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

Backing Up or Mirroring a File
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Avoiding Timeouts
One problem you might face when transferring files via FTP is exceeding the maximum
execution time.You know when this happens because PHP gives you an error message.
This error is especially likely to occur if your server is running over a slow or congested
network, or if you are downloading a large file, such as a movie clip.
The default value of the maximum execution time for all PHP scripts is defined in
the php.ini file. By default, it’s set to 30 seconds.This is designed to catch scripts that
are running out of control. However, when you are transferring files via FTP, if your link
to the rest of the world is slow or if the file is large, the file transfer could well take
longer than this.
Fortunately, you can modify the maximum execution time for a particular script by
using the set_time_limit() function. Calling this function resets the maximum number
of seconds the script is allowed to run, starting from the time the function is called.
For example, if you call
set_time_limit(90);
the script will be able to run for another 90 seconds from the time the function is called.
Using Other FTP Functions
A number of other FTP functions are useful in PHP.The function ftp_size() can tell
you the size of a file on a remote server. It has the following prototype:
int ftp_size(int ftp_connection, string remotefile_path)
This function returns the size of the remote file in bytes or –1 if an error occurs. It is
not supported by all FTP servers.
One handy use of ftp_size() is to work out the maximum execution time to set for
a particular transfer. Given the file size and speed of your connection, you can take a
guess as to how long the transfer ought to take and use the set_time_limit() function
accordingly.
You can get and display a list of files in a directory on a remote FTP server by using
the following code:
$listing = ftp_nlist($conn, dirname($remotefile));
foreach ($listing as $filename)
echo “$filename ”;
This code uses the ftp_nlist() function to get a list of names of files in a particular
directory.
In terms of other FTP functions, almost anything that you can do from an FTP
command line, you can do with the FTP functions.You can find the specific functions
corresponding to each FTP command in the PHP online manual at http://us2.php.net/
manual/en/ref.ftp.php.
The exception is mget (multiple get), but you can use ftp_nlist() to get a list of
files and then fetch them as required.