透析ICMP协议(四): 应用篇ping(RAW Socket)

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电梯直达

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发表于 2011-8-31 08:00:37 |只看该作者 |倒序浏览

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:

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 <winsock2.h>

#include <iostream.h>
#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] << " <host> [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 <winsock2.h>
// 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 <winsock2.h>

#include <ws2tcpip.h>

#include <iostream.h>

#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 = inet_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:zhangliangsd@hotmail.com

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.