During the process of learning websockets, wanted to try out the handshake mechanism using a simple server cooked using netcat/bash script. The script just reads the request message, parses the key, forms the SHA1/base64 response key and sends the response.

Tested it with chromium. Attached are the code and screenshot.

#!/bin/bashrm -rf twhile truedo   read packet   echo $packet >> t   cnt=`echo $packet | wc -c`   if [ $cnt == 2 ] #end of message   then      key=`cat t | grep "Sec-WebSocket-Key:" | cut -f2 -d " "`      keylen=`echo -n $key | wc -c`      keylen=`expr $keylen - 1`      key2=`echo -n $key | cut -c -$keylen`      magic="258EAFA5-E914-47DA-95CA-C5AB0DC85B11"      resp=`echo -n $key2$magic | openssl sha1 -binary | base64`      echo   -n "HTTP/1.1 101 Switching Protocols"$'\r\n'      echo   -n "Connection: Upgrade"$'\r\n'      echo   -n "Upgrade: websocket"$'\r\n'      echo   -n "Sec-WebSocket-Accept: $resp"$'\r\n\r\n'      break   fidone

HTML with websocket call

nvoke netcat as follows and open the above HTML using chromium/firefox

nc -l -p 8888 -e ./wshandshake.sh 

Screenshot of Chromium websocket developer console, post invocation.

 

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