How to list and create download links for remote SFTP files

Question

I am trying to list all the files from a certain directory in a remote SFTP server as download links so that the user can have the option of downloading those files. So far, I have been able to read and list all the files from a specific directory as download links, but when I try to actually download a file by right clicking and choosing save link as... I get a "Failed - No File" message. Picture of my results

<?php
$connection = ssh2_connect('url', 22);
ssh2_auth_password($connection, username, password);

$sftp = ssh2_sftp($connection);
$sftp_fd = intval($sftp);

if ($handle = opendir("ssh2.sftp://$sftp_fd/path/to/remote/dir/")) {

   while (($entry = readdir($handle)) !== false) {
      if ($entry == "." || $entry == "..") { continue; }
      echo '<a href="/path/to/remote/dir/' .$entry. '">' .$entry. '<br>'.'</a>';
   }
   closedir($handle);
}
?>     

Answer 1

Your link in the generated <a> tag points back to the web server, which does not contain the linked file.

What you need to do is to link to a PHP script, giving it a name of the file to download. The script will then download the file from an SFTP server and pass the downloaded file back to the user (to the webbrowser).

echo '<a href="download.php?file='.urlencode($entry).'">'.htmlspecialchars($entry).'</a>';

---

A very trivial version of the download.php script:

<?

header('Content-Type: application/octet-stream');

$connection = ssh2_connect('url', 22);
ssh2_auth_password($connection, username, password);

$sftp = ssh2_sftp($connection);
$sftp_fd = intval($sftp);

echo file_get_contents("ssh2.sftp://$sftp_fd/path/to/remote/dir/" . $_GET["file"]);

---

Though for a really correct solution, you should provide some HTTP headers related to the file, like Content-Length, Content-Type and Content-Disposition.

Also the above trivial example will first download whole file from the SFTP server to the webserver. And only then it will start streaming it to the user (webbrowser). What is a waste of time and also of a memory on the webserver (if the files are large enough).

See a similar (though FTP, not SFTP) question:
Download file via PHP script from FTP server to browser with Content-Length header without storing the file on the web server

You may also want to autodetect Content-Type, unless all your files are of the same type.

---

You can of course use URL rewrite to make the URLs prettier.
I.e. turn download.php?file=myfile.txt to for example download/myfile.txt.