Multi User Domain - Jena Project

The goal of this project is to provide a set of Java utilities to serve resources for the Multi User Domain platform

Using the semantic web technologies, it should be possible to build a Multi User Domain which

Tech Stack:

• Java 8-11
• Apache Tomcat 9
• Jersey
• Apache Jena 3

Separation of Concerns

The framework is currently in only one repository, but is being built with a separation of concerns in mind:

• World Server. Responsible for the physical (shared) objects of a world. Largely just intended to be a layer to protect the data store and define the rules for interaction
• The User's POD: Users store their data themselves, via Solid Pods. This allows them to take characters between worlds, for example. Not provided by this library, relies on the client-side.
• Content Server. The eyes and ears of the player. A client requests from it to describe a particular object, and it will return the associated content which it can from it. (E.g. there may be a game on at the stadium, so I will describe it as busy). A key design concern is that one client may be pulling data from multiple content servers
• Action Server. Provides endpoints allowing the user to act. E.g. I may want to build a house in a settlement. I would POST the Action Server and it should manage this for me
• TODO: Simulation Servers: programs which push content to other servers but which are not players. For example a Sim server which expands populations at a realistic rate, or which randomly packs it with gangs of anarchist bank robbers

By separating these concerns it allows for greater modularity and use of the application. For example I may want to define a World Server and see the interesting ways in which players and programs will change it over time, without wanting to concern myself with providing rich descriptions of the world. I may want to produce Action Server content which allows people to build things in other worlds

Getting Started Locally

Contact us if you have any difficulties!

Installation

• Install a Java IDE for web development, e.g. Eclipse IDE for Java EE developers
• Clone the repository locally

Import into Eclipse workspace

• File -> Import -> from Git -> General Project
• Convert to Maven project so that the dependencies from pom.xml will be installed

Running Tomcat server from Eclipse

The recommended way to run this project is using Docker (see below)

• Click on the servers tab
• Click create new server
• Select Apache -> Apache Tomcat 9
• Install Tomcat 9 if necessary, or select the parent folder of the local install
• Double click on the server to edit it, switch to the 'modules' tab
• Add mud-jena as a module and set the path to /

In older versions of Eclipse

• In Eclipse
• In the Project Explorer, right-click on the MUD project and select Properties
• In the resultant window, select Targeted Runtimes
• Click New
• Select Apache Tomcat v9.0
• Check the box labeled Create a new local server
• Click Next
• In the Tomcat Installation directory field, type the value of your CATALINA_HOME environment variable. For example following the previous tutorial it would be /opt/tomcat/latest/
• Click Finish
• In the Targeted Runtimes dialog, click (mark the checkbox) the newly-created Apache Tomcat v9.0 entry.
• Click OK
• Now the Project Explorer pane should show two entries: one is the project; the other is the test server for your project.
• Please edit the file server.xml in the Tomcat server folder. Under <Host>, find the <Context> tag and edit the path attribute to be an empty string "" (<Host ...> <Context path="" ... /> ... </Host>. We need this because we use /.well-known/.. in the MUD Discovery specs, when a client is discovering the capabilities of a server.
• Select Window / Show View / Servers. That should show your Tomcat test server, whether it needs to be updated (“republish”) and whether it’s running or stopped. Right click it and click "debug"

Useful info to newcomers to Java servers/Tomcat

The file web.xml holds the Java Servlet configuration for the local server (src/main/webapp/WEB-INF/web.xml)

If you're running the application in Tomcat, you will have another server.xml configuration in the Tomcat server

The file pom.xml holds the Maven dependencies for the project

Running Unit Tests

We use JUnit tests (and sometimes the Jersey extension JerseyTest)

Docker

You can build and run the application using the Dockerfile. Building the image requires no specific build args, so can be done simply with:

docker build . -t mud-jena:<branch>

To run the image, simply bind port 8080 to a local port:

docker run -p 8080:8080  mud-jena:<branch>

CI

We run Docker build on PRs in this repo (restricted to contributors only for security reasons), so if you want to checkout a PR or master, you can use our prebuilt images like so:

docker run -p 8080:8080 multiuserdomain/mud-jena:master

docker run -p 8080:8080 multiuserdomain/mud-jena:<branch-name>

Deploying to a production Tomcat server

• In Eclipse, in the Project Explorer, right-click on the MUD project name and select Export / WAR file
• For Destination, click the Browse button
• Navigate to the folder you wish to save the .war file to, choose what to name it, and click Save
• Check Export Source Files. Without this option, your html files would not be included in the .war file.
• Click Finish
• Add the project WAR file to your server
• Please make sure that in your server.xml the path attribute in <Host ...> <Context path="" ... /> ... </Host> is set to an empty string "". This is because we use /.well-known/ in the MUD specs

Contributing

Join our Discord server and say hello! https://discord.gg/sauZA3jCK7