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feat: implement RNS transport (Smol Mail 1.2) over microReticulum

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randogoth 2026-09-28 15:52:37 +03:00
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# 分身 bunshin
A Rust implementation of the [Smol Mail](https://code.randogoth.com/randogoth/smolmail) server: a minimalist, end-to-end encrypted mail protocol over a Noise-secured TCP connection. `bunshin` implements the server side only — receiving, storing and serving sealed mail — not the client.
A Rust implementation of the [Smol Mail](https://code.randogoth.com/randogoth/smolmail) server: a minimalist, end-to-end encrypted mail protocol over a Noise-secured TCP connection, with an optional Reticulum (RNS) mesh carrier behind the `rns` build feature. `bunshin` implements the server side only — receiving, storing and serving sealed mail — not the client.
The server never sees plaintext, sender identities or any private key. It learns only which mailbox an envelope is for, its size, and when it arrived.
@ -34,6 +34,8 @@ Add bunshin as a flake input and import the module:
`services.bunshin` also takes `host`, `port`, `dataDir`, `maxEnvelope`, `quota`, `requestsQuota`, `retentionDays`, `requestsRetentionDays`, `maxTokens`, `rateConnections`, `rateSends` and `rateTokens`; see `flake.nix` for defaults. The module renders a `systemd` unit that runs `bunshin serve` under `DynamicUser`; it does not generate a key.
For the RNS carrier, build `packages.rns`, set `services.bunshin.package` to it, and enable `services.bunshin.rns` with its `keyFile`; see [RNS.md](RNS.md) for the protocol and the remaining options.
Before the first deploy, generate the server's static key once (from a dev shell or `nix run`) and place it at the configured `keyFile`:
```
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`keygen` writes the server's static X25519 key (used for the Noise handshake, distinct from any user's Ed25519 identity) and prints its public key in base32. Publish that public key through a trusted channel — clients pin it, and a mismatch aborts the handshake.
## RNS carrier
The `rns` feature (built by `packages.rns`, wired to the module through `services.bunshin.rns`) serves the same mailbox over the Reticulum Network Stack alongside TCP: `bunshin serve --rns` runs both carriers in one process against one database. The mesh address is the `smolmail.server` destination hash — there is no key to pin, the address is the pin.
```
bunshin rns-keygen --key server.rns.key
bunshin serve --rns --key server.key --rns-key server.rns.key --db mail.db --rns-udp 0.0.0.0:4242
```
`rns-keygen` writes the 64-byte Reticulum identity and prints the destination hash; publish `smol+rns://<user>@<hash>` as the server's address. RNS-specific limits (`--rns-max-envelope`, `--rns-fetch-budget`, `--rns-max-links`, `--rns-rate-link-requests`, `--rns-rate-link-bytes`) default to mesh-friendly 32 KiB caps; the UDP interface is the one supported transport interface so far. See [RNS.md](RNS.md).
## Building
Requires a Rust toolchain (stable, edition 2021) and a C compiler — `rusqlite`'s `bundled` feature compiles SQLite from source rather than linking a system copy, so no separate SQLite install is needed.
Requires a Rust toolchain (stable, edition 2021) and a C compiler — `rusqlite`'s `bundled` feature compiles SQLite from source rather than linking a system copy, so no separate SQLite install is needed. The `rns` feature additionally needs cmake, ninja and a microReticulum checkout pointed at by `MICRORETICULUM_SOURCE_DIR` — the flake's dev shell provides all of it.
```
cargo build --release
@ -65,3 +78,5 @@ bunshin serve --key server.key --db mail.db --host 0.0.0.0 --port 1961
## Status
Implements SPEC.md version 1.1 in full: `AUTH`, `RESOLVE`, `SEND`, `FETCH`, `DELETE` and `REGISTER`, including accept tokens and the main/requests tier split, fetch cursors, 32-byte message ids, `REGISTER` proof of possession, and dual-signed key rotation chains.
With the `rns` feature, implements the version 1.2 RNS transport: the same six operations over Reticulum Links to an announced `smolmail.server` destination, with link-bound AUTH/REGISTER signatures, per-link request and byte limits, and a concurrent-link cap. One server process can serve both carriers over one store.