Modifying lager_default_formatter to make a filtering formatter

lager_sensitive_formatter.erl

%% Copyright (c) 2015 Basho Technologies, Inc.  All Rights Reserved.
%%
%% This file is provided to you 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(lager_sensitive_formatter).

%%
%% Include files
%%
-include("lager.hrl").
-ifdef(TEST).
-include_lib("eunit/include/eunit.hrl").
-endif.

%%
%% Exported Functions
%%
-export([format/2, format/3]).

%%
%% API Functions
%%

%% @doc Provides a generic, default formatting for log messages using a semi-iolist as configuration.  Any iolist allowed
%% elements in the configuration are printed verbatim.  Atoms in the configuration are treated as metadata properties
%% and extracted from the log message.  Optionally, a tuple of {atom(),semi-iolist()} can be used.  The atom will look
%% up the property, but if not found it will use the semi-iolist() instead.  These fallbacks can be similarly nested
%% or refer to other properties, if desired. You can also use a {atom, semi-iolist(), semi-iolist()} formatter, which
%% acts like a ternary operator's true/false branches.
%%
%% The metadata properties date,time, message, and severity will always exist.  
%% The properties pid, file, line, module, and function will always exist if the parser transform is used.
%%
%% Example:
%%
%%    `["Foo"]' -> "Foo", regardless of message content.
%%
%%    `[message]' -> The content of the logged message, alone.
%%
%%    `[{pid,"Unknown Pid"}]' -> "?.?.?" if pid is in the metadata, "Unknown Pid" if not.
%%
%%    `[{pid, ["My pid is ", pid], "Unknown Pid"}]' -> if pid is in the metada print "My pid is ?.?.?", otherwise print "Unknown Pid"
%% @end
-spec format(lager_msg:lager_msg(),list(),list()) -> any().
format(Msg,[], Colors) ->
    format(Msg, [{eol, "\n"}], Colors);
format(Msg,[{eol, EOL}], Colors) ->
    format(Msg,
        [date, " ", time, " ", color, "[", severity, "] ",
            {pid, ""},
            {module, [
                    {pid, ["@"], ""},
                    module,
                    {function, [":", function], ""},
                    {line, [":",line], ""}], ""},
            " ", message, EOL], Colors);
format(Message,Config,Colors) ->
    [ case V of
        color -> output_color(Message,Colors);
        _ -> output(V,Message) 
      end || V <- Config ].

-spec format(lager_msg:lager_msg(),list()) -> any().
format(Msg, Config) ->
    format(Msg, Config, []).

-spec output(term(),lager_msg:lager_msg()) -> iolist().
output(message,Msg) -> 
    MessageIn = lager_msg:message(Msg),
    %% This ip filter is overly simplified for the sake of clarity.  It doesn't
    %% check the validity of the item as an IP list looks for IP-like numbers.
    %% Four components of up to 3 digits seperated by periods
    Message2 = re:replace(MessageIn, "(?:\\d{1,3}\\.){3}\\d{1,3}", "«redacted_ip»",[global]),

    %% This looks for node atoms to be printed out and removes the tailing 
    %% host information
    Message1 = re:replace(Message2, "'(.*@).*'", "'\\1«redacted_host»'",[global]),

    %% Suppress binaries from the logstream
    Message = re:replace(Message1, "<<.*?>>","«redacted_binary»",[global]),

    %% Emit cleaned message
    Message;

output(date,Msg) ->
    {D, _T} = lager_msg:datetime(Msg),
    D;
output(time,Msg) ->
    {_D, T} = lager_msg:datetime(Msg),
    T;
output(severity,Msg) ->
    atom_to_list(lager_msg:severity(Msg));
output(Prop,Msg) when is_atom(Prop) ->
    Metadata = lager_msg:metadata(Msg),
    make_printable(get_metadata(Prop,Metadata,<<"Undefined">>));
output({Prop,Default},Msg) when is_atom(Prop) ->
    Metadata = lager_msg:metadata(Msg),
    make_printable(get_metadata(Prop,Metadata,output(Default,Msg)));
output({Prop, Present, Absent}, Msg) when is_atom(Prop) ->
    %% sort of like a poor man's ternary operator
    Metadata = lager_msg:metadata(Msg),
    case get_metadata(Prop, Metadata) of
        undefined ->
            [ output(V, Msg) || V <- Absent];
        _ ->
            [ output(V, Msg) || V <- Present]
    end;
output(Other,_) -> make_printable(Other).

output_color(_Msg,[]) -> [];
output_color(Msg,Colors) ->
    Level = lager_msg:severity(Msg),
    case lists:keyfind(Level, 1, Colors) of
        {_, Color} -> Color;
        _ -> []
    end.

-spec make_printable(any()) -> iolist().
make_printable(A) when is_atom(A) -> atom_to_list(A);
make_printable(P) when is_pid(P) -> pid_to_list(P);
make_printable(L) when is_list(L) orelse is_binary(L) -> L; 
make_printable(Other) -> io_lib:format("~p",[Other]).

get_metadata(Key, Metadata) ->
    get_metadata(Key, Metadata, undefined).

get_metadata(Key, Metadata, Default) ->
    case lists:keyfind(Key, 1, Metadata) of
        false ->
            Default;
        {Key, Value} ->
            Value
    end.

-ifdef(TEST).
date_time_now() ->
    Now = os:timestamp(),
    {Date, Time} = lager_util:format_time(lager_util:maybe_utc(lager_util:localtime_ms(Now))),
    {Date, Time, Now}.

basic_test_() ->
    {Date, Time, Now} = date_time_now(),
    [{"Default formatting test",
            ?_assertEqual(iolist_to_binary([Date, " ", Time,  " [error] ", pid_to_list(self()), " Message\n"]),
                iolist_to_binary(format(lager_msg:new("Message",
                            Now,
                            error,
                            [{pid, self()}],
                            []),
                        [])))
        },
        {"Basic Formatting",
            ?_assertEqual(<<"Simplist Format">>,
                iolist_to_binary(format(lager_msg:new("Message",
                            Now,
                            error,
                            [{pid, self()}],
                            []),
                        ["Simplist Format"])))
        },
        {"Default equivalent formatting test",
            ?_assertEqual(iolist_to_binary([Date, " ", Time, " [error] ", pid_to_list(self()), " Message\n"]),
                iolist_to_binary(format(lager_msg:new("Message",
                            Now,
                            error,
                            [{pid, self()}],
                            []),
                        [date, " ", time," [",severity,"] ",pid, " ", message, "\n"]
                    )))
        },
        {"Non existant metadata can default to string",
            ?_assertEqual(iolist_to_binary([Date, " ", Time, " [error] Fallback Message\n"]),
                iolist_to_binary(format(lager_msg:new("Message",
                            Now,
                            error,
                            [{pid, self()}],
                            []),
                        [date, " ", time," [",severity,"] ",{does_not_exist,"Fallback"}, " ", message, "\n"]
                    )))
        },
        {"Non existant metadata can default to other metadata",
            ?_assertEqual(iolist_to_binary([Date, " ", Time, " [error] Fallback Message\n"]),
                iolist_to_binary(format(lager_msg:new("Message",
                            Now,
                            error,
                            [{pid, "Fallback"}],
                            []),
                        [date, " ", time," [",severity,"] ",{does_not_exist,pid}, " ", message, "\n"]
                    )))
        }
    ].

-endif.

Hi Charlie,

I have seen that you have some experience working with Riak hooks. Could give some help with this error?
https://gist.github.com/4b42251f54557f1525e9

Thanks in advance,
Humberto