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DESIGN.md

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Design

Goals

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 achieve 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 TypeDoc annotations for most methods and parameters. Documentation is auto-generated from TypeDoc 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.
  • /src/blockchain Contains the Chain class.
  • /src/net Contains all of the network layer classes including Peer, Protocol and its subclasses, Server and its subclasses, and PeerPool.
  • /src/service Contains the main Ethereum services (FullEthereumService and LightEthereumService).
  • /src/rpc Contains the RPC server (optionally) embedded in the client.
  • /src/sync Contains the various chain synchronizers and Fetcher helpers.
  • /src/miner Contains the miner module that can build new blocks on top of the chain.
  • /test Contains test cases, testing helper functions, mocks and test data.

Components

  • 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.
  • 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.
  • 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.
  • Protocol [In Progress] This class and subclasses provide a user-friendly wrapper around the low level ethereum protocols eth/66 and les/4. Subclasses must define the messages provided by the protocol.
    • EthProtocol [In Progress] Implements eth/66 protocol.
    • LesProtocol [In Progress] Implements les/4 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. The fetchers internally make use of streams to handle things like queuing and backpressure.
    • FullSynchronizer [In Progress] Implements full syncing of the blockchain
    • LightSynchronizer [In Progress] Implements light syncing of the blockchain
  • Handler Subclasses of this class implements a protocol message handler. Handlers respond to incoming requests from peers.
    • EthHandler [In Progress] Handles incoming ETH requests
    • LesHandler [In Progress] Handles incoming LES requests
  • Service Subclasses of Service will implement specific functionality of a Client. For example, the EthereumService subclasses will synchronize the blockchain using the full or light sync protocols. Each service must specify which protocols it needs and define a start() and stop() function.
    • FullEthereumService [In Progress] Implementation of ethereum full sync.
    • LightEthereumService [In Progress] Implementation of ethereum light sync.
  • Client [In Progress] Represents the top-level ethereum client, and is responsible for managing the lifecycle of included services.
  • RPCManager [In Progress] Implements an embedded JSON-RPC server to handle incoming RPC requests.