Verify if item is downloadable before downloading it to get better error messages in Joomla for subscriptions

[svenbluege]

By using an installer plugin and the method onInstallerBeforePackageDownload I can update paid extensions.

But the update will fail if the DownloadID is invalid. The Joomla error message is very useless and I want to improve this by checking the DownloadID in the onInstallerBeforePackageDownload method before using it.

I have two ideas how to do this:

1. add a dummy release + item which contains a simple text file and needs a subscription level to get downloaded.
2. ARS supports in the Item controllers download task a parameter like "checkOnly=true". Instead of downloading the item, it would return [success|failed]. A dedicated task might work as well.

If the check succeeds, onInstallerBeforePackageDownload can modify the URL. Otherwise it would attach a message like "Subscription expired, blabla".

In both cases, we would end up with additional entries in the download logs since logging failed download attempts might still be a good idea.

What do you think? Is there maybe a third way which is already in place?

[nikosdion]

These are all horrible ways to deal with a Joomla! architectural issue. The feature request is denied as pointless. You can always do a HEAD request. That said, based on my experience, I consider it a bad idea. First of all, you are using an installer plugin when you can simply insert the dlid=whatever in the database, using a feature I contributed back in Joomla! 3.2. Using an installer plugin is, in my humble opinion, utterly inane. It s far more likely that a user will disable that plugin which they don 't understand what it does (”but I have already installed Example Component, why the fsck do I need to keep published a plugin to install it?”) than having a Download ID issue. Using the database way is more transparent to the user, they can 't cock it up but it needs some more code on your part. The second problem is that you will be doing an HTTP request before returning results to Joomla. If the host has a firewall which prevents the outbound HTTP request and introduces a delay you might end up causing a blank page whenever the client tries to visit the Update page. This breaks their site in a way that is nearly impossible to understand how to fix. If you use the database field method the hang will only happen whenever they try to update anything or fetch new updates. However, this is something which can be troubleshooted and identified very easily. In any case, I don 't see the point for any of that. If the download of the update fails you just need to have a simple documentation page explaining to people what to do. Yes, about 0.3% of your users will still get confused and ask you what s going on. So what?

[svenbluege]

I get your point and will check the database way. Thanks for the feedback!

[innato]

I hit this page because I was also considering using the onInstallerBeforePackageDownload method as mentioned by @svenbluege . Now I understand that this may be a bad idea. However, when I have a subscription-based purchase that expires, I would really like to redirect the updating website to a web page of mine where he/she can renew the subscription when the update fails. How could that be done without a onInstallerBeforePackageDownload process? My extension already includes a system plug-in, so an additional function is not a problem.

[nikosdion]

You can’t. Joomla has stopped showing the server error message when a package download fails. It only shows the HTTP error code (number). You’d probably have to implement a very complicated installer plugin which asks your server whether the subscription is active or redirect the customer to a renewal page. This has atrocious performance, opens your site to abuse and has security issues. In my experience the best thing you can do is absolutely nothing. The few people with expired subscriptions will overwhelmingly come to your site to download the package and see that their subscription expires. The other 0.008% of your subscribers will either contact you or give up. The former you can explain what to do. The latter... do you really care to spend so much effort about them? I wouldn’t.