restore removed jsonrpc:call/3

Restore the jsonrpc:call/3 function inadvertently removed in the
JSON-RPC 2.0 update. Add a new test for it. Remove test/src/httpc.erl
because it conflicted with inets:httpc during the execution of the new
test, and also because it's not used anywhere.

src/jsonrpc.erl

@@ -29,8 +29,72 @@
 -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) ->
+    dbg:tracer(), dbg:p(all, call),
+    dbg:tpl(yaws_api, [{'$1',[],[{message,'$1'},{message,{caller}},{return_trace}]}]),
+    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);

test/src/Makefile

@@ -1,5 +1,5 @@
 include ../support/include.mk
 
-all:	test.beam tftest.beam httpc.beam
+all:	test.beam tftest.beam
 
 clean:	tclean

test/t2/app_test.erl

@@ -273,6 +273,8 @@ streamcontent_test() ->
     gen_tcp:close(Sock),
     ok.
 
+-define(JSON_URI, "http://localhost:8005/jsontest").
+
 json_test() ->
     io:format("json_test\n",[]),
     io:format("  param array1\n", []),
@@ -291,6 +293,10 @@ json_test() ->
                        {struct, [{"jsonrpc", "2.0"},
                                  {"result", -19},
                                  {"id", 2}]}),
+    inets:start(),
+    io:format("  encode/decode\n", []),
+    ?line {ok,{response,[19]}} = jsonrpc:call(?JSON_URI, [],
+                                              {call, "subtract", [42, 23]}),
     io:format("  param obj1\n", []),
     ?line ok = do_json({struct, [{"jsonrpc", "2.0"},
                                  {"method", "subtract"},
@@ -489,7 +495,7 @@ json_send(Req) ->
 json_send(Req, encode) ->
     json_send(json2:encode(Req), no_encode);
 json_send(Req, no_encode) ->
-    Uri = "http://localhost:8005/jsontest",
+    Uri = ?JSON_URI,
     ReqHdrs = [{content_type, "application/json"}],
     ibrowse:send_req(Uri, ReqHdrs, post, Req).