wip: migrate to mono-repo. SPN has already been moved to spn/

spn/ships/mtu.go

@@ -0,0 +1,47 @@
+package ships
+
+import "net"
+
+// MTU Calculation Configuration.
+const (
+	BaseMTU           = 1460 // 1500 with 40 bytes extra space for special cases.
+	IPv4HeaderMTUSize = 20   // Without options, as not common.
+	IPv6HeaderMTUSize = 40   // Without options, as not common.
+	TCPHeaderMTUSize  = 60   // Maximum size with options.
+	UDPHeaderMTUSize  = 8    // Has no options.
+)
+
+func (ship *ShipBase) calculateLoadSize(ip net.IP, addr net.Addr, subtract ...int) {
+	ship.loadSize = BaseMTU
+
+	// Convert addr to IP if needed.
+	if ip == nil && addr != nil {
+		switch v := addr.(type) {
+		case *net.TCPAddr:
+			ip = v.IP
+		case *net.UDPAddr:
+			ip = v.IP
+		case *net.IPAddr:
+			ip = v.IP
+		}
+	}
+
+	// Subtract IP Header, if IP is available.
+	if ip != nil {
+		if ip4 := ip.To4(); ip4 != nil {
+			ship.loadSize -= IPv4HeaderMTUSize
+		} else {
+			ship.loadSize -= IPv6HeaderMTUSize
+		}
+	}
+
+	// Subtract others.
+	for sub := range subtract {
+		ship.loadSize -= sub
+	}
+
+	// Raise buf size to at least load size.
+	if ship.bufSize < ship.loadSize {
+		ship.bufSize = ship.loadSize
+	}
+}