feat: add telemetry to user-scoped tailnet API call (#17065)

Adds support for sending telemetry on calls to the User-scoped tailnet RPC endpoint. This is currently used only by Coder Desktop.

Later PRs will fill in the version, OS information, and device ID via HTTP headers.

coderd/workspaceagents.go

@@ -23,6 +23,8 @@ import (
 	"tailscale.com/tailcfg"
 
 	"cdr.dev/slog"
+	"github.com/coder/websocket"
+
 	"github.com/coder/coder/v2/coderd/agentapi"
 	"github.com/coder/coder/v2/coderd/database"
 	"github.com/coder/coder/v2/coderd/database/db2sdk"
@@ -34,6 +36,7 @@ import (
 	"github.com/coder/coder/v2/coderd/jwtutils"
 	"github.com/coder/coder/v2/coderd/rbac"
 	"github.com/coder/coder/v2/coderd/rbac/policy"
+	"github.com/coder/coder/v2/coderd/telemetry"
 	maputil "github.com/coder/coder/v2/coderd/util/maps"
 	"github.com/coder/coder/v2/coderd/wspubsub"
 	"github.com/coder/coder/v2/codersdk"
@@ -42,7 +45,6 @@ import (
 	"github.com/coder/coder/v2/codersdk/wsjson"
 	"github.com/coder/coder/v2/tailnet"
 	"github.com/coder/coder/v2/tailnet/proto"
-	"github.com/coder/websocket"
 )
 
 // @Summary Get workspace agent by ID
@@ -1635,6 +1637,33 @@ func (api *API) tailnetRPCConn(rw http.ResponseWriter, r *http.Request) {
 	defer wsNetConn.Close()
 	defer conn.Close(websocket.StatusNormalClosure, "")
 
+	// Get user ID for telemetry
+	apiKey := httpmw.APIKey(r)
+	userID := apiKey.UserID.String()
+
+	// Store connection telemetry event
+	now := time.Now()
+	connectionTelemetryEvent := telemetry.UserTailnetConnection{
+		ConnectedAt:         now,
+		DisconnectedAt:      nil,
+		UserID:              userID,
+		PeerID:              peerID.String(),
+		DeviceID:            nil,
+		DeviceOS:            nil,
+		CoderDesktopVersion: nil,
+	}
+	api.Telemetry.Report(&telemetry.Snapshot{
+		UserTailnetConnections: []telemetry.UserTailnetConnection{connectionTelemetryEvent},
+	})
+	defer func() {
+		// Update telemetry event with disconnection time
+		disconnectTime := time.Now()
+		connectionTelemetryEvent.DisconnectedAt = &disconnectTime
+		api.Telemetry.Report(&telemetry.Snapshot{
+			UserTailnetConnections: []telemetry.UserTailnetConnection{connectionTelemetryEvent},
+		})
+	}()
+
 	go httpapi.Heartbeat(ctx, conn)
 	err = api.TailnetClientService.ServeClient(ctx, version, wsNetConn, tailnet.StreamID{
 		Name: "client",