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, 微软公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平台和系统治理员的权限.
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;
// 判定命令行是否合法
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);
/*
* 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, 这里没有必要具体将
// 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;
}
// 下面的包类型具体参见我的第一部分 "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, 这使得假如出现网络问题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.
