add keepalive for tun

handler/tun/metadata.go

@@ -1,22 +1,38 @@
 package tun
 
 import (
+	"time"
+
 	mdata "github.com/go-gost/core/metadata"
 	mdx "github.com/go-gost/x/metadata"
 )
 
+const (
+	defaultKeepAlivePeriod = 10 * time.Second
+)
+
 type metadata struct {
-	bufferSize int
+	bufferSize      int
+	keepAlivePeriod time.Duration
 }
 
 func (h *tunHandler) parseMetadata(md mdata.Metadata) (err error) {
 	const (
-		bufferSize = "bufferSize"
+		bufferSize      = "bufferSize"
+		keepAlive       = "keepAlive"
+		keepAlivePeriod = "ttl"
 	)
 
 	h.md.bufferSize = mdx.GetInt(md, bufferSize)
 	if h.md.bufferSize <= 0 {
 		h.md.bufferSize = 1500
 	}
+
+	if mdx.GetBool(md, keepAlive) {
+		h.md.keepAlivePeriod = mdx.GetDuration(md, keepAlivePeriod)
+		if h.md.keepAlivePeriod <= 0 {
+			h.md.keepAlivePeriod = defaultKeepAlivePeriod
+		}
+	}
 	return
 }