Api support for UE communication

[hmuurine]

Summary

Adds support for browser <-> UE communication through the API:

• emitUIInteraction(data: object | string):
  • sends arbitrary data as an UIInteraction message
• emitCommand(descriptor: object):
  • sends a Command message
  • if the descriptor contains a ConsoleCommand, it is permitted only if the UE app has been started with-AllowPixelStreamingCommands command line argument
• emitConsoleCommand(command: string):
  • sends a ConsoleCommand message
  • permitted only if the UE app has been started with -AllowPixelStreamingCommands command line argument
• addResponseEventListener(name, funct) / removeResponseEventListener(name):
  • register/remove a listener that is triggered when receiving UE -> browser messages

Test plan

Browser <-> UE

• Modified UE Pixel Streaming application to do the following:
  • Monitors for any incoming browser -> UE messages that contain the string EchoBack
  • If one received, send back a response with content EchoResponse: $originalMessage
    
• Modified uiless.ts to do the following:
  • Sends a UIInteraction message starting with EchoBack 10 seconds after page has been opened
  • Logs any responses received from UE
    
• Started uiless.html and waited for 10 seconds
• Verified that the browser -> UE and UE -> browser messages were both logged, ensuring that communication works both ways
  

Custom commands

• Started a Pixel Streaming UE app with command line parameter -AllowPixelStreamingCommands
• Added some code to uiless.ts to toggle FPS counter and degrade video quality 10 seconds after initialization:

setTimeout(() => {
	pixelStreaming.emitCommand({
		ConsoleCommand: "stat fps",
	});
	pixelStreaming.emitCommand({
		"Encoder.MinQP": 51,
	});
}, 10000);

• Opened uiless.html, waited for 10 seconds, and verified that FPS counter was enabled and video quality was degraded
  
  

• Repeated the test with -AllowPixelStreamingCommands command line arg disabled

• Verified that FPS counter was not enabled after 10 seconds, since the console command was rejected. Video was still degraded as expected

[lukehb]

lgtm!