Does a library to prevent duplicate form submissions exist for django?

Question

I am trying to find a way to prevent users from double-submitting my forms. I have javascript that disables the submit button, but there is still an occasional user who finds a way to double-submit.

I have a vision of a re-usable library that I could create to protect from this.

In my ideal library, the code block would look something like this:

try:
    with acquire_lock({'field1':'abc', 'field2':'def'}) as lock:
        response = #do some credit card processing
        lock.response = response
except SubmissionWasDuplicate, e:
    response = e.response

The lock table would look something like this:

duplicate_submission_locks

• submission_hash # a MD5 of the submitted arguments
• response # pickled data
• created_at # used for sweeping this table
• lock_expired # boolean signifying if the lock has expired

Does anyone know if this already exists? It doesn't seem to difficult to write, so if it doesn't exist I may write it myself.

Answer 1

You can use a session to store the hash

import hashlib

def contact(request):
    if request.method == 'POST':
        form = MyForm(request.POST)
        #join all the fields in one string
        hashstring=hashlib.sha1(fieldsstring)
        if request.session.get('sesionform')!=hashstring:
            if form.is_valid() :                                         
                request.session['sesionform'] = hashstring
                #do some stuff...
                return HttpResponseRedirect('/thanks/') # Redirect after POST  
        else
           raise SubmissionWasDuplicate("duplicate")
    else:
        form = MyForm() 

With this approach (not deleting the session cookie) the user can't re-store the data util the session expires, by the way, i'm assuming that exist something who identify the user who send the data