log: Implement local syslog support

README.md

@@ -84,6 +84,8 @@ These can be specified only outside of any configuration block.
   Target can be one of the following:
   * `stderr`
     Write logs to stderr, this is the default.
+  * `syslog`
+    Send logs to the local syslog daemon.
   * `off`
     Do nothing. Useful to disable logging fully: `log off`
   * file path

config.go

@@ -135,6 +135,12 @@ func logOutput(m *config.Map, node *config.Node) (interface{}, error) {
 		switch arg {
 		case "stderr":
 			outs = append(outs, log.StderrLog())
+		case "syslog":
+			syslogOut, err := log.Syslog()
+			if err != nil {
+				return nil, fmt.Errorf("failed to connect to syslog daemon: %v", err)
+			}
+			outs = append(outs, syslogOut)
 		case "off":
 			outs = append(outs, nil)
 		default:

log/log.go

@@ -3,6 +3,7 @@ package log
 import (
 	"fmt"
 	"io"
+	"log/syslog"
 	"os"
 	"time"
 )
@@ -89,6 +90,26 @@ func WriterLog(w io.Writer) FuncLog {
 	}
 }
 
+func Syslog() (FuncLog, error) {
+	w, err := syslog.New(syslog.LOG_MAIL|syslog.LOG_INFO, "maddy")
+	if err != nil {
+		return nil, err
+	}
+
+	return func(t time.Time, debug bool, str string) {
+		var err error
+		if debug {
+			err = w.Debug(str)
+		} else {
+			err = w.Info(str)
+		}
+
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "!!! Failed to send message to syslog daemon: %v", err)
+		}
+	}, nil
+}
+
 func MultiLog(outs ...FuncLog) FuncLog {
 	return func(t time.Time, debug bool, str string) {
 		for _, out := range outs {