在发送和接受的ICMP包头中
  ICMPHeader* send_buf = 0;
  IPHeader* recv_buf = 0;

  // 判断命令行是否合法
  if (argc < 2) {
  cerr << "usage: " << argv[0] << " [data_size] [ttl]" <<
  endl;
  cerr << " data_size can be up to " << MAX_PING_DATA_SIZE <<
  " bytes.  Default is " << DEFAULT_PACKET_SIZE << "." <<
  endl;
  cerr << " ttl should be 255 or lower.  Default is " <<
  DEFAULT_TTL << "." << endl;
  return 1;
  }

  // 处理命令行参数
  int packet_size = DEFAULT_PACKET_SIZE;
  int ttl = DEFAULT_TTL;
  if (argc > 2) {
  int temp = atoi(argv[2]);
  if (temp != 0) {
  packet_size = temp;
  }
  if (argc > 3) {
  temp = atoi(argv[3]);
  if ((temp >= 0) && (temp <= 255)) {
  ttl = temp;
  }
  }
  }
  packet_size = max(sizeof(ICMPHeader),
  min(MAX_PING_DATA_SIZE, (unsigned int)packet_size));

  // 启动 Winsock
  WSAData wsaData;
  if (WSAStartup(MAKEword(2, 1), &wsaData) != 0) {
  cerr << "Failed to find Winsock 2.1 or better." << endl;
  return 1;
  }

  SOCKET sd; // RAW Socket句柄
  sockaddr_in dest, source;
 
  // 三个任务(创建sd, 设置ttl, 初试dest的值)
  if (setup_for_ping(argv[1], ttl, sd, dest) < 0) {
  goto cleanup; //释放资源并退出
  }
  // 为send_buf和recv_buf分配内存
  if (allocate_buffers(send_buf, recv_buf, packet_size) < 0) {
  goto cleanup;
  }
  // 初试化IMCP数据包(type=8,code=0)
  init_ping_packet(send_buf, packet_size, seq_no);

  // 发送ICMP数据包
  if (send_ping(sd, dest, send_buf, packet_size) >= 0) {
  while (1) {
  // 接受回应包
  if (recv_ping(sd, source, recv_buf, MAX_PING_PACKET_SIZE) <
  0) {
  // Pull the sequence number out of the ICMP header.  If
  // it's bad, we just complain, but otherwise we take
  // off, because the read failed for some reason.
  unsigned short header_len = recv_buf->h_len * 4;
  ICMPHeader* icmphdr = (ICMPHeader*)
  ((char*)recv_buf + header_len);
  if (icmphdr->seq != seq_no) {
  cerr << "bad sequence number!" << endl;
  continue;
  }
  else {
  break;
  }
  }
  if (decode_reply(recv_buf, packet_size, &source) != -2) {
  // Success or fatal error (as opposed to a minor error)
  // so take off.
  break;
  }
  }
  }

cleanup:
  delete[]send_buf;  //释放分配的内存
  delete[]recv_buf;
  WSACleanup(); // 清理winsock
  return 0;
}

// 为send_buf 和 recv_buf的内存分配. 太简单, 我略过
int allocate_buffers(ICMPHeader*& send_buf, IPHeader*& recv_buf,
  int packet_size)
{
  // First the send buffer
  send_buf = (ICMPHeader*)new char[packet_size]; 
  if (send_buf == 0) {
  cerr << "Failed to allocate output buffer." << endl;
  return -1;
  }

  // And then the receive buffer
  recv_buf = (IPHeader*)new char[MAX_PING_PACKET_SIZE];
  if (recv_buf == 0) {
  cerr << "Failed to allocate output buffer." << endl;
  return -1;
  }
 
  return 0;
}

/*
 * 程序名: rawping.h
 * 说明: 
 *  主要函数库头文件
 */

#define win32_LEAN_AND_MEAN
#include

// ICMP 包类型, 具体参见本文的第一节
#define ICMP_ECHO_REPLY 0 
#define ICMP_DEST_UNREACH 3
#define ICMP_TTL_EXPIRE 11
#define ICMP_ECHO_REQUEST 8

// 最小的ICMP包大小
#define ICMP_MIN 8

// ip 包头
struct IPHeader {
  BYTE h_len:4;  // Length of the header in dwords
  BYTE version:4;  // Version of IP
  BYTE tos;  // Type of service
  USHORT total_len;  // Length of the packet in dwords
  USHORT ident;  // unique identifier
  USHORT flags;  // Flags
  BYTE ttl;  // Time to live, 这个字段我在下一节中用来实现Tracert功能
  BYTE proto;  // Protocol number (TCP, UDP etc)
  USHORT checksum;  // IP checksum
  ULONG source_ip;
  ULONG dest_ip;
};

// ICMP 包头(实际的包不包括timestamp字段,
// 作者用来计算包的回应时间,其实完全没有必要这样做)
struct ICMPHeader {
  BYTE type;  // ICMP packet type
  BYTE code;  // Type sub code
  USHORT checksum;
  USHORT id;
  USHORT seq;
  ULONG timestamp;  // not part of ICMP, but we need it
};

extern USHORT ip_checksum(USHORT* buffer, int size);
extern int setup_for_ping(char* host, int ttl, SOCKET& sd,  sockaddr_in& dest);
extern int send_ping(SOCKET sd, const sockaddr_in& dest, ICMPHeader* send_buf, int packet_size);
extern int recv_ping(SOCKET sd, sockaddr_in& source, IPHeader* recv_buf,
  int packet_size);
extern int decode_reply(IPHeader* reply, int bytes, sockaddr_in* from);
extern void init_ping_packet(ICMPHeader* icmp_hdr, int packet_size, int seq_no);

/*
 * 程序名: rawping.cpp
 * 说明: 
 *  主要函数库实现部分
 */
 
include
#include
#include
#include "rawping.h"
 
 // 计算ICMP包的校验和的简单算法, 很多地方都有说明, 这里没有必要详细将
 // 只是一点要提, 做校验之前, 务必将ICMP包头的checksum字段置为0
USHORT ip_checksum(USHORT* buffer, int size)
{
  unsigned long cksum = 0;
 
  // Sum all the words together, adding the final byte if size is odd
  while (size > 1) {
  cksum += *buffer++;
  size -= sizeof(USHORT);
  }
  if (size) {
  cksum += *(UCHAR*)buffer;
  }

  // Do a little shuffling
  cksum = (cksum >> 16) + (cksum & 0xffff);
  cksum += (cksum >> 16);
 
  // Return the bitwise complement of the resulting mishmash
  return (USHORT)(~cksum);
}

//初试化RAW Socket, 设置ttl, 初试化dest
// 返回值 <0 表失败

int setup_for_ping(char* host, int ttl, SOCKET& sd, sockaddr_in& dest)
{
  // Create the socket
  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;
  }

  // Initialize the destination host info block
  memset(&dest, 0, sizeof(dest));

  // Turn first passed parameter into an IP address to ping
  unsigned int addr = .net_addr(host);
  if (addr != INADDR_NONE) {
  // It was a dotted quad number, so save result
  dest.sin_addr.s_addr = addr;
  dest.sin_family = AF_INET;
  }
  else {
  // Not in dotted quad form, so try and look it up
  hostent* hp = gethostbyname(host);
  if (hp != 0) {
  // Found an address for that host, so save it
  memcpy(&(dest.sin_addr), hp->h_addr, hp->h_length);
  dest.sin_family = hp->h_addrtype;
  }
  else {
  // Not a recognized hostname either!
  cerr << "Failed to resolve " << host << endl;
  return -1;
  }
  }

  return 0;
}

 

//初试化ICMP的包头, 给data部分填充数据, 最后计算整个包的校验和

void init_ping_packet(ICMPHeader* icmp_hdr, int packet_size, int seq_no)
{
  // Set up the packet's fields
  icmp_hdr->type = ICMP_ECHO_REQUEST;
  icmp_hdr->code = 0;
  icmp_hdr->checksum = 0;
  icmp_hdr->id = (USHORT)GetCurrentProcessId();
  icmp_hdr->seq = seq_no;
  icmp_hdr->timestamp = GetTickCount();

  // "You're dead meat now, packet!"
  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);
  }

  // Calculate a checksum on the result
  icmp_hdr->checksum = ip_checksum((USHORT*)icmp_hdr, packet_size);
}

// 发送生成的ICMP包
// 返回值 <0 表失败

int send_ping(SOCKET sd, const sockaddr_in& dest, ICMPHeader* send_buf,
  int packet_size)
{
  // Send the ping packet in send_buf as-is
  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;
}

// 接受ICMP包
// 返回值 <0 表失败
int recv_ping(SOCKET sd, sockaddr_in& source, IPHeader* recv_buf,
  int packet_size)
{
  // Wait for the ping reply
  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;
}

// 对收到的ICMP解码
// 返回值 -2表忽略, -1 表失败, 0 成功
int decode_reply(IPHeader* reply, int bytes, sockaddr_in* from)
{
  // 跳过IP包头, 找到ICMP的包头
  unsigned short header_len = reply->h_len * 4;
  ICMPHeader* icmphdr = (ICMPHeader*)((char*)reply + header_len);

  // 包的长度合法, header_len + ICMP_MIN为最小ICMP包的长度
  if (bytes < header_len + ICMP_MIN) {
  cerr << "too few bytes from " << inet_ntoa(from->sin_addr) <<
  endl;
  return -1;
  }
  // 下面的包类型详细参见我的第一部分 "透析ICMP协议(一): 协议原理"
  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 != (USHORT)GetCurrentProcessId()) {
 //不是本进程发的包, 可能是同机的其它ping进程发的
  return -2;
  }

  // 指出包传递了多远
  // [bugfree]我认为作者这里有问题, 因为有些系统的ttl初值为128如winxp,
  // 有些为256如我的dns服务器211.97.168.129, 作者假设为256有点武断,
  // 可以一起探讨这个问题, 回eMail:[email protected]
  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;
  }

  // 所有工作结束,打印信息
  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;
}

总结和建议:
-----------
  bugfree建议其中的这些方面需要改进:
   1. 头文件iostream.h 改为 iostream, 后者是标准C++的头文件
    同时添加对std::cout 和 std::endl;的引用
    对于cerr 建议都改为std::cout(因为后者头文件不支持)
   2. 程序的发送和接受采用了同步的方式, 这使得如果出现网络问题recv_ping将陷入持续等待.
    这是我们不想看到的.
    这三种技术可以达到目的:
    - 使用多线程, 将ping封装进线程, 在主程序中对它的超时进行处理
    - 使用select()函数来实现
    - 使用windows的 WSAAsyncSelect()
    这里对这些方法不作具体讨论, 留给读者自已完成. 

 

链接:
-------
我的其它文章,<>, 和其它文章参见:
http://www.csdn.net/develop/author/netauthor/bugfree/

联系方式:
-------
 [email protected]

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