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% Licensed under the Apache License, Version 2.0 (the "License"); you may not
% use this file except in compliance with the License. You may obtain a copy of
% the License at
%
% http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
% License for the specific language governing permissions and limitations under
% the License.
-module(couch_external_manager).
-behaviour(gen_server).
-export([start_link/0, execute/2, config_change/2]).
-export([init/1, terminate/2, code_change/3, handle_call/3, handle_cast/2, handle_info/2]).
-include("couch_db.hrl").
start_link() ->
gen_server:start_link({local, couch_external_manager}, couch_external_manager, [], []).
execute(UrlName, JsonReq) ->
Pid = gen_server:call(couch_external_manager, {get, UrlName}),
case Pid of
{error, Reason} ->
Reason;
_ ->
couch_external_server:execute(Pid, JsonReq)
end.
config_change("external", UrlName) ->
gen_server:call(couch_external_manager, {config, UrlName}).
% gen_server API
init([]) ->
Handlers = ets:new(couch_external_manager_handlers, [set, private]),
lists:foreach(fun({UrlName, Command}) ->
{ok, Pid} = couch_external_server:start_link(UrlName, Command),
true = ets:insert(Handlers, {UrlName, Pid})
end, couch_config:get("external")),
couch_config:register(fun config_change/2),
{ok, Handlers}.
terminate(_Reason, Handlers) ->
ets:foldl(fun({_UrlName, Pid}, nil) ->
couch_external_server:stop(Pid),
nil
end, nil, Handlers),
ok.
handle_call({get, UrlName}, _From, Handlers) ->
Resp = case ets:lookup(Handlers, UrlName) of
[{UrlName, Pid}] ->
Pid;
[] ->
Mesg = lists:flatten(io_lib:format("No server configured for ~p.", [UrlName])),
{error, {unknown_external_server, Mesg}}
end,
{reply, Resp, Handlers};
handle_call({config, UrlName}, _From, Handlers) ->
% A newly added handler and a handler that had it's command
% changed are treated exactly the same.
% Shutdown the old handler.
case ets:lookup(Handlers, UrlName) of
[{UrlName, Pid}] ->
couch_external_server:stop(Pid);
_ ->
ok
end,
case couch_config:get("external", UrlName, nil) of
% Handler no longer exists
nil ->
ok;
% New handler start up.
Command ->
{ok, NewPid} = couch_external_server:start_link(UrlName, Command),
true = ets:insert(Handlers, {Command, NewPid})
end,
{reply, ok, Handlers}.
handle_cast(_Whatever, State) ->
{noreply, State}.
handle_info({'EXIT', Reason, Pid}, Handlers) ->
?LOG_DEBUG("External server ~p died. (reason: ~p)", [Pid, Reason]),
% Remove Pid from the handlers table so we don't try closing
% it a second time in terminate/2.
ets:match_delete(Handlers, {'_', Pid}),
{stop, Handlers}.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
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