How do I / what is the best way to interact with a desktop application from a browser web application?

Question

Situation:

We have a desktop application. We also have a web application.

We need the two to interact with each other. So when a button is pushed in the web application, the desktop application needs to start running a process (pulling data from the cloud using an API we've created). With two local applications, this can be done with ports/listening, editing a flag somewhere locally, and the other application reading this flag, etc.

Can this be done from web -> desktop?

Ideally the web application would have direct communication with the desktop application and notify it to begin pulling data down from the cloud using our API. But if this is not possible, having the desktop app run a process that loops and checks for a flag in a file or something would be a good start.

After minimal research, I've found some stuff like HTML5 File Api which interacts with "Sandbox" directory on the local machine. I've also read that it is impossible to access any thing on the local machine for security reasons.

Also, I dont want the user to be prompted to request a download file everytime, we need things to happen behind the scenes. (Even if the user has to initally set up some lower security / permissions just for this situation)

Any input is appreciated!

Answer 1

Generally speaking, its a good thing that web pages cannot interact with your operating system. You wouldn't want any random site to be able to access your files and programs.

If you need to work around this, a couple of options come to mind. Each will require some effort.

1. turn your web application into a desktop application using a tool/framework such as node-webkit. Then you'll have access to the same local resources a desktop application would have.

2. Host the web application inside a desktop application with an embedded browser. Extend the javascript system to allow the web application to intereact with the host application.

3. Have the/a desktop app act as a web server, listening on port 80. Then within the web application, make calls to localhost:80.

4. Create an ActiveX that runs inside the web application that will handle the link.

5. Create a desktop version of your web application

Answer 2

I would begin by transitioning your data access to a protected service layer. If both the web application and desktop application are modified to pull from the same exact data source then it becomes trivial to establish a sort of "polling" of the service to determine if the action has been engaged and new work needs to begin.

Alternatively, you could retool your desktop application into a windows service that continuously watches either your data store or possibly use a filesystemwatcher to detect changes. If the web application has access to make changes to a file, then the service simply needs to watch for changes in that file to begin its actions.

Even beyond that, you could extend your windows service to accept snmp calls. Basically you would be building your own "server" that would be able to receive simple remote requests from your webserver. In essence, it would be a direct communication between web application and desktop application. I will agree here with @GrandmasterB that this is fairly dangerous if you are unfamiliar with this option as this creates a very dangerous intrusion vector on a public system. The connection will need to be secured to a specific port that is monitored and disallowed for all but the relevant systems, and it would be highly recommended to add some kind of encrypted authentication mechanism to it.

My preference, though, would be to make it a service based polling mechanism. It is easier to maintain, chews up fewer resources on either system, provides fewer intrusion vectors and is very scalable should your desktop application be rebuilt or rewritten for some reason.

Answer 3

Another solution is to have a link with custom URI scheme, such as subl://open. So you put following on the web:

<a href="my-app://action?param1=true&amp;param2=100">Open My App</a>

Then when user click the link, operating system will launch the corresponding local program. Registration of a custom URI scheme is OS dependent; for Windows, see the official documentation and question How do I register a custom URL protocol in Windows?.