Connecting Your Android Device to Your Localhost Backend: A Developer's Guide

By Vikrant Karawande

As an Android developer, testing your app against a local backend server is crucial. But how do you access your laptop's localhost from your physical Android device? "Localhost" refers to your own machine, and it won't work on another device by default. Before we explore the methods, make sure that the backend server listens on ‘0.0.0.0:<port>’ IP address instead of ‘localhost:<port>’ or ‘127.0.0.1:<port>’ to allow traffic from all the IPs Here, we'll explore two effective methods:

Method 1: Using ADB Reverse Socket (For Developers)

This method is ideal for frequent testing and offers more flexibility. It requires setting up ADB (Android Debug Bridge).

1. Enable USB Debugging: On your Android device, go to Settings > Developer options (you might need to enable Developer options first by tapping "Build number" seven times). Enable "USB Debugging."
2. Install ADB (if not already): Download the Android SDK platform-tools package from https://developer.android.com/studio. Extract the downloaded zip file.
3. Connect Your Device: Connect your Android device to your laptop using a USB cable.
4. Run ADB Reverse Socket: Open a command prompt or terminal and navigate to the directory containing the ADB tools (usually the "platform-tools" folder from step 2). Run the following command, replacing 8000 with your desired port number:

5.? adb -s <device name> reverse tcp:8000 tcp:8000

This command creates a tunnel, forwarding traffic from port 8000 on your device to port 8000 on your laptop. To view device names run: adb devices

1. Access Your Backend: On your Android device's browser, simply enter https://localhost:8000 (or the port you specified). Note: Please make sure that IP is ‘localhost’ and not ’10.0.2.2’ as used in Android emulators.

Method 2: Using Your Laptop's IP Address

1. Find Your IP Address: Windows: Open Command Prompt and type ipconfig. Look for the IPv4 address under "Ethernet adapter" (or Wi-Fi adapter). Mac: Open System Preferences > Network. Select your network connection and look for the IP address.
2. Adjust the URL: In your Android device's browser, replace "localhost" with your laptop's IP address. If your backend runs on a specific port (e.g., 8000), include it after the IP address separated by a colon (":"). For example, if your IP is 192.168.1.100 and the port is 8000, you'd enter https://192.168.1.100:8000 in the address bar.
3. If laptop is connected to repeater there is a possibility that backend server might not be accessible, even if android device is connected to same repeater. While running a react native app, react native app was not able to access backend server even though backend server was accessible from chrome browser on same device. On switching laptop to main router react native app was able to access backend server even from repeater

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Method 3: Using ngrok

??????????? Involves initial one time setup like creating ngrok account, downloading windows agent and configuring auth token. Ngrok also allows one free static domain.

1.???? Put your app online: Run following command ngrok http https://localhost:8000

2.???? Access backend using web address provided by Ngrok Ngrok will print an address on command line mentioning ‘Forwarding’ This web address can be used in applications to access your backend, as long as your backend server is running and laptop is connected to internet.

Choosing the Right Method:

• Method 1 is ideal for frequent testing as it creates a persistent tunnel and avoids the need to know the IP address every time.
• Method 2 is simpler for occasional testing, but the IP address can change if you switch networks. Also, the laptop should be connected to main router for this method to work properly.
• Method 3 involves a one-time setup and active internet connection, but is useful for local development as well as remote testing without hosting backend to cloud.

Additional Considerations:

• Firewalls might block connections. Temporarily disable your firewall for testing purposes but remember to re-enable it for security.

By following these steps, you should be able to connect your Android device to your local backend server and streamline your development workflow!