This Python script generates a list of subdomains where is a known format such as us-001.domain.com through us-100.domain.com and then validates each subdomain by performing a DNS lookup to check if it resolves to a valid IP address. The validated subdomains are then written to an output file. This tool can be useful for generating a list of valid subdomains for use in security testing or other applications.
The code is a web application that allows you to check if a list of domain names is valid. The application is written in JavaScript and uses a couple of external services to accomplish its task.
When you open the application, you'll see a simple web page with a text box and a button. To use the application, you simply enter a list of domain names, one per line, into the text box and click the button.
When you click the button, the application uses a JavaScript function called checkDomains() to validate the domain names. This function takes the input text, splits it into individual domain names, and sends a DNS query for each domain name to the Cloudflare DoH JSON API.
The Cloudflare DoH JSON API is an external service that provides a secure way to send DNS queries over HTTPS. When the API receives a DNS query, it looks up the corresponding IP address for the domain name and returns the result as a JSON object.
The checkDomains() function receives the JSON object for each DNS query and checks if it contains a valid IP address. If the JSON object contains a valid IP address, the domain name is added to a list of valid domains. Otherwise, the domain name is skipped.
Once all of the DNS queries have completed, the checkDomains() function updates the output text with the list of valid domain names. The output text is displayed in a separate text box below the input text box.