change proxy based on ip

change proxy based on ip

#!/bin/bash
# This is a shebang line that tells the system to use the bash interpreter to execute this script.

# =====================================================================
# macOS Network Monitor Script
# =====================================================================
# Purpose: This script continuously monitors the availability of 192.168.0.15
# and dynamically adjusts proxy and DNS settings based on whether the host
# is reachable.
#
# Behavior:
# - When 192.168.0.15 is available: Sets this IP as the proxy and configures
#   DNS servers to 192.168.0.15 and 192.168.0.17
# - When 192.168.0.15 is not available: Sets proxy to localhost:3045
# =====================================================================

# ---------------------------------------------------------------------
# Function: log_message
# Purpose: Formats and prints log messages with timestamps
# Parameters:
#   $1 - The message text to log
# ---------------------------------------------------------------------
log_message() {
    # Store the input message in a local variable for clarity
    local message="$1"
    
    # Generate a timestamp in YYYY-MM-DD HH:MM:SS format
    local timestamp=$(date "+%Y-%m-%d %H:%M:%S")
    
    # Print the log message with timestamp to the console
    echo "[$timestamp] $message"
    
    # Note: If you want to save logs to a file, you could add a line like:
    # echo "[$timestamp] $message" >> "/path/to/logfile.log"
}

# ---------------------------------------------------------------------
# Function: get_active_network_service
# Purpose: Detects and returns the name of the current active network
#          service (like "Wi-Fi" or "Ethernet")
# Returns: The name of the active network service as a string
# ---------------------------------------------------------------------
get_active_network_service() {
    # The networksetup command lists all network services on the system
    # grep -v "*" filters out disabled services (they have an asterisk)
    # head -2 takes the first two lines
    # tail -1 takes the last of those two lines (usually the active one)
    # This approach typically gets Wi-Fi on laptops or Ethernet on desktops
    networksetup -listallnetworkservices | grep -v "*" | head -2 | tail -1
}

# ---------------------------------------------------------------------
# Function: set_remote_proxy
# Purpose: Configures system to use 192.168.0.15 as proxy and DNS
# Steps:
#   1. Gets the active network service name
#   2. Sets HTTP and HTTPS proxies to 192.168.0.15
#   3. Enables the proxy settings
#   4. Sets DNS servers to 192.168.0.15 and 192.168.0.17
#   5. Flushes DNS cache to apply changes immediately
# ---------------------------------------------------------------------
set_remote_proxy() {
    # Get the name of the active network service (Wi-Fi, Ethernet, etc.)
    local network_service=$(get_active_network_service)
    
    # Log what we're about to do
    log_message "Setting proxy to 192.168.0.15 and DNS to 192.168.0.15, 192.168.0.17 for $network_service"
    
    # Set HTTP proxy to 192.168.0.15 port 80
    # Parameters: service_name, proxy_domain, proxy_port
    networksetup -setwebproxy "$network_service" 192.168.0.15 80
    
    # Set HTTPS proxy to 192.168.0.15 port 443
    # Parameters: service_name, proxy_domain, proxy_port
    networksetup -setsecurewebproxy "$network_service" 192.168.0.15 443
    
    # Enable the HTTP proxy (turn it on)
    # Parameters: service_name, on/off
    networksetup -setwebproxystate "$network_service" on
    
    # Enable the HTTPS proxy (turn it on)
    # Parameters: service_name, on/off
    networksetup -setsecurewebproxystate "$network_service" on
    
    # Set DNS servers to 192.168.0.15 and 192.168.0.17
    # Parameters: service_name, dns_server1, dns_server2, ...
    networksetup -setdnsservers "$network_service" 192.168.0.15 192.168.0.17
    
    # Flush the DNS cache to ensure new DNS settings take effect immediately
    dscacheutil -flushcache
    
    # Send HUP (hangup) signal to mDNSResponder to restart it
    # This is another step to ensure DNS changes take effect
    killall -HUP mDNSResponder
}

# ---------------------------------------------------------------------
# Function: set_local_proxy
# Purpose: Configures system to use localhost:3045 as proxy
# Steps:
#   1. Gets the active network service name
#   2. Sets HTTP and HTTPS proxies to localhost:3045
#   3. Enables the proxy settings
# Note: This function intentionally does not change DNS settings
# ---------------------------------------------------------------------
set_local_proxy() {
    # Get the name of the active network service
    local network_service=$(get_active_network_service)
    
    # Log what we're about to do
    log_message "Setting proxy to localhost:3045 for $network_service"
    
    # Set HTTP proxy to localhost port 3045
    # Parameters: service_name, proxy_domain, proxy_port
    networksetup -setwebproxy "$network_service" localhost 3045
    
    # Set HTTPS proxy to localhost port 3045
    # Parameters: service_name, proxy_domain, proxy_port
    networksetup -setsecurewebproxy "$network_service" localhost 3045
    
    # Enable the HTTP proxy
    networksetup -setwebproxystate "$network_service" on
    
    # Enable the HTTPS proxy
    networksetup -setsecurewebproxystate "$network_service" on
    
    # Note: We deliberately do not change DNS settings here
    # This allows DNS resolution to continue working when proxy is localhost
}

# ---------------------------------------------------------------------
# Main script execution starts here
# ---------------------------------------------------------------------

# Initialize state tracking variable
# -1 = initial state (unknown)
#  0 = using local proxy (localhost:3045)
#  1 = using remote proxy (192.168.0.15)
current_state=-1

# Print startup messages
log_message "Starting macOS network monitor script"
log_message "Using network service: $(get_active_network_service)"

# Begin infinite loop for continuous monitoring
while true; do
    # Ping 192.168.0.15 to check if it's reachable
    # -c 1: Send only 1 packet
    # -W 1: Wait maximum 1 second for a response
    # &> /dev/null: Redirect both standard output and error to /dev/null (discard them)
    if ping -c 1 -W 1 192.168.0.15 &> /dev/null; then
        # This code runs if the ping was successful (exit code 0)
        
        # Check if we're already using the remote proxy
        # If current_state is not 1, then we need to change settings
        if [ "$current_state" != "1" ]; then
            # Call function to set remote proxy and DNS
            set_remote_proxy
            # Update state tracking variable
            current_state=1
        fi
    else
        # This code runs if the ping failed (non-zero exit code)
        
        # Check if we're already using the local proxy
        # If current_state is not 0, then we need to change settings
        if [ "$current_state" != "0" ]; then
            # Call function to set local proxy
            set_local_proxy
            # Update state tracking variable
            current_state=0
        fi
    fi
    
    # Pause for 1 second before the next check
    # This prevents the script from consuming too much CPU
    sleep 1
    
    # The loop then repeats indefinitely
done

macOS Network Monitor Script

Overview

This script automatically manages your macOS network proxy and DNS settings based on the availability of a specific server (192.168.0.15). It runs continuously in the background, checking connectivity once per second and adjusting your system settings accordingly.

How It Works

The script performs the following operations:

1. Continuous Monitoring: Pings 192.168.0.15 every second to check if it's reachable
2. Dynamic Configuration:
   • When 192.168.0.15 is available:
     • Sets HTTP and HTTPS proxy to 192.168.0.15
     • Sets DNS servers to 192.168.0.15 and 192.168.0.17
     • Flushes DNS cache to ensure immediate effect
   • When 192.168.0.15 is unavailable:
     • Sets HTTP and HTTPS proxy to localhost:3045
     • Leaves DNS settings unchanged
3. Efficient Operation:
   • Only changes settings when network state changes (not on every check)
   • Automatically detects your active network interface (Wi-Fi, Ethernet, etc.)
   • Uses minimal system resources

Requirements

• macOS (tested on macOS Monterey and newer)
• Administrative access (for changing network settings)

Installation

1. Download the script to your preferred location
2. Open Terminal and navigate to the directory containing the script
3. Make the script executable:

   chmod +x network_monitor.sh

Usage

Running Manually

To start the script manually, open Terminal and run:

./network_monitor.sh

The script will display status messages as it runs. To stop it, press Ctrl+C in the Terminal window.

Running in the Background

To run the script in the background:

nohup ./network_monitor.sh &

This will keep the script running even if you close the Terminal window.

Running at Login

To have the script run automatically when you log in, you can create a Launch Agent:

1. Create a file named com.user.networkmonitor.plist in ~/Library/LaunchAgents/
2. Add the following content (adjust the path to your script location):

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.user.networkmonitor</string>
    <key>ProgramArguments</key>
    <array>
        <string>/path/to/network_monitor.sh</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>KeepAlive</key>
    <true/>
    <key>StandardOutPath</key>
    <string>/tmp/networkmonitor.log</string>
    <key>StandardErrorPath</key>
    <string>/tmp/networkmonitor.err</string>
</dict>
</plist>

3. Load the Launch Agent:

launchctl load ~/Library/LaunchAgents/com.user.networkmonitor.plist

Customization

Changing Target IP Address

To monitor a different IP address, edit the script and replace all instances of 192.168.0.15 with your desired IP address.

Changing Proxy Port

To use a different proxy port, edit the set_remote_proxy() or set_local_proxy() functions and change the port numbers.

Changing DNS Servers

To use different DNS servers, edit the networksetup -setdnsservers line in the set_remote_proxy() function.

Troubleshooting

Script Not Changing Network Settings

The script may require administrative privileges to change network settings. Try running it with sudo:

sudo ./network_monitor.sh

Network Service Not Detected

If the script doesn't correctly detect your network service:

1. Find your active network service name:

   networksetup -listallnetworkservices

2. Edit the get_active_network_service() function to explicitly return your service name.

Logging

By default, the script logs status messages to the Terminal. To save logs to a file, modify the log_message() function to append output to a file.

License

This script is provided "as is", without warranty of any kind. Use at your own risk.

Author

This script was created by Jeremy Schoemaker