Setting Up SFTP From PHP

PHP's ftp_ssl_connect() function is for SSL-FTP, where as what I need for a client's application is SFTP. Isn't life grand! Well, it's not really too much trouble... PHP can handle that too with functions from the ssh2 PECL extension. I'm just glad I caught it early on instead of at the 11th hour. I figured though I might as well continue my previous post about setting up this project with a brief description on installing ssh2 and testing it to ensure everything is in working order.

Installation

The ssh2 extension provides bindings to libssh2 which must be installed first on the system. My target platform is CentOS 5.3, so I was able to install libssh2 and libssh2-devel via yum (using the RPMForge repository).

yum install libssh2 libssh2-devel

The ssh2 extension is available from the pecl.php.net website. There is a minor bug in the current version (0.11.0) which prevents it from compiling against PHP 5.3 so I needed to apply this patch.

wget http://remi.fedorapeople.org/ssh2-php53.patch
tar zxf ssh2-0.11.0.tgz
cd ssh2-0.11.0
patch < ../ssh2-php53.patch

I compiled and installed the extension after the code was patched.

phpize
./configure --with-ssh2
make
cp modules/ssh2.so /usr/local/php/lib/php/extensions/

Adding module=ssh2.so to php.ini and restarting Apache completed the installation. I was then ready to move on and test it to make sure it worked as it should.

Testing the Extension

Using the extension to upload and retrieve files programmatically over an SFTP connection is relatively simple. First, a secure shell connection is established with the SFTP server using ssh2_connect(), and then a login is authenticated with ssh2_auth_password(). Both functions return false if they fail:

$sess = @ssh2_connect(SFTP_SERVER, SFTP_PORT);
if ($sess === false) {
   echo "Connection failed.";
   exit(-1);
}
$result = @ssh2_auth_password($sess, SFTP_USERNAME,
   SFTP_PASSWORD);
if ($result === false) {
   echo "Unable to authenticate.";
   exit(-1);
}

Once a session has been established, the ssh2_sftp() function is used to retrieve an SFTP resource.

$sftp = @ssh2_sftp($sess);
if ($sftp === false) {
   echo "Unable to initialize SFTP subsystem.";
   exit(-1);
}

From that point on, the SFTP resource is used with the ssh2.sftp filestream to read and write files.

file_put_contents("ssh2.sftp://" . $sftp . "/tmp/test.txt",
   $data);

In writing my short automated test case, I dumped some bytes from /dev/urandom to generate a test file, wrote the data to the SFTP server, read it back, and compared the results to make sure they matched after the round-trip.

// generate random data for test file
$data = file_get_contents("/dev/urandom", FILE_BINARY, null,
   0, 512);
$data = substr(convert_uuencode($data), 0, 512);

// write data to file on SFTP server
file_put_contents("ssh2.sftp://" . $sftp . "/tmp/test.txt",
   $data);

// retrieve file from SFTP server
$retrieved = file_get_contents("ssh2.sftp://" . $sftp .
   "/tmp/test.txt");

// compare original data with retrieve data
echo ($data == $retrieved) ? "Success!" : "Corruption!";