By "Continuation" I assume you mean HTTP's "100 Continue" feature, as documented in the HTTP RFC.

If the client has "Expect: 100-continue" as one if its request headers, then try replying "100 (Continue)\r\n" when you see the blank header (i.e. "\r\n\r\n"). The client should then send the body of the request. After you've received that, then you send the final response as normal.