owasp-amass/resolve

// Copyright © by Jeff Foley 2021-2024. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
// SPDX-License-Identifier: Apache-2.0

package resolve

import (
    "context"
    "strings"

    "github.com/miekg/dns"
)

// FirstProperSubdomain returns the first subdomain name using the provided name and
// Resolver that responds successfully to a DNS query for the NS record type.
func FirstProperSubdomain(ctx context.Context, r *Resolvers, name string) string {
    var domain string
    // Obtain all parts of the subdomain name
    labels := strings.Split(strings.TrimSpace(name), ".")
loop:
    for i := 0; i < len(labels)-1; i++ {
        sub := strings.Join(labels[i:], ".")

        for i := 0; i < maxQueryAttempts; i++ {
            resp, err := r.QueryBlocking(ctx, QueryMsg(sub, dns.TypeNS))
            if err != nil || resp.Rcode == dns.RcodeNameError {
                continue loop
            }
            if resp.Rcode == dns.RcodeSuccess {
                if len(resp.Answer) == 0 {
                    continue loop
                }
                if d := AnswersByType(ExtractAnswers(resp), dns.TypeNS); len(d) > 0 {
                    domain = sub
                    break loop
                }
            }
        }
    }
    return domain
}