echo 'File downloaded successfully'; // close connection to host ftp_quit$conn; ?> The output from running this script on one occasion is shown in Figure 17.4.. The $remotefilevariable
Trang 1exit;
} echo "Logged in as $user<br />";
// check file times to see if an update is required echo 'Checking file time <br />';
if (file_exists($localfile)) {
$localtime = filemtime($localfile);
echo 'Local file last updated ';
echo date('G:i j-M-Y', $localtime);
echo '<br />';
} else
$localtime=0;
$remotetime = ftp_mdtm($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;
}
Listing 17.4 Continued
Trang 2echo 'File downloaded successfully';
// close connection to host ftp_quit($conn);
?>
</body>
</html>
The output from running this script on one occasion is shown in Figure 17.4
Listing 17.4 Continued
Figure 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/teraterm/ttssh14.zip';
$localfile = "/tmp/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
user-name that anybody can use to connect No password is required, but it is a common courtesy to supply 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.)
Trang 3The $localfilevariable contains the path to the location where we are going to store the downloaded file on our machine In this case we have created a directory called /tmp/writablewith permissions set up so that PHP can write a file there
You should be able to change these variables to adapt this script for your purposes
The 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 parame-ter, and returns either a handle to a connection, or falseif a connection could not be established.The function can also take the port number on the host to connect to as an optional second parameter (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 />";
Trang 4} echo "Logged in as $user<br />";
The 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 window.You can catch the error as we have done here by test-ing $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() func-tion 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 modi-fied, or -1 if there is an error of some kind Not all FTP servers support this feature, so
Trang 5we might not get a useful result from the function In this case, we choose to artificially set the $remotetimevariable 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 param-eter is the FTP mode