%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
%%
%% This file contains code that's included by encode/decode modules
%% generated by diameter_codegen.erl. This code does most of the work, the
%% generated code being kept simple.
%%
-define(THROW(T), throw({?MODULE, T})).
%% Tag common to generated dictionaries.
-define(TAG, diameter_gen).
%% Key to a value in the process dictionary that determines whether or
%% not an unrecognized AVP setting the M-bit should be regarded as an
%% error or not. See is_strict/0. This is only used to relax M-bit
%% interpretation inside Grouped AVPs not setting the M-bit. The
%% service_opt() strict_mbit can be used to disable the check
%% globally.
-define(STRICT_KEY, strict).
%% Key that says whether or not we should do a best-effort decode
%% within Failed-AVP.
-define(FAILED_KEY, failed).
-type parent_name() :: atom(). %% parent = Message or AVP
-type parent_record() :: tuple(). %%
-type avp_name() :: atom().
-type avp_record() :: tuple().
-type avp_values() :: [{avp_name(), term()}].
-type non_grouped_avp() :: #diameter_avp{}.
-type grouped_avp() :: nonempty_improper_list(#diameter_avp{}, [avp()]).
-type avp() :: non_grouped_avp() | grouped_avp().
%% Use a (hopefully) unique key when manipulating the process
%% dictionary.
putr(K,V) ->
put({?TAG, K}, V).
getr(K) ->
case get({?TAG, K}) of
undefined ->
V = erase({?MODULE, K}), %% written in old code
V == undefined orelse putr(K,V),
V;
V ->
V
end.
eraser(K) ->
erase({?TAG, K}).
%% ---------------------------------------------------------------------------
%% # encode_avps/2
%% ---------------------------------------------------------------------------
-spec encode_avps(parent_name(), parent_record() | avp_values())
-> binary()
| no_return().
encode_avps(Name, Vals)
when is_list(Vals) ->
encode_avps(Name, '#set-'(Vals, newrec(Name)));
encode_avps(Name, Rec) ->
try
list_to_binary(encode(Name, Rec))
catch
throw: {?MODULE, Reason} ->
diameter_lib:log({encode, error},
?MODULE,
?LINE,
{Reason, Name, Rec}),
erlang:error(list_to_tuple(Reason ++ [Name]));
error: Reason ->
Stack = erlang:get_stacktrace(),
diameter_lib:log({encode, failure},
?MODULE,
?LINE,
{Reason, Name, Rec, Stack}),
erlang:error({encode_failure, Reason, Name, Stack})
end.
%% encode/2
encode(Name, Rec) ->
lists:flatmap(fun(A) -> encode(Name, A, '#get-'(A, Rec)) end,
'#info-'(element(1, Rec), fields)).
%% encode/3
encode(Name, AvpName, Values) ->
e(Name, AvpName, avp_arity(Name, AvpName), Values).
%% e/4
e(_, AvpName, 1, undefined) ->
?THROW([mandatory_avp_missing, AvpName]);
e(Name, AvpName, 1, Value) ->
e(Name, AvpName, [Value]);
e(_, _, {0,_}, []) ->
[];
e(_, AvpName, _, T)
when not is_list(T) ->
?THROW([repeated_avp_as_non_list, AvpName, T]);
e(_, AvpName, {Min, _}, L)
when length(L) < Min ->
?THROW([repeated_avp_insufficient_arity, AvpName, Min, L]);
e(_, AvpName, {_, Max}, L)
when Max < length(L) ->
?THROW([repeated_avp_excessive_arity, AvpName, Max, L]);
e(Name, AvpName, _, Values) ->
e(Name, AvpName, Values).
%% e/3
e(Name, 'AVP', Values) ->
[pack_AVP(Name, A) || A <- Values];
e(_, AvpName, Values) ->
e(AvpName, Values).
%% e/2
e(AvpName, Values) ->
H = avp_header(AvpName),
[diameter_codec:pack_avp(H, avp(encode, V, AvpName)) || V <- Values].
%% pack_AVP/2
%% No value: assume AVP data is already encoded. The normal case will
%% be when this is passed back from #diameter_packet.errors as a
%% consequence of a failed decode. Any AVP can be encoded this way
%% however, which side-steps any arity checks for known AVP's and
%% could potentially encode something unfortunate.
pack_AVP(_, #diameter_avp{value = undefined} = A) ->
diameter_codec:pack_avp(A);
%% Missing name for value encode.
pack_AVP(_, #diameter_avp{name = N, value = V})
when N == undefined;
N == 'AVP' ->
?THROW([value_with_nameless_avp, N, V]);
%% Or not. Ensure that 'AVP' is the appropriate field. Note that if we
%% don't know this AVP at all then the encode will fail.
pack_AVP(Name, #diameter_avp{name = AvpName,
value = Data}) ->
0 == avp_arity(Name, AvpName)
orelse ?THROW([known_avp_as_AVP, Name, AvpName, Data]),
e(AvpName, [Data]).
%% ---------------------------------------------------------------------------
%% # decode_avps/2
%% ---------------------------------------------------------------------------
-spec decode_avps(parent_name(), [#diameter_avp{}])
-> {parent_record(), [avp()], Failed}
when Failed :: [{5000..5999, #diameter_avp{}}].
decode_avps(Name, Recs) ->
{Avps, {Rec, Failed}}
= lists:foldl(fun(T,A) -> decode(Name, T, A) end,
{[], {newrec(Name), []}},
Recs),
{Rec, Avps, Failed ++ missing(Rec, Name, Failed)}.
%% Append 5005 errors so that errors are reported in the order
%% encountered. Failed-AVP should typically contain the first
%% encountered error accordg to the RFC.
newrec(Name) ->
'#new-'(name2rec(Name)).
%% 3588:
%%
%% DIAMETER_MISSING_AVP 5005
%% The request did not contain an AVP that is required by the Command
%% Code definition. If this value is sent in the Result-Code AVP, a
%% Failed-AVP AVP SHOULD be included in the message. The Failed-AVP
%% AVP MUST contain an example of the missing AVP complete with the
%% Vendor-Id if applicable. The value field of the missing AVP
%% should be of correct minimum length and contain zeros.
missing(Rec, Name, Failed) ->
Avps = lists:foldl(fun({_, #diameter_avp{code = C, vendor_id = V}}, A) ->
sets:add_element({C,V}, A)
end,
sets:new(),
Failed),
[{5005, A} || F <- '#info-'(element(1, Rec), fields),
not has_arity(avp_arity(Name, F), '#get-'(F, Rec)),
#diameter_avp{code = C, vendor_id = V}
= A <- [empty_avp(F)],
not sets:is_element({C,V}, Avps)].
%% Maximum arities have already been checked in building the record.
has_arity({Min, _}, L) ->
has_prefix(Min, L);
has_arity(N, V) ->
N /= 1 orelse V /= undefined.
%% Compare a non-negative integer and the length of a list without
%% computing the length.
has_prefix(0, _) ->
true;
has_prefix(_, []) ->
false;
has_prefix(N, L) ->
has_prefix(N-1, tl(L)).
%% empty_avp/1
empty_avp(Name) ->
{Code, Flags, VId} = avp_header(Name),
{Name, Type} = avp_name(Code, VId),
#diameter_avp{name = Name,
code = Code,
vendor_id = VId,
is_mandatory = 0 /= (Flags band 2#01000000),
need_encryption = 0 /= (Flags band 2#00100000),
data = empty_value(Name),
type = Type}.
%% 3588, ch 7:
%%
%% The Result-Code AVP describes the error that the Diameter node
%% encountered in its processing. In case there are multiple errors,
%% the Diameter node MUST report only the first error it encountered
%% (detected possibly in some implementation dependent order). The
%% specific errors that can be described by this AVP are described in
%% the following section.
%% decode/3
decode(Name, #diameter_avp{code = Code, vendor_id = Vid} = Avp, Acc) ->
decode(Name, avp_name(Code, Vid), Avp, Acc).
%% decode/4
%% AVP is defined in the dictionary ...
decode(Name, {AvpName, Type}, Avp, Acc) ->
d(Name, Avp#diameter_avp{name = AvpName, type = Type}, Acc);
%% ... or not.
decode(Name, 'AVP', Avp, Acc) ->
decode_AVP(Name, Avp, Acc).
%% 6733, 4.4:
%%
%% Receivers of a Grouped AVP that does not have the 'M' (mandatory)
%% bit set and one or more of the encapsulated AVPs within the group
%% has the 'M' (mandatory) bit set MAY simply be ignored if the
%% Grouped AVP itself is unrecognized. The rule applies even if the
%% encapsulated AVP with its 'M' (mandatory) bit set is further
%% encapsulated within other sub-groups, i.e., other Grouped AVPs
%% embedded within the Grouped AVP.
%%
%% The first sentence is slightly mangled, but take it to mean this:
%%
%% An unrecognized AVP of type Grouped that does not set the 'M' bit
%% MAY be ignored even if one of its encapsulated AVPs sets the 'M'
%% bit.
%%
%% The text above is a change from RFC 3588, which instead says this:
%%
%% Further, if any of the AVPs encapsulated within a Grouped AVP has
%% the 'M' (mandatory) bit set, the Grouped AVP itself MUST also
%% include the 'M' bit set.
%%
%% Both of these texts have problems. If the AVP is unknown then its
%% type is unknown since the type isn't sent over the wire, so the
%% 6733 text becomes a non-statement: don't know that the AVP not
%% setting the M-bit is of type Grouped, therefore can't know that its
%% data consists of encapsulated AVPs, therefore can't but ignore that
%% one of these might set the M-bit. It should be no worse if we know
%% the AVP to have type Grouped.
%%
%% Similarly, for the 3588 text: if we receive an AVP that doesn't set
%% the M-bit and don't know that the AVP has type Grouped then we
%% can't realize that its data contains an AVP that sets the M-bit, so
%% can't regard the AVP as erroneous on this account. Again, it should
%% be no worse if the type is known to be Grouped, but in this case
%% the RFC forces us to regard the AVP as erroneous. This is
%% inconsistent, and the 3588 text has never been enforced.
%%
%% So, if an AVP doesn't set the M-bit then we're free to ignore it,
%% regardless of the AVP's type. If we know the type to be Grouped
%% then we must ignore the M-bit on an encapsulated AVP. That means
%% packing such an encapsulated AVP into an 'AVP' field if need be,
%% not regarding the lack of a specific field as an error as is
%% otherwise the case. (The lack of an AVP-specific field being how we
%% defined the RFC's "unrecognized", which is slightly stronger than
%% "not defined".)
%% d/3
d(Name, Avp, Acc) ->
#diameter_avp{name = AvpName,
data = Data,
type = Type,
is_mandatory = M}
= Avp,
%% Use the process dictionary is to keep track of whether or not
%% to ignore an M-bit on an encapsulated AVP. Not ideal, but the
%% alternative requires widespread changes to be able to pass the
%% value around through the entire decode. The solution here is
%% simple in comparison, both to implement and to understand.
Strict = relax(Type, M),
%% Use the process dictionary again to keep track of whether we're
%% decoding within Failed-AVP and should ignore decode errors
%% altogether.
Failed = relax(Name), %% Not AvpName or else a failed Failed-AVP
%% decode is packed into 'AVP'.
Mod = dict(Failed), %% Dictionary to decode in.
%% On decode, a Grouped AVP is represented as a #diameter_avp{}
%% list with AVP as head and component AVPs as tail. On encode,
%% data can be a list of component AVPs.
try Mod:avp(decode, Data, AvpName) of
V ->
{Avps, T} = Acc,
{H, A} = ungroup(V, Avp),
{[H | Avps], pack_avp(Name, A, T)}
catch
throw: {?TAG, {grouped, Error, ComponentAvps}} ->
g(is_failed(), Error, Name, trim(Avp), Acc, ComponentAvps);
error: Reason ->
d(is_failed(), Reason, Name, trim(Avp), Acc)
after
reset(?STRICT_KEY, Strict),
reset(?FAILED_KEY, Failed)
end.
%% trim/1
%%
%% Remove any extra bit that was added in diameter_codec to induce a
%% 5014 error.
trim(#diameter_avp{data = <<0:1, Bin/binary>>} = Avp) ->
Avp#diameter_avp{data = Bin};
trim(Avps)
when is_list(Avps) ->
lists:map(fun trim/1, Avps);
trim(Avp) ->
Avp.
%% dict/1
%%
%% Retrieve the dictionary for the best-effort decode of Failed-AVP,
%% as put by diameter_codec:decode/2. See that function for the
%% explanation.
dict(true) ->
case get({diameter_codec, dictionary}) of
undefined ->
?MODULE;
Mod ->
Mod
end;
dict(_) ->
?MODULE.
%% g/5
%% Ignore decode errors within Failed-AVP (best-effort) ...
g(true, [_Error | Rec], Name, Avp, Acc, _ComponentAvps) ->
decode_AVP(Name, Avp#diameter_avp{value = Rec}, Acc);
g(true, _Error, Name, Avp, Acc, _ComponentAvps) ->
decode_AVP(Name, Avp, Acc);
%% ... or not.
g(false, [Error | _Rec], _Name, Avp, Acc, ComponentAvps) ->
g(Error, Avp, Acc, ComponentAvps);
g(false, Error, _Name, Avp, Acc, ComponentAvps) ->
g(Error, Avp, Acc, ComponentAvps).
%% g/4
g({RC, ErrorData}, Avp, Acc, ComponentAvps) ->
{Avps, {Rec, Errors}} = Acc,
E = Avp#diameter_avp{data = [ErrorData]},
{[[Avp | trim(ComponentAvps)] | Avps], {Rec, [{RC, E} | Errors]}}.
%% d/5
%% Ignore a decode error within Failed-AVP ...
d(true, _, Name, Avp, Acc) ->
decode_AVP(Name, Avp, Acc);
%% ... or not. Failures here won't be visible since they're a "normal"
%% occurrence if the peer sends a faulty AVP that we need to respond
%% sensibly to. Log the occurence for traceability, but the peer will
%% also receive info in the resulting answer message.
d(false, Reason, Name, Avp, {Avps, Acc}) ->
Stack = diameter_lib:get_stacktrace(),
diameter_lib:log(decode_error,
?MODULE,
?LINE,
{Name, Avp#diameter_avp.name, Stack}),
{Rec, Failed} = Acc,
{[Avp|Avps], {Rec, [rc(Reason, Avp) | Failed]}}.
%% relax/2
%% Set false in the process dictionary as soon as we see a Grouped AVP
%% that doesn't set the M-bit, so that is_strict() can say whether or
%% not to ignore the M-bit on an encapsulated AVP.
relax('Grouped', M) ->
case getr(?STRICT_KEY) of
undefined when not M ->
putr(?STRICT_KEY, M);
_ ->
false
end;
relax(_, _) ->
false.
is_strict() ->
diameter_codec:getopt(strict_mbit)
andalso false /= getr(?STRICT_KEY).
%% relax/1
%%
%% Set true in the process dictionary as soon as we see Failed-AVP.
%% Matching on 'Failed-AVP' assumes that this is the RFC AVP.
%% Strictly, this doesn't need to be the case.
relax('Failed-AVP') ->
putr(?FAILED_KEY, true);
relax(_) ->
is_failed().
%% is_failed/0
%%
%% Is the AVP currently being decoded nested within Failed-AVP? Note
%% that this is only true when Failed-AVP is the parent. In
%% particular, it's not true when Failed-AVP itself is being decoded
%% (unless nested).
is_failed() ->
true == getr(?FAILED_KEY).
%% is_failed/1
is_failed(Name) ->
'Failed-AVP' == Name orelse is_failed().
%% reset/2
reset(Key, undefined) ->
eraser(Key);
reset(_, _) ->
ok.
%% decode_AVP/3
%%
%% Don't know this AVP: see if it can be packed in an 'AVP' field
%% undecoded. Note that the type field is 'undefined' in this case.
decode_AVP(Name, Avp, {Avps, Acc}) ->
{[trim(Avp) | Avps], pack_AVP(Name, Avp, Acc)}.
%% rc/1
%% diameter_types will raise an error of this form to communicate
%% DIAMETER_INVALID_AVP_LENGTH (5014). A module specified to a
%% @custom_types tag in a dictionary file can also raise an error of
%% this form.
rc({'DIAMETER', 5014 = RC, _}, #diameter_avp{name = AvpName} = Avp) ->
{RC, Avp#diameter_avp{data = empty_value(AvpName)}};
%% 3588:
%%
%% DIAMETER_INVALID_AVP_VALUE 5004
%% The request contained an AVP with an invalid value in its data
%% portion. A Diameter message indicating this error MUST include
%% the offending AVPs within a Failed-AVP AVP.
rc(_, Avp) ->
{5004, Avp}.
%% ungroup/2
-spec ungroup(term(), #diameter_avp{})
-> {avp(), #diameter_avp{}}.
%% The decoded value in the Grouped case is as returned by grouped_avp/3:
%% a record and a list of component AVP's.
ungroup(V, #diameter_avp{type = 'Grouped'} = Avp) ->
{Rec, As} = V,
A = Avp#diameter_avp{value = Rec},
{[A|As], A};
%% Otherwise it's just a plain value.
ungroup(V, #diameter_avp{} = Avp) ->
A = Avp#diameter_avp{value = V},
{A, A}.
%% pack_avp/3
pack_avp(Name, #diameter_avp{name = AvpName} = Avp, Acc) ->
pack_avp(Name, avp_arity(Name, AvpName), Avp, Acc).
%% pack_avp/4
pack_avp(Name, 0, Avp, Acc) ->
pack_AVP(Name, Avp, Acc);
pack_avp(_, Arity, Avp, Acc) ->
pack(Arity, Avp#diameter_avp.name, Avp, Acc).
%% pack_AVP/3
%% Length failure was induced because of a header/payload length
%% mismatch. The AVP Length is reset to match the received data if
%% this AVP is encoded in an answer message, since the length is
%% computed.
%%
%% Data is a truncated header if command_code = undefined, otherwise
%% payload bytes. The former is padded to the length of a header if
%% the AVP reaches an outgoing encode in diameter_codec.
%%
%% RFC 6733 says that an AVP returned with 5014 can contain a minimal
%% payload for the AVP's type, but in this case we don't know the
%% type.
pack_AVP(_, #diameter_avp{data = <<0:1, Data/binary>>} = Avp, Acc) ->
{Rec, Failed} = Acc,
{Rec, [{5014, Avp#diameter_avp{data = Data}} | Failed]};
pack_AVP(Name, #diameter_avp{is_mandatory = M, name = AvpName} = Avp, Acc) ->
case pack_arity(Name, AvpName, M) of
0 ->
{Rec, Failed} = Acc,
{Rec, [{if M -> 5001; true -> 5008 end, Avp} | Failed]};
Arity ->
pack(Arity, 'AVP', Avp, Acc)
end.
%% Give Failed-AVP special treatment since (1) it'll contain any
%% unrecognized mandatory AVP's and (2) the RFC 3588 grammar failed to
%% allow for Failed-AVP in an answer-message.
pack_arity(Name, AvpName, M) ->
%% Not testing just Name /= 'Failed-AVP' means we're changing the
%% packing of AVPs nested within Failed-AVP, but the point of
%% ignoring errors within Failed-AVP is to decode as much as
%% possible, and failing because a mandatory AVP couldn't be
%% packed into a dedicated field defeats that point. Note
%% is_failed/1 since is_failed/0 will return false when packing
%% 'AVP' within Failed-AVP.
pack_arity(is_failed(Name)
orelse {Name, AvpName} == {'answer-message', 'Failed-AVP'}
orelse not M
orelse not is_strict(),
Name).
pack_arity(true, Name) ->
avp_arity(Name, 'AVP');
pack_arity(false, _) ->
0.
%% 3588:
%%
%% DIAMETER_AVP_UNSUPPORTED 5001
%% The peer received a message that contained an AVP that is not
%% recognized or supported and was marked with the Mandatory bit. A
%% Diameter message with this error MUST contain one or more Failed-
%% AVP AVP containing the AVPs that caused the failure.
%%
%% DIAMETER_AVP_NOT_ALLOWED 5008
%% A message was received with an AVP that MUST NOT be present. The
%% Failed-AVP AVP MUST be included and contain a copy of the
%% offending AVP.
%% pack/4
pack(Arity, FieldName, Avp, {Rec, _} = Acc) ->
pack('#get-'(FieldName, Rec), Arity, FieldName, Avp, Acc).
%% pack/5
pack(undefined, 1, FieldName, Avp, Acc) ->
p(FieldName, fun(V) -> V end, Avp, Acc);
%% 3588:
%%
%% DIAMETER_AVP_OCCURS_TOO_MANY_TIMES 5009
%% A message was received that included an AVP that appeared more
%% often than permitted in the message definition. The Failed-AVP
%% AVP MUST be included and contain a copy of the first instance of
%% the offending AVP that exceeded the maximum number of occurrences
%%
pack(_, 1, _, Avp, {Rec, Failed}) ->
{Rec, [{5009, Avp} | Failed]};
pack(L, {_, Max}, FieldName, Avp, Acc) ->
case '*' /= Max andalso has_prefix(Max, L) of
true ->
{Rec, Failed} = Acc,
{Rec, [{5009, Avp} | Failed]};
false ->
p(FieldName, fun(V) -> [V|L] end, Avp, Acc)
end.
%% p/4
p(F, Fun, Avp, {Rec, Failed}) ->
{'#set-'({F, Fun(value(F, Avp))}, Rec), Failed}.
value('AVP', Avp) ->
Avp;
value(_, Avp) ->
Avp#diameter_avp.value.
%% ---------------------------------------------------------------------------
%% # grouped_avp/3
%% ---------------------------------------------------------------------------
-spec grouped_avp(decode, avp_name(), bitstring())
-> {avp_record(), [avp()]};
(encode, avp_name(), avp_record() | avp_values())
-> binary()
| no_return().
%% Length error induced by diameter_codec:collect_avps/1: the AVP
%% length in the header was too short (insufficient for the extracted
%% header) or too long (past the end of the message). An empty payload
%% is sufficient according to the RFC text for 5014.
grouped_avp(decode, _Name, <<0:1, _/binary>>) ->
throw({?TAG, {grouped, {5014, []}, []}});
grouped_avp(decode, Name, Data) ->
grouped_decode(Name, diameter_codec:collect_avps(Data));
grouped_avp(encode, Name, Data) ->
encode_avps(Name, Data).
%% grouped_decode/2
%%
%% Note that Grouped is the only AVP type that doesn't just return a
%% decoded value, also returning the list of component diameter_avp
%% records.
%% Length error in trailing component AVP.
grouped_decode(_Name, {Error, Acc}) ->
{5014, Avp} = Error,
throw({?TAG, {grouped, Error, [Avp | Acc]}});
%% 7.5. Failed-AVP AVP
%% In the case where the offending AVP is embedded within a Grouped AVP,
%% the Failed-AVP MAY contain the grouped AVP, which in turn contains
%% the single offending AVP. The same method MAY be employed if the
%% grouped AVP itself is embedded in yet another grouped AVP and so on.
%% In this case, the Failed-AVP MAY contain the grouped AVP hierarchy up
%% to the single offending AVP. This enables the recipient to detect
%% the location of the offending AVP when embedded in a group.
%% An error in decoding a component AVP throws the first fauly
%% component, which the catch in d/3 wraps in the Grouped AVP in
%% question. A partially decoded record is only used when ignoring
%% errors in Failed-AVP.
grouped_decode(Name, ComponentAvps) ->
{Rec, Avps, Es} = decode_avps(Name, ComponentAvps),
[] == Es orelse throw({?TAG, {grouped, [{_,_} = hd(Es) | Rec], Avps}}),
{Rec, Avps}.
%% ---------------------------------------------------------------------------
%% # empty_group/1
%% ---------------------------------------------------------------------------
empty_group(Name) ->
list_to_binary(empty_body(Name)).
empty_body(Name) ->
[z(F, avp_arity(Name, F)) || F <- '#info-'(name2rec(Name), fields)].
z(Name, 1) ->
z(Name);
z(_, {0,_}) ->
[];
z(Name, {Min, _}) ->
lists:duplicate(Min, z(Name)).
z('AVP') ->
<<0:64/integer>>; %% minimal header
z(Name) ->
Bin = diameter_codec:pack_avp(avp_header(Name), empty_value(Name)),
<< <<0>> || <<_>> <= Bin >>.
%% ---------------------------------------------------------------------------
%% # empty/1
%% ---------------------------------------------------------------------------
empty(AvpName) ->
avp(encode, zero, AvpName).
