Very slow throughput using sockets

I'm tyring to develop a (very) basic web server, using yap-prolog but I
experience a very slow throughput using the socket functions. The
following program is just an excerpt of a bigger program, but
it experiences the same problem.
It sends a small file (test.txt) about 40kb in size, regardless of the
input query.

To try it just create a text file called test.txt, about 40/50 kb in
size, load the program in yap, open a browser and query http://127.0.0.1

I've tried it with different files, both text files than images (gif and
png). In the console window you can see two messages, 'before' and
'after', issued just before and after the sending of the file.
You will notice the delay.
Then try with a bigger file (200/300 kb).
The delay becomes intollerable.


Any suggestion?

Regards
Maurizio.

%----------------------------------------------------------------------%
%                            global include                            %
%----------------------------------------------------------------------%

:- use_module(library(system)).
:- use_module(library(lists)).
:- use_module(library(charsio)).
:- use_module(library(readutil)).
:- set_prolog_flag(unknown,error).

%----------------------------------------------------------------------%
%                            i/o   handling                            %
%----------------------------------------------------------------------%



send_message(Sout,Rcode,Contype,Message):-
   send_message_header(Sout,Rcode,Contype,"",Message).

send_message_header(Sout,Rcode,Contype,Header,Message):-
   put_bytes("HTTP/1.0 ",Sout), put_bytes(Rcode,Sout),
put_bytes("\r\n",Sout),
   put_bytes("Content-Type: ",Sout), put_bytes(Contype,Sout),
put_bytes("\r\n",Sout),
   put_bytes(Header,Sout),
   code_len(Message,Size),
   put_bytes("Content-Length: ",Sout),  put_bytes(Size,Sout),
put_bytes("\r\n\r\n",Sout),
   put_bytes(Message,Sout).

code_len(Message,Len):-    
   length(Message,Size),
   number_codes(Size,Len).

put_bytes([],_Sout).
put_bytes([C|R],Sout):-  put_byte(Sout,C), put_bytes(R,Sout).

 
read_in_list(Name,List):-
    open(Name,read,S,[type(binary)]),
    read_stream_to_codes(S,List),
    close(S).

send_file(Filename,Type,Sout):-
  read_in_list(Filename,L),
  write(before),nl,
  send_message(Sout,"200 OK",Type,L),
  write(after),nl.
 
 

%----------------------------------------------------------------------%
%                            main                                      %
%----------------------------------------------------------------------%
 
:- initialization(go).


go:-
    socket('AF_INET',Sock),
    socket_bind(Sock,'AF_INET'(_,80)),
    socket_listen(Sock,5),
    main_loop(Sock).
   
main_loop(Sock) :-
    repeat,
    socket_accept(Sock,Sin),
    send_file('test.txt',"text/plain",Sin),
    flush_output(Sin),
    close(Sin),
    fail.

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