PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Backing Up or Mirroring a File
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If the URL is valid, you then go on to check the email address. First, you split it into
username and hostname with a call to explode():
$email = explode(‘@’, $email);
$emailhost = $email[1];
When you have the host part of the address, you can check to see whether there is a
place for that mail to go by using the dns_get_mx() function:
dns_get_mx($emailhost, $mxhostsarr);
This function returns the set of Mail Exchange (MX) records for an address in the array
you supply at $mxhostsarr.
An MX record is stored at the DNS and is looked up like a hostname.The machine
listed in the MX record isn’t necessarily the machine where the email will eventually
end up. Instead, it’s a machine that knows where to route that email. (There can be more
than one; hence, this function returns an array rather than a hostname string.) If you
don’t have an MX record in the DNS, there’s nowhere for the mail to go.
Note that the dns_get_mx() function is not implemented in Windows versions of
PHP. If you are using Windows, you should look into the PEAR::Net_DNS package,
which will work for you (http://pear.php.net/package/NET_DNS).
If all these checks are okay, you can put this form data in a database for later review
by a staff member.
In addition to the functions you just used, you can use the more generic function
checkdnsrr(), which takes a hostname and returns true if any record of it appears in
the DNS.
Backing Up or Mirroring a File
File Transfer Protocol, or FTP, is used to transfer files between hosts on a network. Using
PHP, you can use fopen() and the various file functions with FTP as you can with
HTTP connections, to connect to and transfer files to and from an FTP server.
However, a set of FTP-specific functions also comes with the standard PHP install.
These functions are not built into the standard install by default.To use them under
Unix, you need to run the PHP configure program with the --enable-ftp option and
then rerun make. If you are using the standard Windows install, FTP functions are
enabled automatically.
(For more details on configuring PHP, see Appendix A,“Installing PHP and MySQL.”)
Using FTP to Back Up or Mirror a File
The FTP functions are useful for moving and copying files from and to other hosts. One
common use you might make of this capability is to back up your website or mirror files
at another location. Let’s look at a simple example using the FTP functions to mirror a
file.This script is shown in Listing 20.4.