First, we split it into username and hostname with a call to explode: $email = explode“@”, $email; $emailhost = $email[1]; When we have the host part of the address, we can check to see
Trang 1<form method=post action=”directory_submit.php”>
URL: <input type=text name=”url” size=30 value=”http://”><br>
Email contact: <input type=text name=”email” size=23><br>
<input type=”submit” name=”Submit site”>
</form>
</body>
</html>
This is a very simple form—the rendered version, with some sample data entered, is shown in
Figure 17.2
17
L ISTING 17.2 Continued
F IGURE 17.2
Directory submissions typically require your URL and some contact details so directory administrators can notify you
when your site is added to the directory.
When the submit button is pressed, we want to check, first, that the URL is hosted on a real
machine, and, second, that the host part of the email address is also on a real machine We
have written a script to check these things, and the output is shown in Figure 17.3
F IGURE 17.3
This version of the script displays the results of checking the hostnames for the URL and email address—a production
version might not display these results, but it is interesting to see the information returned from our checks.
Trang 2The script that performs these checks uses two functions from the PHP network functions suite—gethostbyname()and getmxrr() The full script is shown in Listing 17.3
L ISTING 17.3 directory_submit.php—Script to Verify URL and Email Address
<html>
<head>
<title>Site submission results</title>
</head>
<body>
<h1>Site submission results</h1>
<?
// Check the URL
$url = parse_url($url);
$host = $url[host];
if(!($ip = gethostbyname($host))) {
echo “Host for URL does not have valid IP”;
exit;
} echo “Host is at IP $ip <br>”;
// Check the email address
$email = explode(“@”, $email);
$emailhost = $email[1];
if (!getmxrr($emailhost, $mxhostsarr)) {
echo “Email address is not at valid host”;
exit;
} echo “Email is delivered via: “;
foreach ($mxhostsarr as $mx) echo “$mx “;
// If reached here, all ok echo “<br>All submitted details are ok.<br>”;
echo “Thank you for submitting your site.<br>”
.”It will be visited by one of our staff members soon.”
// In real case, add to db of waiting sites
Trang 3</body>
</html>
Lets’ go through the interesting parts of this script
First, we take the URL and apply the parse_url()function to it This function returns an
associative array of the different parts of an URL The available pieces of information are the
scheme,user,pass,host,port,path,query, and fragment Typically, you aren’t going to
need all of these, but here’s an example of how they make up an URL
Given an URL such as
http://nobody:secret@bigcompany.com:80/script.php?variable=value#anchor
the values of each of the parts of the array would be
• scheme:http://
• user:nobody
• pass:secret
• host:bigcompany.com
• port:80
• path:script.php
• query:variable=value
• fragment:anchor
In our script, we only want the hostinformation, so we pull it out of the array as follows:
$url = parse_url($url);
$host = $url[host];
After we’ve done this, we can get the IP address of that host, if it is in the DNS We can do
this using the gethostbyname()function, which will return the IP if there is one, or false
if not:
$ip = gethostbyname($host)
You can also go the other way using the gethostbyaddr()function, which takes an IP as
para-meter and returns the hostname If you call these functions in succession, you might well end
up with a different hostname from the one you began with This can mean that a site is using a
virtual hosting service
17
L ISTING 17.3 Continued
Trang 4If the URL is valid, we then go on to check the email address First, we split it into username and hostname with a call to explode():
$email = explode(“@”, $email);
$emailhost = $email[1];
When we have the host part of the address, we can check to see if there is a place for that mail
to go using the getmxrr()function:
getmxrr($emailhost, $mxhostsarr)
This function returns the set of MX (Mail Exchange) records for an address in the array you supply at $mxhostarr
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 we don’t have an MX record in the DNS, then there’s nowhere for the mail to go
If all these checks are okay, we can put this form data in a database for later review by a staff member
In addition to the functions we’ve just used, you can use the more generic function
checkdnsrr(), which takes a hostname and returns trueif there is any record of it in the DNS
Using FTP
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 connec-tions, to connect to and transfer files to and from an FTP server However, there is also a set of FTP-specific functions that comes with the standard PHP install
These functions are not built in to the standard install by default In order to use them under UNIX, you will need to run the PHP configureprogram with the enable-ftpoption, and then rerun make To use the FTP functions with the Win32 binary, you will need to add the line
extension=php_ftp.dll
under the “Windows Extensions” section of your php.inifile (For more details on configur-ing PHP, see Appendix A, “Installconfigur-ing PHP 4 and MySQL.”)
Trang 5Using FTP to Back Up or Mirror a File
The FTP functions are useful for moving and copying files from and to other hosts One
com-mon use you might make of this is to back up your Web site or mirror files at another location
We will look at a simple example using the FTP functions to mirror a file This script is shown
in Listing 17.4
L ISTING 17.4 ftpmirror.php—Script to Download New Versions of a File from an FTP
Server
<html>
<head>
<title>Mirror update</title>
</head>
<body>
<h1>Mirror update</h1>
<?
// set up variables - change these to suit application
$host = “ftp.cs.rmit.edu.au”;
$user = “anonymous”;
$password = “laura@tangledweb.com.au”;
$remotefile = “/pub/tsg/ttssh14.zip”;
$localfile = “$DOCUMENT_ROOT/ /writable/ttssh14.zip”;
// connect to host
$conn = ftp_connect(“$host”);
if (!$conn)
{
echo “Error: Could not connect to ftp server<br>”;
exit;
}
echo “Connected to $host.<br>”;
// log in to host
@ $result = ftp_login($conn, $user, $pass);
if (!$result)
{
echo “Error: Could not log on as $user<br>”;
ftp_quit($conn);
exit;
}
echo “Logged in as $user<br>”;
// check file times to see if an update is required
17
Trang 6echo “Checking file time <br>”;
if (file_exists($localfile)) {
$localtime = filemtime($localfile);
echo “Local file last updated “;
echo date(“G:i j-M-Y”, $localtime);
echo “<br>”;
} else
$localtime=0;
$remotetime = ftp_mdtm($conn, $remotefile);
if (!($remotetime >= 0)) {
// This doesn’t mean the file’s not there, server may not support mod time echo “Can’t access remote file time.<br>”;
$remotetime=$localtime+1; // make sure of an update }
else { echo “Remote file last updated “;
echo date(“G:i j-M-Y”, $remotetime);
echo “<br>”;
}
if (!($remotetime > $localtime)) {
echo “Local copy is up to date.<br>”;
exit;
} // download file echo “Getting file from server <br>”;
$fp = fopen ($localfile, “w”);
if (!$success = ftp_fget($conn, $fp, $remotefile, FTP_BINARY)) {
echo “Error: Could not download file”;
ftp_quit($conn);
exit;
} fclose($fp);
echo “File downloaded successfully”;
// close connection to host ftp_quit($conn);
L ISTING 17.4 Continued
Trang 7</body>
</html>
The output from running this script on one occasion is shown in Figure 17.4
17
L ISTING 17.4 Continued
F IGURE 17.4
The FTP mirroring script checks whether the local version of a file is up-to-date, and downloads a new version if not.
This is quite a generic script You’ll see that it begins by setting up some variables:
$host = “ftp.cs.rmit.edu.au”;
$user = “anonymous”;
$password = “laura@tangledweb.com.au”;
$remotefile = “/pub/tsg/ttssh14.zip”;
$localfile = “$DOCUMENT_ROOT/ /writable/ttssh14.zip”;
The $hostvariable should contain the name of the FTP server you want to connect to, and the
$userand $passwordcorrespond to the username and password you would like to log in with
Many FTP sites support what is called anonymous login, that is, a freely available username
that anybody can use to connect No password is required, but it is a common courtesy to
sup-ply your email address as a password so that the system’s administrators can see where their
users are coming from We have followed this convention here
The $remotefilevariable contains the path to the file we would like to download In this case
we are downloading and mirroring a local copy of Tera Term SSH, an SSH client for Windows
(SSH stands for secure shell This is an encrypted form of Telnet.)
The $localfilevariable contains the path to the location where we are going to store the
downloaded file on our machine
You should be able to change these variables to adapt this script for your purposes
Trang 8The basic steps we follow in this script are the same as if you wanted to manually FTP the file from a command line interface:
1 Connect to the remote FTP server
2 Log in (either as a user or anonymous)
3 Check whether the remote file has been updated
4 If it has, download it
5 Close the FTP connection
Let’s take each of these in turn
Connecting to the Remote FTP Server
This step is equivalent to typing
ftp hostname
at a command prompt on either a Windows or UNIX platform We accomplish this step in PHP with the following code:
$conn = ftp_connect(“$host”);
if (!$conn) {
echo “Error: Could not connect to ftp server<br>”;
exit;
} echo “Connected to $host.<br>”;
The function call here is to ftp_connect() This function takes a hostname as parameter, and returns either a handle to a connection, or falseif a connection could not be established The function can also takes the port number on the host to connect to as an optional second para-meter (We have not used this here.) If you don’t specify a port number, it will default to port
21, the default for FTP
Logging In to the FTP Server
The next step is to log in as a particular user with a particular password You can achieve this using the ftp_login()function:
@ $result = ftp_login($conn, $user, $pass);
if (!$result) {
echo “Error: Could not log on as $user<br>”;
ftp_quit($conn);
exit;
} echo “Logged in as $user<br>”;
Trang 9The function takes three parameters: an FTP connection (obtained from ftp_connect()), a
username, and a password It will return trueif the user can be logged in, and falseif he
can’t You will notice that we put an @symbol at the start of the line to suppress errors We do
this because, if the user cannot be logged in, you will get a PHP warning in your browser
win-dow You can catch the error as we have done here by testing $result, and supplying your
own, more user-friendly error message
Notice that if the login attempt fails, we actually close the FTP connection using
ftp_quit()—more on this in a minute
Checking File Update Times
Given that we are updating a local copy of a file, it is sensible to check whether the file needs
updating first because you don’t want to have to re-download a file, particularly a large one, if
it’s up to date This will avoid unnecessary network traffic Let’s look at the code that does
this
First, we check that we have a local copy of the file, using the file_exists()function If we
don’t then obviously we need to download the file If it does exist, we get the last modified
time of the file using the filemtime()function, and store it in the $localtimevariable If it
doesn’t exist, we set the $localtimevariable to 0so that it will be “older” than any possible
remote file modification time:
echo “Checking file time <br>”;
if (file_exists($localfile))
{
$localtime = filemtime($localfile);
echo “Local file last updated “;
echo date(“G:i j-M-Y”, $localtime);
echo “<br>”;
}
else
$localtime=0;
(You can read more about the file_exists()and filemtime()functions in Chapter 2 and
Chapter 16, “Interacting with the File System and the Server,” respectively.)
After we have sorted out the local time, we need to get the modification time of the remote
file You can get this using the ftp_mdtm()function:
$remotetime = ftp_mdtm($conn, $remotefile);
This function takes two parameters—the FTP connection handle, and the path to the remote
file—and returns either the UNIX time stamp of the time the file was last modified, or -1 if
there is an error of some kind Not all FTP servers support this feature, so we might not get a
17
Trang 10useful result from the function In this case, we choose to artificially set the $remotetime vari-able to be “newer” than the $localtimevariable by adding 1 to it This will ensure that an attempt is made to download the file:
if (!($remotetime >= 0)) {
// This doesn’t mean the file’s not there, server may not support mod time echo “Can’t access remote file time.<br>”;
$remotetime=$localtime+1; // make sure of an update }
else { echo “Remote file last updated “;
echo date(“G:i j-M-Y”, $remotetime);
echo “<br>”;
}
When we have both times, we can compare them to see whether we need to download the file
or not:
if (!($remotetime > $localtime)) {
echo “Local copy is up to date.<br>”;
exit;
}
Downloading the File
At this stage we will try to download the file from the server:
echo “Getting file from server <br>”;
$fp = fopen ($localfile, “w”);
if (!$success = ftp_fget($conn, $fp, $remotefile, FTP_BINARY)) {
echo “Error: Could not download file”;
fclose($fp);
ftp_quit($conn);
exit;
} fclose($fp);
echo “File downloaded successfully”;
We open a local file using fopen()as we have seen previously After we have done this, we call the function ftp_fget(), which attempts to download the file and store in a local file This function takes four parameters The first three are straightforward—the FTP connection, the local file handle, and the path to the remote file The fourth parameter is the FTP mode