DNS Server in Go

This project implements a simple DNS server in Go that listens for DNS queries and resolves domain names to IP addresses. The server can either resolve known records from a local mapping or perform external DNS lookups for unknown domains.

Demo

Link : https://youtu.be/2TGCAw0e63k

Features

• Listen for DNS queries on a specified UDP port.
• Resolve domain names to IP addresses.
• Cache resolved domain names for future requests.
• Perform external DNS resolution for unknown domains.
• Configurable logging and port settings via .env file.

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Table of Contents

1. Installation
2. Configuration
3. Usage
4. Testing
5. Build
6. Project Structure
7. License

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Installation

To run the DNS server locally, follow these steps:

1. Clone the repository:

   git clone https://github.com/your-username/dns-server-go.git
   cd dns-server-go

2. Ensure you have Go installed on your machine.

3. Install the required dependencies:

   go mod tidy

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Configuration

The server uses environment variables for configuration. Create a .env file in the root directory and define the following variables:

DNS_SERVER_PORT=9000
DNS_LOG_FILE=dns_server.log

• DNS_SERVER_PORT: The port on which the DNS server will listen.
• DNS_LOG_FILE: The file where logs will be stored.

Make sure to load the environment variables before running the server:

source .env

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Usage

1. Start the DNS Server: To start the DNS server, simply run the following command:

   go run ./src

   The server will start listening on 127.0.0.1:9000 (or the port specified in .env).

2. Test the Server with dig: Use the dig command to test your server's DNS resolution. For example:

   dig @127.0.0.1 -p 9000 google.com

   The server will respond with an IP address if the domain is resolved in the local records. If the domain is not found, it will attempt an external resolution and cache the result for future queries.

3. External Domain Resolution: If the server cannot find a domain in its local records, it will perform an external DNS query to resolve the IP. For example, if google.com is not in the local records, the server will resolve it via an external DNS service.

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Testing

Run Tests

Execute the following command to run all tests:

go test ./tests -v

What is Tested?

• Ensures LoadConfig() correctly loads environment variables.
• Verifies default values are used when environment variables are missing.
• Confirms that the server IP, port, and log file configurations are set correctly.

If tests pass, the output should indicate success. If there are errors, debug by checking the .env configuration or updating test cases accordingly.

Manual Testing

You can manually test the DNS server via dig, as shown in the usage section. Here’s how to test with dig:

1. Open a terminal or command prompt.

2. Run:

   dig @127.0.0.1 -p 9000 rudrasankha.in

   If the domain is found in the server's records, you will get the resolved IP. If not, the server will attempt to resolve it externally and return the IP.

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Build

To build the DNS server executable, run:

go build -o dns-server ./src

This will create a dns-server binary that you can execute.

To run the built binary:

./dns-server

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Project Structure

The project is organized as follows:

dns-server-go/
│── src/
│   ├── main.go        # Entry point of the DNS server
│   ├── records.go     # Manages local DNS records
│   ├── resolve.go     # Handles external DNS resolution
│   ├── sendDns.go     # Constructs and sends DNS responses
│   ├── serveDns.go    # Handles incoming DNS queries and routing
│   ├── utils/
│       ├── config.go  # Loads environment variables from .env
│       ├── logger.go  # Configures logging
│
├── .env                # Configuration file for server settings
├── go.mod              # Go module definition
├── tests/              # Unit tests for configuration and functionality
│   ├── config.tests.go # Unit tests for configuration loading
├── README.md           # Project documentation

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License

This project is licensed under the MIT License - see the LICENSE file for details.

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