analyzer: strip resolver address from DNS lookup error messages

Wrap user-facing lookup errors through a new formatDNSError helper that
clears net.DNSError.Server so the " on <addr>" suffix no longer leaks the
upstream resolver (e.g. "on 127.0.0.11:53") to end users.

Closes: https://framagit.org/happyDomain/happydeliver/-/work_items/2

pkg/analyzer/dns_bimi.go

@@ -45,7 +45,7 @@ func (d *DNSAnalyzer) checkBIMIRecord(domain, selector string) *model.BIMIRecord
 			Selector: selector,
 			Domain:   domain,
 			Valid:    false,
-			Error:    utils.PtrTo(fmt.Sprintf("Failed to lookup BIMI record: %v", err)),
+			Error:    utils.PtrTo(fmt.Sprintf("Failed to lookup BIMI record: %s", formatDNSError(err))),
 		}
 	}
 

pkg/analyzer/dns_dkim.go

@@ -122,7 +122,7 @@ func (d *DNSAnalyzer) checkDKIMRecord(h DKIMHeader) *model.DKIMRecord {
 			Domain:           h.Domain,
 			SigningAlgorithm: signingAlgorithmPtr(h.Algorithm),
 			Valid:            false,
-			Error:            utils.PtrTo(fmt.Sprintf("Failed to lookup DKIM record: %v", err)),
+			Error:            utils.PtrTo(fmt.Sprintf("Failed to lookup DKIM record: %s", formatDNSError(err))),
 		}
 	}
 

pkg/analyzer/dns_dmarc.go

@@ -193,7 +193,7 @@ func (d *DNSAnalyzer) checkDMARCRecord(domain string) *model.DMARCRecord {
 	if err != nil {
 		return &model.DMARCRecord{
 			Valid: false,
-			Error: utils.PtrTo(fmt.Sprintf("Failed to lookup DMARC record: %v", err)),
+			Error: utils.PtrTo(fmt.Sprintf("Failed to lookup DMARC record: %s", formatDNSError(err))),
 		}
 	}
 	if foundDomain == "" {

pkg/analyzer/dns_mx.go

@@ -39,7 +39,7 @@ func (d *DNSAnalyzer) checkMXRecords(domain string) *[]model.MXRecord {
 		return &[]model.MXRecord{
 			{
 				Valid: false,
-				Error: utils.PtrTo(fmt.Sprintf("Failed to lookup MX records: %v", err)),
+				Error: utils.PtrTo(fmt.Sprintf("Failed to lookup MX records: %s", formatDNSError(err))),
 			},
 		}
 	}

pkg/analyzer/dns_resolver.go

@@ -23,9 +23,22 @@ package analyzer
 
 import (
 	"context"
+	"errors"
 	"net"
 )
 
+// formatDNSError renders a resolution error without exposing the upstream
+// resolver address that net.DNSError.Error() normally appends as " on <addr>".
+func formatDNSError(err error) string {
+	var dnsErr *net.DNSError
+	if errors.As(err, &dnsErr) {
+		sanitized := *dnsErr
+		sanitized.Server = ""
+		return sanitized.Error()
+	}
+	return err.Error()
+}
+
 // DNSResolver defines the interface for DNS resolution operations.
 // This interface abstracts DNS lookups to allow for custom implementations,
 // such as mock resolvers for testing or caching resolvers for performance.

pkg/analyzer/dns_spf.go

@@ -67,7 +67,7 @@ func (d *DNSAnalyzer) resolveSPFRecords(domain string, visited map[string]bool,
 			{
 				Domain: &domain,
 				Valid:  false,
-				Error:  utils.PtrTo(fmt.Sprintf("Failed to lookup TXT records: %v", err)),
+				Error:  utils.PtrTo(fmt.Sprintf("Failed to lookup TXT records: %s", formatDNSError(err))),
 			},
 		}
 	}