feat: collect new up metric from fail2ban socket

Add support for connecting the exporter directly to the fail2ban server's
socket to send requests and receive data. The path to the socket file is
optional and specified on startup.
Export a new metric based on the response of the `ping` command sent to the
fail2ban server. The metric is set to 1 if the server responds with `pong`
and 0 in any other case. This metric is only shown if the path to the
socket file was provided on startup.

src/cfg/cfg.go

@@ -15,6 +15,7 @@ type AppSettings struct {
 	VersionMode        bool
 	MetricsPort        int
 	Fail2BanDbPath     string
+	Fail2BanSocketPath string
 }
 
 func Parse() *AppSettings {
@@ -22,6 +23,7 @@ func Parse() *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.StringVar(&appSettings.Fail2BanSocketPath, "socket", "", "path to the fail2ban server socket")
 
 	flag.Parse()
 	appSettings.validateFlags()
@@ -31,8 +33,8 @@ func Parse() *AppSettings {
 func (settings *AppSettings) validateFlags() {
 	var flagsValid = true
 	if !settings.VersionMode {
-		if settings.Fail2BanDbPath == "" {
-			fmt.Println("missing flag 'db'")
+		if settings.Fail2BanDbPath == "" && settings.Fail2BanSocketPath == "" {
+			fmt.Println("at least one of the following flags must be provided: 'db', 'socket'")
 			flagsValid = false
 		}
 		if settings.MetricsPort < minServerPort || settings.MetricsPort > maxServerPort {

src/exporter.go

@@ -3,15 +3,20 @@ package main
 import (
 	"fail2ban-prometheus-exporter/cfg"
 	fail2banDb "fail2ban-prometheus-exporter/db"
+	"fail2ban-prometheus-exporter/socket"
 	"fmt"
+	"log"
+	"net/http"
+
 	_ "github.com/mattn/go-sqlite3"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
-	"log"
-	"net/http"
 )
 
-const namespace = "fail2ban"
+const (
+	namespace     = "fail2ban"
+	sockNamespace = "f2b"
+)
 
 var (
 	version = "dev"
@@ -44,28 +49,44 @@ var (
 		"Number of errors found since startup.",
 		[]string{"type"}, nil,
 	)
+	metricServerPing = prometheus.NewDesc(
+		prometheus.BuildFQName(sockNamespace, "", "up"),
+		"Check if the fail2ban server is up",
+		nil, nil,
+	)
 )
 
 type Exporter struct {
 	db           *fail2banDb.Fail2BanDB
+	socket       *socket.Fail2BanSocket
 	lastError    error
 	dbErrorCount int
 }
 
 func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
+	if e.db != nil {
 		ch <- metricUp
 		ch <- metricBadIpsPerJail
 		ch <- metricBannedIpsPerJail
 		ch <- metricEnabledJails
 		ch <- metricErrorCount
+	}
+	if e.socket != nil {
+		ch <- metricServerPing
+	}
 }
 
 func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
+	if e.db != nil {
 		e.collectBadIpsPerJailMetrics(ch)
 		e.collectBannedIpsPerJailMetrics(ch)
 		e.collectEnabledJailMetrics(ch)
 		e.collectUpMetric(ch)
 		e.collectErrorCountMetric(ch)
+	}
+	if e.socket != nil {
+		e.collectServerPingMetric(ch)
+	}
 }
 
 func (e *Exporter) collectUpMetric(ch chan<- prometheus.Metric) {
@@ -132,6 +153,17 @@ func (e *Exporter) collectEnabledJailMetrics(ch chan<- prometheus.Metric) {
 	}
 }
 
+func (e *Exporter) collectServerPingMetric(ch chan<- prometheus.Metric) {
+	pingSuccess := e.socket.Ping()
+	var pingSuccessInt float64 = 1
+	if !pingSuccess {
+		pingSuccessInt = 0
+	}
+	ch <- prometheus.MustNewConstMetric(
+		metricServerPing, prometheus.GaugeValue, pingSuccessInt,
+	)
+}
+
 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)
@@ -144,8 +176,12 @@ func main() {
 	} else {
 		log.Print("starting fail2ban exporter")
 
-		exporter := &Exporter{
-			db: fail2banDb.MustConnectToDb(appSettings.Fail2BanDbPath),
+		exporter := &Exporter{}
+		if appSettings.Fail2BanDbPath != "" {
+			exporter.db = fail2banDb.MustConnectToDb(appSettings.Fail2BanDbPath)
+		}
+		if appSettings.Fail2BanSocketPath != "" {
+			exporter.socket = socket.MustConnectToSocket(appSettings.Fail2BanSocketPath)
 		}
 		prometheus.MustRegister(exporter)
 

src/go.mod

@@ -3,6 +3,8 @@ module fail2ban-prometheus-exporter
 go 1.15
 
 require (
+	github.com/kisielk/og-rek v1.1.0
 	github.com/mattn/go-sqlite3 v1.14.6
+	github.com/nlpodyssey/gopickle v0.1.0
 	github.com/prometheus/client_golang v1.9.0
 )

src/go.sum

@@ -137,6 +137,8 @@ github.com/julienschmidt/httprouter v1.2.0/go.mod h1:SYymIcj16QtmaHHD7aYtjjsJG7V
 github.com/julienschmidt/httprouter v1.3.0/go.mod h1:JR6WtHb+2LUe8TCKY3cZOxFyyO8IZAc4RVcycCCAKdM=
 github.com/kisielk/errcheck v1.1.0/go.mod h1:EZBBE59ingxPouuu3KfxchcWSUPOHkagtvWXihfKN4Q=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
+github.com/kisielk/og-rek v1.1.0 h1:u10TvQbPtrlY/6H4+BiFsBywwSVTGFsx0YOVtpx3IbI=
+github.com/kisielk/og-rek v1.1.0/go.mod h1:6ihsOSzSAxR/65S3Bn9zNihoEqRquhDQZ2c6I2+MG3c=
 github.com/konsorten/go-windows-terminal-sequences v1.0.1/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/konsorten/go-windows-terminal-sequences v1.0.3/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/kr/logfmt v0.0.0-20140226030751-b84e30acd515/go.mod h1:+0opPa2QZZtGFBFZlji/RkVcI2GknAs/DXo4wKdlNEc=
@@ -175,6 +177,8 @@ github.com/nats-io/nats.go v1.9.1/go.mod h1:ZjDU1L/7fJ09jvUSRVBR2e7+RnLiiIQyqyzE
 github.com/nats-io/nkeys v0.1.0/go.mod h1:xpnFELMwJABBLVhffcfd1MZx6VsNRFpEugbxziKVo7w=
 github.com/nats-io/nkeys v0.1.3/go.mod h1:xpnFELMwJABBLVhffcfd1MZx6VsNRFpEugbxziKVo7w=
 github.com/nats-io/nuid v1.0.1/go.mod h1:19wcPz3Ph3q0Jbyiqsd0kePYG7A95tJPxeL+1OSON2c=
+github.com/nlpodyssey/gopickle v0.1.0 h1:9wjwRqXsOSYWZl4c4ko472b6RW+VB1I441ZcfFg1r5g=
+github.com/nlpodyssey/gopickle v0.1.0/go.mod h1:YIUwjJ2O7+vnBsxUN+MHAAI3N+adqEGiw+nDpwW95bY=
 github.com/oklog/oklog v0.3.2/go.mod h1:FCV+B7mhrz4o+ueLpx+KqkyXRGMWOYEvfiXtdGtbWGs=
 github.com/oklog/run v1.0.0/go.mod h1:dlhp/R75TPv97u0XWUtDeV/lRKWPKSdTuV0TZvrmrQA=
 github.com/olekukonko/tablewriter v0.0.0-20170122224234-a0225b3f23b5/go.mod h1:vsDQFd/mU46D+Z4whnwzcISnGGzXWMclvtLoiIKAKIo=

src/socket/decoder.go

@@ -0,0 +1,8 @@
+package socket
+
+// Py_builtins_str is used by the pickle decoder to parse the server response into a format Go can understand
+type Py_builtins_str struct{}
+
+func (c Py_builtins_str) Call(args ...interface{}) (interface{}, error) {
+	return args[0], nil
+}

src/socket/fail2banSocket.go

@@ -0,0 +1,42 @@
+package socket
+
+import (
+	"log"
+	"net"
+
+	"github.com/kisielk/og-rek"
+	"github.com/nlpodyssey/gopickle/types"
+)
+
+type Fail2BanSocket struct {
+	socket  net.Conn
+	encoder *ogórek.Encoder
+}
+
+func MustConnectToSocket(path string) *Fail2BanSocket {
+	c, err := net.Dial("unix", path)
+	if err != nil {
+		log.Fatalf("failed to open fail2ban socket: %v", err)
+	}
+	return &Fail2BanSocket{
+		socket:  c,
+		encoder: ogórek.NewEncoder(c),
+	}
+}
+
+func (s *Fail2BanSocket) Ping() bool {
+	response, err := s.sendCommand([]string{pingCommand, "100"})
+	if err != nil {
+		log.Printf("server ping failed: %v", err)
+		return false
+	}
+
+	if t, ok := response.(*types.Tuple); ok {
+		if (*t)[1] == "pong" {
+			return true
+		}
+		log.Printf("unexpected response data: %s", t)
+	}
+	log.Printf("unexpected response format - cannot parse: %v", response)
+	return false
+}

src/socket/protocol.go

@@ -0,0 +1,53 @@
+package socket
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/nlpodyssey/gopickle/pickle"
+)
+
+const (
+	commandTerminator    = "<F2B_END_COMMAND>"
+	pingCommand          = "ping"
+	socketReadBufferSize = 10000
+)
+
+func (s *Fail2BanSocket) sendCommand(command []string) (interface{}, error) {
+	err := s.write(command)
+	if err != nil {
+		return nil, err
+	}
+	return s.read()
+}
+
+func (s *Fail2BanSocket) write(command []string) error {
+	err := s.encoder.Encode(command)
+	if err != nil {
+		return err
+	}
+	_, err = s.socket.Write([]byte(commandTerminator))
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func (s *Fail2BanSocket) read() (interface{}, error) {
+	buf := make([]byte, socketReadBufferSize)
+	_, err := s.socket.Read(buf)
+	if err != nil {
+		return nil, err
+	}
+
+	bufReader := bytes.NewReader(buf)
+	unpickler := pickle.NewUnpickler(bufReader)
+
+	unpickler.FindClass = func(module, name string) (interface{}, error) {
+		if module == "builtins" && name == "str" {
+			return &Py_builtins_str{}, nil
+		}
+		return nil, fmt.Errorf("class not found: " + module + " : " + name)
+	}
+
+	return unpickler.Load()
+}