# CORE Developer's Guide

* Table of Contents
{:toc}

## Repository Overview

The CORE source consists of several different programming languages for historical reasons.
Current development focuses on the Python modules and daemon. Here is a brief description of the source directories.

| Directory | Description |
|---|---|
|daemon|Python CORE daemon code that handles receiving API calls and creating containers|
|docs|Markdown Documentation currently hosted on GitHub|
|gui|Tcl/Tk GUI|
|man|Template files for creating man pages for various CORE command line utilities|
|netns|Python C extension modules for creating CORE containers|
|ns3|Experimental python ns3 script support for running CORE|
|scripts|Template files used for running CORE as a service|

## Getting started

Overview for setting up the pipenv environment, building core, installing the GUI and netns, then running
the core-daemon for development.

### Clone CORE Repo

```shell
git clone https://github.com/coreemu/core.git
cd core
```

### Setup Python Environment

To leverage the dev environment you need python 3.6+.

```shell
# change to daemon directory
cd $REPO/daemon

# copy setup.py for installation
cp setup.py.in setup.py

# install pipenv
pip3 install pipenv

# setup a virtual environment and install all required development dependencies
python3 -m pipenv install --dev
```

### Setup pre-commit

Install pre-commit hooks to help automate running tool checks against code. Once installed every time a commit is made
python utilities will be ran to check validity of code, potentially failing and backing out the commit. This allows
one to review changes being made by tools ro the fix the issue noted. Then add the changes and commit again.

```shell
python3 -m pipenv run pre-commit install
```

### Build CORE

```shell
./bootstrap.sh
./configure --prefix=/usr
make
```

### Install netns and GUI

Below commands assume your development will be focused on the daemon.

```shell
# install GUI
cd $REPO/gui
sudo make install

# install netns scripts
cd $REPO/netns
sudo make install
```

### Adding EMANE to Pipenv

EMANE bindings are not available through pip, you will need to build and install from source.

[Build EMANE](https://github.com/adjacentlink/emane/wiki/Build#general-build-instructions)

```shell
# after building emane above
# ./autogen.sh && ./configure --prefix=/usr && make
python3 -m pipenv install $EMANEREPO/src/python
```

### Running CORE

This will run the core-daemon server using the configuration files within the repo.

```shell
sudo python3 -m pipenv run core
```

### Running CORE Python GUI

Must be ran after the daemon above or will fail to connect.

```shell
python3 -m pipenv run coretk
```

## Linux Network Namespace Commands

Linux network namespace containers are often managed using the *Linux Container Tools* or *lxc-tools* package. 
The lxc-tools website is available here http://lxc.sourceforge.net/ for more information.  CORE does not use these 
management utilities, but includes its own set of tools for instantiating and configuring network namespace containers. 
This section describes these tools.

### vnoded

The *vnoded* daemon is the program used to create a new namespace, and listen on a control channel for commands that 
may instantiate other processes. This daemon runs as PID 1 in the container. It is launched automatically by the CORE 
daemon. The control channel is a UNIX domain socket usually named */tmp/pycore.23098/n3*, for node 3 running on CORE 
session 23098, for example. Root privileges are required for creating a new namespace.

### vcmd

The *vcmd* program is used to connect to the *vnoded* daemon in a Linux network namespace, for running commands in the 
namespace. The CORE daemon uses the same channel for setting up a node and running processes within it. This program 
has two required arguments, the control channel name, and the command line to be run within the namespace. This command 
does not need to run with root privileges.

When you double-click on a node in a running emulation, CORE will open a shell window for that node using a command 
such as:

```shell
gnome-terminal -e vcmd -c /tmp/pycore.50160/n1 -- bash
```

Similarly, the IPv4 routes Observer Widget will run a command to display the routing table using a command such as:

```shell
vcmd -c /tmp/pycore.50160/n1 -- /sbin/ip -4 ro
```

### core-cleanup script

A script named *core-cleanup* is provided to clean up any running CORE emulations. It will attempt to kill any 
remaining vnoded processes, kill any EMANE processes, remove the :file:`/tmp/pycore.*` session directories, and remove 
any bridges or *ebtables* rules.  With a *-d* option, it will also kill any running CORE daemon.

### netns command

The *netns* command is not used by CORE directly. This utility can be used to run a command in a new network namespace 
for testing purposes. It does not open a control channel for receiving further commands.

### Other Useful Commands

Here are some other Linux commands that are useful for managing the Linux network namespace emulation.

```shell
# view the Linux bridging setup
brctl show
# view the netem rules used for applying link effects
tc qdisc show
# view the rules that make the wireless LAN work
ebtables -L
```