PHP : Internet Services - [17.7] Getting and Putting Files with FTP

17.7.1 Problem

You want to transfer files using FTP.

17.7.2 Solution

Use PHP's built-in FTP functions:

$c = ftp_connect('ftp.example.com')     or die("Can't connect");
ftp_login($c, $username, $password)     or die("Can't login");
ftp_put($c, $remote, $local, FTP_ASCII) or die("Can't transfer");
ftp_close($c);                          or die("Can't close");

You can also use the cURL extension:

$c = curl_init("ftp://$username:$password@ftp.example.com/$remote");
// $local is the location to store file on local machine
$fh = fopen($local, 'w') or die($php_errormsg); 
curl_setopt($c, CURLOPT_FILE, $fh);
curl_exec($c);
curl_close($c);

17.7.3 Discussion

FTP stands for File Transfer Protocol and is a method of exchanging files between one computer and another. Unlike with HTTP servers, it's easy to set up an FTP server to both send and receive files.

Using the built-in FTP functions doesn't require additional libraries, but you must specifically enable them with --enable-ftp . Because these functions are specialized to FTP, they're easy to use when transferring files.

All FTP transactions begin with establishing a connection from your computer, the local client, to another computer, the remote server:

$c = ftp_connect('ftp.example.com')     or die("Can't connect");

Once connected, you need to send your username and password; the remote server can then authenticate you and allow you to enter:

ftp_login($c, $username, $password)     or die("Can't login");

Some FTP servers support a feature known as anonymous FTP. Under anonymous FTP, users can log in without an account on the remote system. When you use anonymous FTP, your username is anonymous, and your password is your email address.

Here's how to transfer files with ftp_put( ) and ftp_get( ):

ftp_put($c, $remote, $local,  FTP_ASCII) or die("Can't transfer");
ftp_get($c, $local,  $remote, FTP_ASCII) or die("Can't transfer");

The ftp_put( ) function takes a file on your computer and copies it to the remote server; ftp_get( ) copies a file on the remote server to your computer. In the previous code, $remote is the pathname to the remote file, and $local points at the file on your computer.

There are two final parameters passed to these functions. The FTP_ASCII parameter, used here, transfers the file as if it were ASCII text. Under this option, linefeed endings are automatically converted as you move from one operating system to another. The other option is FTP_BINARY, which is used for nonplaintext files, so no linefeed conversions take place.

Use ftp_fget( ) and ftp_fput( ) to download or upload a file to an existing open file pointer (opened using fopen( )) instead of to a location on the filesystem. For example, here's how to retrieve a file and write it to the existing file pointer, $fp:

$fp = fopen($file, 'w');
ftp_fget($c, $fp, $remote, FTP_ASCII)   or die("Can't transfer");

Finally, to disconnect from the remote host, call ftp_close( ) to log out:

ftp_close($c);                          or die("Can't close");

To adjust the amount of seconds the connection takes to time out, use ftp_set_option( ) :

// Up the time out value to two minutes:
set_time_limit(120)
$c = ftp_connect('ftp.example.com');
ftp_set_option($c, FTP_TIMEOUT_SEC, 120);

The default value is 90 seconds; however, the default max_execution_time of a PHP script is 30 seconds. So, if your connection times out too early, be sure to check both values.

To use the cURL extension, you must download cURL from http://curl.haxx.se/ and set the --with-curl configuration option when building PHP. To use cURL, start by creating a cURL handle with curl_init( ) , and then specify what you want to do using curl_setopt( ). The curl_setopt( ) function takes three parameters: a cURL resource, the name of a cURL constant to modify, and value to assign to the second parameter. In the Solution, the CURLOPT_FILE constant is used:

$c = curl_init("ftp://$username:$password@ftp.example.com/$remote");
// $local is the location to store file on local client
$fh = fopen($local, 'w') or die($php_errormsg); 
curl_setopt($c, CURLOPT_FILE, $fh);
curl_exec($c);
curl_close($c);

You pass the URL to use to curl_init( ). Because the URL begins with ftp://, cURL knows to use the FTP protocol. Instead of a separate call to log on to the remote server, you embed the username and password directly into the URL. Next, you set the location to store the file on your server. Now you open a file named $local for writing and pass the file handle to curl_setopt( ) as the value for CURLOPT_FILE. When cURL transfers the file, it automatically writes to the file handle. Once everything is configured, you call curl_exec( ) to initiate the transaction and then curl_close( ) to close the connection.