Validating HTML form details before submitting it - using php

Question

I had an upload form on my website, where users entered details about their upload file, selected the file and uploaded to the webserver.

The POST action of the form was to submit the file to a php page called upload_control.php, where the post details were validated, and if correct the file was stored on disk an entry was placed in the database. The file was renamed to ID_name before storing, where the ID was taken from the database, as the largest ID so far (just a counter).

Now things have changed and it makes more sense to upload the file to storage elsewhere. This is done straight by the user, the action of the form points to the other server which stores the file if the form was submitted correctly. [ I have no control over the processing done by the other server, it's a storage solution like amazon s3 ]

The problem is: How do I get the last used ID from my database, so that I rename the file to ID_filename with javascript before uploading? (I can store the filename on a hidden form field and the remote server will understand to rename it when it receives it).

Better yet: Is there a way to validate all the form details - using php. not javascript, before submiting the form to the storage solution?

My thoughts are towards sending the form details to a php script on my server with ajax, upon hitting the submit button but before posting, so that the php script can get the latest id from the database, validate the request, send back the new details or the new id, and then really submit the form. -- But how can this by done?

Answer 1

on button click call php function through ajax, and pass all the data collected from page to service as json, php is very strong at parsing json. and you can return result from that method to indicate whether to data is authenticated or not. A nice tutorial to hook you up is this.

http://www.queness.com/post/328/a-simple-ajax-driven-website-with-jqueryphp