Add decode_format record_from_map

Undocumented, for transforming a map decode to record.

The record decode becomes more expensive the larger the number of AVPs
in the message definition in question, since the record is recreated
each time an AVP value is set in it. The map decode can potentially do
better.

3 files changed, 16 insertions, 6 deletions

diff --git a/lib/diameter/src/base/diameter.erl b/lib/diameter/src/base/diameter.erl
index 75deaad511..85a54c8e61 100644
--- a/lib/diameter/src/base/diameter.erl
+++ b/lib/diameter/src/base/diameter.erl
@@ -332,7 +332,11 @@ call(SvcName, App, Message) ->
    :: 0..16#FFFFFF.
 
 -type decode_format()
-   :: record | list | map | false.
+   :: record
+    | list
+    | map
+    | false
+    | record_from_map.
 
 %% Options passed to start_service/2
 
diff --git a/lib/diameter/src/base/diameter_config.erl b/lib/diameter/src/base/diameter_config.erl
index 09018308d5..d591fa903e 100644
--- a/lib/diameter/src/base/diameter_config.erl
+++ b/lib/diameter/src/base/diameter_config.erl
@@ -771,7 +771,8 @@ opt(K, true = B)
 opt(decode_format, T)
   when T == record;
        T == list;
-       T == map ->
+       T == map;
+       T == record_from_map ->
     T;
 
 opt(restrict_connections, T)
diff --git a/lib/diameter/src/base/diameter_gen.erl b/lib/diameter/src/base/diameter_gen.erl
index 239d4a535f..78d8bd2fa3 100644
--- a/lib/diameter/src/base/diameter_gen.erl
+++ b/lib/diameter/src/base/diameter_gen.erl
@@ -186,7 +186,7 @@ decode_avps(Name, Recs, #{module := Mod, decode_format := Fmt} = Opts) ->
     %% AM counts the number of top-level AVPs, which missing/4 then
     %% uses when adding 5005 errors.
     Arities = Mod:avp_arity(Name),
-    {reformat(Rec, Arities, Fmt),
+    {reformat(Rec, Arities, Mod, Fmt),
      Avps,
      Failed ++ missing(Arities, Opts, Mod, AM)}.
 
@@ -760,12 +760,17 @@ newrec(_, Name, _) ->
 newrec(Mod, Name) ->
     Mod:'#new-'(Mod:name2rec(Name)).
 
-%% reformat/3
+%% reformat/4
 
-reformat(Map, Arities, list) ->
+reformat(Map, Arities, _Mod, list) ->
     [{F,V} || {F,_} <- Arities, #{F := V} <- [Map]];
 
-reformat(Rec, _, _) ->
+reformat(Map, Arities, Mod, record_from_map) ->
+    #{':name' := Name} = Map,
+    RecName = Mod:name2rec(Name),
+    list_to_tuple([RecName | [maps:get(F, Map, def(A)) || {F,A} <- Arities]]);
+
+reformat(Rec, _, _, _) ->
     Rec.
 
 %% def/1