Go-PortScanner

A lightweight, concurrent TCP port scanner written in Go with optional banner grabbing support to identify running services. Includes a companion Python test server that emulates common network services for testing and demonstration.

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Features

• Concurrent scanning of port ranges for improved speed
• Banner grabbing for service identification (e.g., SSH, HTTP, SMTP)
• Timeout handling to prevent indefinite blocking
• Port range validation for safety and correctness
• Uses only the Go standard library

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Project Structure

go-portscanner/
├── main.go               # Entry point — parses args and runs the scan
├── scanner/
│   └── scanner.go        # Handles concurrent TCP port scanning
├── banners/
│   └── banners.go        # Implements banner grabbing for open ports
├── utils/
│   └── utils.go          # Provides input validation utilities
└── test_server/
    └── fake_services.py  # Python test script to simulate network services

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Installation

Prerequisites

• Go 1.18+ installed
• (Optional) Python 3.8+ if you want to run the fake banner test server

Clone the repository

git clone https://github.com/yourusername/go-portscanner.git
cd go-portscanner

Build the scanner

go build -o portscanner main.go

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Usage

Syntax

./portscanner <host> <start_port> <end_port>

Example

./portscanner 127.0.0.1 20 1000

Example output

Port 21 open: "220 FTP Server ready"
Port 22 open: "SSH-2.0-OpenSSH_8.0"
Port 80 open: "HTTP/1.1 200 OK"
Open ports on 127.0.0.1:
  - 21
  - 22
  - 80

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How It Works

1. main.go parses command-line arguments and validates the port range using utils.ValidatePortRange.

2. scanner.ScanPorts runs concurrent TCP connection attempts with a 1-second timeout.

3. For each successful connection, banners.GrabBanner attempts to read a service banner:

   • For ports 80 and 8080, an HTTP GET request is sent first.
   • The function reads up to the first newline from the service response.

4. The scanner prints open ports and any banners captured.

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Testing with the Fake Banner Server

You can test locally using the included Python script.

Start the fake server

python3 test_server/fake_services.py

This script opens multiple local ports (e.g., 21, 22, 80, 8080) and responds with simulated banners.

Run the scanner

./portscanner 127.0.0.1 20 10000

The scanner should detect and print the simulated services.

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Disclaimer

This tool is for educational and authorized testing purposes only. Do not use it to scan systems without explicit permission.

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Future Enhancements

• Add UDP scanning support
• Implement JSON/CSV output formatting
• Add progress indicators or scan rate limits
• Improve service detection using signature matching