Keysend Messenger

Overview

Learning objectives

• Ship a working Keysend Messenger that matches the description
• Cover the core skills: Keysend, Onion payloads, Node RPC
• Document setup, demo steps, and known limitations in the README

Prerequisites

• Onion Routing
• HTLC Mechanics

Part of the lightning roadmap.

Architecture diagram

app/          primary interface (CLI, API, or UI)
domain/       protocol and business logic
adapters/     Bitcoin Core, Lightning node, or indexer clients
tests/        smoke and regression coverage

Requirements

• Implements the stated goal: Send and receive spontaneous keysend payments with a tiny TLV payload for chat-like demos on testnet.
• Runs against regtest, signet, or documented testnet endpoints (never assume mainnet funds)
• Includes a README with install, run, and demo instructions
• Has at least one automated test or scripted smoke check
• Fails safely with clear errors when dependencies are offline

Stretch goals

• Add a short architecture diagram to the README
• Publish a demo recording or asciinema session
• Compare two implementation approaches and note tradeoffs
• Add CI that runs the smoke test on every push

Recommended resources

• Mastering the Lightning Network
• Lightning BOLTs
• Bitcoin Optech Lightning topics

Example repositories

• Polar

  Local Lightning lab for multi-node experiments.

• LDK sample node

  Embeddable Lightning patterns.

Submission instructions

• Public GitHub repository with a clear README
• Setup steps for local dependencies (regtest, Polar, Docker, etc.)
• Demo evidence (commands, screenshots, or short recording)
• Lab evidence pack: happy-path transcript + one intentional failure case + what error you saw
• Note difficulty assumptions and what you deliberately left out

Discussion