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

464 Chapter 20 Using Network and Protocol Functions
The function takes three parameters: an FTP connection (obtained from
ftp_connect()), a username, and a password. It returns true if the user can be logged in
and false if she can’t. Notice that we put an @ symbol at the start of the line to suppress
errors.We did this because, if the user cannot be logged in, a PHP warning appears in
the browser window.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, you actually close the FTP connection by using
ftp_quit().We discuss this function more later.
Checking File Update Times
Given that you are updating a local copy of a file, checking whether the file needs
updating first is sensible because you don’t want to have to redownload a file, particularly
a large one, if it’s up to date.This way, you can avoid unnecessary network traffic. Let’s
look at the code that checks file update times.
File times are the reason that you use the FTP functions rather than a much simpler
call to a file function.The file functions can easily read and, in some cases, write files
over network interfaces, but most of the status functions such as filemtime() do not
work remotely.
To begin deciding whether you need to download a file, you check that you have a
local copy of the file by using the file_exists() function. If you don’t, obviously you
need to download the file. If it does exist, you get the last modified time of the file by
using the filemtime() function and store it in the $localtime variable. If it doesn’t
exist, you set the $localtime variable to 0 so that it will be “older” than any possible
remote file modification time:
echo ‘Checking file time...’;
if (file_exists($localfile))
{
$localtime = filemtime($localfile);
echo ‘Local file last updated ‘;
echo date(‘G:i j-M-Y’, $localtime);
echo ‘’;
}
else
$localtime=0;
(You can read more about the file_exists() and filemtime() functions in Chapters 2,
“Storing and Retrieving Data” and 19,“Interacting with the File System and the Server,”
respectively.)
After you have sorted out the local time, you need to get the modification time of
the remote file.You can get this time by using the ftp_mdtm() function:
$remotetime = ftp_mdtm($conn, $remotefile);