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# Implement Saga Pattern for Swap Operations with Recovery Mechanism ## Overview This PR refactors the swap operation implementation to use the saga pattern - a distributed transaction pattern that provides reliable transaction management through explicit state tracking and compensation-based error handling. The implementation includes a robust recovery mechanism that automatically handles swap operations interrupted by crashes, power loss, or network failures. ## What Changed **Saga Pattern Implementation:** - Introduced a strict linear state machine for swaps: `Initial` → `SetupComplete` → `Signed` → `Completed` - New modular `swap_saga` module with state validation, compensation logic, and saga orchestration - Automatic rollback of database changes on failure, ensuring atomic swap operations - Replaced previous swap implementation (`swap.rs`, `blinded_message_writer.rs`) with saga-based approach **Recovery Mechanism:** - Added `operation_id` and `operation_kind` columns to database schema for tracking which operation proofs belong to - New `recover_from_bad_swaps()` method that runs on mint startup to handle incomplete swaps - For proofs left in `PENDING` state from swap operations: - If blind signatures exist: marks proofs as `SPENT` (swap completed but not finalized) - If no blind signatures exist: removes proofs from database (swap failed partway through) - Database migrations included for both PostgreSQL and SQLite
Warning
This project is in early development, it does however work with real sats! Always use amounts you don't mind losing.
Cashu Development Kit
CDK is a collection of rust crates for Cashu wallets and mints written in Rust.
ALPHA This library is in early development, the api will change and should be used with caution.
Project structure
The project is split up into several crates in the crates/ directory:
- Libraries:
- cashu: Core Cashu protocol implementation.
- cdk: Rust implementation of Cashu protocol.
- cdk-sqlite: SQLite Storage backend.
- cdk-postgres: PostgreSQL Storage backend.
- cdk-redb: Redb Storage backend.
- cdk-axum: Axum webserver for mint.
- cdk-cln: CLN Lightning backend for mint.
- cdk-lnd: Lnd Lightning backend for mint.
- cdk-lnbits: LNbits Lightning backend for mint. Note: Only LNBits v1 API is supported.
- cdk-ldk-node: LDK Node Lightning backend for mint.
- cdk-fake-wallet: Fake Lightning backend for mint. To be used only for testing, quotes are automatically filled.
- cdk-common: Common utilities and shared code.
- cdk-sql-common: Common SQL utilities for storage backends.
- cdk-signatory: Signing utilities and cryptographic operations.
- cdk-payment-processor: Payment processing functionality.
- cdk-prometheus: Prometheus metrics integration.
- cdk-ffi: Foreign Function Interface bindings for other languages.
- cdk-integration-tests: Integration test suite.
- cdk-mint-rpc: Mint management gRPC server and cli.
- Binaries:
- cdk-cli: Cashu wallet CLI.
- cdk-mintd: Cashu Mint Binary.
- cdk-mint-cli: Cashu Mint management gRPC client cli.
Development
For a guide to settings up a development environment see DEVELOPMENT.md
Implemented NUTs:
Mandatory
| NUT # | Description |
|---|---|
| 00 | Cryptography and Models |
| 01 | Mint public keys |
| 02 | Keysets and fees |
| 03 | Swapping tokens |
| 04 | Minting tokens |
| 05 | Melting tokens |
| 06 | Mint info |
Optional
| # | Description | Status |
|---|---|---|
| 07 | Token state check | ✔️ |
| 08 | Overpaid Lightning fees | ✔️ |
| 09 | Signature restore | ✔️ |
| 10 | Spending conditions | ✔️ |
| 11 | Pay-To-Pubkey (P2PK) | ✔️ |
| 12 | DLEQ proofs | ✔️ |
| 13 | Deterministic secrets | ✔️ |
| 14 | Hashed Timelock Contracts (HTLCs) | ✔️ |
| 15 | Partial multi-path payments (MPP) | ✔️ |
| 16 | Animated QR codes | ❌ |
| 17 | WebSocket subscriptions | ✔️ |
| 18 | Payment Requests | ✔️ |
| 19 | Cached responses | ✔️ |
| 20 | Signature on Mint Quote | ✔️ |
| 21 | Clear Authentication | ✔️ |
| 22 | Blind Authentication | ✔️ |
| 23 | Payment Method: BOLT11 | ✔️ |
| 25 | Payment Method: BOLT12 | ✔️ |
License
Code is under the MIT License
Contribution
All contributions are welcome.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, shall be licensed as above, without any additional terms or conditions.
Please see the development guide.