Besu Execution Client

This is a brief summary of important information you need to know when starting to contribute to Besu, a Java implementation of the execution client.

Code directory explanation

It is a multi-module gradle project. You can take a look to settings.gradle to see all modules:
- Each module has its own build.gradle:
  - You can specify its module name: archiveBaseName
  - You can specify its dependencies but without versions.
- Each module has its own source code here: /src/main/java
There are top-level modules:
- config:
  - Where most of the configuration is assembled, validated.
  - You can find the genesis information.
- besu:
  - All the CL arguments are being defined.
  - Is where the main method is located.
There are complementary modules:
- crypto:
  - Everything relative to cryptographic keys.
- data types:
  - Data types being used by Besu.
- metrics:
  - OpenTelemetry/Prometheus not tight to internal Besu.
- ethereum:
  - Is not a module but contains modules :
    - api :
      - All interaction you want to have with ethereum, world state.
    - core:
      - Storing date, quorum setup.
- evm:
  - EVM behavior
  - In this module you can find each opcode operation implementation.
There are enterprise modules:
- enclave, plugin-api, privacy-contracts

gradlew (file) :
- It is a bash script that will check if gradle is installed or not ( will install the wrapper for you and download the whole distribution)
- Gradle itself is managed as part of a wrapper that is used by calling this script.
gradle (folder):
- gradle-wrapper.properties:
  - distributionURL : points to the distribution to be used when calling ./gradlew
- versions.gradle (file):
  - It is where all module's versions are defined. It is used by gradlew.
build.gradle (file):
- plugins:
  - spotless: Code formatting, check licensing, etc,
    - Command: ./gradlew spotlessApply
  - errorprone: Compliance with best practices in Java.
    - Command: ./gradlew errorProne
- distribution:
  - It defines where the building output is left by taking all projects into an application:
    - .tar .zip distributions. You can see a .tar or .zip under builder/distributions.
build (folder):
- It's not a module.
- distributions (folder):
  - Location of the Besu distribution.
  - If you go deeper to build/distribution/besu-{version}-SNAPSHOT/lib you can see each version of each component and libraries.

Unit tests:
- Each module has its unit testing under src/test/java
Integration tests:
- Each module has its integration test under src/integration-test/java:
- Are more rare.
- Are run outside of the inner internals of the code.
- Are involved in more expensive runs.
Acceptance tests:
- Are located under the acceptance-test-module.
- Runs multiple Beau's nodes to create consensus algorithms between them and performs task adjusting and propagating blocks.
Reference tests:
- Taken after Ethereum tests, borrowed by the Ethereum foundation.
- Are the same for all clients: https://github.com/ethereum/tests
- Are stored in JSON:
  - Location: ethereum/referencetests/
Other info:
- JUnit 4

BesuControllerBuilder:
- Manages all the components that are going to be used and needed to setup the client.
- On the build method you can see if you are building the correct domain object.
- It returns a BesuController.
BesuCommand:
- Represents the main Besu CLI command.
ForkIdManager:
- Responsible for building and representing the latest fork synchronized.
- We always need to know where we are in terms of our own chain. This check is done constantly.
- It is created on EthProtocolManager which is created on BesuControllerBuilder.
ProtocolSchedule:
- Keeps track of all the configuration items as part of a specific range of block numbers for a chain.
ProtocolSpec:
- Let's you configure every aspect of how things work inside the protocol.
MainnetProtocolSpec:
- You will find every spec since frontier.
- Each new spec is built on top of the previous one and add or change what is necessary.
MainnetEVMs:
- Provides to the EVM the appropriate operations for mainnet hard forks.
- It is an aggregate state where most of the time you will be adding new features to the spec itself.
- New operations will be registered here.
JsonRpcMethodsFactory:
- A builder class for RPC methods.
- From here you can understand how to create new RPC methods.

https://doc.libsodium.org/:
- Sodium is a modern, easy-to-use software library for encryption, decryption, signatures, password hashing, and more.
https://github.com/nss-dev/nss:
- Network Security Services (NSS) is a set of libraries designed to support cross-platform development of security-enabled client and server applications. NSS supports TLS 1.2, TLS 1.3, PKCS #5, PKCS#7, PKCS #11, PKCS #12, S/MIME, X.509 v3 certificates, and other security standards.