feat: Allow usage for top-level domains

internal/dns/dns.go

@@ -2,6 +2,7 @@ package dns
 
 import (
 	"net"
+	"errors"
 	"strings"
 	"time"
 
@@ -15,6 +16,10 @@ const (
 	// The key that the TXT record will have to start with, e.g.
 	// "repo=some-random-repo".
 	TxtRepoKey = "repo="
+
+	TxtCNAMERecord = "_rio-cname."
+
+	TxtCNAMEKey = "cname="
 )
 
 var (
@@ -61,14 +66,53 @@ func LookupCNAME(domain string) (string, error) {
 		return cname.(string), nil
 	}
 
+	cname, err := lookupCNAME(domain)
+	if err == nil {
+		cnameCache.Set(domain, cname, cache.DefaultExpiration)
+		return cname.(string), nil
+	}
+
+	altCname, err := lookupCNAMETxt(domain)
+	if err == nil {
+		cnameCache.Set(domain, altCname, cache.DefaultExpiration)
+		return altCname, nil
+	}
+
+	return "", err
+}
+
+// Lookup the CNAME by trying to find a CNAME RR. Contrary to net.LookupCNAME,
+// this method fails if we find no CNAME RR.
+func lookupCNAME(domain string) (string, error) {
 	query, err := net.LookupCNAME(domain)
 	if err == nil {
 		if query[len(query)-1] == '.' {
 			query = query[:len(query)-1]
 		}
-		cnameCache.Set(domain, query, cache.DefaultExpiration)
+
+		// Fail if we have no CNAME RR.
+		if query == domain {
+			return "", errors.New("CNAME is equal to domain")
+		}
+
 		return query, nil
 	}
 
 	return "", err
 }
+
+// Performs an alternative CNAME lookup by looking for a special TXT record.
+func lookupCNAMETxt(domain string) (string, error) {
+	txts, err := net.LookupTXT(TxtCNAMERecord+domain)
+	if err == nil {
+		for _, txt := range txts {
+			if !strings.HasPrefix(txt, TxtCNAMEKey) {
+				continue
+			}
+
+			return strings.TrimPrefix(txt, TxtCNAMEKey), nil
+		}
+	}
+	
+	return "", err
+}

internal/dns/dns_test.go

@@ -0,0 +1,32 @@
+package dns
+
+import "testing"
+
+func cleanCache() {
+	cnameCache.Flush()
+	txtRepoCache.Flush()
+}
+
+func TestAltCNAME(t *testing.T) {
+	defer cleanCache()
+
+	res, err := lookupCNAMETxt("moxxy.org")
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	if res != "moxxy.pages.polynom.me" {
+		t.Fatalf("Unexpected alt CNAME: %s", res)
+	}
+}
+
+func TestLookupCNAMEWithAlt(t *testing.T) {
+	defer cleanCache()
+
+	res, err := LookupCNAME("moxxy.org")
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	if res != "moxxy.pages.polynom.me" {
+		t.Fatalf("Unexpected alt CNAME: %s", res)
+	}
+}