up

resolver/dnscheck.go

@@ -0,0 +1,88 @@
+package resolver
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/miekg/dns"
+)
+
+var resolvers = []string{"1.1.1.1:53", "8.8.8.8:53"}
+
+func lookupTXT(domain string) ([]string, error) {
+	for _, server := range resolvers {
+		m := new(dns.Msg)
+		m.SetQuestion(dns.Fqdn(domain), dns.TypeTXT)
+		resp, err := dns.Exchange(m, server)
+		if err != nil || resp == nil {
+			continue
+		}
+		var results []string
+		for _, ans := range resp.Answer {
+			if txt, ok := ans.(*dns.TXT); ok {
+				results = append(results, txt.Txt...)
+			}
+		}
+		if len(results) > 0 {
+			return results, nil
+		}
+	}
+	return nil, fmt.Errorf("no TXT records found")
+}
+
+func CheckSPF(domain string) (string, bool) {
+	txts, err := lookupTXT(domain)
+	if err != nil {
+		return "", false
+	}
+	for _, txt := range txts {
+		if strings.HasPrefix(txt, "v=spf1") {
+			return txt, true
+		}
+	}
+	return "", false
+}
+
+func CheckDMARC(domain string) (string, bool) {
+	dmarc := "_dmarc." + domain
+	txts, err := lookupTXT(dmarc)
+	if err != nil || len(txts) == 0 {
+		return "", false
+	}
+	return txts[0], true
+}
+
+var rbls = []string{
+	"zen.spamhaus.org",
+	"bl.spamcop.net",
+	"b.barracudacentral.org",
+}
+
+func CheckBlacklists(ip string) []string {
+	var listed []string
+	parts := strings.Split(ip, ".")
+	if len(parts) != 4 {
+		return listed
+	}
+	reversed := fmt.Sprintf("%s.%s.%s.%s", parts[3], parts[2], parts[1], parts[0])
+	for _, rbl := range rbls {
+		query := fmt.Sprintf("%s.%s.", reversed, rbl)
+		m := new(dns.Msg)
+		m.SetQuestion(query, dns.TypeA)
+		for _, resolver := range resolvers {
+			resp, err := dns.Exchange(m, resolver)
+			if err == nil && resp != nil && len(resp.Answer) > 0 {
+				for _, ans := range resp.Answer {
+					if a, ok := ans.(*dns.A); ok {
+						ip := a.A.String()
+						if strings.HasPrefix(ip, "127.0.0.") {
+							listed = append(listed, rbl)
+							break
+						}
+					}
+				}
+			}
+		}
+	}
+	return listed
+}