Logging to a Graylog server

Added the --log-graylog command line argument which sends logs to a
Graylog server using GELF/UDP.

README.md

@@ -52,8 +52,6 @@ go build
 To Do
 ------
 
-* Proper logging, work in progress:
-  * Sending logs to... well, Graylog... through CLI switches.
 * Document command line flags.
 * Add TLS options (skip checks / specify CA) for the Graylog API.
 * Read object ownership using `grn_permissions` to preserve privileges on users'

go.mod

@@ -3,6 +3,7 @@ module glgroups
 go 1.15
 
 require (
+	github.com/gemnasium/logrus-graylog-hook/v3 v3.0.2
 	github.com/go-ldap/ldap v3.0.3+incompatible
 	github.com/sirupsen/logrus v1.7.0
 	gopkg.in/asn1-ber.v1 v1.0.0-20181015200546-f715ec2f112d // indirect

main.go

@@ -5,6 +5,7 @@ import (
 	"io/ioutil"
 	"os"
 
+	lrh_gl "github.com/gemnasium/logrus-graylog-hook/v3"
 	"github.com/sirupsen/logrus"
 	lrh_wr "github.com/sirupsen/logrus/hooks/writer"
 )
@@ -22,6 +23,8 @@ type (
 		logLevel string
 		// A file to write logs into.
 		logFile string
+		// Graylog server to send logs to (using GELF/UDP). Format is <hostname>:<port>.
+		logGraylog string
 	}
 )
 
@@ -34,10 +37,11 @@ var (
 func parseCommandLine() cliFlags {
 	flags := cliFlags{}
 	flag.StringVar(&flags.cfgFile, "c", "graylog-groups.yml", "Configuration file.")
-	flag.StringVar(&flags.instance, "i", "", "Instance identifier.")
-	flag.BoolVar(&flags.quiet, "q", false, "Quiet mode.")
-	flag.StringVar(&flags.logLevel, "L", "", "Log level.")
-	flag.StringVar(&flags.logFile, "log-file", "", "Log file.")
+	flag.StringVar(&flags.instance, "i", "", "Instance identifier")
+	flag.BoolVar(&flags.quiet, "q", false, "Quiet mode")
+	flag.StringVar(&flags.logLevel, "L", "", "Log level")
+	flag.StringVar(&flags.logFile, "log-file", "", "Log file")
+	flag.StringVar(&flags.logGraylog, "log-graylog", "", "Log to Graylog server (format: <host>:<port>)")
 	flag.Parse()
 	return flags
 }
@@ -94,6 +98,9 @@ func configureLogging(flags cliFlags) {
 	if flags.logFile != "" {
 		configureLogFile(flags.logFile)
 	}
+	if flags.logGraylog != "" {
+		log.Logger.AddHook(lrh_gl.NewGraylogHook(flags.logGraylog, nil))
+	}
 	if flags.quiet {
 		log.Logger.SetOutput(ioutil.Discard)
 	}