downgrade to udp when retrying dns queries

lib/httpx/resolver/native.rb

@@ -144,6 +144,8 @@ module HTTPX
 
       if !@timeouts[host].empty?
         log { "resolver: timeout after #{timeout}s, retry(#{@timeouts[host].first}) #{host}..." }
+        # must downgrade to tcp AND retry on same host as last
+        downgrade_socket
         resolve(connection)
       elsif @ns_index + 1 < @nameserver.size
         # try on the next nameserver
@@ -189,10 +191,9 @@ module HTTPX
             next unless @large_packet.full?
 
             parse(@large_packet.to_s)
-            @socket_type = @resolver_options.fetch(:socket_type, :udp)
             @large_packet = nil
-            transition(:idle)
-            transition(:open)
+            # downgrade to udp again
+            downgrade_socket
             return
           else
             size = @read_buffer[0, 2].unpack1("n")
@@ -313,6 +314,12 @@ module HTTPX
           if catch(:coalesced) { early_resolve(connection, hostname: hostname_alias) }
             @connections.delete(connection)
           else
+            if @socket_type == :tcp
+              # must downgrade to udp if tcp
+              @socket_type = @resolver_options.fetch(:socket_type, :udp)
+              transition(:idle)
+              transition(:open)
+            end
             log { "resolver: ALIAS #{hostname_alias} for #{name}" }
             resolve(connection, hostname_alias)
             return
@@ -390,6 +397,14 @@ module HTTPX
       end
     end
 
+    def downgrade_socket
+      return unless @socket_type == :tcp
+
+      @socket_type = @resolver_options.fetch(:socket_type, :udp)
+      transition(:idle)
+      transition(:open)
+    end
+
     def transition(nextstate)
       case nextstate
       when :idle

sig/resolver/native.rbs

@@ -59,6 +59,8 @@ module HTTPX
 
       def build_socket: () -> (UDP | TCP)
 
+      def downgrade_socket: () -> void
+
       def transition: (Symbol nextstate) -> void
 
       def handle_error: (NativeResolveError | StandardError) -> void