Here are all the important resources that can help us to study further. These resources include different technology standards, research papers, etc. Resources are divided into sections and all the resources contain a mirror resource, in case the original one is not available at the time you are checking.
W3/WhatWG Server-Sent Events(SSE) Standard
W3/WhatWG standard for Server-Sent Events(SSE).
Here are some important resources for WebSockets
W3/WhatWG WebSockets Standard
W3/WhatWG standard for WebSockets.
RFC 6455 – The WebSocket Protocol
The WebSocket Protocol definition – [RFC 6455]