fix(dns): fast-failed on RST

dns/cache.go

@@ -0,0 +1,31 @@
+package dns
+
+import (
+	"context"
+	"time"
+
+	"github.com/FloatTech/ttl"
+	"github.com/fumiama/terasu/ip"
+)
+
+var lookupTable = ttl.NewCache[string, []string](time.Hour)
+
+// LookupHost use default resolver with its fallback
+func LookupHost(ctx context.Context, host string) (addrs []string, err error) {
+	addrs = lookupTable.Get(host)
+	if len(addrs) == 0 {
+		addrs, err = DefaultResolver.LookupHost(ctx, host)
+		if err != nil {
+			if ip.IsIPv6Available.Get() {
+				addrs, err = IPv6Servers.lookupHostDoH(ctx, host)
+			} else {
+				addrs, err = IPv4Servers.lookupHostDoH(ctx, host)
+			}
+			if err != nil {
+				return nil, err
+			}
+		}
+		lookupTable.Set(host, addrs)
+	}
+	return
+}