[#521] Use handler to register dial events

While frostfs-node uses dial handler to udpate metric
value, gateway starts with simple event logging.

Signed-off-by: Alex Vanin <a.vanin@yadro.com>

internal/net/event_handler.go

@@ -0,0 +1,28 @@
+package net
+
+import (
+	"net"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
+	"go.uber.org/zap"
+)
+
+type LogEventHandler struct {
+	logger *zap.Logger
+}
+
+func (l LogEventHandler) DialPerformed(sourceIP net.Addr, _, address string, err error) {
+	sourceIPString := "undefined"
+	if sourceIP != nil {
+		sourceIPString = sourceIP.Network() + "://" + sourceIP.String()
+	}
+	if err == nil {
+		l.logger.Debug(logs.MultinetDialSuccess, zap.String("source", sourceIPString), zap.String("destination", address))
+	} else {
+		l.logger.Debug(logs.MultinetDialFail, zap.String("source", sourceIPString), zap.String("destination", address), zap.Error(err))
+	}
+}
+
+func NewLogEventHandler(logger *zap.Logger) LogEventHandler {
+	return LogEventHandler{logger: logger}
+}