From 552330fa258cdba3d07e15aac7216b3b0eb304c4 Mon Sep 17 00:00:00 2001
From: mimi89999 <michel@lebihan.pl>
Date: Wed, 15 Jan 2025 17:53:09 +0100
Subject: [PATCH 1/2] dmarc: fix handling if multiple records

Fixes #72
---
 dmarc/lookup.go | 47 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 3 deletions(-)

diff --git a/dmarc/lookup.go b/dmarc/lookup.go
index 7d862e5..80c6135 100644
--- a/dmarc/lookup.go
+++ b/dmarc/lookup.go
@@ -51,13 +51,54 @@ func LookupWithOptions(domain string, options *LookupOptions) (*Record, error) {
 		}
 		return nil, errors.New("dmarc: failed to lookup TXT record: " + err.Error())
 	}
+
+	// net.LookupTXT will concatenate strings contained in a single TXT record.
+	// In other words, net.LookupTXT returns one entry per TXT record, even if
+	// a record contains multiple strings.
 	if len(txts) == 0 {
 		return nil, ErrNoPolicy
 	}
 
-	// Long keys are split in multiple parts
-	txt := strings.Join(txts, "")
-	return Parse(txt)
+	// RFC 6376:
+	// Records that do not start with a "v=" tag that identifies the
+	// current version of DMARC are discarded.
+	dmarcRecords := make([]string, 0, len(txts))
+	for _, record := range txts {
+		if IsDmarcRecord(record) {
+			dmarcRecords = append(dmarcRecords, record)
+		}
+	}
+
+	if len(dmarcRecords) != 1 {
+		return nil, ErrNoPolicy
+	}
+
+	return Parse(dmarcRecords[0])
+}
+
+func IsDmarcRecord(txt string) bool {
+	// RFC 6376:
+	// DMARC records follow the extensible "tag-value" syntax for DNS-based
+	// key records defined in DKIM.
+	firstTagSpec, _, _ := strings.Cut(txt, ";")
+
+	tagName, tagValue, found := strings.Cut(firstTagSpec, "=")
+	if !found {
+		return false
+	}
+
+	// RFC 6376:
+	// Note that WSP is allowed anywhere around tags.  In particular, any
+	// WSP after the "=" and any WSP before the terminating ";" is not part
+	// of the value; however, WSP inside the value is significant.
+	if strings.TrimSpace(tagName) != "v" {
+		return false
+	}
+	if strings.TrimSpace(tagValue) != "DMARC1" {
+		return false
+	}
+
+	return true
 }
 
 func Parse(txt string) (*Record, error) {

From 748ade071351538fc9e19b40264c33070d655ba7 Mon Sep 17 00:00:00 2001
From: mimi89999 <michel@lebihan.pl>
Date: Fri, 7 Feb 2025 13:35:27 +0100
Subject: [PATCH 2/2] Do not use a separate function

---
 dmarc/lookup.go | 79 ++++++++++++++++++-------------------------------
 1 file changed, 28 insertions(+), 51 deletions(-)

diff --git a/dmarc/lookup.go b/dmarc/lookup.go
index 80c6135..11daf1e 100644
--- a/dmarc/lookup.go
+++ b/dmarc/lookup.go
@@ -62,53 +62,27 @@ func LookupWithOptions(domain string, options *LookupOptions) (*Record, error) {
 	// RFC 6376:
 	// Records that do not start with a "v=" tag that identifies the
 	// current version of DMARC are discarded.
-	dmarcRecords := make([]string, 0, len(txts))
 	for _, record := range txts {
-		if IsDmarcRecord(record) {
-			dmarcRecords = append(dmarcRecords, record)
+		rec, err := Parse(record)
+		if err != nil {
+			if err.Error() != "dmarc: not a DMARC1 record" {
+				return nil, err
+			}
+		} else {
+			return rec, nil
 		}
 	}
 
-	if len(dmarcRecords) != 1 {
-		return nil, ErrNoPolicy
-	}
-
-	return Parse(dmarcRecords[0])
-}
-
-func IsDmarcRecord(txt string) bool {
-	// RFC 6376:
-	// DMARC records follow the extensible "tag-value" syntax for DNS-based
-	// key records defined in DKIM.
-	firstTagSpec, _, _ := strings.Cut(txt, ";")
-
-	tagName, tagValue, found := strings.Cut(firstTagSpec, "=")
-	if !found {
-		return false
-	}
-
-	// RFC 6376:
-	// Note that WSP is allowed anywhere around tags.  In particular, any
-	// WSP after the "=" and any WSP before the terminating ";" is not part
-	// of the value; however, WSP inside the value is significant.
-	if strings.TrimSpace(tagName) != "v" {
-		return false
-	}
-	if strings.TrimSpace(tagValue) != "DMARC1" {
-		return false
-	}
-
-	return true
+	return nil, ErrNoPolicy
 }
 
 func Parse(txt string) (*Record, error) {
-	params, err := parseParams(txt)
-	if err != nil {
-		return nil, err
-	}
+	var err error = nil
+	params := parseParams(txt)
 
-	if params["v"] != "DMARC1" {
-		return nil, errors.New("dmarc: unsupported DMARC version")
+	v, ok := params["v"]
+	if !ok || v != "DMARC1" {
+		return nil, errors.New("dmarc: not a DMARC1 record")
 	}
 
 	rec := new(Record)
@@ -198,21 +172,24 @@ func Parse(txt string) (*Record, error) {
 	return rec, nil
 }
 
-func parseParams(s string) (map[string]string, error) {
-	pairs := strings.Split(s, ";")
+func parseParams(s string) map[string]string {
+	tagSpecs := strings.Split(s, ";")
 	params := make(map[string]string)
-	for _, s := range pairs {
-		kv := strings.SplitN(s, "=", 2)
-		if len(kv) != 2 {
-			if strings.TrimSpace(s) == "" {
-				continue
-			}
-			return params, errors.New("dmarc: malformed params")
-		}
 
-		params[strings.TrimSpace(kv[0])] = strings.TrimSpace(kv[1])
+	for _, tagSpec := range tagSpecs {
+		tagName, tagValue, ok := strings.Cut(tagSpec, "=")
+		// RFC 6376:
+		// Syntax errors in the remainder of the record SHOULD be discarded in
+		// favor of default values (if any) or ignored outright.
+		if ok {
+			// RFC 6376:
+			// Note that WSP is allowed anywhere around tags. In particular, any
+			// WSP after the "=" and any WSP before the terminating ";" is not
+			// part of the value; however, WSP inside the value is significant.
+			params[strings.TrimSpace(tagName)] = strings.TrimSpace(tagValue)
+		}
 	}
-	return params, nil
+	return params
 }
 
 func parsePolicy(s, param string) (Policy, error) {