protocol interface

You might try with the:
Experimental: Play with the RunServer

http://www.sikulix.com/support.html

... and tell me a bit about your experiences.

Reading the documentation, these are the commands that the api accepts:

stop - stops the server
start - initiates a JavaScript runner, so the next run request will start the script without delay
startp - initiates a Jython runner, so the next run request will start the script without delay *
scripts/folder/folder/folder/... - sets the folder where the runner finds the scripts **
images/folder/folder/folder/... - sets the folder where the runner finds the images used in a script (image path) **
run/script - looks for the script in the given folder and runs it (starts the respective runner if not yet done) ***

It appears that there is only a way to run a file, and not a string containing a script content. So I have to save the string into a file first and then run it. This is a bit annoying. Am I missing something ?

--- This is a bit annoying
Yes, but it is as it is, so take it or leave it ;-)

... you might write your own snippet, to save a given string to a file and then run it.

... or you might setup your own socket based server to do what you want.