108 lines
8.9 KiB
Markdown
108 lines
8.9 KiB
Markdown
# 文 fumi
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[](LICENSE) [](https://ai-declaration.md)
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A Rust client for [Smol Mail](https://code.randogoth.com/randogoth/smolmail): a minimalist, end-to-end encrypted mail protocol over a Noise-secured TCP connection. `fumi` derives an identity from one 32-byte master secret, seals and opens mail, and talks to a mailbox; it is the counterpart to [bunshin](https://code.randogoth.com/randogoth/bunshin), the server.
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## Status
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Both carriers are implemented: the TCP carrier (SPEC.md 1.1) and the Reticulum carrier of RNS.md (1.2), the latter behind the `rns` cargo feature (`nix build .#rns`). `fumi` interoperates in both directions with the reference stack — `smolmail.py`/`smolmaild.py` over TCP and `smolmail_rns.py`/`smolmaild_rns.py` over Reticulum — and with `bunshin` over both carriers, including the cross-transport case upstream section 15 promises: send over TCP, fetch over the mesh, one mailbox.
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## Addressing
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```
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alice@example.org[:1961] short form, resolved via the server
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smol://alice@example.org/mfrggzdfzt... self-certifying, 52-char base32 identity
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smol+rns://alice@8f2c1d0a7b6e5f4c3d2a1b0e9f8c7d6a short form over Reticulum (rns feature)
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smol+rns://alice@8f2c1d0a7b6e5f4c3d2a1b0e9f8c7d6a/mfrggzdfzt... self-certifying over Reticulum
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```
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## Usage
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One master per store, selected by the global `--key` and `--db` flags; a second identity is a second pair of files.
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```
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fumi [--key identity.key] [--db fumi.db] [--timeout 30] <command>
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# identity
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fumi keygen [--force] create a master secret
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fumi whoami address, public key, fingerprint, rotation index
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fumi restore <address> recover local state from the master alone
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fumi rotate advance the rotation index, sign and push the certificate
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# servers and contacts
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fumi trust <host> <key-b32> [--force] pin a server's Noise static key
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fumi register <address> [--invite TOKEN] bind this identity to a username
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fumi resolve <address> look up a contact's key, walk the chain, pin it
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fumi import <smol-uri> add a contact from a self-certifying address
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fumi contacts known keys and how each was learned
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# accept tokens
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fumi accept <address> issue a token, admit to the main tier, sync the set
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fumi block <address> withdraw it, sync the set
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# mail
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fumi send <address> [--subject S] [--body TEXT | --file F | -] [--header K:V] [--reply-to ID] [--anonymous] [--no-pad]
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fumi fetch [--keep] [--reset] retrieve, verify, store, acknowledge
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fumi delete <id>... remove from the server explicitly
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fumi list [--sent] [--requests]
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fumi read <id> [--sent]
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# RNS carrier (built with --features rns / nix build .#rns); addresses select
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# it by scheme, so these flags apply only to smol+rns:// dials:
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fumi --rns-udp <host:port> --rns-udp-forward <host:port> [--rns-storage DIR] <command>
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```
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On the mesh the destination hash is the pin (RNS.md 13.4): there is no `trust`, no static key, and a client creates no Reticulum identity (13.8). The `--rns-udp-forward` target is effectively required for a client, which speaks first; it should point at an `rnsd` or at the server's UDP interface. Requests carry an explicit 30-second timeout (13.5), links are torn down when a session ends (13.10), and a resend is safe because ids are derived.
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Mail is stored sealed and opened on demand; there is no plaintext at rest. A first contact is learned by trust on first use and marked unverified when the server's key was not pinned; a key change is accepted only when a signed rotation chain leads from the key held to the one offered, and is surfaced rather than applied silently.
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## Build
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```
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nix build # or: nix develop -c cargo build
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nix develop -c cargo test --workspace
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```
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The crate is a workspace: `core/` is the `fumi-core` library — everything but the command line — and `cli/` is the `fumi` binary. GUI hosts depend on `fumi-core` alone; it pulls no argument parsing, no logging globals, and no keyfile conventions. `bundled-sqlite` (default) vendors libsqlite3; embedders that link their own SQLite, as Android's NDK does, build with `default-features = false`.
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`bunshin` and the reference clients make a complete test rig: register against a local server, exchange mail in both directions, then rotate and fetch the mail that the superseded key still receives.
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## Embedding
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`fumi-core` is the protocol core of a GUI client, not just this CLI's engine. The contract an embedder can rely on:
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- **Secrets stay bytes in the API, files stay in the CLI.** `Account::new(master, index)` takes the master as bytes and `Store::open(path)` takes only mail and state; `identity.key` next to `fumi.db` is a CLI convention. A GUI keeps the master wherever its platform wants it (Android Keystore, OS keychain) and hands it over per operation.
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- **One shareable store handle.** `Store` is `Send + Sync`: every operation locks an inner mutex, and the database runs in WAL mode, so a host holds one `Store` behind an executor and reads it while a fetch writes. Each envelope is committed as it is verified — a concurrent reader listing the inbox sees fetch progress without any callback.
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- **Decisions, not prose.** `error::Error` is an enum: `NotPinned`, `PinMismatch`, `KeyChanged { address, known, offered }`, `NotRegistered`, `AuthFailed`, `RateLimited`, `QuotaExceeded`, `SchemaVersion`, ... — the distinctions a UI routes on. `Display` still produces the message the CLI prints.
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- **Long operations can stop.** `fetch_with` takes a `FetchOptions` with a cancellation token checked between pages; the cursor is saved per page, so a cancelled fetch resumes rather than repeats.
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- **Composable flows.** `restore` remains the one-call convenience, but its pieces are public: `connect` + `resolve`, `account::find_rotation_index`, then the `Store` setters — a wizard can hold the master and the address before it has connectivity, and show each step. Trust outcomes arrive as values: `TrustChange` from `trust_key` and `send`, `Session::unpinned_static` for the sec 4 warning.
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- **A versioned store.** The schema carries a `user_version`; a store written by a newer build is refused (`Error::SchemaVersion`) rather than misread, and within a version the schema is stable. The host, not the library, decides when to upgrade the binary.
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- **Binding from other languages.** The API is `Send`-friendly and free of CLI globals, so plain Rust bindings (flutter_rust_bridge, uniffi) work against it. `core/vectors.json` holds the reference vectors the unit tests pin — derivations, seals, a full envelope — so a port or FFI binding can verify itself end to end without the reference stack.
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The intended call graph: `Store::open` once, `Account::new(master, rotations)` per session, then `client::*` operations taking `&Store` and `&Account`. The store outlives accounts; nothing in the library caches between calls.
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## Modules
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| File | Contents |
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|---|---|
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| `core/src/crypto.rs` | base32, HKDF, HMAC, SHA-256, the Ed25519→X25519 map with SPEC.md §2's checks |
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| `core/src/address.rs` | parsing for all four address forms, username validation, fingerprints |
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| `core/src/account.rs` | master, `seed_n` derivation, accept-key and tokens, rotation certificates, `find_rotation_index` |
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| `core/src/message.rs` | envelope seal/open (§5.1–§5.3), message id (§5.4), frontmatter (§5.5) |
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| `core/src/transport.rs` | `Transport` trait, bind values, operation and status constants |
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| `core/src/tcp.rs` | Noise_NX initiator, `len u32 \|\| op u8 \|\| body` framing, static-key pinning |
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| `core/src/rns/` | the Reticulum carrier behind the `rns` feature: FFI over `core/shim/`, path discovery, one link per session |
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| `core/src/client.rs` | the six operations, AUTH, chain walking, token sync, fetch pipeline with cancellation |
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| `core/src/store.rs` | SQLite: state, contacts, accepted, tokens, seen ids, inbox, sent; `Send + Sync`, WAL, versioned schema |
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| `core/src/error.rs` | the `Error` enum embedders match on, the status-code mapping |
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| `core/vectors.json` | the committed reference vectors, the tests' source of truth |
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| `cli/src/main.rs` | the command line: keyfile and `--db` conventions, hints, output |
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Unit tests pin every derivation against `vectors.json`, whose values were generated from `smolmail.py`, including a full envelope reproduced byte for byte.
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## References
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- [SPEC.md](https://code.randogoth.com/randogoth/smolmail/src/branch/main/SPEC.md) — protocol 1.1
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- [RNS.md](https://code.randogoth.com/randogoth/smolmail/src/branch/main/RNS.md) — the 1.2 Reticulum addendum
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- [bunshin](https://code.randogoth.com/randogoth/bunshin) — the server
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