refactor(relay): implement factory pattern with Mastodon and LitePub relay support

[sij411]

Summary

This PR refactors the @fedify/relay package to introduce a factory pattern that supports multiple relay implementations, specifically Mastodon and LitePub relay protocols. The changes improve code organization, maintainability, and extensibility for future relay implementations.

Key Changes

• Factory Pattern: Introduced createRelay() factory function that instantiates relay implementations based on type ("mastodon" or "litepub")
• Separate Relay Implementations:
  • MastodonRelay: Implements Mastodon's relay protocol with immediate follower acceptance
  • LitePubRelay: Implements LitePub's relay protocol with reciprocal follow pattern (pending → accepted states)
• Refactored Core Module: Extracted common relay infrastructure into relay.ts with shared:
  • Actor dispatcher for relay server actor
  • Key pair management (RSA + Ed25519)
  • Followers/Following collection dispatchers
• Comprehensive Test Coverage: Added dedicated test suites for both implementations:
  • mastodon.test.ts: 896 lines of tests covering Mastodon relay behavior
  • litepub.test.ts: 896 lines of tests covering LitePub relay behavior with reciprocal follows
  • Removed old monolithic relay.test.ts

Protocol Differences

Mastodon Relay:

• Immediately accepts Follow activities and adds followers to the active list
• Simpler subscription flow without reciprocal follow requirement
• Suitable for permissive relay scenarios

LitePub Relay:

• Implements reciprocal follow pattern (relay follows back the follower)
• Two-state follower lifecycle: pending → accepted
• Follower is only activated after accepting the relay's Follow activity
• More secure and controlled subscription process

Architecture Improvements

• Modular Design: Each relay type is self-contained with its own file and tests
• Extensibility: Easy to add new relay implementations (e.g., Akkoma, Pleroma variants)
• Shared Infrastructure: Common functionality centralized in relay.ts and relayBuilder
• Type Safety: Strong TypeScript typing with proper interfaces (RelayOptions, LitePubFollower)

Migration Guide

Before:

import { MastodonRelay, LitePubRelay } from "@fedify/relay";
const mastodonRelay = new MastodonRelay(options);
const litepubRelay = new LitePubRelay(options);

After:

import { createRelay } from "@fedify/relay";

// For Mastodon-compatible relay
const mastodonRelay = createRelay("mastodon", options);

// For LitePub-compatible relay
const litepubRelay = createRelay("litepub", options);

Files Changed

• packages/relay/src/relay.ts: Refactored to shared infrastructure (771 → 161 lines)
• packages/relay/src/mastodon.ts: New Mastodon relay implementation (191 lines)
• packages/relay/src/litepub.ts: New LitePub relay implementation (297 lines)
• packages/relay/src/mastodon.test.ts: New comprehensive test suite (784 lines)
• packages/relay/src/litepub.test.ts: New comprehensive test suite (896 lines)
• packages/relay/src/relay.test.ts: Removed old monolithic tests (1128 lines deleted)
• packages/relay/src/mod.ts: Updated exports to include new relay classes

Test Plan

• All Mastodon relay tests pass (784 lines of test coverage)
• All LitePub relay tests pass (896 lines of test coverage)
• Factory function correctly instantiates both relay types
• Follower management works correctly for both protocols
• Activity forwarding (Create, Update, Delete, Move, Announce) tested for both
• Subscription approval/rejection flows tested
• Reciprocal follow pattern tested for LitePub
• HTTP signature verification works across both implementations

Breaking Changes

This is a breaking change that requires updates to existing relay usage code:

• The Relay class constructor is replaced with createRelay() factory function
• Users must specify relay type: "mastodon" or "litepub"
• Default behavior changes based on selected relay type

Related Commits

• 36b6574: Add relay factory pattern with federation builder
• 03ea8aa: Add create factory function for mastodon and litepub
• 1e7c16f: Add mastodon relay and its test
• 0e17411: Add litepub relay and its test
• 7902d02: Delete old relay test

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