透析ICMP协议(4): 应用篇ping(RAW Socket)

原理简介:

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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:

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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.

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/*
* 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 << "\tdata_size can be up to " << MAX_PING_DATA_SIZE <<
" bytes. Default is " << DEFAULT_PACKET_SIZE << "." <<
endl;
cerr << "\tttl 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);