External Web Interface for a C++ Application [closed]

Question

I am developing a web interface for a C++ application that runs on an embedded system.

I was wondering if it was possible to make a web interface that could be used to manage (set and get values) and display data provided by the application. (Something like Nagios.)

My question is: is there any technology that allows me to "communicate" between the Web interface and the C++ application?

Keep in mind that I have to do this on an embedded system, so I can't use frameworks or other things that are too heavy.

The Web Interface has to be outside the C++ Application (I don't want to code the interface in the C++ Applicaiton).

My idea was to use HTML5 and Javascript for the Web Interface, the web server which i will use is also lightweight (nginx).

If someone could give me any pointers it would be nice. Thank you in advance.

Answer 1

So you need two things: a local interface your web page can use to configure the C++ app, and the web page itself.

There are a few common mechanisms for such local interfaces:

1. modify a config file, and send SIGHUP to make the application re-read it

   • advantage is that you can test (and use) it directly from a shell, independently of the web interface
   • also note that changes persist automatically
   • disadvantage is that you need some scheme for storing a "last good" config file in case the edited one is damaged

2. use a local streams socket and simple protocol (either a UNIX socket if supported, or a localhost:port loopback-only TCP socket)

   • advantage is that you don't touch (and possibly damage) the config file(s)
   • disadvantages are that you then need some other way of persisting changes, if you want to, and that you have to write this protocol in the first place
   • note that so long as the protocol is text-based and not binary, you can at least still test it with telnet or netcat, so you can still use it directly from the shell
     • simple protocol like set variable=value, get variable etc. shouldn't be too hard

If you really want to decouple the web and C++ applications, make sure you can query the available options, ideally giving types, valid ranges and groups for them. Then, you can avoid re-coding the web page every time you add or modify an option.

You can manage that with magic comments in a config file (make sure nothing is silently defaulted with no comment), or with a list command to the stream socket.

With a bit of effort, you can probably build your grouping, data type and validation constraints into the type system of your C++ application, so both the local interface and web app can be driven automatically.