Informática geek, matemáticas, pensamiento crítico y alguna otra cosa de vez en cuando.


Automated upload to GMail via IMAP

Some time ago, there was a Python library called libgmail which was able to communicate with GMail using their proprietary protocol. However, proprietary protocols have a serious drawback: they can be changed at any time without prior notice, and when that happens, those who have reverse-engineered them have to figure out the changes. Furthermore, there's an explicit rule in Google's ToS forbidding access «by any means other than through the interface that is provided by Google». Combine it with the fact that libgmail has now been abandoned for a while, and you can figure out the result: libgmail is no longer usable.

There are, however, other ways of using GMail to do automated attachment uploads. The one that probably provides the most flexibility is to use the IMAP protocol to do the transfers. IMAP access is explicitly provided by GMail so that users do not need to use the web interface and can use an email client that supports IMAP to handle mail, thus it's arguable that using IMAP is in accordance with the ToS. I am not a lawyer, though, so ask one if you want to be sure.

Unfortunately, there's currently no library similar to libgmail which supports IMAP instead of the proprietary GMail protocol. [Update 2011-03-09: I just learned that there's a new version of GMailFS which uses the IMAP protocol. However, it is a filesystem for Linux, not a cross-platform command line utility. I don't know yet of a command line tool that is compatible across systems, besides the one presented here.] I've written a PHP program as a proof-of-concept of such a tool. It's a complete example that creates a message with the tag 'ftp', having an attached file with MIME type 'application/octet-stream', in a GMail account. The program requires the IMAP extension to be installed in PHP. In Debian Lenny, that means to install the package php5-imap.

IMAP access must be enabled in the target GMail account before starting. The files are tagged with the label 'ftp' which must already exist, so create it before trying to upload. After uploading, you can retrieve the file via the GMail web interface.

A drawback when compared to libgmail is that, as it uses Base64 encoding for files, the upload time is about 33% greater. It would be theoretically possible to upload files using Base85 encoding, which reduces the overhead to 25%. However, in that case the retrieval of the file would need a Base85 decoder and it would probably not be possible to just click on the file to download it.

Here's the PHP code, intended for being used with the PHP command line interface. Usage is:
php imap-upload.php <file_to_upload>


 * Configuration section

// User name (full email address)
$usr = '';

// Password. Leave unset for being asked (sorry, with echo - yuck!)

// IMAP server
$svr = '';

// IMAP port
$prt = 993;

// Folder / Tag (must exist prior to running this)
//$folder = '[Gmail]/Drafts'; // This one would use the actual GMail drafts folder.
                              // NOTE: must be localized, e.g. in spanish the name
                              // is '[Gmail]/Borradores'
$folder = 'ftp';  // Same tag used by

// Encoding for the filename string we are passing from the command line
$filename_enc = 'UTF-8';

 * End of configuration section

// Encode the subject in MIME quoted-printable format as per RFC 2047
function encode_subject($title, $encoding)
  $ret = "=?$encoding?Q?";
  $linelength = 9; // length of "Subject: "

  for ($i = 0; $i < strlen($title); $i++)
    if ($linelength >= 65)
      $ret .= "?=\r\n =?$encoding?Q?";
      $linelength = 1; // length of initial space

    if ($title[$i] >= ' ' and $title[$i] <= '~'
        and $title[$i] != '=' and $title[$i] != '?'
        and $title[$i] != '_')
      if ($title[$i] == ' ')
        $ret .= '_';
        $ret .= $title[$i];
      $ret .= '=' . strtoupper(bin2hex($title[$i]));
      $linelength += 3;
  return $ret . '?=';

// quoted-string for parameters as per RFC 822
function quoted_string($string)
  return '"' . strtr($string, array("\\"=>"\\\\",
                                    "\n"=>"\\\n")) . '"';

// grab 7-11 random lowercase letters
function randword()
  $result = '';
  for ($i = 0; $i < 7 + mt_rand(0, 4); $i++)
    $result .= chr(mt_rand(0, 25) + 97);
  return $result;

$filepath = $argv[1];

if (! isset($filepath))
  die("No filename specified to upload\n");

$filename = basename($filepath);

if ($prt == 993) $prt = ''; else $prt = ':' . $prt;

if (! isset($pwd))
  echo "pwd: ";
  $pwd = substr(fgets(STDIN), 0, -1); // remove extra \n

// Open the imap stream
$stream = imap_open("\x7B$svr$prt/ssl}$folder", $usr, $pwd);

// Report all possible errors

// Exit on trouble
if ($stream === false) die("\nStopping\n");

$rnd1 = randword();
$rnd2 = randword();
$bndr = "------------" . randword() . randword();

$result = imap_append(
            , "\x7B$svr$prt/ssl}$folder"
            , "From: $usr"
              . "\r\nTo: $rnd1@$"
              . "\r\nSubject: " . encode_subject($filename, $filename_enc)
              . "\r\nMIME-Version: 1.0"
              . "\r\nContent-type: multipart/mixed;"
              . "\r\n boundary=\"$bndr\""
              . "\r\n"
              . "\r\nThis is a multi-part message in MIME format."
              . "\r\n--$bndr"
              . "\r\nContent-Type: text/plain; charset=$filename_enc; format=flowed"
              . "\r\nContent-Transfer-Encoding: quoted-printable"
              . "\r\n"
              . "\r\n" . imap_8bit($filename)
              . "\r\n"
              . "\r\n--$bndr"
              . "\r\nContent-Type: application/octet-stream;"
              . "\r\n name=" . quoted_string($filename)
              . "\r\nContent-Transfer-Encoding: base64"
              . "\r\nContent-Disposition: attachment;"
              . "\r\n filename=" . quoted_string($filename)
              . "\r\n"
              . "\r\n" . imap_binary(file_get_contents($filepath))
              . "--$bndr--"
              . "\r\n"
              . "\r\n"

if ($result)
  echo "Succeeded adding file\n";

$check = imap_check($stream);
echo "There are now ". $check->Nmsgs . " messages in the $folder folder\n";





Here's a little bonus brainteaser. The generator of random lowercase letters can generate 7 to 11 characters. What's the probability of each length? Hint: it's not 1/5.


Anonymous said...

Can't believe I only just found this. Works like a charm. Thank you!

pgimeno said...

I'm glad it's useful for you, that's the intention :)