Backend Development 10 min read

How to Install and Use websocketd for Real‑Time WebSocket Scripts

This guide explains how to install the websocketd daemon, configure it to run shell scripts as WebSocket back‑ends, create simple HTML clients, monitor system memory in real time, and fine‑tune parameters such as static file serving, developer console, SSL, and Nginx proxying.

Open Source Tech Hub

Dec 24, 2023

How to Install and Use websocketd for Real‑Time WebSocket Scripts

Installation

// Download
wget https://github.com/joewalnes/websocketd/releases/download/v0.4.1/websocketd-0.4.1-linux_amd64.zip

// Unzip
unzip websocketd-0.4.1-linux_amd64.zip

After extraction the executable websocketd is available.

Check the version: ./websocketd -version Output example: websocketd 0.4.1 (go1.15.7 linux-amd64)

Simple Example – Counter Script

Shell script (counter.sh)

#!/bin/bash
for ((COUNT = 1; COUNT <= 10; COUNT++)); do
  echo $COUNT
  sleep 1
done

Start websocketd

chmod 777 counter.sh
/var/www/websocketd/websocketd --port=8888 /var/www/websocketd/counter.sh

The command launches a WebSocket server on port 8888. Each client connection triggers counter.sh, and its output is streamed to the client.

HTML client

<!doctype html>
<html lang="">
<head>
  <meta charset="utf-8">
  <meta name="description" content="">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>websocketd client test</title>
</head>
<body>
  <h2>websocketd client test</h2>
  <pre id="message" style="font-size: 24px;"></pre>
  <script>
    function log(msg){
      document.getElementById('message').textContent += msg + '
';
    }
    var ws = new WebSocket('ws://127.0.0.1:8888/');
    ws.onopen = function(){ console.log('CONNECT'); };
    ws.onclose = function(){ console.log('DISCONNECT'); ws.close(); };
    ws.onmessage = function(event){
      console.log('MESSAGE: ' + event.data);
      log('websocketd server response: ' + event.data);
    };
  </script>
</body>
</html>

Real‑Time Memory Monitoring

Shell script (system_info.sh)

#!/bin/bash
PATH=/usr/local/bin:/usr/bin:/bin

SHELL_DIR="/var/www/websocketd"
SHELL_NAME="system_info"
SHELL_TIME=$(date '+%Y-%m-%d')
SHELL_LOG="${SHELL_DIR}/${SHELL_NAME}-${SHELL_TIME}.log"

while true; do
  FIND_DATA=$(cat /proc/meminfo | grep "MemFree:" | awk '{print $2}')
  echo "[${SHELL_TIME}]: FIND_DATA = ${FIND_DATA}" >> $SHELL_LOG
  echo '{"data":"'${FIND_DATA}'","errcode":0,"errmsg":0}'
  sleep 2
done

Start websocketd for monitoring

chmod 777 system_info.sh
/var/www/websocketd/websocketd --port=8888 /var/www/websocketd/system_info.sh

Parameter Configuration

Static file serving

Use --staticdir= to let websocketd serve static files such as counter.html or count.sh.

Example count script and HTML

#!/bin/bash
for COUNT in $(seq 1 10); do
  echo $COUNT
  sleep 1
done

<!DOCTYPE html>
<html>
  <head>
    <title>websocketd count example</title>
    <style>#count {font: bold 150px arial; margin:auto; padding:10px; text-align:center;}</style>
  </head>
  <body>
    <div id="count"></div>
    <script>
      var ws = new WebSocket('ws://127.0.0.1:8888/');
      ws.onopen = function(){ document.body.style.backgroundColor = '#cfc'; };
      ws.onclose = function(){ document.body.style.backgroundColor = null; };
      ws.onmessage = function(event){
        document.getElementById('count').textContent = event.data;
      };
    </script>
  </body>
</html>

Run with:

/var/www/websocketd/websocketd --port=8888 --staticdir=. ./count.sh

Developer Console

Enable an interactive console without writing JavaScript by adding the --devconsole flag:

/var/www/websocketd/websocketd --port=8888 --dir=/var/www/websocketd --devconsole

Running as a Daemon

nohup /var/www/websocketd/websocketd --port=8888 /var/www/websocketd/system_info.sh > /dev/null 2>&1 &

SSL Certificate Loading

sudo websocketd \
  --port=8888 \
  --ssl \
  --sslcert="/etc/letsencrypt/live/www.tinywan.com/fullchain.pem" \
  --sslkey="/etc/letsencrypt/live/www.tinywan.com/privkey.pem" \
  /var/www/websocketd/system.sh

Nginx Proxy Configuration

server {
    listen 443 ssl http2;
    server_name wallet.tinywan.com;

    ssl_certificate /etc/letsencrypt/wallet.tinywan.com/full_chain.pem;
    ssl_certificate_key /etc/letsencrypt/wallet.tinywan.com/private.key;

    location /wssd {
        proxy_pass http://127.0.0.1:8888;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_set_header X-Real-IP $remote_addr;
        proxy_read_timeout 600;
    }
}

Clients can connect via:

var ws = new WebSocket('wss://wallet.tinywan.com/wssd');

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