I'm trying to build a small utility in C to be used through web extension native messaging, following this MDN document. I have the extension side completed but am having some trouble on the application side. The examples are in Python and node.js and I need to use C.
I'd like to do what this poster did in C# described in this SO question.
Also, in this SO question, the poster's C program is being opened by Java and passed some data. It fits what I'm trying to do, if the Java side is performed by the extension.
My question is that I don't understand how stdin "knows" to get the input from the extension's message rather than the keyboard, for example. In the C code, in the statement fscanf(stdin, "%s", buff); from the last link above, how is stdin associated with the Java program, or does it not need to be and will read whatever source of input it receives?
If that is the case, and the communication port is set up such that the native application remains open for multiple messages from the extension, do you just repeat the fscanf or fread after a message is processed and the C program will wait for new input from any source again?
Lastly, if fread is always used, will that guarantee that stdin won't read input from any source other than the extension when it remains open in between messages?
Thank you.