# SmartProxy Metrics System

## Architecture

Two-tier design separating the data plane from the observation plane:

**Hot path (per-chunk, lock-free):** All recording in the proxy data plane touches only `AtomicU64` counters. No `Mutex` is ever acquired on the forwarding path. `CountingBody` batches flushes every 64KB to reduce DashMap shard contention.

**Cold path (1Hz sampling):** A background tokio task drains pending atomics into `ThroughputTracker` circular buffers (Mutex-guarded), producing per-second throughput history. Same task prunes orphaned entries and cleans up rate limiter state.

**Read path (on-demand):** `snapshot()` reads all atomics and locks ThroughputTrackers to build a serializable `Metrics` struct. TypeScript polls this at 1s intervals via IPC.

```
Data Plane (lock-free)                Background (1Hz)              Read Path
─────────────────────                 ──────────────────             ─────────
record_bytes() ──> AtomicU64 ──┐
record_http_request() ──> AtomicU64 ──┤
connection_opened/closed() ──> AtomicU64 ──┤     sample_all()        snapshot()
backend_*() ──> DashMap<AtomicU64> ──┤────> drain atomics ──────> Metrics struct
protocol_*() ──> AtomicU64 ──┤       feed ThroughputTrackers      ──> JSON
datagram_*() ──> AtomicU64 ──┘       prune orphans                ──> IPC stdout
                                                                   ──> TS cache
                                                                   ──> IMetrics API
```

### Key Types

| Type | Crate | Purpose |
|---|---|---|
| `MetricsCollector` | `rustproxy-metrics` | Central store. All DashMaps, atomics, and throughput trackers |
| `ThroughputTracker` | `rustproxy-metrics` | Circular buffer of 1Hz samples. Default 3600 capacity (1 hour) |
| `ForwardMetricsCtx` | `rustproxy-passthrough` | Carries `Arc<MetricsCollector>` + route_id + source_ip through TCP forwarding |
| `CountingBody` | `rustproxy-http` | Wraps HTTP bodies, batches byte recording per 64KB, flushes on drop |
| `ProtocolGuard` | `rustproxy-http` | RAII guard for frontend/backend protocol active/total counters |
| `ConnectionGuard` | `rustproxy-passthrough` | RAII guard calling `connection_closed()` on drop |
| `RustMetricsAdapter` | TypeScript | Polls Rust via IPC, implements `IMetrics` interface over cached JSON |

---

## What's Collected

### Global Counters

| Metric | Type | Updated by |
|---|---|---|
| Active connections | AtomicU64 | `connection_opened/closed` |
| Total connections (lifetime) | AtomicU64 | `connection_opened` |
| Total bytes in | AtomicU64 | `record_bytes` |
| Total bytes out | AtomicU64 | `record_bytes` |
| Total HTTP requests | AtomicU64 | `record_http_request` |
| Active UDP sessions | AtomicU64 | `udp_session_opened/closed` |
| Total UDP sessions | AtomicU64 | `udp_session_opened` |
| Total datagrams in | AtomicU64 | `record_datagram_in` |
| Total datagrams out | AtomicU64 | `record_datagram_out` |

### Per-Route Metrics (keyed by route ID string)

| Metric | Storage |
|---|---|
| Active connections | `DashMap<String, AtomicU64>` |
| Total connections | `DashMap<String, AtomicU64>` |
| Bytes in / out | `DashMap<String, AtomicU64>` |
| Pending throughput (in, out) | `DashMap<String, (AtomicU64, AtomicU64)>` |
| Throughput history | `DashMap<String, Mutex<ThroughputTracker>>` |

Entries are pruned via `retain_routes()` when routes are removed.

### Per-IP Metrics (keyed by IP string)

| Metric | Storage |
|---|---|
| Active connections | `DashMap<String, AtomicU64>` |
| Total connections | `DashMap<String, AtomicU64>` |
| Bytes in / out | `DashMap<String, AtomicU64>` |
| Pending throughput (in, out) | `DashMap<String, (AtomicU64, AtomicU64)>` |
| Throughput history | `DashMap<String, Mutex<ThroughputTracker>>` |
| Domain requests | `DashMap<String, DashMap<String, AtomicU64>>` (IP → domain → count) |

All seven maps for an IP are evicted when its active connection count drops to 0. Safety-net pruning in `sample_all()` catches entries orphaned by races. Snapshots cap at 100 IPs, sorted by active connections descending.

**Domain request tracking:** Records which domains each frontend IP has requested. Populated from HTTP Host headers (for HTTP/1.1, HTTP/2, HTTP/3 requests) and from SNI (for TLS passthrough connections). Capped at 256 domains per IP (`MAX_DOMAINS_PER_IP`) to prevent subdomain-spray abuse. Inner DashMap uses 2 shards to minimise base memory per IP (~200 bytes). Common case (IP + domain both known) is two DashMap reads + one atomic increment with zero allocation.

### Per-Backend Metrics (keyed by "host:port")

| Metric | Storage |
|---|---|
| Active connections | `DashMap<String, AtomicU64>` |
| Total connections | `DashMap<String, AtomicU64>` |
| Detected protocol (h1/h2/h3) | `DashMap<String, String>` |
| Connect errors | `DashMap<String, AtomicU64>` |
| Handshake errors | `DashMap<String, AtomicU64>` |
| Request errors | `DashMap<String, AtomicU64>` |
| Total connect time (microseconds) | `DashMap<String, AtomicU64>` |
| Connect count | `DashMap<String, AtomicU64>` |
| Pool hits | `DashMap<String, AtomicU64>` |
| Pool misses | `DashMap<String, AtomicU64>` |
| H2 failures (fallback to H1) | `DashMap<String, AtomicU64>` |

All per-backend maps are evicted when active count reaches 0. Pruned via `retain_backends()`.

### Frontend Protocol Distribution

Tracked via `ProtocolGuard` RAII guards and `FrontendProtocolTracker`. Five protocol categories, each with active + total counters (AtomicU64):

| Protocol | Where detected |
|---|---|
| h1 | `FrontendProtocolTracker` on first HTTP/1.x request |
| h2 | `FrontendProtocolTracker` on first HTTP/2 request |
| h3 | `ProtocolGuard::frontend("h3")` in H3ProxyService |
| ws | `ProtocolGuard::frontend("ws")` on WebSocket upgrade |
| other | Fallback (TCP passthrough without HTTP) |

Uses `fetch_update` for saturating decrements to prevent underflow races.

### Backend Protocol Distribution

Same five categories (h1/h2/h3/ws/other), tracked via `ProtocolGuard::backend()` at connection establishment. Backend h2 failures (fallback to h1) are separately counted.

### Throughput History

`ThroughputTracker` is a circular buffer storing `ThroughputSample { timestamp_ms, bytes_in, bytes_out }` at 1Hz.

- Global tracker: 1 instance, default 3600 capacity
- Per-route trackers: 1 per active route
- Per-IP trackers: 1 per connected IP (evicted with the IP)
- HTTP request tracker: reuses ThroughputTracker with bytes_in = request count, bytes_out = 0

Query methods:
- `instant()` — last 1 second average
- `recent()` — last 10 seconds average
- `throughput(N)` — last N seconds average
- `history(N)` — last N raw samples in chronological order

Snapshots return 60 samples of global throughput history.

### Protocol Detection Cache

Not part of MetricsCollector. Maintained by `HttpProxyService`'s protocol detection system. Injected into the metrics snapshot at read time by `get_metrics()`.

Each entry records: host, port, domain, detected protocol (h1/h2/h3), H3 port, age, last accessed, last probed, suppression flags, cooldown timers, consecutive failure counts.

---

## Instrumentation Points

### TCP Passthrough (`rustproxy-passthrough`)

**Connection lifecycle** — `tcp_listener.rs`:
- Accept: `conn_tracker.connection_opened(&ip)` (rate limiter) + `ConnectionTrackerGuard` RAII
- Route match: `metrics.connection_opened(route_id, source_ip)` + `ConnectionGuard` RAII
- Close: Both guards call their respective `_closed()` methods on drop

**Byte recording** — `forwarder.rs` (`forward_bidirectional_with_timeouts`):
- Initial peeked data recorded immediately
- Per-chunk in both directions: `record_bytes(n, 0, ...)` / `record_bytes(0, n, ...)`
- Same pattern in `forward_bidirectional_split_with_timeouts` (tcp_listener.rs) for TLS-terminated paths

### HTTP Proxy (`rustproxy-http`)

**Request counting** — `proxy_service.rs`:
- `record_http_request()` called once per request after route matching succeeds

**Body byte counting** — `counting_body.rs` wrapping:
- Request bodies: `CountingBody::new(body, ..., Direction::In)` — counts client-to-upstream bytes
- Response bodies: `CountingBody::new(body, ..., Direction::Out)` — counts upstream-to-client bytes
- Batched flush every 64KB (`BYTE_FLUSH_THRESHOLD = 65_536`), remainder flushed on drop
- Also updates `connection_activity` atomic (idle watchdog) and `active_requests` counter (streaming detection)

**Backend metrics** — `proxy_service.rs`:
- `backend_connection_opened(key, connect_time)` — after TCP/TLS connect succeeds
- `backend_connection_closed(key)` — on teardown
- `backend_connect_error(key)` — TCP/TLS connect failure or timeout
- `backend_handshake_error(key)` — H1/H2 protocol handshake failure
- `backend_request_error(key)` — send_request failure
- `backend_h2_failure(key)` — H2 attempted, fell back to H1
- `backend_pool_hit(key)` / `backend_pool_miss(key)` — connection pool reuse
- `set_backend_protocol(key, proto)` — records detected protocol

**WebSocket** — `proxy_service.rs`:
- Does NOT use CountingBody; records bytes directly per-chunk in both directions of the bidirectional copy loop

### QUIC (`rustproxy-passthrough`)

**Connection level** — `quic_handler.rs`:
- `connection_opened` / `connection_closed` via `QuicConnGuard` RAII
- `conn_tracker.connection_opened/closed` for rate limiting

**Stream level**:
- For QUIC-to-TCP stream forwarding: `record_bytes(bytes_in, bytes_out, ...)` called once per stream at completion (post-hoc, not per-chunk)
- For HTTP/3: delegates to `HttpProxyService.handle_request()`, so all HTTP proxy metrics apply

**H3 specifics** — `h3_service.rs`:
- `ProtocolGuard::frontend("h3")` tracks the H3 connection
- H3 request bodies: `record_bytes(data.len(), 0, ...)` called directly (not CountingBody) since H3 uses `stream.send_data()`
- H3 response bodies: wrapped in CountingBody like HTTP/1 and HTTP/2

### UDP (`rustproxy-passthrough`)

**Session lifecycle** — `udp_listener.rs` / `udp_session.rs`:
- `udp_session_opened()` + `connection_opened(route_id, source_ip)` on new session
- `udp_session_closed()` + `connection_closed(route_id, source_ip)` on idle reap or port drain

**Datagram counting** — `udp_listener.rs`:
- Inbound: `record_bytes(len, 0, ...)` + `record_datagram_in()`
- Outbound (backend reply): `record_bytes(0, len, ...)` + `record_datagram_out()`

---

## Sampling Loop

`lib.rs` spawns a tokio task at configurable interval (default 1000ms):

```rust
loop {
    tokio::select! {
        _ = cancel => break,
        _ = interval.tick() => {
            metrics.sample_all();
            conn_tracker.cleanup_stale_timestamps();
            http_proxy.cleanup_all_rate_limiters();
        }
    }
}
```

`sample_all()` performs in one pass:
1. Drains `global_pending_tp_in/out` into global ThroughputTracker, samples
2. Drains per-route pending counters into per-route trackers, samples each
3. Samples idle route trackers (no new data) to advance their window
4. Drains per-IP pending counters into per-IP trackers, samples each
5. Drains `pending_http_requests` into HTTP request throughput tracker
6. Prunes orphaned per-IP entries (bytes/throughput maps with no matching ip_connections key)
7. Prunes orphaned per-backend entries (error/stats maps with no matching active/total key)

---

## Data Flow: Rust to TypeScript

```
MetricsCollector.snapshot()
    ├── reads all AtomicU64 counters
    ├── iterates DashMaps (routes, IPs, backends)
    ├── locks ThroughputTrackers for instant/recent rates + history
    └── produces Metrics struct

RustProxy::get_metrics()
    ├── calls snapshot()
    ├── enriches with detectedProtocols from HTTP proxy protocol cache
    └── returns Metrics

management.rs "getMetrics" IPC command
    ├── calls get_metrics()
    ├── serde_json::to_value (camelCase)
    └── writes JSON to stdout

RustProxyBridge (TypeScript)
    ├── reads JSON from Rust process stdout
    └── returns parsed object

RustMetricsAdapter
    ├── setInterval polls bridge.getMetrics() every 1s
    ├── stores raw JSON in this.cache
    └── IMetrics methods read synchronously from cache

SmartProxy.getMetrics()
    └── returns the RustMetricsAdapter instance
```

### IPC JSON Shape (Metrics)

```json
{
  "activeConnections": 42,
  "totalConnections": 1000,
  "bytesIn": 123456789,
  "bytesOut": 987654321,
  "throughputInBytesPerSec": 50000,
  "throughputOutBytesPerSec": 80000,
  "throughputRecentInBytesPerSec": 45000,
  "throughputRecentOutBytesPerSec": 75000,
  "routes": {
    "<route-id>": {
      "activeConnections": 5,
      "totalConnections": 100,
      "bytesIn": 0, "bytesOut": 0,
      "throughputInBytesPerSec": 0, "throughputOutBytesPerSec": 0,
      "throughputRecentInBytesPerSec": 0, "throughputRecentOutBytesPerSec": 0
    }
  },
  "ips": {
    "<ip>": {
      "activeConnections": 2, "totalConnections": 10,
      "bytesIn": 0, "bytesOut": 0,
      "throughputInBytesPerSec": 0, "throughputOutBytesPerSec": 0,
      "domainRequests": {
        "example.com": 4821,
        "api.example.com": 312
      }
    }
  },
  "backends": {
    "<host:port>": {
      "activeConnections": 3, "totalConnections": 50,
      "protocol": "h2",
      "connectErrors": 0, "handshakeErrors": 0, "requestErrors": 0,
      "totalConnectTimeUs": 150000, "connectCount": 50,
      "poolHits": 40, "poolMisses": 10, "h2Failures": 1
    }
  },
  "throughputHistory": [
    { "timestampMs": 1713000000000, "bytesIn": 50000, "bytesOut": 80000 }
  ],
  "totalHttpRequests": 5000,
  "httpRequestsPerSec": 100,
  "httpRequestsPerSecRecent": 95,
  "activeUdpSessions": 0, "totalUdpSessions": 5,
  "totalDatagramsIn": 1000, "totalDatagramsOut": 1000,
  "frontendProtocols": {
    "h1Active": 10, "h1Total": 500,
    "h2Active": 5, "h2Total": 200,
    "h3Active": 1, "h3Total": 50,
    "wsActive": 2, "wsTotal": 30,
    "otherActive": 0, "otherTotal": 0
  },
  "backendProtocols": { "...same shape..." },
  "detectedProtocols": [
    {
      "host": "backend", "port": 443, "domain": "example.com",
      "protocol": "h2", "h3Port": 443,
      "ageSecs": 120, "lastAccessedSecs": 5, "lastProbedSecs": 120,
      "h2Suppressed": false, "h3Suppressed": false,
      "h2CooldownRemainingSecs": null, "h3CooldownRemainingSecs": null,
      "h2ConsecutiveFailures": null, "h3ConsecutiveFailures": null
    }
  ]
}
```

### IPC JSON Shape (Statistics)

Lightweight administrative summary, fetched on-demand (not polled):

```json
{
  "activeConnections": 42,
  "totalConnections": 1000,
  "routesCount": 5,
  "listeningPorts": [80, 443, 8443],
  "uptimeSeconds": 86400
}
```

---

## TypeScript Consumer API

`SmartProxy.getMetrics()` returns an `IMetrics` object. All members are synchronous methods reading from the polled cache.

### connections

| Method | Return | Source |
|---|---|---|
| `active()` | `number` | `cache.activeConnections` |
| `total()` | `number` | `cache.totalConnections` |
| `byRoute()` | `Map<string, number>` | `cache.routes[name].activeConnections` |
| `byIP()` | `Map<string, number>` | `cache.ips[ip].activeConnections` |
| `topIPs(limit?)` | `Array<{ip, count}>` | `cache.ips` sorted by active desc, default 10 |
| `domainRequestsByIP()` | `Map<string, Map<string, number>>` | `cache.ips[ip].domainRequests` |
| `topDomainRequests(limit?)` | `Array<{ip, domain, count}>` | Flattened from all IPs, sorted by count desc, default 20 |
| `frontendProtocols()` | `IProtocolDistribution` | `cache.frontendProtocols.*` |
| `backendProtocols()` | `IProtocolDistribution` | `cache.backendProtocols.*` |

### throughput

| Method | Return | Source |
|---|---|---|
| `instant()` | `{in, out}` | `cache.throughputInBytesPerSec/Out` |
| `recent()` | `{in, out}` | `cache.throughputRecentInBytesPerSec/Out` |
| `average()` | `{in, out}` | Falls back to `instant()` (not wired to windowed average) |
| `custom(seconds)` | `{in, out}` | Falls back to `instant()` (not wired) |
| `history(seconds)` | `IThroughputHistoryPoint[]` | `cache.throughputHistory` sliced to last N entries |
| `byRoute(windowSeconds?)` | `Map<string, {in, out}>` | `cache.routes[name].throughputIn/OutBytesPerSec` |
| `byIP(windowSeconds?)` | `Map<string, {in, out}>` | `cache.ips[ip].throughputIn/OutBytesPerSec` |

### requests

| Method | Return | Source |
|---|---|---|
| `perSecond()` | `number` | `cache.httpRequestsPerSec` |
| `perMinute()` | `number` | `cache.httpRequestsPerSecRecent * 60` |
| `total()` | `number` | `cache.totalHttpRequests` (fallback: totalConnections) |

### totals

| Method | Return | Source |
|---|---|---|
| `bytesIn()` | `number` | `cache.bytesIn` |
| `bytesOut()` | `number` | `cache.bytesOut` |
| `connections()` | `number` | `cache.totalConnections` |

### backends

| Method | Return | Source |
|---|---|---|
| `byBackend()` | `Map<string, IBackendMetrics>` | `cache.backends[key].*` with computed `avgConnectTimeMs` and `poolHitRate` |
| `protocols()` | `Map<string, string>` | `cache.backends[key].protocol` |
| `topByErrors(limit?)` | `IBackendMetrics[]` | Sorted by total errors desc |
| `detectedProtocols()` | `IProtocolCacheEntry[]` | `cache.detectedProtocols` passthrough |

`IBackendMetrics`: `{ protocol, activeConnections, totalConnections, connectErrors, handshakeErrors, requestErrors, avgConnectTimeMs, poolHitRate, h2Failures }`

### udp

| Method | Return | Source |
|---|---|---|
| `activeSessions()` | `number` | `cache.activeUdpSessions` |
| `totalSessions()` | `number` | `cache.totalUdpSessions` |
| `datagramsIn()` | `number` | `cache.totalDatagramsIn` |
| `datagramsOut()` | `number` | `cache.totalDatagramsOut` |

### percentiles (stub)

`connectionDuration()` and `bytesTransferred()` always return zeros. Not implemented.

---

## Configuration

```typescript
interface IMetricsConfig {
  enabled: boolean;              // default true
  sampleIntervalMs: number;      // default 1000 (1Hz sampling + TS polling)
  retentionSeconds: number;      // default 3600 (ThroughputTracker capacity)
  enableDetailedTracking: boolean;
  enablePercentiles: boolean;
  cacheResultsMs: number;
  prometheusEnabled: boolean;    // not wired
  prometheusPath: string;        // not wired
  prometheusPrefix: string;      // not wired
}
```

Rust-side config (`MetricsConfig` in `rustproxy-config`):

```rust
pub struct MetricsConfig {
    pub enabled: Option<bool>,
    pub sample_interval_ms: Option<u64>,   // default 1000
    pub retention_seconds: Option<u64>,    // default 3600
}
```

---

## Design Decisions

**Lock-free hot path.** `record_bytes()` is the most frequently called method (per-chunk in TCP, per-64KB in HTTP). It only touches `AtomicU64` with `Relaxed` ordering and short-circuits zero-byte directions to skip DashMap lookups entirely.

**CountingBody batching.** HTTP body frames are typically 16KB. Flushing to MetricsCollector every 64KB reduces DashMap shard contention by ~4x compared to per-frame recording.

**RAII guards everywhere.** `ConnectionGuard`, `ConnectionTrackerGuard`, `QuicConnGuard`, `ProtocolGuard`, `FrontendProtocolTracker` all use Drop to guarantee counter cleanup on all exit paths including panics.

**Saturating decrements.** Protocol counters use `fetch_update` loops instead of `fetch_sub` to prevent underflow to `u64::MAX` from concurrent close races.

**Bounded memory.** Per-IP entries evicted on last connection close. Per-backend entries evicted on last connection close. Snapshot caps IPs and backends at 100 each. `sample_all()` prunes orphaned entries every second.

**Two-phase throughput.** Pending bytes accumulate in lock-free atomics. The 1Hz cold path drains them into Mutex-guarded ThroughputTrackers. This means the hot path never contends on a Mutex, while the cold path does minimal work (one drain + one sample per tracker).

---

## Known Gaps

| Gap | Status |
|---|---|
| `throughput.average()` / `throughput.custom(seconds)` | Fall back to `instant()`. Not wired to Rust windowed queries. |
| `percentiles.connectionDuration()` / `percentiles.bytesTransferred()` | Stub returning zeros. No histogram in Rust. |
| Prometheus export | Config fields exist but not wired to any exporter. |
| `LogDeduplicator` | Implemented in `rustproxy-metrics` but not connected to any call site. |
| Rate limit hit counters | Rate-limited requests return 429 but no counter is recorded in MetricsCollector. |
| QUIC stream byte counting | Post-hoc (per-stream totals after close), not per-chunk like TCP. |
| Throughput history in snapshot | Capped at 60 samples. TS `history(seconds)` cannot return more than 60 points regardless of `retentionSeconds`. |
| Per-route total connections / bytes | Available in Rust JSON but `IMetrics.connections.byRoute()` only exposes active connections. |
| Per-IP total connections / bytes | Available in Rust JSON but `IMetrics.connections.byIP()` only exposes active connections. |
| IPC response typing | `RustProxyBridge` declares `result: any` for both metrics commands. No type-safe response. |