How to return a "noop" document over HTTP

Question

I have a CGI script that does a lot things. I'm trying to keep the script very simple and portable. I just need some way for the user to send a message to the server without having to lose the current page. So far, I have the following process:

1. User loads a "status page" from a CGI script.
2. The status page has a javascript timer that will read data (not the entire page) from the server every two seconds and alter the status page accordingly.
3. User clicks a hyperlink element to launch a job on the server.
4. The CGI receives the parameters from the click and starts the job.
5. The CGI sends a response of \n

At this point Firefox asks the user if they want to download the CGI script and of course the script is just the \n that the CGI sent. Instead, I want the browser to ignore the response altogether. If my CGI script does not echo a \n apache gives an error. What could I do to tell the browser to ignore the response and stay on the current page? Note that I would rather not reload the current page. I'm thinking there must be some sort of "noop" HTTP response for such a case.

Answer 1

Send back a response with the 204 HTTP status code. From RFC 2616 aka Hypertext Transfer Protocol -- HTTP/1.1:

10.2.5 204 No Content

The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation. The response MAY include new or updated metainformation in the form of entity-headers, which if present SHOULD be associated with the requested variant.

If the client is a user agent, it SHOULD NOT change its document view from that which caused the request to be sent. This response is primarily intended to allow input for actions to take place without causing a change to the user agent's active document view, although any new or updated metainformation SHOULD be applied to the document currently in the user agent's active view.

The 204 response MUST NOT include a message-body, and thus is always terminated by the first empty line after the header fields.

Answer 2

Instead of trying to solve this problem on the server side, you might want to investigate a client side solution. For example, using jQuery you can easily initiate an AJAX asynchronous request to the server on a button click. You don't have to load a new page on the browser at all.