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ADR 002: Light Client ADR Index

Changelog

  • 2019-10-30: First draft.
  • 2019-12-27: Add diagram and align with the code.
  • 2020-01-22: Refactor into multiple ADRs

Status

ADR Index.

Context

This is the first of multiple ADRs about the Tendermint light client in Rust. Light client specification and implementation is an ongoing work in progress, in English, TLA+, Go, and Rust. Note/TODO these links will soon be stale and need updating.

It is especially important to review the Motivation and Structure of the Light Client as described in the English Specification before reading these ADRs for the necessary context.

Here we are concerned primarily with the implementation of a light node in Rust. The light node process makes RPC requests to full nodes for blockchain data, uses the core verification library to verify this data, and updates its state accordingly. It also makes requests to other full nodes to detect and report on forks.

That said, as much as possible, we would like the implementation here to be reusable for the IBC protocol, which supports communiction between blockchains. In this case, instead of making RPC requests, IBC-enabled blockchains receive the relevant data in transactions and verify it using the same core verification library. Thus implementations should abstract over the source of data as necessary. For more information on IBC, see the spec repo, especially the specifications for client semantics and handler interface

A complete implementation of the light node includes many components, each of which deserves their own ADR. This ADR thus serves as an index for those, and may be updated over time as other components come into view or existing components are iterated upon.

Components include (TODO: links):

  • ADR-003 - Core Verification Library: Data types, traits, and public API for the core verification protocol, with support for use in light nodes and IBC implemented
  • ADR-004 - Command Line Interface: Choice of framework for the CLI and daemon, including config, arguments, logging, errors, etc.
  • ADR-005 - Fork Detection Module: Simple module to manage an address book of peers and search for conflicting commits

A schematic diagram of the light node, as taken from the English specification, is provided below:

Light Node Diagram.