[logger] Allow report callback with two arguments returning a string

If the report callback is a fun of arity 2, then the second argument
is a map with the keys 'encoding', 'depth' and 'chars_limit', and the
fun must return a string which is size limited according to the given
depth and chars_limit.

If the report callback is a fun of arity 1, then it must return a
tuple containing a format string and a list of arguments. The
formatter will produce the string, and limit it's size.

6 files changed, 200 insertions, 74 deletions

diff --git a/lib/kernel/doc/src/logger.xml b/lib/kernel/doc/src/logger.xml
index 8bf62a6b39..f1830a8224 100644
--- a/lib/kernel/doc/src/logger.xml
+++ b/lib/kernel/doc/src/logger.xml
@@ -227,7 +227,10 @@ logger:error("error happened because: ~p", [Reason]). % Without macro
 	      a <seealso marker="#type-report"><c>report()</c></seealso>,
 	      the <c>report_cb</c> key can be associated with a fun
 	      (report callback) that converts the report to a format
-	      string and arguments. See
+	      string and arguments, or directly to a string. See the
+	      type definition
+	      of <seealso marker="#type-report_cb"><c>report_cb()</c></seealso>,
+	      and
 	      section <seealso marker="logger_chapter#log_message">Log
 	      Message</seealso> in the User's Guide for more
 	      information about report callbacks.</p>
@@ -260,6 +263,22 @@ logger:error("error happened because: ~p", [Reason]). % Without macro
       </desc>
     </datatype>
     <datatype>
+      <name name="report_cb"/>
+      <desc>
+	<p>A fun which converts a <seealso marker="#type-report"><c>report()</c>
+	  </seealso> to a format string and arguments, or directly to a string.
+	  See section <seealso marker="logger_chapter#log_message">Log
+	    Message</seealso> in the User's Guide for more
+	  information.</p>
+      </desc>
+    </datatype>
+    <datatype>
+      <name name="report_cb_config"/>
+      <desc>
+	<p></p>
+      </desc>
+    </datatype>
+    <datatype>
       <name name="timestamp"/>
       <desc>
 	<p>A timestamp produced
diff --git a/lib/kernel/doc/src/logger_chapter.xml b/lib/kernel/doc/src/logger_chapter.xml
index 23a289f2ee..dc68d5c761 100644
--- a/lib/kernel/doc/src/logger_chapter.xml
+++ b/lib/kernel/doc/src/logger_chapter.xml
@@ -194,10 +194,26 @@
 	the log event's <seealso marker="#metadata">metadata</seealso>.
 	The report callback is a convenience function that
 	the <seealso marker="#formatters">formatter</seealso> can use
-	to convert the report to a format string and arguments. The
+	to convert the report to a format string and arguments, or
+	directly to a string. The
 	formatter can also use its own conversion function, if no
 	callback is provided, or if a customized formatting is
 	desired.</p>
+      <p>The report callback must be a fun with one or two
+	arguments. If it takes one argument, this is the report
+	itself, and the fun returns a format string and arguments:</p>
+      <pre>fun((<seealso marker="logger#type-report"><c>logger:report()</c></seealso>) -> {<seealso marker="stdlib:io#type-format"><c>io:format()</c></seealso>,[term()]})</pre>
+      <p>If it takes two arguments, the first is the report, and the
+	second is a map containing extra data that allows direct
+	coversion to a string:</p>
+      <pre>fun((<seealso marker="logger#type-report"><c>logger:report()</c></seealso>,<seealso marker="logger#type-report_cb_config"><c>logger:report_cb_config()</c></seealso>) -> <seealso marker="stdlib:unicode#type-chardata"><c>unicode:chardata()</c></seealso>)
+      </pre>
+      <p>The fun must obey the <c>encoding</c>, <c>depth</c>
+	and <c>chars_limit</c> parameters provided in the second
+	argument, as the formatter can not do anything useful of these
+	parameters with the returned string. This variant is used when
+	the formatting of the report depends on the size and encoding
+	parameters.</p>
       <p>Example, format string and arguments:</p>
       <code>logger:error("The file does not exist: ~ts",[Filename])</code>
       <p>Example, string:</p>
diff --git a/lib/kernel/doc/src/logger_formatter.xml b/lib/kernel/doc/src/logger_formatter.xml
index a482d02293..9226d19834 100644
--- a/lib/kernel/doc/src/logger_formatter.xml
+++ b/lib/kernel/doc/src/logger_formatter.xml
@@ -82,6 +82,13 @@
 	      in STDLIB.</p>
 	    <p>Defaults to <c>unlimited</c>.</p>
 	  </item>
+	  <tag><c>encoding = </c><seealso marker="stdlib:unicode#type-encoding">
+	      <c>unicode:encoding()</c></seealso></tag>
+	  <item>
+	    <p>This parameter must reflect the encoding of the device
+	      that the handler prints to.</p>
+	    <p>Defaults to <c>utf8</c></p>
+	  </item>
 	  <tag><c>legacy_header = boolean()</c></tag>
 	  <item>
 	    <p>If set to <c>true</c> a header field is added to
@@ -105,7 +112,8 @@
 	      by <c>chars_limit</c> or <c>depth</c>, it is truncated.</p>
 	    <p>Defaults to <c>unlimited</c>.</p>
 	  </item>
-	  <tag><c>report_cb = fun((</c><seealso marker="logger#type-report"><c>logger:report()</c></seealso><c>) -> {</c><seealso marker="stdlib:io#type-format"><c>io:format()</c></seealso><c>, [term()]})</c></tag>
+	  <tag><c>report_cb = </c><seealso marker="logger#type-report_cb">
+	      <c>logger:report_cb()</c></seealso></tag>
 	  <item>
 	    <p>A report callback is used by the formatter to transform
 	      log messages on report form to a format string and
@@ -119,9 +127,6 @@
 	      both the default report callback, and any report
 	      callback found in metadata. That is, all reports are
 	      converted by this configured function.</p>
-	    <p>The value must be a function with arity 1,
-	      returning <c>{Format,Args}</c>, and it will be called
-	      with a report as only argument.</p>
 	  </item>
 	  <tag><c>single_line = boolean()</c></tag>
 	  <item>
diff --git a/lib/kernel/src/logger.erl b/lib/kernel/src/logger.erl
index c78f5372f0..4924c6cb4f 100644
--- a/lib/kernel/src/logger.erl
+++ b/lib/kernel/src/logger.erl
@@ -74,6 +74,11 @@
 -type level() :: emergency | alert | critical | error |
                  warning | notice | info | debug.
 -type report() :: map() | [{atom(),term()}].
+-type report_cb() :: fun((report()) -> {io:format(),[term()]}) |
+                     fun((report(),report_cb_config()) -> unicode:chardata()).
+-type report_cb_config() :: #{encoding    := unicode:encoding(),
+                              depth       := pos_integer() | unlimited,
+                              chars_limit := pos_integer() | unlimited}.
 -type msg_fun() :: fun((term()) -> {io:format(),[term()]} |
                                    report() |
                                    unicode:chardata()).
@@ -84,7 +89,7 @@
                       file   => file:filename(),
                       line   => non_neg_integer(),
                       domain => [atom()],
-                      report_cb => fun((report()) -> {io:format(),[term()]}),
+                      report_cb => report_cb(),
                       atom() => term()}.
 -type location() :: #{mfa  := {module(),atom(),non_neg_integer()},
                       file := file:filename(),
@@ -110,10 +115,22 @@
 
 -type config_handler() :: {handler, handler_id(), module(), handler_config()}.
 
--export_type([log_event/0,level/0,report/0,msg_fun/0,metadata/0,
-              primary_config/0,handler_config/0,handler_id/0,
-              filter_id/0,filter/0,filter_arg/0,filter_return/0,
-              config_handler/0,formatter_config/0]).
+-export_type([log_event/0,
+              level/0,
+              report/0,
+              report_cb/0,
+              report_cb_config/0,
+              msg_fun/0,
+              metadata/0,
+              primary_config/0,
+              handler_config/0,
+              handler_id/0,
+              filter_id/0,
+              filter/0,
+              filter_arg/0,
+              filter_return/0,
+              config_handler/0,
+              formatter_config/0]).
 
 %%%-----------------------------------------------------------------
 %%% API
diff --git a/lib/kernel/src/logger_formatter.erl b/lib/kernel/src/logger_formatter.erl
index 456b0c9e8d..937e7f859b 100644
--- a/lib/kernel/src/logger_formatter.erl
+++ b/lib/kernel/src/logger_formatter.erl
@@ -26,16 +26,17 @@
 
 %%%-----------------------------------------------------------------
 %%% Types
--type config() :: #{chars_limit=>pos_integer()| unlimited,
-                    depth=>pos_integer() | unlimited,
-                    legacy_header=>boolean(),
-                    max_size=>pos_integer() | unlimited,
-                    report_cb=>fun((logger:report()) -> {io:format(),[term()]}),
-                    single_line=>boolean(),
-                    template=>template(),
-                    time_designator=>byte(),
-                    time_offset=>integer()|[byte()]}.
--type template() :: [metakey()|{metakey(),template(),template()}|string()].
+-type config() :: #{chars_limit     => pos_integer() | unlimited,
+                    depth           => pos_integer() | unlimited,
+                    encoding        => unicode:encoding(),
+                    legacy_header   => boolean(),
+                    max_size        => pos_integer() | unlimited,
+                    report_cb       => logger:report_cb(),
+                    single_line     => boolean(),
+                    template        => template(),
+                    time_designator => byte(),
+                    time_offset     => integer() | [byte()]}.
+-type template() :: [metakey() | {metakey(),template(),template()} | string()].
 -type metakey() :: atom() | [atom()].
 
 %%%-----------------------------------------------------------------
@@ -119,65 +120,96 @@ value(_,_) ->
 
 to_string(time,Time,Config) ->
     format_time(Time,Config);
-to_string(mfa,MFA,_Config) ->
-    format_mfa(MFA);
-to_string(_,Value,_Config) ->
-    to_string(Value).
+to_string(mfa,MFA,Config) ->
+    format_mfa(MFA,Config);
+to_string(_,Value,Config) ->
+    to_string(Value,Config).
 
-to_string(X) when is_atom(X) ->
+to_string(X,_) when is_atom(X) ->
     atom_to_list(X);
-to_string(X) when is_integer(X) ->
+to_string(X,_) when is_integer(X) ->
     integer_to_list(X);
-to_string(X) when is_pid(X) ->
+to_string(X,_) when is_pid(X) ->
     pid_to_list(X);
-to_string(X) when is_reference(X) ->
+to_string(X,_) when is_reference(X) ->
     ref_to_list(X);
-to_string(X) when is_list(X) ->
-    case io_lib:printable_unicode_list(lists:flatten(X)) of
+to_string(X,Config) when is_list(X) ->
+    case printable_list(lists:flatten(X)) of
         true -> X;
-        _ -> io_lib:format("~tp",[X])
+        _ -> io_lib:format(p(Config),[X])
     end;
-to_string(X) ->
-    io_lib:format("~tp",[X]).
+to_string(X,Config) ->
+    io_lib:format(p(Config),[X]).
+
+printable_list([]) ->
+    false;
+printable_list(X) ->
+    io_lib:printable_list(X).
 
 format_msg({string,Chardata},Meta,Config) ->
-    format_msg({"~ts",[Chardata]},Meta,Config);
-format_msg({report,_}=Msg,Meta,#{report_cb:=Fun}=Config) when is_function(Fun,1) ->
+    format_msg({s(Config),[Chardata]},Meta,Config);
+format_msg({report,_}=Msg,Meta,#{report_cb:=Fun}=Config)
+  when is_function(Fun,1); is_function(Fun,2) ->
     format_msg(Msg,Meta#{report_cb=>Fun},maps:remove(report_cb,Config));
 format_msg({report,Report},#{report_cb:=Fun}=Meta,Config) when is_function(Fun,1) ->
     try Fun(Report) of
         {Format,Args} when is_list(Format), is_list(Args) ->
             format_msg({Format,Args},maps:remove(report_cb,Meta),Config);
         Other ->
-            format_msg({"REPORT_CB ERROR: ~tp; Returned: ~tp",
+            P = p(Config),
+            format_msg({"REPORT_CB/1 ERROR: "++P++"; Returned: "++P,
+                        [Report,Other]},Meta,Config)
+    catch C:R:S ->
+            P = p(Config),
+            format_msg({"REPORT_CB/1 CRASH: "++P++"; Reason: "++P,
+                        [Report,{C,R,logger:filter_stacktrace(?MODULE,S)}]},
+                       Meta,Config)
+    end;
+format_msg({report,Report},#{report_cb:=Fun}=Meta,Config) when is_function(Fun,2) ->
+    try Fun(Report,maps:with([encoding,depth,chars_limit],Config)) of
+        String when ?IS_STRING(String) ->
+            try unicode:characters_to_list(String)
+            catch _:_ ->
+                    P = p(Config),
+                    format_msg({"REPORT_CB/2 ERROR: "++P++"; Returned: "++P,
+                                [Report,String]},Meta,Config)
+            end;
+        Other ->
+            P = p(Config),
+            format_msg({"REPORT_CB/2 ERROR: "++P++"; Returned: "++P,
                         [Report,Other]},Meta,Config)
-    catch C:R ->
-            format_msg({"REPORT_CB CRASH: ~tp; Reason: ~tp",
-                        [Report,{C,R}]},Meta,Config)
+    catch C:R:S ->
+            P = p(Config),
+            format_msg({"REPORT_CB/2 CRASH: "++P++"; Reason: "++P,
+                        [Report,{C,R,logger:filter_stacktrace(?MODULE,S)}]},
+                       Meta,Config)
     end;
 format_msg({report,Report},Meta,Config) ->
     format_msg({report,Report},
                Meta#{report_cb=>fun logger:format_report/1},
                Config);
-format_msg(Msg,_Meta,#{depth:=Depth,chars_limit:=CharsLimit}) ->
-    limit_size(Msg, Depth, CharsLimit).
-
-limit_size(Msg,Depth,unlimited) ->
-    limit_size(Msg,Depth,[]);
-limit_size(Msg,Depth,CharsLimit) when is_integer(CharsLimit) ->
-    limit_size(Msg,Depth,[{chars_limit,CharsLimit}]);
-limit_size({Format,Args},unlimited,Opts) when is_list(Opts) ->
+format_msg(Msg,_Meta,#{depth:=Depth,chars_limit:=CharsLimit,encoding:=Enc}) ->
+    limit_size(Msg, Depth, CharsLimit, Enc).
+
+limit_size(Msg,Depth,unlimited,Enc) ->
+    limit_size(Msg,Depth,[],Enc);
+limit_size(Msg,Depth,CharsLimit,Enc) when is_integer(CharsLimit) ->
+    limit_size(Msg,Depth,[{chars_limit,CharsLimit}],Enc);
+limit_size({Format,Args},unlimited,Opts,Enc) when is_list(Opts) ->
     try io_lib:format(Format,Args,Opts)
     catch _:_ ->
-            io_lib:format("FORMAT ERROR: ~tp - ~tp",[Format,Args],Opts)
+            P = p(Enc),
+            io_lib:format("FORMAT ERROR: "++P++" - "++P,[Format,Args],Opts)
     end;
-limit_size({Format0,Args},Depth,Opts) when is_integer(Depth) ->
+limit_size({Format0,Args},Depth,Opts,Enc) when is_integer(Depth) ->
     try
         Format1 = io_lib:scan_format(Format0, Args),
         Format = limit_format(Format1, Depth),
         io_lib:build_text(Format,Opts)
     catch _:_ ->
-            limit_size({"FORMAT ERROR: ~tp - ~tp",[Format0,Args]},Depth,Opts)
+            P = p(Enc),
+            limit_size({"FORMAT ERROR: "++P++" - "++P,[Format0,Args]},
+                       Depth,Opts,Enc)
     end.
 
 limit_format([#{control_char:=C0}=M0|T], Depth) when C0 =:= $p;
@@ -225,22 +257,23 @@ timestamp_to_datetimemicro(SysTime,Config) when is_integer(SysTime) ->
         end,
     {Date,Time,Micro,UtcStr}.
 
-format_mfa({M,F,A}) when is_atom(M), is_atom(F), is_integer(A) ->
+format_mfa({M,F,A},_) when is_atom(M), is_atom(F), is_integer(A) ->
     atom_to_list(M)++":"++atom_to_list(F)++"/"++integer_to_list(A);
-format_mfa({M,F,A}) when is_atom(M), is_atom(F), is_list(A) ->
-    format_mfa({M,F,length(A)});
-format_mfa(MFA) ->
-    to_string(MFA).
+format_mfa({M,F,A},Config) when is_atom(M), is_atom(F), is_list(A) ->
+    format_mfa({M,F,length(A)},Config);
+format_mfa(MFA,Config) ->
+    to_string(MFA,Config).
 
 maybe_add_legacy_header(Level,
                         #{time:=Timestamp}=Meta,
                         #{legacy_header:=true}=Config) ->
     #{title:=Title}=MyMeta = add_legacy_title(Level,Meta,Config),
-    {{Y,Mo,D},{H,Mi,S},Micro,UtcStr} =
+    {{Y,Mo,D},{H,Mi,Sec},Micro,UtcStr} =
         timestamp_to_datetimemicro(Timestamp,Config),
+    S = s(Config),
     Header =
-        io_lib:format("=~ts==== ~w-~s-~4w::~2..0w:~2..0w:~2..0w.~6..0w ~s===",
-                      [Title,D,month(Mo),Y,H,Mi,S,Micro,UtcStr]),
+        io_lib:format("="++S++"==== ~w-~s-~4w::~2..0w:~2..0w:~2..0w.~6..0w ~s===",
+                      [Title,D,month(Mo),Y,H,Mi,Sec,Micro,UtcStr]),
     Meta#{?MODULE=>MyMeta#{header=>Header}};
 maybe_add_legacy_header(_,Meta,_) ->
     Meta.
@@ -280,10 +313,11 @@ month(12) -> "Dec".
 %% configuration map
 add_default_config(Config0) ->
     Default =
-        #{legacy_header=>false,
+        #{chars_limit=>unlimited,
+          encoding=>utf8,
           error_logger_notice_header=>info,
+          legacy_header=>false,
           single_line=>true,
-          chars_limit=>unlimited,
           time_designator=>$T},
     MaxSize = get_max_size(maps:get(max_size,Config0,undefined)),
     Depth = get_depth(maps:get(depth,Config0,undefined)),
@@ -369,7 +403,8 @@ do_check_config([{legacy_header,LH}|Config]) when is_boolean(LH) ->
 do_check_config([{error_logger_notice_header,ELNH}|Config]) when ELNH == info;
                                                                  ELNH == notice ->
     do_check_config(Config);
-do_check_config([{report_cb,RCB}|Config]) when is_function(RCB,1) ->
+do_check_config([{report_cb,RCB}|Config]) when is_function(RCB,1);
+                                               is_function(RCB,2) ->
     do_check_config(Config);
 do_check_config([{template,T}|Config]) ->
     case check_template(T) of
@@ -456,3 +491,17 @@ check_timezone(Tz) ->
     catch _:_ ->
             error
     end.
+
+p(#{encoding:=Enc}) ->
+    p(Enc);
+p(latin1) ->
+    "~p";
+p(_) ->
+    "~tp".
+
+s(#{encoding:=Enc}) ->
+    s(Enc);
+s(latin1) ->
+    "~s";
+s(_) ->
+    "~ts".
diff --git a/lib/kernel/test/logger_formatter_SUITE.erl b/lib/kernel/test/logger_formatter_SUITE.erl
index 8fe8d5199b..aa8dc42691 100644
--- a/lib/kernel/test/logger_formatter_SUITE.erl
+++ b/lib/kernel/test/logger_formatter_SUITE.erl
@@ -312,30 +312,48 @@ format_msg(_Config) ->
                      #{report_cb=>fun(_)-> faulty_return end},
                      #{template=>Template}),
     ct:log(String5),
-    "REPORT_CB ERROR: term; Returned: faulty_return" = String5,
+    "REPORT_CB/1 ERROR: term; Returned: faulty_return" = String5,
 
     String6 = format(info,{report,term},
                      #{report_cb=>fun(_)-> erlang:error(fun_crashed) end},
                      #{template=>Template}),
     ct:log(String6),
-    "REPORT_CB CRASH: term; Reason: {error,fun_crashed}" = String6,
+    "REPORT_CB/1 CRASH: term; Reason: {error,fun_crashed,"++_ = String6,
+
+    String7 = format(info,{report,term},
+                     #{report_cb=>fun(_,_)-> ['not',a,string] end},
+                     #{template=>Template}),
+    ct:log(String7),
+    "REPORT_CB/2 ERROR: term; Returned: ['not',a,string]" = String7,
+
+    String8 = format(info,{report,term},
+                     #{report_cb=>fun(_,_)-> faulty_return end},
+                     #{template=>Template}),
+    ct:log(String8),
+    "REPORT_CB/2 ERROR: term; Returned: faulty_return" = String8,
+
+    String9 = format(info,{report,term},
+                     #{report_cb=>fun(_,_)-> erlang:error(fun_crashed) end},
+                     #{template=>Template}),
+    ct:log(String9),
+    "REPORT_CB/2 CRASH: term; Reason: {error,fun_crashed,"++_ = String9,
 
     %% strings are not formatted
-    String7 = format(info,{string,"string"},
+    String10 = format(info,{string,"string"},
                      #{report_cb=>fun(_)-> {"formatted",[]} end},
                      #{template=>Template}),
-    ct:log(String7),
-    "string" = String7,
+    ct:log(String10),
+    "string" = String10,
 
-    String8 = format(info,{string,['not',printable,list]},
+    String11 = format(info,{string,['not',printable,list]},
                      #{report_cb=>fun(_)-> {"formatted",[]} end},
                      #{template=>Template}),
-    ct:log("~ts",[String8]), % avoiding ct_log crash
-    "FORMAT ERROR: \"~ts\" - [['not',printable,list]]" = String8,
+    ct:log("~ts",[String11]), % avoiding ct_log crash
+    "FORMAT ERROR: \"~ts\" - [['not',printable,list]]" = String11,
 
-    String9 = format(info,{string,"string"},#{},#{template=>Template}),
-    ct:log(String9),
-    "string" = String9,
+    String12 = format(info,{string,"string"},#{},#{template=>Template}),
+    ct:log(String12),
+    "string" = String12,
 
     ok.
 
@@ -639,8 +657,10 @@ check_config(_Config) ->
     ?cfgerr({max_size,bad}) =
         logger_formatter:check_config(#{max_size => bad}),
 
+    ok =
+        logger_formatter:check_config(#{report_cb => fun(_,_) -> "" end}),
     ?cfgerr({report_cb,F}) =
-        logger_formatter:check_config(#{report_cb => F=fun(_,_) -> {"",[]} end}),
+        logger_formatter:check_config(#{report_cb => F=fun(_,_,_) -> {"",[]} end}),
     ?cfgerr({report_cb,bad}) =
         logger_formatter:check_config(#{report_cb => bad}),