117 lines
4.6 KiB
Markdown
117 lines
4.6 KiB
Markdown
# Chanora Server Prefetch Crate Design
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Date: 2026-05-28
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## Goal
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Move server-resolution prefetch policy out of `chanora_core` into a focused Rust crate named `chanora_prefetch`, without changing connection behavior, Flutter APIs, or protocol dialing semantics.
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## Non-Goals
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- Do not change resolver behavior or DNS/SRV/TSDNS ordering.
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- Do not change `ConnectConfig.resolved_address` semantics in `chanora_protocol`.
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- Do not expose prefetch state in the UI.
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- Do not prefetch bookmarks or additional hosts.
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- Do not persist prefetched addresses.
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## Architecture
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Add a workspace member at `crates/chanora_prefetch`.
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Responsibilities:
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- Normalize server host keys by trimming and lowercasing.
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- Track one active prefetch generation.
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- Store at most one successful prefetched socket address.
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- Reject stale async completions by generation.
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- Return a prefetched address only for an exact normalized host match.
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- Enforce the 2-minute freshness TTL.
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- Resolve server addresses by calling `chanora_resolver::ChanoraResolver::resolve_client_address`.
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- Log prefetch start, success, miss/stale, and failure diagnostics.
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Dependencies:
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- `chanora_resolver` for actual server address resolution.
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- `tokio` for `Mutex` and spawned prefetch tasks.
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- `tracing` for diagnostics.
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- `thiserror` for a narrow `ServerPrefetchError` public error type.
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## Public API
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The crate exposes this small async owner type:
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```rust
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pub struct ServerPrefetcher { ... }
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impl ServerPrefetcher {
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pub fn new() -> Self;
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pub async fn prefetch(&self, host: String) -> Result<(), ServerPrefetchError>;
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pub async fn fresh_match(&self, host: &str) -> Option<std::net::SocketAddr>;
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}
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```
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`prefetch` returns after scheduling work, preserving the current invisible, non-blocking behavior. Empty normalized hosts are ignored successfully. Resolution failures are stored only as diagnostics and do not affect connect semantics.
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## Core Integration
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`chanora_core` replaces its private prefetch cache fields and helpers with `ServerPrefetcher`.
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Core remains the trust boundary for connection config:
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- It clears any caller-provided `ConnectConfig.resolved_address` before lookup.
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- It asks `ServerPrefetcher::fresh_match` for the current host.
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- It sets `dial_cfg.resolved_address` only from a fresh exact cache hit.
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- It stores supervisor/reconnect config with `resolved_address: None`.
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The Flutter bridge keeps calling the same core API, `prefetch_server_resolution(host)`. No Dart API change is intended.
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## Data Flow
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1. Flutter host editing schedules `ChanoraSession::prefetch_server_resolution(host)`.
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2. Core delegates to `ServerPrefetcher::prefetch(host)`.
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3. The prefetcher normalizes the host, increments generation, and spawns resolver work.
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4. On success, the prefetcher stores the resolved socket address if the generation is still current.
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5. On connect, core prepares `(stored_cfg, dial_cfg)`.
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6. Core clears untrusted `resolved_address`, asks the prefetcher for a fresh exact match, and applies the result only to `dial_cfg`.
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7. Protocol uses `dial_cfg.resolved_address` if present; otherwise it resolves normally.
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## Error Handling
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- Prefetch failures remain invisible to users.
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- Prefetch failures are logged through `tracing`.
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- If prefetch misses, is stale, or fails, connect falls back to normal protocol resolution.
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- A caller-supplied `resolved_address` is never trusted by core.
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## Testing
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Move cache-policy tests from `chanora_core` into `chanora_prefetch`:
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- fresh exact match returns the socket address.
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- stale entries are ignored.
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- different hosts are ignored.
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- stale generation completions are ignored.
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- blank normalized hosts return `Ok(())` and do not update generation or spawn resolver work.
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Keep core tests for connection trust-boundary behavior:
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- untrusted `resolved_address` is cleared on cache miss.
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- prepared stored/supervisor config has `resolved_address: None`.
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- prepared dial config can receive a fresh prefetched address.
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Run at minimum:
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- `cargo test -p chanora_prefetch --lib`
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- `cargo test -p chanora_core --lib`
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- `cargo test -p chanora_protocol --lib`
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For final confidence, rerun the Android server connect smoke path that verifies prefetch logs and connected UI.
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## Acceptance Criteria
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- Workspace builds with the new crate member.
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- `chanora_core` no longer owns the prefetch cache implementation.
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- `chanora_prefetch` owns prefetch normalization, TTL, generation, storage, and resolver-backed warming.
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- Public Flutter and Rust protocol behavior is unchanged.
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- Existing server connect and reconnect safety tests pass.
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- Android connect still reaches the connected server UI and does not get stuck in `Connecting` or `Synchronizing`.
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