How do you prevent a user from posting data multiple times on a website

Question

I am working on a web application (J2EE) and I would like to know the options that are available for handling a double post from the browser.

The solutions that I have seen and used in the past are all client-side:

• Disable the submit button as soon as the user clicks it.
• Follow a POST-Redirect-GET pattern to prevent POSTs when the user clicks the back button.
• Handle the onSubmit event of the form and keep track of the submission status with JavaScript.

I would prefer to implement a server side solution if possible. Are there any better approaches than the ones I have mentioned above, or are client-side solutions best?

Answer 1

Its hard to implement an idiot-proof solution (as they are alway improving the idiots). No matter what you do, the client side can be manipulated or perform incorrectly.

Your solution has got to be server side to be reliable and secure. That said, one approach is to review the request and check system/database state or logs to determine if it was already processed. Ideally, the process on the server side should be idempotent if possible, and it will have to protect against dupe submits if it can't be.

Answer 2

You could supply a "ticket" as part of the form, some random number - and make sure it doesn't get accepted twice, on the server side.

Answer 3

Two server-side solutions come to mind:

1. Create one-time use "tokens" in a hidden form field. Once a token is used, it is deleted from whatever database or session context object you're storing it in. The second time, it's not accepted.
2. Cache information received, and if an identical form is received within a certain time period (10 minutes? an hour? You decide!) it is ignored.

Answer 4

Implement a uniqueid to go with the request and log it along with the execution. If the id was already logged, you don't do the job again. This is kinda like the fallback solution - you should try and disable the button or link clientside as well as you suggested yourself

Answer 5

we use a time sensitive, one time ticket. It's like a session id of sort. But it is tied to the form/page.

You discard the ticket when the user submits the page, and you only process pages that comes with a valid ticket. You can, at the same time, tighten security by attaching the ticket to a user, so tat if a ticket comes in that is submitted by a user that is not the user that the ticket was submitted to, you reject the request.

Answer 6

Struts has something like this built in if you happen to be using it.

http://struts.apache.org/1.x/apidocs/org/apache/struts/util/TokenProcessor.html

Answer 7

I'd use a timestamp and compare values with your server side code. If two timestamps are close enough and have the same IP address, ignore the second form submission.