✨ feat: Add streaming support (#125)

This adds:
- [x] Keyboard and mouse handling on the frontend
- [x] Video and audio streaming from the backend to the frontend
- [x] Input server that works with Websockets

Update - 17/11
- [ ] Master docker container to run this
- [ ] Steam runtime
- [ ] Entrypoint.sh

---------

Co-authored-by: Kristian Ollikainen <14197772+DatCaptainHorse@users.noreply.github.com>
Co-authored-by: Kristian Ollikainen <DatCaptainHorse@users.noreply.github.com>

packages/relay/internal/datachannel.go

@@ -0,0 +1,72 @@
+package relay
+
+import (
+	"github.com/pion/webrtc/v4"
+	"log"
+)
+
+// NestriDataChannel is a custom data channel with callbacks
+type NestriDataChannel struct {
+	*webrtc.DataChannel
+	binaryCallbacks map[string]OnMessageCallback // MessageBase type -> callback
+}
+
+// NewNestriDataChannel creates a new NestriDataChannel from *webrtc.DataChannel
+func NewNestriDataChannel(dc *webrtc.DataChannel) *NestriDataChannel {
+	ndc := &NestriDataChannel{
+		DataChannel:     dc,
+		binaryCallbacks: make(map[string]OnMessageCallback),
+	}
+
+	// Handler for incoming messages
+	ndc.OnMessage(func(msg webrtc.DataChannelMessage) {
+		// If string type message, ignore
+		if msg.IsString {
+			return
+		}
+
+		// Decode message
+		var base MessageBase
+		if err := DecodeMessage(msg.Data, &base); err != nil {
+			log.Printf("Failed to decode binary DataChannel message, reason: %s\n", err)
+			return
+		}
+
+		// Handle message type callback
+		if callback, ok := ndc.binaryCallbacks[base.PayloadType]; ok {
+			go callback(msg.Data)
+		} // TODO: Log unknown message type?
+	})
+
+	return ndc
+}
+
+// SendBinary sends a binary message to the data channel
+func (ndc *NestriDataChannel) SendBinary(data []byte) error {
+	return ndc.Send(data)
+}
+
+// RegisterMessageCallback registers a callback for a given binary message type
+func (ndc *NestriDataChannel) RegisterMessageCallback(msgType string, callback OnMessageCallback) {
+	if ndc.binaryCallbacks == nil {
+		ndc.binaryCallbacks = make(map[string]OnMessageCallback)
+	}
+	ndc.binaryCallbacks[msgType] = callback
+}
+
+// UnregisterMessageCallback removes the callback for a given binary message type
+func (ndc *NestriDataChannel) UnregisterMessageCallback(msgType string) {
+	if ndc.binaryCallbacks != nil {
+		delete(ndc.binaryCallbacks, msgType)
+	}
+}
+
+// RegisterOnOpen registers a callback for the data channel opening
+func (ndc *NestriDataChannel) RegisterOnOpen(callback func()) {
+	ndc.OnOpen(callback)
+}
+
+// RegisterOnClose registers a callback for the data channel closing
+func (ndc *NestriDataChannel) RegisterOnClose(callback func()) {
+	ndc.OnClose(callback)
+}