Uploadify is a wonderful plugin for jQuery that allows you to upload several files at once, it does the uploads transparently using flash (take a look at the demo on this link).
Apart of uploading files, you can also upload any other variables or data (take a look to scriptData). This can be really useful if you want, for example,to send the data in another form at the same time a file is being uploaded.
The great disadvantage of uploadify, is that each file is sent in a separate request. This means that if you are uplading 30 files, each file is sent in a separate HTTP request. Please note that the problem here is not the speed, because you can easily make uploadify sends several files at once, in parallel, the problem appears if you have to send form data on the first request only… The fact that are different requests makes things a little more difficult to handle on the server, but anyway, this only happens on specific cases…
Anyway, I recently used uploadify in a project where users should be logged in, in order to upload files. The thing is, when I first tried uploadify, it didn’t work… files were being apparently uploaded, but they were not stored in the server. I tried again and again, and the same problem… Finally I discovered why.
Uploadify does not send cookies, and because of that, it cannot send session information on the request, so the server does not know that the user sending the files is registered, it thinks it’s an annonymous user. The good thing, is that once I realiced what was the problem, the solution was quite simple.
The solution to keep the session using uploadify is the same as when the client cannot store cookies. Basically is just adding session name and identifier at the end of the URL, as a GET request.
In PHP, adding session to the URL would be something like:
$url = $url . '?' . session_name() . '=' . session_id();
Once I did that, the application was working with uploadify