jsonrpc.erl

%% Copyright (C) 2006 Gaspar Chilingarov <nm@web.am>
%%                    Gurgen Tumanyan <barbarian@armkb.com>
%% 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 AUTHOR ``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 AUTHOR 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(jsonrpc).
-author("Gaspar Chilingarov <nm@web.am>, Gurgen Tumanyan <barbarian@armkb.com>").
-vsn("3").
-export([call/3]).
-export([s/2]).        % extract element from proplist

%%%
%%% call function calls json-rpc method on remote host
%%%
%%% URL - remote server url (may use https)
%%% Options - option list to be passed to http:request
%%% (ssl options ot timeout, for example)
%%% Payload -> {call, MethodName, Args} tuple
%%% MethodName -> atom
%%% Args -> list
%%%
call(URL, Options, Payload) ->
    try
        {ok, CallPayloadDeep} = encode_call_payload(Payload),
        CallPayload = lists:flatten(CallPayloadDeep),
        {ok, Response} = httpc:request(
                           post,
                           {URL,[{"Content-Length",length(CallPayload)}],
                            "application/x-www-form-urlencoded",CallPayload},
                           Options, []),

        RespBody = if
                       (size(Response) == 2) or (size(Response) == 3) ->
                           element(size(Response), Response)
                   end,
        decode_call_payload(RespBody)
    catch
        error:Err->
            error_logger:error_report([{'json_rpc:call', error},
                                       {error, Err},
                                       {stack, erlang:get_stacktrace()}]),
            {error,Err}
    end.

%%%
%%% json-rpc.org defines such structure for making call
%%%
encode_call_payload({call, Method, Args}) when is_list(Args) ->
    %% id makes sense when there are many requests in same
    %% communication channel and replies can come in random
    %% order here it can be changed to something less expensive
    ID = element(3, erlang:now()),
    Struct =  json2:encode({struct, [{"jsonrpc", "2.0"},
                                     {method, Method},
                                     {params, {array, Args}},
                                     {id, ID}]}),
    {ok, Struct}.

%%%
%%% decode response structure
%%%
decode_call_payload(JSonStr) ->
    {ok, JSON} = json2:decode_string(JSonStr),
    Result = s(JSON, result),
    Error = s(JSON, error),
    case Error of
        undefined ->
            {ok,{response,[Result]}}; % make it compliant with xmlrpc response
        Error ->
            {error, Error}
    end.

%%% lookup element in proplist
s({struct, List}, ElemName) ->
    s(List, ElemName);
s(List, ElemName) when is_list(List) ->
    case lists:keysearch(ElemName,1,List) of
        {value,{ElemName,Val}} ->
            Val;
        false when is_atom(ElemName) ->
            ElemList = atom_to_list(ElemName),
            case lists:keysearch(ElemList,1,List) of
                {value,{ElemList,Val}} ->
                    Val;
                _ ->
                    undefined
            end;
        _ ->
            undefined
    end.


% vim: tabstop=4 ft=erlang