Add Prometheus for some Owncast metrics (#1744)

* Add Prometheus for some Owncast metrics. Closes #1303

* Wrap prometheus metrics endpoint in admin middleware

core/chat/chat.go

@@ -5,12 +5,19 @@ import (
 	"net/http"
 	"sort"
 
+	"github.com/owncast/owncast/config"
 	"github.com/owncast/owncast/core/chat/events"
+	"github.com/owncast/owncast/core/data"
 	"github.com/owncast/owncast/models"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 	log "github.com/sirupsen/logrus"
 )
 
-var getStatus func() models.Status
+var (
+	getStatus               func() models.Status
+	chatMessagesSentCounter prometheus.Gauge
+)
 
 // Start begins the chat server.
 func Start(getStatusFunc func() models.Status) error {
@@ -23,6 +30,15 @@ func Start(getStatusFunc func() models.Status) error {
 
 	log.Traceln("Chat server started with max connection count of", _server.maxSocketConnectionLimit)
 
+	chatMessagesSentCounter = promauto.NewGauge(prometheus.GaugeOpts{
+		Name: "total_chat_message_count",
+		Help: "The number of chat messages incremented over time.",
+		ConstLabels: map[string]string{
+			"version": config.VersionNumber,
+			"host":    data.GetServerURL(),
+		},
+	})
+
 	return nil
 }
 
@@ -51,6 +67,10 @@ func FindClientByID(clientID uint) (*Client, bool) {
 func GetClients() []*Client {
 	clients := []*Client{}
 
+	if _server == nil {
+		return clients
+	}
+
 	// Convert the keyed map to a slice.
 	for _, client := range _server.clients {
 		clients = append(clients, client)

core/chat/events.go

@@ -108,9 +108,9 @@ func (s *Server) userMessageSent(eventData chatClientEvent) {
 
 	// Send chat message sent webhook
 	webhooks.SendChatEvent(&event)
+	chatMessagesSentCounter.Inc()
 
 	SaveUserMessage(event)
-
 	eventData.client.MessageCount++
 	_lastSeenCache[event.User.ID] = time.Now()
 }