How to generate a .so file - linux

Question

I am writing an extension for the Scratch text editor application on Elementary OS Luna. But the documentation is practically non-existent for extension creation and I have no idea how to proceed after writing my main code for the extension.
I've already written the extension. I cannot use or test it yet as it needs to be "installed". I spent hours looking for docs but they do not exist. I did however, find a comment on the scratch launchpad page that says
Generally you have to generate a pluginname.so file and put it in
lib/scratch/plugins/pluginname with a pluginname.plugin file
Great. This seems like the last part of creating an extension for Scratch. What is a .so file, and how do I generate one? I've already created the other necessary files like the .plugin file and the .vala file.
Yes, I have searched for .so files but all I found were random things about it like using it with C, or C++ headers but obviously that won't work for me, since I'm using Vala?
How do I generate a .so file? What do I generate it from?

Answer 1

I think the The Vala tutorial could be helpful on creating the actual Shared library or Shared Object.
You can use the autotools, cmake or you can compile and link a shared library directly from the command line, quoted from the Vala tutorial:
Compilation and linking using Command Line
Vala is not yet capable of directly creating dynamic or static
libraries. To create a library, proceed with the -c (compile only)
switch and link the object files with your favourite linker, i.e.
libtool or ar.
$ valac -c ...(source files)
$ ar cx ...(object files)
or by compiling the intermediate C code with gcc
$ valac -C ...(source files)
$ gcc -o my-best-library.so --shared -fPIC ...(compiled C code files)...

Answer 2

From the Scratch Wiki
Due to browser security restrictions, Scratch 2.0 cannot interact with
hardware devices directly. Instead, hardware extensions come with a
helper app, a separate application that the user must install and run
on their computer. Scratch communicates with the helper app via HTTP
requests, and the helper app talks to the hardware. In the future,
some extensions may package their helper apps as browser plugins.
Here are the steps for creating and testing a Scratch extension:
Create an extension description file
Create your helper app and start it
Open the Scratch 2 Offline Editor
Import the extension description (shift-click on "File" and select "Import Experimental Extension" from the menu)
The new extension blocks will appear in the More Blocks palette
Test your extension and iterate!
Helper apps can be written in any language that supports server sockets, such as Python, Node.js, Java, C, etc.
Like you I've chased around the wiki but I cannot find an example with source. So all I can do is to address your question generally.
If you look at Build .so file from .c file using gcc command line you'll see how a simple .so can be created. However what code goes into a Scratch extension I don't know. Sorry.
Edit: More googling and I've found a sample from Nathan Dinsmore on GitHub that doesn't use C rather it uses JavaScript, and though it doesn't create a .so extension, it does have what appears to be a full description of creating an extension. He also provides a couple of tutorials.
Edit++ : And here is another sample written in Java.