Split dns.go in one file per check

pkg/analyzer/dns_fcr.go

@@ -0,0 +1,94 @@
+// This file is part of the happyDeliver (R) project.
+// Copyright (c) 2025 happyDomain
+// Authors: Pierre-Olivier Mercier, et al.
+//
+// This program is offered under a commercial and under the AGPL license.
+// For commercial licensing, contact us at <contact@happydomain.org>.
+//
+// For AGPL licensing:
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package analyzer
+
+import (
+	"context"
+
+	"git.happydns.org/happyDeliver/internal/api"
+)
+
+// checkPTRAndForward performs reverse DNS lookup (PTR) and forward confirmation (A/AAAA)
+// Returns PTR hostnames and their corresponding forward-resolved IPs
+func (d *DNSAnalyzer) checkPTRAndForward(ip string) ([]string, []string) {
+	ctx, cancel := context.WithTimeout(context.Background(), d.Timeout)
+	defer cancel()
+
+	// Perform reverse DNS lookup (PTR)
+	ptrNames, err := d.resolver.LookupAddr(ctx, ip)
+	if err != nil || len(ptrNames) == 0 {
+		return nil, nil
+	}
+
+	var forwardIPs []string
+	seenIPs := make(map[string]bool)
+
+	// For each PTR record, perform forward DNS lookup (A/AAAA)
+	for _, ptrName := range ptrNames {
+		// Look up A records
+		ctx, cancel := context.WithTimeout(context.Background(), d.Timeout)
+		aRecords, err := d.resolver.LookupHost(ctx, ptrName)
+		cancel()
+
+		if err == nil {
+			for _, forwardIP := range aRecords {
+				if !seenIPs[forwardIP] {
+					forwardIPs = append(forwardIPs, forwardIP)
+					seenIPs[forwardIP] = true
+				}
+			}
+		}
+	}
+
+	return ptrNames, forwardIPs
+}
+
+// Proper reverse DNS (PTR) and forward-confirmed reverse DNS (FCrDNS) is important for deliverability
+func (d *DNSAnalyzer) calculatePTRScore(results *api.DNSResults, senderIP string) (score int) {
+	if results.PtrRecords != nil && len(*results.PtrRecords) > 0 {
+		// 50 points for having PTR records
+		score += 50
+
+		if len(*results.PtrRecords) > 1 {
+			// Penalty has it's bad to have multiple PTR records
+			score -= 15
+		}
+
+		// Additional 50 points for forward-confirmed reverse DNS (FCrDNS)
+		// This means the PTR hostname resolves back to IPs that include the original sender IP
+		if results.PtrForwardRecords != nil && len(*results.PtrForwardRecords) > 0 && senderIP != "" {
+			// Verify that the sender IP is in the list of forward-resolved IPs
+			fcrDnsValid := false
+			for _, forwardIP := range *results.PtrForwardRecords {
+				if forwardIP == senderIP {
+					fcrDnsValid = true
+					break
+				}
+			}
+			if fcrDnsValid {
+				score += 50
+			}
+		}
+	}
+
+	return
+}