Now supports socket activation

cmd/qddns-server/main.go

@@ -3,10 +3,11 @@ package main
 import (
 	"flag"
 	"fmt"
+	"github.com/coreos/go-systemd/activation"
 	"github.com/gin-gonic/gin"
 	"github.com/thequux/qddns/common"
 	"github.com/thequux/qddns/db"
-	_ "go.uber.org/zap"
+	"github.com/thequux/qddns/multilistener"
 	"net"
 	"net/http"
 	"os"
@@ -96,7 +97,16 @@ func main() {
 	r.POST("/update/:domain", Update)
 
 	var err error
-	if _, err = net.ResolveTCPAddr("tcp", *listen); err == nil {
+	if listeners, err := activation.Listeners(); err == nil && len(listeners) > 0 {
+		// Socket activation
+		var listener net.Listener
+		if len(listeners) > 1 {
+			listener, _ = multilistener.New(listeners...)
+		} else {
+			listener = listeners[0]
+		}
+		err = r.RunListener(listener)
+	} else if _, err = net.ResolveTCPAddr("tcp", *listen); err == nil {
 		err = r.Run(*listen)
 	} else {
 		// Probably a UNIX address