fix: prevent failures when unable to connect to *.nagios.com

Fixes #50

- Creates an HTTP client with a specified timeout to catch 'connection timeout' errors instead of only waiting for an HTTP status code
- Skip updating the metric if a version isn't returned from GetLatestNagiosXIVersion

get_nagios_version/get_nagios_version.go

@@ -3,14 +3,20 @@ package get_nagios_version
 import (
 	"net/http"
 	"strings"
+	"time"
 
 	"golang.org/x/net/html"
 )
 
 func GetLatestNagiosXIVersion(NagiosXIURL string) (version string, err error) {
 
+	// Initialize a client with a timeout in case of connection issues
+	client := &http.Client{
+		Timeout: 10 * time.Second,
+	}
+
 	// Fetch the HTML source data from the URL
-	resp, err := http.Get(NagiosXIURL)
+	resp, err := client.Get(NagiosXIURL)
 	if err != nil {
 		return "", err
 	}

nagios_exporter.go

@@ -465,11 +465,17 @@ func (e *Exporter) QueryAPIsAndUpdateMetrics(ch chan<- prometheus.Metric, sslVer
 			log.Warn(err)
 		}
 
-		updateMetric := CompareNagiosVersions(nagiosVersion, systemInfoObject.Version)
-		ch <- prometheus.MustNewConstMetric(
-			updateAvailable, prometheus.GaugeValue, updateMetric,
-			// updateMetric 0 = no update, updateMetric 1 = update available
-		)
+		// Ensure that nagiosVersion is not empty before comparing versions
+		if nagiosVersion != "" {
+			updateMetric := CompareNagiosVersions(nagiosVersion, systemInfoObject.Version)
+			ch <- prometheus.MustNewConstMetric(
+				updateAvailable, prometheus.GaugeValue, updateMetric,
+				// updateMetric 0 = no update, updateMetric 1 = update available
+			)
+		}
+
+		log.Warn("Nagios version wasn't found, skipping version comparison")
+
 	} else { // user did not want to compare nagios versions externally so just say there aren't any updates (0)
 		ch <- prometheus.MustNewConstMetric(
 			updateAvailable, prometheus.GaugeValue, 0,