/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2009-2017, University of Amsterdam
VU University Amsterdam
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
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
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/
:- module(http_exception,
[ map_exception_to_http_status/4, % +Exception, -Reply,
% -HdrExtra, -Context
in_or_exclude_backtrace/2 % +Error, -CleanedError
]).
/** <module> Map Prolog exceptions to HTTP errors
This module maps exceptions from various parts of the HTTP libraries as
well as exceptions from user handler predicates into meaningful HTTP
error codes such as 4XX and 5XX codes. For example, existence errors on
http locations are mapped to 404 while out-of-stack is mapped to 503.
This library provides two hooks:
- http:map_exception_to_http_status_hook/4 can be used to map
additional exceptions to any HTTP status code.
- http:bad_request_error/2 can be extended to map exceptions into 400
bad request responses.
@see http_header.pl, http_wrapper.pl
*/
:- multifile
http:bad_request_error/2, % Formal, Context
http:map_exception_to_http_status_hook/4. % Exception, Reply, HdrExtra, Ctx
%! map_exception_to_http_status(+Exception, -Reply, -HdrExtra, -Context)
%
% Map certain exceptions to HTTP status codes. The http(not_modified)
% provides backward compatibility to http_reply(not_modified).
map_exception_to_http_status(Exception, Reply, HdrExtra, Context) :-
http:map_exception_to_http_status_hook(Exception, Reply, HdrExtra, Context),
!.
map_exception_to_http_status(http(not_modified),
not_modified,
[connection('Keep-Alive')],
[]) :- !.
map_exception_to_http_status(http_reply(Reply),
Reply,
[connection(Close)],
[]) :-
!,
keep_alive(Reply, Close).
map_exception_to_http_status(http_reply(Reply, HdrExtra0),
Reply,
HdrExtra,
Context) :-
!,
map_exception_to_http_status(http_reply(Reply, HdrExtra0, []),
Reply,
HdrExtra,
Context).
map_exception_to_http_status(http_reply(Reply, HdrExtra0, Context),
Reply,
HdrExtra,
Context):-
!,
( memberchk(connection(_), HdrExtra0)
-> HdrExtra = HdrExtra0
; HdrExtra = [connection(Close)|HdrExtra0],
keep_alive(Reply, Close)
).
map_exception_to_http_status(error(existence_error(http_location, Location), _),
not_found(Location),
[connection(close)],
[]) :- !.
map_exception_to_http_status(error(permission_error(http_method, Method, Location), _),
method_not_allowed(Method, Location),
[connection(close)],
[]) :- !.
map_exception_to_http_status(error(permission_error(_, http_location, Location), _),
forbidden(Location),
[connection(close)],
[]) :- !.
map_exception_to_http_status(error(threads_in_pool(_Pool), _),
busy,
[connection(close)],
[]) :- !.
map_exception_to_http_status(E,
resource_error(E),
[connection(close)],
[]) :-
is_resource_error(E),
!.
map_exception_to_http_status(E,
bad_request(E2),
[connection(close)],
[]) :-
bad_request_exception(E),
!,
discard_stack_trace(E, E2).
map_exception_to_http_status(E,
server_error(E),
[connection(close)],
[]).
is_resource_error(error(resource_error(_), _)).
bad_request_exception(error(Error, Context)) :-
nonvar(Error),
bad_request_error(Error, ContextGeneral),
( var(ContextGeneral)
-> true
; Context = context(_Stack, ContextInstance)
-> subsumes_term(ContextGeneral, ContextInstance)
),
!.
bad_request_error(Error, Context) :-
http:bad_request_error(Error, Context).
bad_request_error(Error, Context) :-
default_bad_request_error(Error, Context).
default_bad_request_error(domain_error(http_request, _), _).
default_bad_request_error(existence_error(http_parameter, _), _).
default_bad_request_error(type_error(_, _), http_parameter(_)).
default_bad_request_error(syntax_error(http_request_line(_)), _).
default_bad_request_error(syntax_error(http_request(_)), _).
default_bad_request_error(syntax_error(_), in_http_request).
discard_stack_trace(error(Formal, context(_,Msg)),
error(Formal, context(_,Msg))).
%! in_or_exclude_backtrace(+ErrorIn, -ErrorOut)
%
% Remove the stacktrace from the exception, unless setting
% `http:client_backtrace` is `true`.
in_or_exclude_backtrace(Error, Error) :-
current_setting(http:client_backtrace),
setting(http:client_backtrace, true),
!.
in_or_exclude_backtrace(Error0, Error) :-
discard_stack_trace(Error0, Error),
!.
in_or_exclude_backtrace(Exception, Exception).
%! http:bad_request_error(+Formal, -ContextTemplate) is semidet.
%
% If an exception of the term error(Formal, context(Stack,
% Context)) is caught and subsumes_term(ContextTemplate, Context)
% is true, translate the exception into an HTTP 400 exception. If
% the exception contains a stack-trace, this is stripped from the
% response.
%
% The idea behind this hook is that applications can raise 400
% responses by
%
% - Throwing a specific (error) exception and adding a rule
% to this predicate to interpret this as 400.
% - Define rules for prolog:error_message//1 to formulate
% an appropriate message.
%! keep_alive(+Reply) is semidet.
%! keep_alive(+Reply, -Connection) is det.
%
% If true for Reply, the default is to keep the connection open.
keep_alive(Reply, Connection) :-
( keep_alive(Reply)
-> Connection = 'Keep-Alive'
; Connection = close
).
keep_alive(not_modified).
keep_alive(bytes(_Type, _Bytes)).
keep_alive(file(_Type, _File)).
keep_alive(tmp_file(_Type, _File)).
keep_alive(stream(_In, _Len)).
keep_alive(cgi_stream(_In, _Len)).
keep_alive(switching_protocols(_Goal, _)).
/*******************************
* IDE SUPPORT *
*******************************/
% See library('trace/exceptions')
:- multifile
prolog:general_exception/2.
prolog:general_exception(http_reply(_), http_reply(_)).
prolog:general_exception(http_reply(_,_), http_reply(_,_)).