feat: connect to fail2ban db and extract total bad ips

Add dependencies on `sqlite` to allow connecting to the fail2ban database.
Add a new `db` module to handle all the database connections and data
queries used to generate metrics.
Export a new metric for the total number of bad IPs stored in the fail2ban
database.

db/db.go

@@ -0,0 +1,50 @@
+package db
+
+import (
+	"database/sql"
+	"log"
+	"strconv"
+)
+
+const queryCountTotalBadIps = "SELECT COUNT(1) FROM bips"
+
+type Fail2BanDB struct {
+	DatabasePath string
+	sqliteDB *sql.DB
+}
+
+func MustConnectToDb(databasePath string) *Fail2BanDB {
+	db, err := sql.Open("sqlite3", databasePath)
+	if err != nil {
+		log.Fatal(err)
+	}
+	return &Fail2BanDB{
+		DatabasePath: databasePath,
+		sqliteDB:     db,
+	}
+}
+
+func (db *Fail2BanDB) CountTotalBadIps() (int, error) {
+	stmt, err := db.sqliteDB.Prepare(queryCountTotalBadIps)
+	defer db.mustCloseStatement(stmt)
+
+	if err != nil {
+		return -1, err
+	}
+
+	result := ""
+	err = stmt.QueryRow().Scan(&result)
+
+	if err != nil {
+		return -1, err
+	}
+
+	return strconv.Atoi(result)
+}
+
+func (db *Fail2BanDB) mustCloseStatement(stmt *sql.Stmt) {
+	err := stmt.Close()
+	if err != nil {
+		log.Fatal(err)
+	}
+}

exporter.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	fail2banDb "fail2ban-prometheus-exporter/db"
+	_ "github.com/mattn/go-sqlite3"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"log"
@@ -9,23 +11,41 @@ import (
 
 const namespace = "fail2ban"
 
-var up = prometheus.NewDesc(
+var (
+	db       = fail2banDb.MustConnectToDb("fail2ban.sqlite3")
+	metricUp = prometheus.NewDesc(
 		prometheus.BuildFQName(namespace, "", "up"),
 		"Was the last fail2ban query successful.",
 		nil, nil,
 	)
+	metricBadIpTotal = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, "", "badip_total"),
+		"Total number of bad IPs stored in the database.",
+		nil, nil,
+	)
+)
 
 type Exporter struct {
 }
 
 func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
-	ch <- up
+	ch <- metricUp
+	ch <- metricBadIpTotal
 }
 
 func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
 	ch <- prometheus.MustNewConstMetric(
-		up, prometheus.GaugeValue, 1,
+		metricUp, prometheus.GaugeValue, 1,
 	)
+	ch <- *collectTotalBadIpMetric()
+}
+
+func collectTotalBadIpMetric() *prometheus.Metric {
+	count, _ := db.CountTotalBadIps()
+	metric := prometheus.MustNewConstMetric(
+		metricBadIpTotal, prometheus.GaugeValue, float64(count),
+	)
+	return &metric
 }
 
 func main() {

go.mod

@@ -2,4 +2,7 @@ module fail2ban-prometheus-exporter
 
 go 1.15
 
-require github.com/prometheus/client_golang v1.9.0
+require (
+	github.com/mattn/go-sqlite3 v1.14.6
+	github.com/prometheus/client_golang v1.9.0
+)

go.sum

@@ -150,6 +150,8 @@ github.com/mattn/go-colorable v0.0.9/go.mod h1:9vuHe8Xs5qXnSaW/c/ABM9alt+Vo+STaO
 github.com/mattn/go-isatty v0.0.3/go.mod h1:M+lRXTBqGeGNdLjl/ufCoiOlB5xdOkqRJdNxMWT7Zi4=
 github.com/mattn/go-isatty v0.0.4/go.mod h1:M+lRXTBqGeGNdLjl/ufCoiOlB5xdOkqRJdNxMWT7Zi4=
 github.com/mattn/go-runewidth v0.0.2/go.mod h1:LwmH8dsx7+W8Uxz3IHJYH5QSwggIsqBzpuz5H//U1FU=
+github.com/mattn/go-sqlite3 v1.14.6 h1:dNPt6NO46WmLVt2DLNpwczCmdV5boIZ6g/tlDrlRUbg=
+github.com/mattn/go-sqlite3 v1.14.6/go.mod h1:NyWgC/yNuGj7Q9rpYnZvas74GogHl5/Z4A/KQRfk6bU=
 github.com/matttproud/golang_protobuf_extensions v1.0.1 h1:4hp9jkHxhMHkqkrB3Ix0jegS5sx/RkqARlsWZ6pIwiU=
 github.com/matttproud/golang_protobuf_extensions v1.0.1/go.mod h1:D8He9yQNgCq6Z5Ld7szi9bcBfOoFv/3dc6xSMkL2PC0=
 github.com/miekg/dns v1.0.14/go.mod h1:W1PPwlIAgtquWBMBEV9nkV9Cazfe8ScdGz/Lj7v3Nrg=