Syslog integration (#1952)

* Syslog integration, part 1

* Add protocol, make sure syslog actually logs

* Make golangci-lint happy about shadow variables

* Add syslog tag, wrap syslog in logLevelHook

internal/log.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"log/syslog"
 	"net/http"
 	"os"
 	"path"
@@ -30,6 +31,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/dugong"
 	"github.com/sirupsen/logrus"
+	lSyslog "github.com/sirupsen/logrus/hooks/syslog"
 )
 
 type utcFormatter struct {
@@ -128,6 +130,9 @@ func SetupHookLogging(hooks []config.LogrusHook, componentName string) {
 		case "file":
 			checkFileHookParams(hook.Params)
 			setupFileHook(hook, level, componentName)
+		case "syslog":
+			checkSyslogHookParams(hook.Params)
+			setupSyslogHook(hook, level, componentName)
 		default:
 			logrus.Fatalf("Unrecognised logging hook type: %s", hook.Type)
 		}
@@ -173,6 +178,34 @@ func setupFileHook(hook config.LogrusHook, level logrus.Level, componentName str
 	})
 }
 
+func checkSyslogHookParams(params map[string]interface{}) {
+	addr, ok := params["address"]
+	if !ok {
+		logrus.Fatalf("Expecting a parameter \"address\" for logging hook of type \"syslog\"")
+	}
+
+	if _, ok := addr.(string); !ok {
+		logrus.Fatalf("Parameter \"address\" for logging hook of type \"syslog\" should be a string")
+	}
+
+	proto, ok2 := params["protocol"]
+	if !ok2 {
+		logrus.Fatalf("Expecting a parameter \"protocol\" for logging hook of type \"syslog\"")
+	}
+
+	if _, ok2 := proto.(string); !ok2 {
+		logrus.Fatalf("Parameter \"protocol\" for logging hook of type \"syslog\" should be a string")
+	}
+
+}
+
+func setupSyslogHook(hook config.LogrusHook, level logrus.Level, componentName string) {
+	syslogHook, err := lSyslog.NewSyslogHook(hook.Params["protocol"].(string), hook.Params["address"].(string), syslog.LOG_INFO, componentName)
+	if err == nil {
+		logrus.AddHook(&logLevelHook{level, syslogHook})
+	}
+}
+
 //CloseAndLogIfError Closes io.Closer and logs the error if any
 func CloseAndLogIfError(ctx context.Context, closer io.Closer, message string) {
 	if closer == nil {