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CopyRight owned by the original author.--(www.MegaEntry.com)
-------------------------------------------------------------------------------- inetd programming 利用inetd来做网路程式设计是个既简单又稳定的设计方法，您不需要考虑到复杂的socket programming。您的设计工作几乎在设计好通讯协定後就完成了，所需要的技巧，仅为简单的文字分析技巧。 goodie inet serviceMegaEntry - Social networking and discussion site!
首先，我们先来撰写一个称为goodie的服务程式。 goodie.c #includeCopyRight owned by the original author.--(www.MegaEntry.com)
void main(void) { printf( "Welcome to goodie service! "); } 这个程式很简单，不是吗?CopyRight owned by the original author.--(www.MegaEntry.com)
编译 gcc -o goodie goodie.c 设定/etc/services及/etc/inetd.conf 在/etc/services中加入以下这一行 goodie 20001/tcpMegaEntry - Social networking and discussion site!
其意义为goodie这项服务是在port 20001、TCP协定。 接下来在/etc/inetd.conf中加入以下这一行 goodie stream tcp nowait root /full_goodie_path_name/goodieMegaEntry - Social networking and discussion site!
各项参数的意义为MegaEntry - Social networking and discussion site!
proto一般用tcp/udp。 flags有wait/nowait。 user是您指定该程式要以那一个使用者来启动，这个例子中用的是root，如果有安全性的考量，应该要改用nobody。一般来说，建议您用低权限的使用者，除非必要，不开放root使用权。 server_path及args，这是您的服务程式的位置及您所想加入的参数。 接下来重新启动inetdCopyRight owned by the original author.--(www.MegaEntry.com)
killall inetd inetd 这样我们便建立起一个port 20001的goodie service。 现在我们来检验一下goodie是否可以执行:MegaEntry - Social networking and discussion site!
telnet localhost 20001 或 telnet your_host_name 20001 执行结果CopyRight owned by the original author.--(www.MegaEntry.com)
Trying 127.0.0.1... Connected to localhost. Escape character is '^] '. Welcome to goodie service! Connection closed by foreign host. 很简单不是吗? 信不信由您，telnet/pop3/imap/ftp都是靠这种方式建立起来的服务。CopyRight owned by the original author.--(www.MegaEntry.com)
我们现在来建立一点小小的 "网路协定 "，这个协定使我们可以输入 "exit "时，离开程式，而其他的指令都是输出与输入相同的字串。 #includeCopyRight owned by the original author.--(www.MegaEntry.com)
void main(void) { char buf[1024]; int ok;MegaEntry - Social networking and discussion site!
printf( "Welcome to goodie service! "); fflush(stdout); ok=0; do { while (fgets(buf,1023,stdin)==NULL);MegaEntry - Social networking and discussion site!
if (strncasecmp(buf, "exit ",4)==0) ok=1; printf(buf); fflush(stdout); } while (!ok); }MegaEntry - Social networking and discussion site!
执行结果 telnet localhost 20001 或 telnet your_host_name 20001 Trying 127.0.0.1...MegaEntry - Social networking and discussion site!
Connected to localhost. Escape character is '^] '. Welcome to goodie service! 输入 "help "MegaEntry - Social networking and discussion site!
help help 输入 "exit " exitCopyRight owned by the original author.--(www.MegaEntry.com)
exit Connection closed by foreign host. 接下来，我们将设计一个稍微复杂一点点的通讯协定，比较通用於一般用途。 #includeCopyRight owned by the original author.--(www.MegaEntry.com)
#includeCopyRight owned by the original author.--(www.MegaEntry.com)
"bye ", "exit ", NULL }; int getcmd(char *cmd)MegaEntry - Social networking and discussion site!
{ int n=0; while (cmds[n]!=NULL) { if (strncasecmp(cmd,cmds[n],strlen(cmds[n]))==0) return n; n++; }MegaEntry - Social networking and discussion site!
return -1; } void main(void) { char buf[1024];CopyRight owned by the original author.--(www.MegaEntry.com)
int ok; printf( "Welcome to goodie service! "); fflush(stdout); ok=0;MegaEntry - Social networking and discussion site!
do { while (fgets(buf,1023,stdin)==NULL); switch (getcmd(buf)) { case -1: printf( "Unknown command! "); break; case 0: printf( "How may I help you, sir? "); break; case 1: printf( "I will say %s ",&buf[3]); break;MegaEntry - Social networking and discussion site!
case 2: printf( "How 're you doing today? "); break; case 3: printf( "Si ya, mate! "); ok=1; break; case 4: printf( "Go ahead! "); ok=1; break; } fflush(stdout); } while (!ok);MegaEntry - Social networking and discussion site!
} telnet localhost 20001 或 telnet your_host_name 20001CopyRight owned by the original author.--(www.MegaEntry.com)
试试看输入 "help "、 "say "、 "hello "、 "bye "、 "exit "等等指令，及其它一些不在命令列中的指令。 在设计inetd服务程式时，要特别注意buffer overflow的问题，也就是以下这种状况: char buffer_overflow[64];MegaEntry - Social networking and discussion site!
fscanf(stdin, "%s ",buffer_overflow); 历来几乎所有的安全漏洞都是由此而来的。 你一定不可这样用，不论任何理由，类同的用法也不可以。Cracker可以透过将您的buffer塞爆，然後塞进他自己的程式进来执行。CopyRight owned by the original author.--(www.MegaEntry.com)
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