feat: add cli parameters for db path and metrics port (#4)

Add support for configuring CLI parameters in the application using a new
`cfg` package. The `cfg` package exports an `AppSettings` struct that
contains the settings the application was run with.
Update the application to use the new CLI parameters to set the db to open
and the port to use for the metrics server.
Add support for setting the app version during build. The app includes a
`-version` flag to print the stored version data.

cfg/cfg.go

@@ -0,0 +1,48 @@
+package cfg
+
+import (
+	"flag"
+	"fmt"
+	"os"
+)
+
+const (
+	minServerPort = 1000
+	maxServerPort = 65535
+)
+
+type AppSettings struct {
+	VersionMode    bool
+	MetricsPort    int
+	Fail2BanDbPath string
+}
+
+func Parse() *AppSettings {
+	appSettings := &AppSettings{}
+	flag.BoolVar(&appSettings.VersionMode, "version", false, "show version info and exit")
+	flag.IntVar(&appSettings.MetricsPort, "port", 9191, "port to use for the metrics server")
+	flag.StringVar(&appSettings.Fail2BanDbPath, "db", "", "path to the fail2ban sqlite database")
+
+	flag.Parse()
+	appSettings.validateFlags()
+	return appSettings
+}
+
+func (settings *AppSettings) validateFlags() {
+	var flagsValid = true
+	if !settings.VersionMode {
+		if settings.Fail2BanDbPath == "" {
+			fmt.Println("missing flag 'db'")
+			flagsValid = false
+		}
+		if settings.MetricsPort < minServerPort || settings.MetricsPort > maxServerPort {
+			fmt.Printf("invalid server port, must be within %d and %d (found %d)\n",
+				minServerPort, maxServerPort, settings.MetricsPort)
+			flagsValid = false
+		}
+	}
+	if !flagsValid {
+		flag.Usage()
+		os.Exit(1)
+	}
+}

exporter.go

@@ -1,7 +1,9 @@
 package main
 
 import (
+	"fail2ban-prometheus-exporter/cfg"
 	fail2banDb "fail2ban-prometheus-exporter/db"
+	"fmt"
 	_ "github.com/mattn/go-sqlite3"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
@@ -12,7 +14,11 @@ import (
 const namespace = "fail2ban"
 
 var (
-	db       = fail2banDb.MustConnectToDb("fail2ban.sqlite3")
+	version = "dev"
+	commit  = "none"
+	date    = "unknown"
+	builtBy = "unknown"
+
 	metricUp = prometheus.NewDesc(
 		prometheus.BuildFQName(namespace, "", "up"),
 		"Was the last fail2ban query successful.",
@@ -31,6 +37,7 @@ var (
 )
 
 type Exporter struct {
+	db *fail2banDb.Fail2BanDB
 }
 
 func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
@@ -43,12 +50,12 @@ func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
 	ch <- prometheus.MustNewConstMetric(
 		metricUp, prometheus.GaugeValue, 1,
 	)
-	collectBadIpsPerJailMetrics(ch)
+	e.collectBadIpsPerJailMetrics(ch)
-	collectBannedIpsPerJailMetrics(ch)
+	e.collectBannedIpsPerJailMetrics(ch)
 }
 
-func collectBadIpsPerJailMetrics(ch chan<- prometheus.Metric) {
+func (e *Exporter) collectBadIpsPerJailMetrics(ch chan<- prometheus.Metric) {
-	jailNameToCountMap, err := db.CountBadIpsPerJail()
+	jailNameToCountMap, err := e.db.CountBadIpsPerJail()
 	if err != nil {
 		log.Print(err)
 	}
@@ -60,8 +67,8 @@ func collectBadIpsPerJailMetrics(ch chan<- prometheus.Metric) {
 	}
 }
 
-func collectBannedIpsPerJailMetrics(ch chan<- prometheus.Metric) {
+func (e *Exporter) collectBannedIpsPerJailMetrics(ch chan<- prometheus.Metric) {
-	jailNameToCountMap, err := db.CountBannedIpsPerJail()
+	jailNameToCountMap, err := e.db.CountBannedIpsPerJail()
 	if err != nil {
 		log.Print(err)
 	}
@@ -73,12 +80,24 @@ func collectBannedIpsPerJailMetrics(ch chan<- prometheus.Metric) {
 	}
 }
 
+func printAppVersion() {
+	fmt.Println(version)
+	fmt.Printf("    build date:  %s\r\n    commit hash: %s\r\n    built by:    %s\r\n", date, commit, builtBy)
+}
+
 func main() {
+	appSettings := cfg.Parse()
+	if appSettings.VersionMode {
+		printAppVersion()
+	} else {
 		log.Print("starting fail2ban exporter")
 
-	exporter := &Exporter{}
+		exporter := &Exporter{
+			db: fail2banDb.MustConnectToDb(appSettings.Fail2BanDbPath),
+		}
 		prometheus.MustRegister(exporter)
 
 		http.Handle("/metrics", promhttp.Handler())
-	log.Fatal(http.ListenAndServe(":9101", nil))
+		log.Fatal(http.ListenAndServe(fmt.Sprintf(":%d", appSettings.MetricsPort), nil))
+	}
 }