Create new etherpad using PHP and CURL

I'm trying to write a simple PHP script which automatically sets up new etherpads (see http://etherpad.com/).

They don't have an API (yet) for creating new pads so I'm trying to figure if I can do things another way.

After playing around some, I found that if you append a random string to etherpad.com to a not-yet-created pad, it'll come back with a form asking if you want to create a new etherpad at that address. If you submit that form, a new pad will be created at that URL.

My thought then was I could just create a PHP script using CURL that would duplicate that form and trick etherpad into creating a new pad at whatever URL I give it. I wrote the script but so far I can't get it working. Can someone tell me what I'm doing wrong?

First, here's the HTML form on the etherpad creation page:

<p><tt id="padurl">http://etherpad.com/lsdjfsljfa-fdj-lsdf</tt></p>

<br/>
<p>There is no EtherPad document here. Would you like to create one?</p>

<input type="hidden" value="lsdjfsljfa-fdj-lsdf" name="padId"/>
<input type="submit" value="Create Pad" id="createPad"/>

Then here's my code which tries to submit the form using CURL

$ch = curl_init();

//set POST variables
$url = "http://etherpad.com/ep/pad/create?padId=ldjfal-djfa-ldkfjal";
$fields = array(
  'padId'=>urlencode("ldjfal-djfa-ldkfjal"),
);

$useragent="Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30)";  

// set user agent  
curl_setopt($ch, CURLOPT_USERAGENT, $useragent); 

//url-ify the data for the POST
foreach($fields as $key=>$value) { $fields_string .= $key.'='.$value; }
print_r($fields_string);

//open connection
$ch = curl_init();

//set the url, number of POST vars, POST data
curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch,CURLOPT_POST,count($fields));
curl_setopt($ch,CURLOPT_POSTFIELDS,$fields_string);

//execute post
$result = curl_exec($ch);
print_r($result);
//close connection
curl_close($ch);

When I run the script, PHP reports back that everything executed correctly but etherpad doesn't create my pad. Any clues what's going on?

Solution

Here's the answer a friend helped me come up with:

They're apparently doing some cookie validation, that's why your script isn't working. You can find this out by loading the new pad creation prompt page, clearing your cookies, and then reloading the page. It won't work. Tricky, but effective for most casual bots.

Here's a script that gets around the limitation. Just insert your desired $padId and away you go.

<?php

$padId = 'asdfjklsjfgadslkjflskj';

$ch = curl_init();

# for debugging
curl_setopt($ch, CURLOPT_HEADER, true);

# parse cookies and follow all redirects
curl_setopt($ch, CURLOPT_COOKIEFILE, '/dev/null');
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);

# first, post to get a cookie
curl_setopt($ch, CURLOPT_URL, 'http://etherpad.com/' . urlencode 
($padId));
$result = curl_exec($ch);
echo $result;

# next, post to actually create the etherpad
curl_setopt($ch, CURLOPT_URL, 'http://etherpad.com/ep/pad/create');
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, 'padId=' . urlencode($padId));
$result = curl_exec($ch);
echo $result;

curl_close($ch);