HOWTO: using drupal_http_request() in POST mode with a custom Java HttpServlet

Hello everyone!

I've been struggling for a day or two to get drupal_http_request() to function correctly with a custom Java HttpServlet I've written. The servlet never seemed to recieve the data I sent to it. Searching around on Google and drupal.org, I could not find decent documentation nor examples. I was using the following code from a custom Drupal module, using hook_nodeapi() tying into the 'update' action:

$url = http://localhost:8080/myservlet;

$headers = array();
			
$data = array (
	'key' => 'A160FDE523826CD438260CABFCD43892DCA75'),
	'id' => $node->nid,
	'action' => $action
	);
				
$response = drupal_http_request($url, $headers, 'POST', http_build_query($data));

Notice how I chose not to send any additional headers with the drupal_http_request() call. However, to correctly do a POST call there has to be a header called 'Content-Type' set to 'application/x-www-form-urlencoded'. Normally, this is done by default. I said Normally, so not in this case ;-)

To do a correct POST with simple form data, we can easily fix the above code as follows:

$url = http://localhost:8080/myservlet;

$headers = array('Content-Type' => 'application/x-www-form-urlencoded');
			
$data = array (
	'key' => 'A160FDE523826CD438260CABFCD43892DCA75'),
	'id' => $node->nid,
	'action' => $action
	);
				
$response = drupal_http_request($url, $headers, 'POST', http_build_query($data));

If you're not familiar with http_build_query(), you can read up on it here: http://be.php.net/http_build_query

You will now notice that your Java HttpServlet will be able to properly get the post data by using the common request.getParameter("paramName") call. Best practice to me seems to always include the 'Content-Type' header to avoid (future) problems.

If you're trying to send binary data to a servlet (images, documents, ...), the 'Content-Type' header needs to be set to 'multipart/form-data'. Be ware that binary data can only be submitted using POST!

I hope this will be of some help to anyone out there.

Cheers,

mlc