*`stable` - latest stable release - **this branch is recommended for most users**
*`testing` - pre-release branch with features and bugfixes slated for the next stable release - this branch is suitable for use on testnets and for adventerous users that want to live on the edge.
*`unstable` - main development branch against which PR's are merged - if you want to contribute to Nimbus, start here.
To get started with developing Nimbus itself, see the [developer handbook](https://nimbus.guide/developers.html). The code follows the [Status Nim Style Guide](https://status-im.github.io/nim-style-guide/).
Nimbus is built in the [Nim language](https://nim-lang.org) - the compiler is automatically installed when building the project for the first time. More information - in particular security-related information about the language - can be found in the [Auditor Handbook](https://nimbus.guide/auditors-book/).
The state transition simulator can quickly run the Beacon chain state transition function in isolation and output JSON snapshots of the state. The simulation runs without networking and blocks are processed without slot time delays.
```bash
# build and run the state simulator, then display its help ("-d:release" speeds it
# up substantially, allowing the simulation of longer runs in reasonable time)
The local network simulation will create a full peer-to-peer network of beacon nodes and validators on a single machine, and run the beacon chain in real time.
Parameters such as shard, validator counts, and data folders are configured [vars.sh](tests/simulation/vars.sh). They can be set in as environment variables before launching the simulation.
You can find out more about it in the [development update](https://our.status.im/nimbus-development-update-2018-12-2/).
_Alternatively, fire up our [experimental Vagrant instance with Nim pre-installed](https://our.status.im/setting-up-a-local-vagrant-environment-for-nim-development/) and give us yout feedback about the process!_
### Visualising simulation metrics
The [generic instructions from the Nimbus repo](https://github.com/status-im/nimbus/#metric-visualisation) apply here as well.
The [inspector tool](./beacon_chain/inspector.nim) can help monitor the libp2p network and the various channels where blocks and attestations are being transmitted, showing message and connectivity metadata. By default, it will monitor all ethereum 2 gossip traffic.
```bash
. ./env.sh
# Build inspector for minimal config:
./env.sh nim c -d:const_preset=minimal -o:build/inspector_minimal beacon_chain/inspector.nim
# Build inspector for mainnet config:
./env.sh nim c -d:const_preset=mainnet -o:build/inspector_mainnet beacon_chain/inspector.nim
# See available options
./env.sh build/inspector_minimal --help
# Connect to a network from eth2 testnet repo bootstrap file - --decode option attempts to decode the messages as well
./env.sh build/inspector_minimal --decode -b:$(curl -s https://raw.githubusercontent.com/eth2-clients/eth2-testnets/master/nimbus/testnet0/bootstrap_nodes.txt | head -n1)
Local testnets run for 4 epochs each, to test finalization. That happens only on Jenkins Linux hosts, and their logs are available for download as artifacts, from the job's page. Don't expect these artifacts to be kept more than a day after the corresponding branch is deleted.
