ESP_IDF has an excellent support for TCP/UDP sockets but Clients mainly Browsers can only communicate over Websockets. Websocets are not TCP sockets. Websockets are above the socket layer and are wrapped with HTTP requests with meta information.
For browsers to communicate over websockets they must establish a "Handshake" with the server. ESP32 acts as psuedo Websocket server which obtains Websocket connection and strips the data and handshakes.
Websocket request looks like this
Host: 192.168.4.1:9998
Connection: Upgrade
Pragma: no-cache
Cache-Control: no-cache
Upgrade: websocket
Origin: file://
Sec-WebSocket-Version: 13
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36
Accept-Encoding: gzip, deflate, sdch
Accept-Language: de-DE,de;q=0.8,en-US;q=0.6,en;q=0.4
Sec-WebSocket-Key: Sb0llpkUl572foZxqBOxMw==
Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits
The server has to read Sec-WebSocket-Key, concatinate the magic string 258EAFA5-E914-47DA-95CA-C5AB0DC85B11 to it, take the SHA1 of it, and return the base64 encoded result to the client For acknowledgement as Handshake.
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