[client] Match DNS wildcard handlers on label boundaries (#6255)

client/internal/dns/handler_chain.go

@@ -339,8 +339,7 @@ func (c *HandlerChain) isHandlerMatch(qname string, entry HandlerEntry) bool {
 	case entry.Pattern == ".":
 		return true
 	case entry.IsWildcard:
-		parts := strings.Split(strings.TrimSuffix(qname, entry.Pattern), ".")
-		return len(parts) >= 2 && strings.HasSuffix(qname, entry.Pattern)
+		return strings.HasSuffix(qname, "."+entry.Pattern)
 	default:
 		// For non-wildcard patterns:
 		// If handler wants subdomain matching, allow suffix match

client/internal/dns/handler_chain_test.go

@@ -164,6 +164,54 @@ func TestHandlerChain_ServeDNS_DomainMatching(t *testing.T) {
 			matchSubdomains: true,
 			shouldMatch:     true,
 		},
+		{
+			name:            "wildcard label-boundary mismatch (suffix overlap)",
+			handlerDomain:   "*.b.test.",
+			queryDomain:     "x.ab.test.",
+			isWildcard:      true,
+			matchSubdomains: false,
+			shouldMatch:     false,
+		},
+		{
+			name:            "wildcard label-boundary match",
+			handlerDomain:   "*.b.test.",
+			queryDomain:     "x.b.test.",
+			isWildcard:      true,
+			matchSubdomains: false,
+			shouldMatch:     true,
+		},
+		{
+			name:            "wildcard multi-label match",
+			handlerDomain:   "*.b.test.",
+			queryDomain:     "x.y.b.test.",
+			isWildcard:      true,
+			matchSubdomains: false,
+			shouldMatch:     true,
+		},
+		{
+			name:            "wildcard no match on multi-label apex",
+			handlerDomain:   "*.b.test.",
+			queryDomain:     "b.test.",
+			isWildcard:      true,
+			matchSubdomains: false,
+			shouldMatch:     false,
+		},
+		{
+			name:            "wildcard no match on unrelated suffix containment",
+			handlerDomain:   "*.example.com.",
+			queryDomain:     "notexample.com.",
+			isWildcard:      true,
+			matchSubdomains: false,
+			shouldMatch:     false,
+		},
+		{
+			name:            "wildcard accepts pattern registered without trailing dot",
+			handlerDomain:   "*.b.test",
+			queryDomain:     "x.b.test.",
+			isWildcard:      true,
+			matchSubdomains: false,
+			shouldMatch:     true,
+		},
 	}
 
 	for _, tt := range tests {
@@ -273,6 +321,19 @@ func TestHandlerChain_ServeDNS_OverlappingDomains(t *testing.T) {
 			expectedCalls:   1,
 			expectedHandler: 2, // highest priority matching handler should be called
 		},
+		{
+			name: "overlapping wildcard suffixes route to correct handler",
+			handlers: []struct {
+				pattern  string
+				priority int
+			}{
+				{pattern: "*.b.test.", priority: nbdns.PriorityDNSRoute},
+				{pattern: "*.ab.test.", priority: nbdns.PriorityDNSRoute},
+			},
+			queryDomain:     "app.ab.test.",
+			expectedCalls:   1,
+			expectedHandler: 1,
+		},
 		{
 			name: "root zone with specific domain",
 			handlers: []struct {