透析ICMP协议(4): 应用篇ping(RAW Socket)

/*
* 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.