Question

I am developing an application in C# ASP.NET to allow users to customise a number of graphics templates with their company logo.

Typically,

1. User uploads their company logo.
2. User selects a number of templates (through a HTML form) of different file types for customising.
3. My web application will accept the user’s request, go through each individual item requested and determine its file type. It will then call the appropriate module depending on the file type (e.g. to customise a PDF) and finally insert the logo in the template. These steps are repeated for each file requested.
4. Once all requested templates for a user are generated, they are grouped together in a zip file and a link for downloading is sent via email.

I would like some advice on how best to accept the user’s requests and process the files in ASP.NET.

One way of doing this is to keep the user waiting until all files are generated, therefore until the form handling script would have completed its execution. I reckon this is likely to trigger script timeout errors quite easily for requests that take long to be processed (large number of templates requested or sizable number of concurrent users), and as such is not a very efficient solution.

Another option would be to register the user’s request, redirect him/her to another page immediately after (explaining that an email will be sent shortly with a download link), and then proceed to process the files on the server using some background job or similar without the risk of script timeouts. An email is sent when all files for that user are generated.

I am familiar with web application development but this is one of my first forays into .NET development so your help is greatly appreciated.

How can I implement the second option in C#?

Answer 1

It sounds like what you want is a web site which accepts the user input and then passes control to an offline process (such as a Windows Service) to perform the more intensive tasks asynchronously from the site, allowing the user to continue using the site (or go do something else) while processing takes place. Something like this:

1. User “initiates” a “batch” on the website. Whether it’s setting up some values, uploading some kind of batch of things to process, etc. is entirely up to what you’re doing. The main point is that the user starts it off.
2. The necessary information for the process to do its magic is persisted to the database and the user is told that the process has been queued for processing. The user can now go about doing other things.
3. The back-end application (or multiple applications) polls the database periodically (every minute, every 5 minutes, etc.) or, in the case of an uploaded “batch” file could use something like a FileSystemWatcher, to look for new things to do and does them. Use multi-threading or whatever you need to make that happen, but the main point is that it’s an “offline” process that the website isn’t waiting on.
4. When the process completes, some flag is set in the database (on the record being processed, or maybe a “message” record in the user’s “inbox” or whatever) indicating that the process is done.
5. The website UI has some indicator which, any time it’s loaded, checks for the aforementioned flag(s) to indicate to the user that a queued process has been completed and is ready to be viewed.

So, essentially, you have a single database accessed by two applications (your web application and your Windows Service (or console app run by a task scheduler, etc.).

Is that basically what you’re looking for? I feel like I could be more specific, do you have any specific concerns about the setup?