WebRTC ping over data channel (#23)

* add datachannel ping to webrtc.

* add ping pong decode func.

internal/webrtc/payload/receive.go

@@ -1,5 +1,7 @@
 package payload
 
+import "math"
+
 const (
 	OP_MOVE     = 0x01
 	OP_SCROLL   = 0x02
@@ -7,6 +9,7 @@ const (
 	OP_KEY_UP   = 0x04
 	OP_BTN_DOWN = 0x05
 	OP_BTN_UP   = 0x06
+	OP_PING     = 0x07
 )
 
 type Move struct {
@@ -28,3 +31,15 @@ type Key struct {
 
 	Key uint32
 }
+
+type Ping struct {
+	Header
+
+	// client's timestamp split into two uint32
+	ClientTs1 uint32
+	ClientTs2 uint32
+}
+
+func (p Ping) ClientTs() uint64 {
+	return (uint64(p.ClientTs1) * uint64(math.MaxUint32)) + uint64(p.ClientTs2)
+}

internal/webrtc/payload/send.go

@@ -1,8 +1,11 @@
 package payload
 
+import "math"
+
 const (
 	OP_CURSOR_POSITION = 0x01
 	OP_CURSOR_IMAGE    = 0x02
+	OP_PONG            = 0x03
 )
 
 type CursorPosition struct {
@@ -20,3 +23,15 @@ type CursorImage struct {
 	Xhot   uint16
 	Yhot   uint16
 }
+
+type Pong struct {
+	Ping
+
+	// server's timestamp split into two uint32
+	ServerTs1 uint32
+	ServerTs2 uint32
+}
+
+func (p Pong) ServerTs() uint64 {
+	return (uint64(p.ServerTs1) * uint64(math.MaxUint32)) + uint64(p.ServerTs2)
+}