From c9fd2e6c47eabb9044e37d29476367d3b5ce68ea Mon Sep 17 00:00:00 2001
From: Alvar Penning <post@0x21.biz>
Date: Thu, 5 Sep 2019 11:01:40 +0200
Subject: [PATCH] TCPCL: Keepalive/Session Upkeep Message

---
 cla/tcpcl/message_keepalive.go      | 44 +++++++++++++++++++++++++++++
 cla/tcpcl/message_keepalive_test.go | 35 +++++++++++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 cla/tcpcl/message_keepalive.go
 create mode 100644 cla/tcpcl/message_keepalive_test.go

diff --git a/cla/tcpcl/message_keepalive.go b/cla/tcpcl/message_keepalive.go
new file mode 100644
index 00000000..317e887f
--- /dev/null
+++ b/cla/tcpcl/message_keepalive.go
@@ -0,0 +1,44 @@
+package tcpcl
+
+import "fmt"
+
+// KEEPALIVE is the Message Header code for a Keepalive Message.
+const KEEPALIVE uint8 = 0x04
+
+// KeepaliveMessage is the KEEPALIVE message for session upkeep.
+type KeepaliveMessage uint8
+
+// NewKeepaliveMessage creates a new KeepaliveMessage.
+func NewKeepaliveMessage() KeepaliveMessage {
+	return KeepaliveMessage(KEEPALIVE)
+}
+
+func (_ KeepaliveMessage) String() string {
+	return "KEEPALIVE"
+}
+
+// MarshalBinary encodes this KeepaliveMessage into its binary form.
+func (km KeepaliveMessage) MarshalBinary() (data []byte, err error) {
+	if uint8(km) != KEEPALIVE {
+		err = fmt.Errorf("KEEPALIVE's value is %d instead of %d", uint8(km), KEEPALIVE)
+		return
+	}
+
+	data = []byte{KEEPALIVE}
+	return
+}
+
+// UnmarshalBinary decodes a KeepaliveMessage from its binary form.
+func (km *KeepaliveMessage) UnmarshalBinary(data []byte) error {
+	if len(data) != 1 {
+		return fmt.Errorf("KEEPALIVE's octet length is %d instead of 1", len(data))
+	}
+
+	if x := uint8(data[0]); x != KEEPALIVE {
+		return fmt.Errorf("KEEPALIVE's value is %d instead of %d", x, KEEPALIVE)
+	} else {
+		*km = KeepaliveMessage(x)
+	}
+
+	return nil
+}
diff --git a/cla/tcpcl/message_keepalive_test.go b/cla/tcpcl/message_keepalive_test.go
new file mode 100644
index 00000000..0287a79d
--- /dev/null
+++ b/cla/tcpcl/message_keepalive_test.go
@@ -0,0 +1,35 @@
+package tcpcl
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestKeepaliveMessage(t *testing.T) {
+	tests := []struct {
+		valid bool
+		data  []byte
+	}{
+		{true, []byte{KEEPALIVE}},
+		{false, []byte{0x21}},
+		{false, []byte{}},
+		{false, []byte{0x23, 0x42}},
+	}
+
+	for _, test := range tests {
+		var km KeepaliveMessage
+
+		if err := km.UnmarshalBinary(test.data); (err == nil) != test.valid {
+			t.Fatalf("Error state was not expected; valid := %t, got := %v", test.valid, err)
+		} else if !test.valid {
+			continue
+		}
+
+		if data, err := NewKeepaliveMessage().MarshalBinary(); err != nil {
+			t.Fatal(err)
+		} else if !bytes.Equal(data, test.data) {
+			t.Fatalf("Data does not match, expected %x and got %x", test.data, data)
+		}
+
+	}
+}