1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2010-2016, University of Amsterdam,
    7                              VU University Amsterdam
    8    All rights reserved.
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   11    modification, are permitted provided that the following conditions
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   35
   36:- module(http_host,
   37          [ http_public_url/2,          % +Request, -PublicURL
   38            http_public_host_url/2,     % +Request, -HostURL
   39            http_public_host/4,         % +Request, -Host, -Port, +Options
   40                                        % deprecated
   41            http_current_host/4         % +Request, -Host, -Port, +Options
   42          ]).   43:- use_module(library(http/thread_httpd)).   44:- use_module(library(http/http_wrapper)).   45:- use_module(library(socket)).   46:- use_module(library(option)).   47:- use_module(library(settings)).   48
   49:- setting(http:public_host, atom, '',
   50           'Name the outside world can use to contact me').   51:- setting(http:public_port, integer, 80,
   52           'Port on the public server').   53:- setting(http:public_scheme, oneof([http,https]), http,
   54           'Default URL scheme to use').   55
   56:- predicate_options(http_public_host/4, 4, [global(boolean)]).   57:- predicate_options(http_current_host/4, 4,
   58                     [pass_to(http_public_host/4, 4)]).

 http_public_url(+Request, -URL) is det

True when URL is an absolute URL for the current request. Typically, the login page should redirect to this URL to avoid losing the session.

   78http_public_url(Request, URL) :-
   79    http_public_host_url(Request, HostURL),
   80    option(request_uri(RequestURI), Request),
   81    atomic_list_concat([HostURL, RequestURI], URL).

 http_public_host_url(+Request, -URL) is det

True when URL is the public URL at which this server can be contacted. This value is not easy to obtain. See http_public_host/4 for the hardest part: find the host and port.

   91http_public_host_url(Request, URL) :-
   92    http_public_host(Request, Host, Port,
   93                      [ global(true)
   94                      ]),
   95    setting(http:public_scheme, Scheme),
   96    (   scheme_port(Scheme, Port)
   97    ->  format(atom(URL), '~w://~w', [Scheme, Host])
   98    ;   format(atom(URL), '~w://~w:~w', [Scheme, Host, Port])
   99    ).
  100
  101scheme_port(http, 80).
  102scheme_port(https, 443).

 http_public_host(?Request, -Hostname, -Port, +Options) is det

Current global host and port of the HTTP server. This is the basis to form absolute address, which we need for redirection based interaction such as the OpenID protocol. Options are:

global(+Bool)

If true (default false), try to replace a local hostname by a world-wide accessible name.

This predicate performs the following steps to find the host and port:

1. Use the settings http:public_host and http:public_port
2. Use X-Forwarded-Host header, which applies if this server runs behind a proxy.
3. Use the Host header, which applies for HTTP 1.1 if we are contacted directly.
4. Use gethostname/1 to find the host and http_current_server/2 to find the port.

Arguments:

Request

- is the current request. If it is left unbound, and the request is needed, it is obtained with http_current_request/1.

  129http_public_host(_Request, Host, Port, _) :-
  130    setting(http:public_host, PublicHost), PublicHost \== '',
  131    !,
  132    Host = PublicHost,
  133    setting(http:public_port, Port).
  134http_public_host(Request, Host, Port, Options) :-
  135    (   var(Request)
  136    ->  http_current_request(Request)
  137    ;   true
  138    ),
  139    (   memberchk(x_forwarded_host(Forwarded), Request)
  140    ->  Port = 80,
  141        primary_forwarded_host(Forwarded, Host)
  142    ;   memberchk(host(Host0), Request),
  143        (   option(global(true), Options, false)
  144        ->  global_host(Host0, Host)
  145        ;   Host = Host0
  146        ),
  147        option(port(Port), Request, 80)
  148    ),
  149    !.
  150http_public_host(_Request, Host, Port, _Options) :-
  151    gethostname(Host),
  152    http_current_server(_:_Pred, Port).

 http_current_host(?Request, -Hostname, -Port, +Options) is det

deprecated

- Use http_public_host/4 (same semantics)

  158http_current_host(Request, Hostname, Port, Options) :-
  159    http_public_host(Request, Hostname, Port, Options).

 primary_forwarded_host(+Spec, -Host) is det

x_forwarded host contains multiple hosts separated by ', ' if there are multiple proxy servers in between. The first one is the one the user's browser knows about.

  167primary_forwarded_host(Spec, Host) :-
  168    sub_atom(Spec, B, _, _, ','),
  169    !,
  170    sub_atom(Spec, 0, B, _, Host).
  171primary_forwarded_host(Host, Host).

 global_host(+HostIn, -Host)

Globalize a hostname. Used if we need to pass our hostname to a client and expect the client to be able to contact us. In this case we cannot use a name such as `localhost' or the plain hostname of the machine. We assume (possibly wrongly) that if the host contains a '.', it is globally accessible.

If the heuristics used by this predicate do not suffice, the setting http:public_host can be used to override.

  185global_host(_, Host) :-
  186    setting(http:public_host, PublicHost), PublicHost \== '',
  187    !,
  188    Host = PublicHost.
  189global_host(localhost, Host) :-
  190    !,
  191    gethostname(Host).
  192global_host(Local, Host) :-
  193    sub_atom(Local, _, _, _, '.'),
  194    !,
  195    Host = Local.
  196global_host(Local, Host) :-
  197    tcp_host_to_address(Local, IP),
  198    tcp_host_to_address(Host, IP)