CUB-117: Port Moonraker + MQTT printer integrations to Go

- Moonraker REST client with GetPrinterInfo, GetPrintStats, GetPrintHistory
- Moonraker WebSocket client with auto-reconnect + telemetry parsing
- MQTT client via paho.mqtt.golang with TLS support for Bambu Lab
- Moonraker poller worker: background polling, dedup, usage logging to PostgreSQL
- MQTT subscriber worker: Bambu telemetry parsing, print job tracking
- Config: 7 new env vars (MOONRAKER_URL, MQTT_BROKER, etc.)
- main.go: per-printer worker discovery, graceful shutdown

backend/internal/clients/moonraker_ws.go

@@ -0,0 +1,229 @@
+package clients
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"log/slog"
+	"net/http"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/gorilla/websocket"
+)
+
+// ── WebSocket message types ─────────────────────────────────────────────────
+
+// moonrakerWSMessage is a single JSON-RPC frame from the Moonraker WebSocket.
+type moonrakerWSMessage struct {
+	JSONRPC string          `json:"jsonrpc"`
+	Method  string          `json:"method"`
+	Params  json.RawMessage `json:"params"`
+	ID      *int            `json:"id"`
+}
+
+// MoonrakerPrintEvent is the payload delivered by the "notify_status_update"
+// subscription when print_stats or display_status change.
+type MoonrakerPrintEvent struct {
+	PrintStats    *MoonrakerPrintStats    `json:"print_stats"`
+	DisplayStatus *MoonrakerDisplayStatus `json:"display_status"`
+}
+
+// MoonrakerDisplayStatus carries progress and the LCD message.
+type MoonrakerDisplayStatus struct {
+	Progress float64 `json:"progress"`
+	Message  string  `json:"message"`
+}
+
+// MoonrakerStatusHandler is called for every status update received from the
+// Moonraker WebSocket. It receives the parsed event and the raw JSON.
+type MoonrakerStatusHandler func(event MoonrakerPrintEvent) error
+
+// ── WebSocket client ────────────────────────────────────────────────────────
+
+// MoonrakerWSClient maintains a persistent WebSocket connection to the
+// Moonraker server and delivers parsed status updates to a handler.
+type MoonrakerWSClient struct {
+	wsURL   string
+	handler MoonrakerStatusHandler
+	dialer  *websocket.Dialer
+
+	mu     sync.Mutex
+	conn   *websocket.Conn
+	done   chan struct{}
+	once   sync.Once
+}
+
+// NewMoonrakerWSClient creates a WebSocket client for the given Moonraker base
+// URL. The handler is invoked on every status update.
+func NewMoonrakerWSClient(baseURL string, handler MoonrakerStatusHandler) *MoonrakerWSClient {
+	baseURL = strings.TrimRight(baseURL, "/")
+	wsURL := strings.Replace(baseURL, "http://", "ws://", 1)
+	wsURL = strings.Replace(wsURL, "https://", "wss://", 1)
+	wsURL += "/websocket"
+
+	return &MoonrakerWSClient{
+		wsURL:   wsURL,
+		handler: handler,
+		dialer: &websocket.Dialer{
+			Proxy:            http.ProxyFromEnvironment,
+			HandshakeTimeout: 10 * time.Second,
+		},
+		done: make(chan struct{}),
+	}
+}
+
+// Connect establishes the WebSocket, subscribes to status updates, and
+// starts the read loop in a background goroutine. It retries on failure
+// with exponential backoff up to a 60-second cap.
+func (c *MoonrakerWSClient) Connect(ctx context.Context) {
+	go c.run(ctx)
+}
+
+// Shutdown gracefully closes the WebSocket and stops the read loop.
+func (c *MoonrakerWSClient) Shutdown() {
+	c.once.Do(func() {
+		close(c.done)
+	})
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.conn != nil {
+		c.conn.Close()
+		c.conn = nil
+	}
+}
+
+// run is the main connection loop with reconnect backoff.
+func (c *MoonrakerWSClient) run(ctx context.Context) {
+	backoff := 1 * time.Second
+	const maxBackoff = 60 * time.Second
+
+	for {
+		select {
+		case <-ctx.Done():
+			slog.Info("moonraker ws: context cancelled, stopping")
+			return
+		case <-c.done:
+			slog.Info("moonraker ws: shutdown requested")
+			return
+		default:
+		}
+
+		if err := c.connectAndRead(ctx); err != nil {
+			slog.Error("moonraker ws: connection error, retrying", "error", err, "backoff", backoff)
+		}
+
+		// Exponential backoff.
+		select {
+		case <-ctx.Done():
+			return
+		case <-c.done:
+			return
+		case <-time.After(backoff):
+		}
+		backoff *= 2
+		if backoff > maxBackoff {
+			backoff = maxBackoff
+		}
+	}
+}
+
+func (c *MoonrakerWSClient) connectAndRead(ctx context.Context) error {
+	slog.Info("moonraker ws: connecting", "url", c.wsURL)
+
+	conn, _, err := c.dialer.DialContext(ctx, c.wsURL, nil)
+	if err != nil {
+		return fmt.Errorf("dial failed: %w", err)
+	}
+
+	c.mu.Lock()
+	if c.conn != nil {
+		c.conn.Close()
+	}
+	c.conn = conn
+	c.mu.Unlock()
+
+	defer func() {
+		c.mu.Lock()
+		if c.conn == conn {
+			c.conn = nil
+		}
+		c.mu.Unlock()
+		conn.Close()
+	}()
+
+	// Subscribe to status updates.
+	subReq := map[string]interface{}{
+		"jsonrpc": "2.0",
+		"method":  "printer.objects.subscribe",
+		"params": map[string]interface{}{
+			"objects": map[string]interface{}{
+				"print_stats":    nil,
+				"display_status": nil,
+			},
+		},
+		"id": 1,
+	}
+	if err := conn.WriteJSON(subReq); err != nil {
+		return fmt.Errorf("subscribe failed: %w", err)
+	}
+
+	slog.Info("moonraker ws: subscribed to status updates")
+
+	// Set read deadline to detect stale connections.
+	// 120s is long enough to avoid false positives.
+	pingPeriod := 60 * time.Second
+
+	for {
+		// Set read deadline.
+		if err := conn.SetReadDeadline(time.Now().Add(150 * time.Second)); err != nil {
+			return fmt.Errorf("set read deadline: %w", err)
+		}
+
+		_, raw, err := conn.ReadMessage()
+		if err != nil {
+			return fmt.Errorf("read message: %w", err)
+		}
+
+		// Send periodic pings to keep the connection alive.
+		go func() {
+			time.Sleep(pingPeriod)
+			c.mu.Lock()
+			if c.conn == conn {
+				c.conn.WriteControl(websocket.PingMessage, []byte{}, time.Now().Add(10*time.Second))
+			}
+			c.mu.Unlock()
+		}()
+
+		var msg moonrakerWSMessage
+		if err := json.Unmarshal(raw, &msg); err != nil {
+			slog.Warn("moonraker ws: failed to parse message", "error", err)
+			continue
+		}
+
+		// Only process notify_status_update messages.
+		if msg.Method != "notify_status_update" {
+			continue
+		}
+
+		var statusWrapper []MoonrakerPrintEvent
+		if err := json.Unmarshal(msg.Params, &statusWrapper); err != nil {
+			// Params might be an object, not an array.
+			var singleEvent MoonrakerPrintEvent
+			if err2 := json.Unmarshal(msg.Params, &singleEvent); err2 != nil {
+				slog.Warn("moonraker ws: failed to unmarshal status params", "error", err2)
+				continue
+			}
+			statusWrapper = []MoonrakerPrintEvent{singleEvent}
+		}
+
+		for _, ev := range statusWrapper {
+			if c.handler != nil {
+				if err := c.handler(ev); err != nil {
+					slog.Error("moonraker ws: handler error", "error", err)
+				}
+			}
+		}
+	}
+}