[client] Refactor DNSForwarder to improve handle wildcard domain resource id matching (#3651)

[client] Refactor DNSForwarder to improve handle wildcard domain resource id matching (#3651)

client/internal/dnsfwd/forwarder.go

@@ -3,6 +3,7 @@ package dnsfwd
 import (
 	"context"
 	"errors"
+	"math"
 	"net"
 	"net/netip"
 	"strings"
@@ -62,7 +63,6 @@ func (f *DNSForwarder) UpdateDomains(domains []string, resIds map[string]string)
 
 	for _, d := range f.domains {
 		f.mux.HandleRemove(d)
-		f.statusRecorder.RemoveResolvedIPLookupEntry(d)
 	}
 	f.resId.Clear()
 
@@ -122,8 +122,8 @@ func (f *DNSForwarder) handleDNSQuery(w dns.ResponseWriter, query *dns.Msg) {
 		return
 	}
 
-	resId, ok := f.resId.Load(strings.TrimSuffix(domain, "."))
-	if ok {
+	resId := f.getResIdForDomain(strings.TrimSuffix(domain, "."))
+	if resId != "" {
 		for _, ip := range ips {
 			var ipWithSuffix string
 			if ip.Is4() {
@@ -133,7 +133,7 @@ func (f *DNSForwarder) handleDNSQuery(w dns.ResponseWriter, query *dns.Msg) {
 				ipWithSuffix = ip.String() + "/128"
 				log.Tracef("resolved domain=%s to IPv6=%s", domain, ipWithSuffix)
 			}
-			f.statusRecorder.AddResolvedIPLookupEntry(ipWithSuffix, resId.(string))
+			f.statusRecorder.AddResolvedIPLookupEntry(ipWithSuffix, resId)
 		}
 	}
 
@@ -204,6 +204,36 @@ func (f *DNSForwarder) addIPsToResponse(resp *dns.Msg, domain string, ips []neti
 	}
 }
 
+func (f *DNSForwarder) getResIdForDomain(domain string) string {
+	var selectedResId string
+	var bestScore int
+
+	f.resId.Range(func(key, value interface{}) bool {
+		var score int
+		pattern := key.(string)
+
+		switch {
+		case strings.HasPrefix(pattern, "*."):
+			baseDomain := strings.TrimPrefix(pattern, "*.")
+			if domain == baseDomain || strings.HasSuffix(domain, "."+baseDomain) {
+				score = len(baseDomain)
+			}
+		case domain == pattern:
+			score = math.MaxInt
+		default:
+			return true
+		}
+
+		if score > bestScore {
+			bestScore = score
+			selectedResId = value.(string)
+		}
+		return true
+	})
+
+	return selectedResId
+}
+
 // filterDomains returns a list of normalized domains
 func filterDomains(domains []string) []string {
 	newDomains := make([]string, 0, len(domains))

client/internal/dnsfwd/forwarder_test.go

@@ -0,0 +1,95 @@
+package dnsfwd
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestGetResIdForDomain(t *testing.T) {
+	testCases := []struct {
+		name           string
+		storedMappings map[string]string // key: domain pattern, value: resId
+		queryDomain    string
+		expectedResId  string
+	}{
+		{
+			name:           "Empty map returns empty string",
+			storedMappings: map[string]string{},
+			queryDomain:    "example.com",
+			expectedResId:  "",
+		},
+		{
+			name:           "Exact match returns stored resId",
+			storedMappings: map[string]string{"example.com": "res1"},
+			queryDomain:    "example.com",
+			expectedResId:  "res1",
+		},
+		{
+			name:           "Wildcard pattern matches base domain",
+			storedMappings: map[string]string{"*.example.com": "res2"},
+			queryDomain:    "example.com",
+			expectedResId:  "res2",
+		},
+		{
+			name:           "Wildcard pattern matches subdomain",
+			storedMappings: map[string]string{"*.example.com": "res3"},
+			queryDomain:    "foo.example.com",
+			expectedResId:  "res3",
+		},
+		{
+			name:           "Wildcard pattern does not match different domain",
+			storedMappings: map[string]string{"*.example.com": "res4"},
+			queryDomain:    "foo.notexample.com",
+			expectedResId:  "",
+		},
+		{
+			name:           "Non-wildcard pattern does not match subdomain",
+			storedMappings: map[string]string{"example.com": "res5"},
+			queryDomain:    "foo.example.com",
+			expectedResId:  "",
+		},
+		{
+			name: "Exact match over overlapping wildcard",
+			storedMappings: map[string]string{
+				"*.example.com":   "resWildcard",
+				"foo.example.com": "resExact",
+			},
+			queryDomain:   "foo.example.com",
+			expectedResId: "resExact",
+		},
+		{
+			name: "Overlapping wildcards: Select more specific wildcard",
+			storedMappings: map[string]string{
+				"*.example.com":     "resA",
+				"*.sub.example.com": "resB",
+			},
+			queryDomain:   "bar.sub.example.com",
+			expectedResId: "resB",
+		},
+		{
+			name: "Wildcard multi-level subdomain match",
+			storedMappings: map[string]string{
+				"*.example.com": "resMulti",
+			},
+			queryDomain:   "a.b.example.com",
+			expectedResId: "resMulti",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			fwd := &DNSForwarder{
+				resId: sync.Map{},
+			}
+
+			for domainPattern, resId := range tc.storedMappings {
+				fwd.resId.Store(domainPattern, resId)
+			}
+
+			got := fwd.getResIdForDomain(tc.queryDomain)
+			if got != tc.expectedResId {
+				t.Errorf("For query domain %q, expected resId %q, but got %q", tc.queryDomain, tc.expectedResId, got)
+			}
+		})
+	}
+}