[IN DEVELOPMENT] EthereumJS client implementation
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vpulim Merge pull request #49 from ethereumjs/lightsync
Added LES flow control and support for serving headers
Latest commit 1d507ed Sep 24, 2018



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This is the work repository for the EthereumJS main chain client implementation project. This is a community project. See Development Stages for idea about the current project status, issues for open issues and a project layout and read through Community Project if you want to join.

See Technical Guidelines if you directly want to dive into development info.



For a summary of the project focus, some outline of a roadmap and information on the team and how to contribute/join see this document.


Client Setup

Installing the Client

npm install -g ethereumjs-client

Running the Client

Some building blocks for the client have already been implemented or outlined to further build upon.

You can run the current state of the client with:

ethereumjs --network=mainnet [--loglevel=debug]

Or show the help with

ethereumjs help

If you want to have verbose logging output for the p2p communication you can use...


for all output or something more targeted by listing the loggers like

DEBUG=devp2p:rlpx,devp2p:eth,-babel [CLIENT_START_COMMAND]


API Reference

Environment / Ecosystem

EthereumJS Ecosystem

This project will be embedded in the EthereumJS ecosystem and many submodules already exist and can be used within the project, have a look e.g. at ethereumjs-block, ethereumjs-vm, the merkle-patricia-tree or the ethereumjs-devp2p implementation.

To play well together within a client context, many sub module libraries need enhancements, e.g. to create a common logging context. There are also larger building blocks still missing, e.g. the Node Discovery V5 p2p implementation being necessary for a proper working light client sync. Due to the distributed nature of EthereumJS there will be internal (to be done in this repo) and external issues (to be done in other EthereumJS repos) to be worked on.

All (hopefully :-)) issues referring to the client implementation will be provided with a ethereumjs-client label which should be discoverable with a label search on GitHub:

Basic Environment

For library development the following basic environment is targeted. Some base requirements like the testing tool arise from the need of maintaining a somewhat unified EthereumJS environment where developers can switch between with some ease without the need to learn (too much) new tooling.



Contributors should aim to achieve the following goals when making design decisions:

  • Loosely coupled components: Components should require as little knowledge of the definitions of other components as possible. This reduces dependencies between PRs and encourages contributors to work in parallel. It also improves extensibility of the code as new features like sharding and libp2p support are added.
  • Easily tested: The design should make testing of individual components as easy as possible. This goes hand in hand with the previous goal of loose coupling.
  • Readable code: More readable code should encourage more contributions from the community and help with bug fixing.
  • Well documented: Similar to above, this will help both contributors and users of the project.

The current design tries to achieves the goals of loose coupling and ease of testing by using an event-driven architecture where possible. Readability is improved by using features of JavaScript ES6 such as classes, async/await, promises, arrow functions, for...of, template literals and destructuring assignment among others. Shorter names are used when possible and long functions are broken up into smaller helpers, along with JSDoc annotations for most methods and parameters. Documentation is auto-generated from JSDoc comments and many examples of usage are provided (TO DO).

We will now briefly describe the directory structure and main components of the Ethereumjs client to help contributors better understand how the project is organized.

Directory structure

  • /bin Contains the CLI script for the ethereumjs command
  • /docs Contains auto-generated API docs as well as other supporting documentation
  • /lib/blockchain Contains the Chain, BlockPool and HeaderPool classes.
  • /lib/net Contains all of the network layer classes including Peer, Protocol and its subclasses, Server and its subclasses, and PeerPool.
  • /lib/service Contains the various services. Currently, only EthService is implemented.
  • /lib/rpc Contains the RPC server (optionally) embedded in the client.
  • /lib/sync Contains the various chain synchronizers. Currently, only FastSynchronizer is implemented.
  • /tests Contains test cases, testing helper functions, mocks and test data


  • Chain [In Progress] This class represents the blockchain and is a wrapper around ethereumjs-blockchain. It handles creation of the data directory, provides basic blockchain operations and maintains an updated current state of the blockchain, including current height, total difficulty, and latest block.
  • BlockPool [In Progress] This class holds segments of the blockchain that have been downloaded from other peers. Once valid, sequential segments are available, they are automatically added to the blockchain
    • HeaderPool [In Progress] This is a subclass of BlockPool that holds header segments instead of block segments. It is useful for light syncs when downloading sequential headers in parallel.
  • Server This class represents a server that discovers new peers and handles incoming and dropped connections. When a new peer connects, the Server class will negotiate protocols and emit a connected event with a new Peerinstance. The peer will have properties corresponding to each protocol. For example, if a new peer understands the eth protocol, it will contain an eth property that provides all eth protocol methods (for example: peer.eth.getBlockHeaders())
    • RlpxServer [In Progress] Subclass of Server that implements the devp2p/rlpx transport.
    • Libp2pServer [Not Started] Subclass of Server that implements the libp2p transport.
  • Peer Represents a network peer. Instances of Peer are generated by the Server subclasses and contain instances of supported protocol classes as properties. Instances of Peer subclasses can also be used to directly connect to other nodes via the connect() method. Peers emit message events whenever a new message is received using any of the supported protocols.
    • RlpxPeer [In Progress] Subclass of Peer that implements the devp2p/rlpx transport.
    • Libp2pPeer [Not Started] Subclass of Peer that implements the libp2p transport.
  • Protocol [In Progress] This class and subclasses provide a user-friendly wrapper around the low level ethereum protocols such as eth/62, eth/62 and les/2. Subclasses must define the messages provided by the protocol.
    • EthProtocol [In Progress] Implements the eth/62 and eth/63 protocols.
    • LesProtocol [In Progress] Implements the les/2 protocol.
    • ShhProtocol [Not Started] Implements the whisper protocol.
  • PeerPool [In Progress] Represents a pool of network peers. PeerPool instances emit added and removed events when new peers are added and removed and also emit the message event whenever any of the peers in the pool emit a message. Each Service has an associated PeerPool and they are used primarily by Synchronizers to help with blockchain synchronization.
  • Synchronizer Subclasses of this class implements a specific blockchain synchronization strategy. They also make use of subclasses of the Fetcher class that help fetch headers and bodies from pool peers.
    • FastSynchronizer [Not Started] Implements fast syncing of the blockchain
    • LightSynchronizer [In Progress] Implements light syncing of the blockchain
  • Service Subclasses of Service will implement specific functionality of a Node. For example, the EthService will synchronize the blockchain using the fast or light sync protocols. Each service must specify which protocols it needs and define a start() and stop() function.
    • EthService [In Progress] Implementation of an ethereum fast sync and light sync node.
    • ShhService [Not Started] Implementation of an ethereum whisper node.
  • Node [In Progress] Represents the top-level ethereum node, and is responsible for managing the lifecycle of included services.
  • RPCManager [In Progress] Implements an embedded JSON-RPC server to handle incoming RPC requests.

Contribution Guidelines

Communication This is distributed team effort. If you plan to take on larger issues always pre-announce your work intention on the issue page and drop a short note on what you are planning to do. If there is no issue for the stuff you want to work on create one and describe the problem and outline the intended implementation before start working.

Branch Structure

Development will take place via feature branches being merged against a protected master branch. Always develop on branch also when being on your own fork, use meaningful branch names like new-debug-cl-option or fixed-this-really-annoying-bug.


No meaningful new PR will be accepted without associated tests (exceptions might be done on a case-by-case basis). Test coverage should not increase (significantly) by a new PR. You might also want to consider writing your tests first and then directly push them, since this would be a good starting point for discussing the scope/implementation of a feature.