From 895d5fea41177e444c18f4fdc820fffa5f67d5bf Mon Sep 17 00:00:00 2001
From: Rasmus Dahlberg <rasmus@rgdd.se>
Date: Sat, 9 Dec 2023 17:08:45 +0100
Subject: Add drafty skeleton

---
 pkg/monitor/matcher.go | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 pkg/monitor/matcher.go

(limited to 'pkg/monitor/matcher.go')

diff --git a/pkg/monitor/matcher.go b/pkg/monitor/matcher.go
new file mode 100644
index 0000000..fa3a894
--- /dev/null
+++ b/pkg/monitor/matcher.go
@@ -0,0 +1,90 @@
+package monitor
+
+import (
+	"fmt"
+	"strings"
+
+	ct "github.com/google/certificate-transparency-go"
+)
+
+type Matcher interface {
+	Match(leafInput, extraData []byte) (bool, error)
+}
+
+// MatchAll matches all certificates
+type MatchAll struct{}
+
+func (m *MatchAll) Match(leafInput, extraData []byte) (bool, error) {
+	return true, nil
+}
+
+// MatchWildcards matches a list of wildcards, see the MatchWildcard type
+type MatchWildcards []MatchWildcard
+
+func (m *MatchWildcards) Match(leafInput, extraData []byte) (bool, error) {
+	sans, err := getSANs(ct.LeafEntry{LeafInput: leafInput, ExtraData: extraData})
+	if err != nil {
+		return false, err
+	}
+	return m.match(sans), nil
+}
+
+func (m *MatchWildcards) match(sans []string) bool {
+	for _, mw := range (*m)[:] {
+		if mw.match(sans) {
+			return true
+		}
+	}
+	return false
+}
+
+// MatchWildcard exclude matches for `.*<Exclude>\.<Wildcard>`, but will
+// otherwise match on any `.*\.<Wildcard>` as well as SANs equal to <Wildcard>.
+//
+// For example, let <Wildcard> be example.org and Exclude be [foo, bar].  Then
+// example.org and www.example.org would match, whereas foo.example.org,
+// sub.foo.example.org, and bar.example.org. would not match.
+type MatchWildcard struct {
+	Wildcard string   `json:"wildcard"`
+	Excludes []string `json:"excludes"`
+}
+
+func (m *MatchWildcard) match(sans []string) bool {
+	for _, san := range sans {
+		if san == m.Wildcard {
+			return true
+		}
+		if strings.HasSuffix(san, "."+m.Wildcard) && !m.exclude(san) {
+			return true
+		}
+	}
+	return false
+}
+
+func (m *MatchWildcard) exclude(san string) bool {
+	for _, exclude := range m.Excludes {
+		suffix := exclude + "." + m.Wildcard
+		if strings.HasSuffix(san, suffix) {
+			return true
+		}
+	}
+	return false
+}
+
+func getSANs(entry ct.LeafEntry) ([]string, error) {
+	// Warning: here be dragons, parsing of DNS names in certificates...
+	e, err := ct.LogEntryFromLeaf(0, &entry)
+	if err != nil {
+		return nil, fmt.Errorf("parse leaf: %v", err)
+	}
+	if e.Precert == nil && e.X509Cert == nil {
+		return nil, fmt.Errorf("neither precertificate nor certificate in leaf")
+	}
+	if e.Precert != nil && e.X509Cert != nil {
+		return nil, fmt.Errorf("both certificate and precertificate in leaf")
+	}
+	if e.Precert != nil {
+		return e.Precert.TBSCertificate.DNSNames, nil
+	}
+	return e.X509Cert.DNSNames, nil
+}
-- 
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