WebSocket Client Script with Dynamic User Prompts and Auto Installation of websocat

websocket_script.md

This Bash script establishes a WebSocket connection to a server, allowing users to send a sequence of messages interactively. It is particularly useful for testing WebSocket APIs or automating WebSocket-based data subscriptions.

The script leverages websocat for WebSocket communication. If websocat is not installed, the script will prompt the user to install it automatically.

Features

• Interactive Setup: The script prompts the user for essential parameters, including:
• WebSocket URL: Defaults to wss://example.com if left blank.
• Username and Password: For authentication in the WebSocket server.
• Currency (CCY): Used to specify the currency in the subscription message.
• Customizable Sleep Time: Allows a delay between messages, with the first message having a fixed 1-second delay and subsequent messages using a user-defined interval.
• Automatic websocat Installation: If websocat is not installed, the script prompts the user to install it. Upon confirmation, it downloads the latest version of websocat from GitHub, makes it executable, and moves it to /usr/local/bin/ for system-wide access.
• Sequential Message Sending: Sends messages in a specified sequence, waiting for a server response after each message.
• Response Capture: Reads and displays server responses in real-time, allowing the user to observe responses to each message.

Example Usage

1. Run the Script:

chmod +x ./websocket_script.sh
./websocket_script.sh

2. Follow the Prompts:

• Enter the WebSocket URL or press Enter to use the default URL.
• Provide your username, password, and currency for the subscription.
• Set a custom sleep time for subsequent messages, or press Enter to default to 1 second.

3. Observe Responses:

• The script sends each message in sequence, starting with a login request and followed by a subscription request for the specified currency.
• Each server response is displayed in real-time as "Received: "

websocket_script.sh

#!/bin/bash

# Check if websocat is installed
if ! command -v websocat &> /dev/null; then
    read -p "websocat is not installed. Would you like to install it now? (y/n): " install_websocat

    if [[ "$install_websocat" == "y" || "$install_websocat" == "Y" ]]; then
        # Attempt to download and install websocat
        echo "Installing websocat..."
        wget -q https://github.com/vi/websocat/releases/latest/download/websocat.x86_64-linux -O websocat
        chmod +x websocat
        sudo mv websocat /usr/local/bin/
        
        # Verify if installation was successful
        if command -v websocat &> /dev/null; then
            echo "websocat installed successfully."
        else
            echo "Failed to install websocat. Please install it manually from https://github.com/vi/websocat."
            exit 1
        fi
    else
        echo "websocat is required to run this script. Exiting."
        exit 1
    fi
fi

# Prompt for WebSocket URL with a default value
read -p "Enter WebSocket URL (default is wss://example.com): " WEBSOCKET_URL
WEBSOCKET_URL=${WEBSOCKET_URL:-wss://example.com}

# Prompt for USERNAME, PASSWORD, CCY, and optional SLEEP time
read -p "Enter Username: " USERNAME
read -s -p "Enter Password: " PASSWORD
echo
read -p "Enter Currency (CCY): " CCY
read -p "Enter sleep time for subsequent messages (default is 1 second): " SLEEP

# Use default sleep time of 1 second if the user leaves input blank
SLEEP=${SLEEP:-1}

# Array of messages to send in sequence with user-provided values
messages=(
    "{\"request\": \"login\", \"username\": \"$USERNAME\", \"password\": \"$PASSWORD\"}"
    "{\"request\": \"subscribe\", \"ccy\": \"$CCY\"}"
)

# Start websocat in interactive mode, and pipe commands to it
{
    # Sleep for 2 second before sending the first message to allow websocket connection established
    sleep 2
    for i in "${!messages[@]}"; do
        # Send each message
        echo "${messages[$i]}"
        
        # Use a 1-second sleep for the first message, and user-defined sleep for others
        if [ "$i" -eq 0 ]; then
            sleep 1
        else
            sleep "$SLEEP"
        fi
    done
} | websocat "$WEBSOCKET_URL" | while IFS= read -r response; do
    echo "Received: $response"
done