support for sending commands over socket

Add support for sending a ping command to the fail2ban server over the
socket file. This includes encoding the command data using og-rek and
decoding the response using `gopickle`.

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 +1,38 @@
+package socket
+
+import (
+	"github.com/kisielk/og-rek"
+	"log"
+	"net"
+)
+
+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.NewEncoderWithConfig(c, &ogórek.EncoderConfig{
+			Protocol: 5,
+		}),
+	}
+}
+
+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 v, ok := response.([]string); ok && v[1] == "pong" {
+		return true
+	}
+	log.Printf("unexpected response from server: %v", response)
+	return false
+}

src/socket/protocol.go

@@ -0,0 +1,55 @@
+package socket
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/kisielk/og-rek"
+	"github.com/nlpodyssey/gopickle/pickle"
+	"net"
+)
+
+const (
+	commandTerminator    = "<F2B_END_COMMAND>"
+	pingCommand          = "ping"
+	socketReadBufferSize = 10000
+)
+
+func (s *Fail2BanSocket) sendCommand(command []string) (interface{}, error) {
+	err := write(s.encoder, command)
+	if err != nil {
+		return nil, err
+	}
+	return read(&s.socket)
+}
+
+func write(encoder *ogórek.Encoder, command []string) error {
+	err := encoder.Encode(command)
+	if err != nil {
+		return err
+	}
+	err = encoder.Encode(commandTerminator)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func read(s *net.Conn) (interface{}, error) {
+	buf := make([]byte, socketReadBufferSize)
+	_, err := (*s).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()
+}