This doesn't get all the data
      let rec get_all () =
        match U.recv a_socket a_buffer 0 1024 [] with
        | 0 | -1 -> ()
        | n ->
          Buffer.add_bytes final_result (Bytes.sub a_buffer 0 n)
      in

This stalls

      let rec get_all () =
        match U.recv a_socket a_buffer 0 1024 [] with
        | 0 | -1 -> ()
        | n ->
          Buffer.add_bytes final_result (Bytes.sub a_buffer 0 n);
          get_all ()
      in