http_ssl_plugin.pl

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2007-2022, University of Amsterdam
                              VU University Amsterdam
    All rights reserved.

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    modification, are permitted provided that the following conditions
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       notice, this list of conditions and the following disclaimer.

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       notice, this list of conditions and the following disclaimer in
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       distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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*/

:- module(http_ssl_plugin, []).
% Requires ssl:upgrade_legacy_options/2 hook
:- use_module(library(ssl),
              [ ssl_context/3,
                ssl_secure_ciphers/1,
                ssl_property/2,
                ssl_set_options/3,
                ssl_negotiate/5
              ]).
:- use_module(library(debug),[debug/3]).
:- use_module(library(socket),
              [ tcp_socket/1,
                tcp_setopt/2,
                tcp_bind/2,
                tcp_listen/2,
                tcp_accept/3,
                tcp_open_socket/3,
                tcp_connect/3
              ]).

:- autoload(library(lists),[select/3]).
:- autoload(library(option),[option/2,option/3]).
:- autoload(library(apply), [include/3]).
:- autoload(library(http/http_header),[http_read_reply_header/2]).
:- autoload(library(http/thread_httpd),[http_enough_workers/3]).

/** <module> SSL plugin for HTTP libraries

This  module  can  be   loaded    next   to   library(thread_httpd)  and
library(http_open) to provide secure HTTP   (HTTPS)  services and client
access.

An example secure server using self-signed  certificates can be found in
the <plbase>/doc/packages/examples/ssl/https.pl, where <plbase>   is the
SWI-Prolog installation directory.
*/

:- multifile
    thread_httpd:make_socket_hook/3,
    thread_httpd:accept_hook/2,
    thread_httpd:open_client_hook/6,
    thread_httpd:discard_client_hook/1,
    http:http_protocol_hook/5,
    http:open_options/2,
    http:http_connection_over_proxy/6,
    http:ssl_server_create_hook/3,
    http:ssl_server_open_client_hook/3.


                 /*******************************
                 *          SERVER HOOKS        *
                 *******************************/

%!  thread_httpd:make_socket_hook(?Port, :OptionsIn, -OptionsOut)
%!                                                          is semidet.
%
%   Hook into http_server/2 to create an   SSL  server if the option
%   ssl(SSLOptions) is provided.
%
%   @see thread_httpd:accept_hook/2 handles the corresponding accept

thread_httpd:make_socket_hook(Port, M:Options0, Options) :-
    select(ssl(SSLOptions0), Options0, Options1),
    !,
    add_secure_ciphers(SSLOptions0, SSLOptions1),
    disable_sslv3(SSLOptions1, SSLOptions),
    make_socket(Port, Socket, Options1),
    ssl_context(server, SSL0, M:[close_parent(true)|SSLOptions]),
    (   http:ssl_server_create_hook(SSL0, SSL1, Options1)
    ->  ensure_close_parent(SSL1, SSL)
    ;   SSL = SSL0
    ),
    port(Port, PortNum),
    atom_concat('httpsd', PortNum, Queue),
    Options = [ queue(Queue),
                tcp_socket(Socket),
                ssl_instance(SSL)
              | Options1
              ].

port(_Host:Port0, Port) => Port = Port0.
port(Port0, Port), integer(Port0) => Port = Port0.

ensure_close_parent(SSL0, SSL) :-
    (   ssl_property(SSL0, close_parent(true))
    ->  SSL = SSL0
    ;   ssl_set_options(SSL0, SSL, [close_parent(true)])
    ).

%!  add_secure_ciphers(+SSLOptions0, -SSLOptions)
%
%   Add ciphers from ssl_secure_ciphers/1 if no ciphers are provided.

add_secure_ciphers(SSLOptions0, SSLOptions) :-
    (   option(cipher_list(_), SSLOptions0)
    ->  SSLOptions = SSLOptions0
    ;   ssl_secure_ciphers(Ciphers),
        SSLOptions = [cipher_list(Ciphers)|SSLOptions0]
    ).

%!  disable_sslv3(+SSLOptions0, -SSLOptions)
%
%   Disable SSLv3, which  is  considered   insecure  unless  the  caller
%   specifies the allowed versions explicitly, so   we assume s/he knows
%   what s/he is doing.

disable_sslv3(SSLOptions0, SSLOptions) :-
    (   option(min_protocol_version(_), SSLOptions0)
    ;   option(disable_ssl_methods(_), SSLOptions0)
    ),
    !,
    SSLOptions = SSLOptions0.
disable_sslv3(SSLOptions0,
              [ disable_ssl_methods([sslv3,sslv23]), % old OpenSSL versions
                min_protocol_version(tlsv1)          % OpenSSL 1.1.0 and later
              | SSLOptions0
              ]).


make_socket(_Port, Socket, Options) :-
    option(tcp_socket(Socket), Options),
    !.
make_socket(Port, Socket, _Options) :-
    tcp_socket(Socket),
    tcp_setopt(Socket, reuseaddr),
    tcp_bind(Socket, Port),
    tcp_listen(Socket, 5).


%!  thread_httpd:accept_hook(:Goal, +Options) is semidet.
%
%   Implement the accept for HTTPS connections.

thread_httpd:accept_hook(Goal, Options) :-
    memberchk(ssl_instance(SSL0), Options),
    !,
    ensure_close_parent(SSL0, SSL),
    memberchk(queue(Queue), Options),
    memberchk(tcp_socket(Socket), Options),
    tcp_accept(Socket, Client, Peer),
    sig_atomic(send_to_worker(Queue, SSL, Client, Goal, Peer)),
    http_enough_workers(Queue, accept, Peer).

send_to_worker(Queue, SSL, Client, Goal, Peer) :-
    debug(http(connection), 'New HTTPS connection from ~p', [Peer]),
    thread_send_message(Queue, ssl_client(SSL, Client, Goal, Peer)).

%!  thread_httpd:discard_client_hook(+Msg)
%
%   Handles connections that where accepted during server shutdown.

thread_httpd:discard_client_hook(ssl_client(_SSL, Client, _Goal, _Peer)) :-
    tcp_close_socket(Client).


%!  http:ssl_server_create_hook(+SSL0, -SSL, +Options) is semidet.
%
%   Extensible predicate that is called  once   after  creating an HTTPS
%   server. If this predicate succeeds, SSL is  the context that is used
%   for negotiating new connections. Otherwise, SSL0   is used, which is
%   the context that was created with the given options.
%
%   @see ssl_context/3 for creating an SSL context


%!  http:ssl_server_open_client_hook(+SSL0, -SSL, +Options) is semidet.
%
%   Extensible predicate that is called before  each connection that the
%   server negotiates with a client. If  this predicate succeeds, SSL is
%   the context that is used for the  new connection. Otherwise, SSL0 is
%   used, which is the  context  that   was  created  when launching the
%   server.
%
%   @see ssl_context/3 for creating an SSL context


thread_httpd:open_client_hook(ssl_client(SSL0, Client, Goal, Peer),
                              Goal, In, Out,
                              [peer(Peer), protocol(https)],
                              Options) :-
    (   http:ssl_server_open_client_hook(SSL0, SSL, Options)
    ->  true
    ;   SSL = SSL0
    ),
    option(timeout(TMO), Options, 60),
    tcp_open_socket(Client, Read, Write),
    set_stream(Read, timeout(TMO)),
    set_stream(Write, timeout(TMO)),
    catch(ssl_negotiate(SSL, Read, Write, In, Out),
          E,
          ssl_failed(Read, Write, E)).

ssl_failed(Read, Write, E) :-
    close(Write, [force(true)]),
    close(Read,  [force(true)]),
    throw(E).


                 /*******************************
                 *         CLIENT HOOKS         *
                 *******************************/

%!  http:http_protocol_hook(+Scheme, +Parts, +PlainStreamPair,
%!                          -StreamPair, +Options) is semidet.
%
%   Hook for http_open/3 to connect  to   an  HTTPS (SSL-based HTTP)
%   server.

http:http_protocol_hook(https, Parts, PlainStreamPair, StreamPair, Options) :-
    ssl_protocol_hook(Parts, PlainStreamPair, StreamPair, Options).
http:http_protocol_hook(wss, Parts, PlainStreamPair, StreamPair, Options) :-
    ssl_protocol_hook(Parts, PlainStreamPair, StreamPair, Options).

ssl_protocol_hook(Parts, PlainStreamPair, StreamPair, Options) :-
    memberchk(host(Host), Parts),
    include(ssl_option, Options, SSLOptions),
    ssl_context(client, SSL, [ host(Host),
                               close_parent(true)
                             | SSLOptions
                             ]),
    stream_pair(PlainStreamPair, PlainIn, PlainOut),
    % if an exception arises, http_open/3 closes the stream for us
    ssl_negotiate(SSL, PlainIn, PlainOut, In, Out),
    stream_pair(StreamPair, In, Out).

% Might be better to be more  selective,   but  passing the options from
% http_open/3 with more than 1 argument makes ssl_context/3 fail.

ssl_option(Term) :-
    compound(Term),
    compound_name_arity(Term, _, 1).

%!  http:http_connection_over_proxy(+Proxy, +Parts, +HostPort, -StreamPair,
%!                                  +OptionsIn, -OptionsOut)
%
%   Facilitate an HTTPS connection via a   proxy using HTTP CONNECT.
%   Note that most proxies will only  support this for connecting on
%   port 443

http:http_connection_over_proxy(proxy(ProxyHost, ProxyPort), Parts,
                                Host:Port, StreamPair, Options, Options) :-
    memberchk(scheme(https), Parts),
    !,
    tcp_connect(ProxyHost:ProxyPort, StreamPair, [bypass_proxy(true)]),
    catch(negotiate_http_connect(StreamPair, Host:Port),
          Error,
          ( close(StreamPair, [force(true)]),
            throw(Error)
          )).

negotiate_http_connect(StreamPair, Address):-
    format(StreamPair, 'CONNECT ~w HTTP/1.1\r\n\r\n', [Address]),
    flush_output(StreamPair),
    http_read_reply_header(StreamPair, Header),
    memberchk(status(_, Status, Message), Header),
    (   Status == ok
    ->  true
    ;   throw(error(proxy_rejection(Message), _))
    ).