An online judge REST API which grades algorithmic task solutions automatically.

• Solve algorithmic problems in given time and memory limits
• Task and test case creation
• Support for task solutions in multiple programming languages
• Tags for tasks
• User profiles showing solved tasks

The operating system requirement for the server is Linux because of its nifty features. I have used Debian-based Ubuntu 18.04 for testing but it's probably possible to use other Linux distributions as well, with few to no changes.

1. Install cgroup tools for manipulation of cgroups (cgcreate, cgset, cgget, cgexec, cgdelete)

$ sudo apt install cgroup-tools

2. Create a non-privileged Linux user that will be used to run user programs (you will be prompted to select a password). We will also add him to a newly created Linux group with disabled network access. Execute the following commands:

$ sudo adduser coderunner

$ sudo addgroup no-network

$ sudo adduser coderunner no-network

$ sudo iptables -I OUTPUT 1 -m owner --gid-owner no-network -j DROP

3. Allow some commands to be usable as sudo without a password in the /etc/sudoers file. This is a requirement for the system to be autonomous. Because user solutions will be executed by a non-privileged Linux user, as opposed to the privileged user <YOUR_LINUX_USERNAME> who will be starting the REST API service, this change does not pose a security threat. Execute the following command and insert the below line, with the username replaced, at the end of the file:

$ sudo visudo -f /etc/sudoers

<YOUR_LINUX_USERNAME> ALL = (root) NOPASSWD: /usr/bin/cgcreate,/usr/bin/cgset,/usr/bin/cgexec,/usr/bin/cgdelete,/usr/bin/timeout

4. Make a directory executionroot in your Linux user's home directory (~) to serve as a chroot jail from which the task solutions will be executed. You can use a different directory for this, but be sure to update the reference in the project.
5. Copy /bin/bash and its dependencies (using ldd and cp) into ~/executionroot/ with these commands:

$ chr=~/executionroot

$ cp -v --parents /bin/bash "${chr}"

$ list="$(ldd /bin/bash | egrep -o '/lib.*\.[0-9]')"

$ for i in $list; do cp -v --parents "$i" "${chr}"; done

1. Run the two SQL scripts from the /database-scripts/ directory to create the project MySQL database schema and to populate it with initial data.
2. The project back end assumes the following MySQL connection pairs: localhost for the server, root for the username and no password. If needed, change the connection string in the /OnlineJudgeApi/appsettings.json file.

ASP.NET Core Web API version used: 3.1
Authentication handled via JSON Web Tokens (JWT)

Versions used:

• .NET Core 3.1 SDK
• MySQL 8.0.11

Link to Angular front-end web app repository

To serve the REST API locally run the following command from the /OnlineJudgeApi/ directory:

dotnet run

• JSON Web Tokens - Authorization tokens for a RESTful API