%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2007-2026. All Rights Reserved.
%%
%% 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.
%%
%% %CopyrightEnd%
%%

%%
%%----------------------------------------------------------------------
%% Purpose: Handle TLS/SSL record protocol. (Parts that are not shared with DTLS)
%%----------------------------------------------------------------------

-module(tls_record).
-moduledoc false.

-include("tls_record.hrl").
-include("ssl_internal.hrl").
-include("ssl_alert.hrl").
-include("tls_handshake.hrl").
-include("ssl_cipher.hrl").
-include_lib("kernel/include/logger.hrl").

%% Handling of incoming data
-export([get_tls_records/5,
         init_connection_states/4]).

%% Encoding TLS records
-export([encode_handshake/3, encode_alert_record/3,
	 encode_change_cipher_spec/2, encode_data/3]).
-export([encode_plain_text/4, split_iovec/2]).

%% Decoding
-export([decode_cipher_text/4]).

%% Logging helper
-export([build_tls_record/1]).

%% Protocol version handling
-export([protocol_version/1, protocol_version_name/1,  lowest_protocol_version/1, lowest_protocol_version/2,
	 highest_protocol_version/1, highest_protocol_version/2,
	 is_higher/2, supported_protocol_versions/0, sufficient_crypto_support/1,
	 is_acceptable_version/1, is_acceptable_version/2, hello_version/1]).

-export_type([tls_version/0, tls_atom_version/0, tls_max_frag_len/0]).

-type tls_version()       :: ssl_record:ssl_version().
-type tls_atom_version()  :: sslv3 | tlsv1 | 'tlsv1.1' | 'tlsv1.2' | 'tlsv1.3'.
-type tls_max_frag_len()  :: undefined | 512 | 1024 | 2048 | 4096.

-compile(inline).

%%====================================================================
%% Handling of incoming data
%%====================================================================
%%--------------------------------------------------------------------
%%
%% Description: Creates a connection_states record with appropriate
%% values for the initial SSL connection setup.
%%--------------------------------------------------------------------
-spec init_connection_states(Role, Version, BeastMitigation,
                             MaxEarlyDataSize) ->
          ssl_record:connection_states() when
      Role :: client | server,
      Version :: tls_version(),
      BeastMitigation :: one_n_minus_one | zero_n | disabled,
      MaxEarlyDataSize :: non_neg_integer().

init_connection_states(Role, Version, BeastMitigation, MaxEarlyDataSize) ->
    ConnectionEnd = ssl_record:record_protocol_role(Role),
    Current = initial_connection_state(ConnectionEnd, MaxEarlyDataSize),
    Pending = ssl_record:empty_connection_state(ConnectionEnd, Version, MaxEarlyDataSize),
    CS = #{current_read  => Current,  pending_read  => Pending,
           current_write => Current,  pending_write => Pending},
    case BeastMitigation of
        disabled -> CS;
        _NotDisabled -> CS#{beast_mitigation => BeastMitigation}
    end.

%%--------------------------------------------------------------------
-spec get_tls_records(
        binary(),
        [tls_version()] | tls_version(),
        Buffer0 :: binary() | {'undefined' | #ssl_tls{}, {[binary()],non_neg_integer(),[binary()]}},
        tls_max_frag_len(),
        Downgrade :: {NewController::pid(), From::gen_statem:from()} | 'undefined') ->
          {Records :: [#ssl_tls{}],
           Buffer :: {'undefined' | #ssl_tls{}, {[binary()],non_neg_integer(),[binary()]}}} |
          #alert{}.
%%
%% and returns it as a list of binaries also returns leftover
%% Description: Given old buffer and new data from TCP, packs up a records
%% data
%%--------------------------------------------------------------------
get_tls_records(Data, Versions, Buffer, MaxFragLen, Downgrade) when is_binary(Buffer) ->
    parse_tls_records(Versions, {[Data],byte_size(Data),[]}, MaxFragLen, Downgrade, undefined);
get_tls_records(Data, Versions, {Hdr, {Front,Size,Rear}}, MaxFragLen, Downgrade) ->
    parse_tls_records(Versions, {Front,Size + byte_size(Data),[Data|Rear]}, MaxFragLen, Downgrade, Hdr).

%%====================================================================
%% Encoding
%%====================================================================

%%--------------------------------------------------------------------
-spec encode_handshake(iolist(), tls_version(), ssl_record:connection_states()) ->
			      {iolist(), ssl_record:connection_states()}.
%
%% Description: Encodes a handshake message to send on the ssl-socket.
%%--------------------------------------------------------------------
encode_handshake(Frag, ?TLS_1_3, ConnectionStates) ->
    tls_record_1_3:encode_handshake(Frag, ConnectionStates);
encode_handshake(Frag, Version,
		 #{current_write :=
		       #{security_parameters := #security_parameters{bulk_cipher_algorithm = BCA}}
                  } = ConnectionStates) ->
    MaxLength = maps:get(max_fragment_length, ConnectionStates, ?MAX_PLAIN_TEXT_LENGTH),
    BeastM = maps:get(beast_mitigation, ConnectionStates, disabled),
    case iolist_size(Frag) of
	N when N > MaxLength ->
            Data = split_iovec(erlang:iolist_to_iovec(Frag), Version, BCA, BeastM, MaxLength),
	    encode_fragments(?HANDSHAKE, Version, Data, ConnectionStates);
	_  ->
	    encode_plain_text(?HANDSHAKE, Version, Frag, ConnectionStates)
    end.

%%--------------------------------------------------------------------
-spec encode_alert_record(#alert{}, tls_version(), ssl_record:connection_states()) ->
				 {iolist(), ssl_record:connection_states()}.
%%
%% Description: Encodes an alert message to send on the ssl-socket.
%%--------------------------------------------------------------------
encode_alert_record(Alert, ?TLS_1_3, ConnectionStates) ->
    tls_record_1_3:encode_alert_record(Alert, ConnectionStates);
encode_alert_record(#alert{level = Level, description = Description},
                    Version, ConnectionStates) ->
    encode_plain_text(?ALERT, Version, <<?BYTE(Level), ?BYTE(Description)>>,
		      ConnectionStates).

%%--------------------------------------------------------------------
-spec encode_change_cipher_spec(tls_version(), ssl_record:connection_states()) ->
				       {iolist(), ssl_record:connection_states()}.
%%
%% Description: Encodes a change_cipher_spec-message to send on the ssl socket.
%%--------------------------------------------------------------------
encode_change_cipher_spec(Version, ConnectionStates) ->
    encode_plain_text(?CHANGE_CIPHER_SPEC, Version, ?byte(?CHANGE_CIPHER_SPEC_PROTO), ConnectionStates).

%%--------------------------------------------------------------------
-spec encode_data([binary()], tls_version(), ssl_record:connection_states()) ->
			 {[[binary()]], ssl_record:connection_states()}.
%%
%% Description: Encodes data to send on the ssl-socket.
%%--------------------------------------------------------------------
encode_data(Data, ?TLS_1_3, ConnectionStates) ->
    tls_record_1_3:encode_data(Data, ConnectionStates);
encode_data(Data, Version,
	    #{current_write :=
                  #{security_parameters := #security_parameters{bulk_cipher_algorithm = BCA}}
             } = ConnectionStates) ->
    MaxLength = maps:get(max_fragment_length, ConnectionStates, ?MAX_PLAIN_TEXT_LENGTH),
    BeastM = maps:get(beast_mitigation, ConnectionStates, disabled),
    Fragments = split_iovec(Data, Version, BCA, BeastM, MaxLength),
    encode_fragments(?APPLICATION_DATA, Version, Fragments, ConnectionStates).

%%====================================================================
%% Decoding
%%====================================================================

%%--------------------------------------------------------------------
-spec decode_cipher_text(tls_version(), #ssl_tls{}, ssl_record:connection_states(), boolean()) ->
				{#ssl_tls{} | no_record,
                                 ssl_record:connection_states()}| #alert{}.
%%
%% Description: Decode cipher text
%%--------------------------------------------------------------------
decode_cipher_text(?TLS_1_3, CipherTextRecord, ConnectionStates, _) ->
    tls_record_1_3:decode_cipher_text(CipherTextRecord, ConnectionStates);
decode_cipher_text(_, CipherTextRecord,
		   #{current_read :=
			 #{sequence_number := Seq,
			   security_parameters :=
                               #security_parameters{cipher_type = ?AEAD,
                                                    bulk_cipher_algorithm = BulkCipherAlgo},
                           cipher_state := CipherS0
                          }
                    } = ConnectionStates0, _) ->
    SeqBin = <<?UINT64(Seq)>>,
    #ssl_tls{type = Type, version = Version, fragment = Fragment} = CipherTextRecord,
    {MajVer,MinVer} = Version,
    StartAdditionalData = <<SeqBin/binary, ?BYTE(Type), ?BYTE(MajVer), ?BYTE(MinVer)>>,
    CipherS = ssl_record:nonce_seed(BulkCipherAlgo, SeqBin, CipherS0),
    case ssl_record:decipher_aead(
           BulkCipherAlgo, CipherS, StartAdditionalData, Fragment, Version)
    of
	PlainFragment when is_binary(PlainFragment) ->
            #{current_read := ReadState0} = ConnectionStates0,
            ConnectionStates =
                ConnectionStates0#{current_read => ReadState0#{cipher_state => CipherS,
                                                               sequence_number => Seq + 1}},
            {CipherTextRecord#ssl_tls{fragment = PlainFragment}, ConnectionStates};
	#alert{} = Alert ->
	    Alert
    end;

decode_cipher_text(_, #ssl_tls{version = Version,
                               fragment = CipherFragment} = CipherTextRecord,
		   #{current_read := ReadState0} = ConnnectionStates0, PaddingCheck) ->
    case ssl_record:decipher(Version, CipherFragment, ReadState0, PaddingCheck) of
	{PlainFragment, Mac, ReadState1} ->
	    MacHash = ssl_cipher:calc_mac_hash(CipherTextRecord#ssl_tls.type, Version,
                                               PlainFragment, ReadState1),
	    case ssl_record:is_correct_mac(Mac, MacHash) of
		true ->
                    #{sequence_number := Seq} = ReadState0,
		    ConnnectionStates =
                        ConnnectionStates0#{current_read =>
                                                ReadState1#{sequence_number => Seq + 1}},
		    {CipherTextRecord#ssl_tls{fragment = PlainFragment}, ConnnectionStates};
		false ->
                    ?ALERT_REC(?FATAL, ?BAD_RECORD_MAC)
	    end;
        #alert{} = Alert ->
	    Alert
    end.

%%====================================================================
%% Protocol version handling
%%====================================================================

%%--------------------------------------------------------------------
-spec protocol_version_name(tls_atom_version()) -> tls_version().
%%     
%% Description: Creates a protocol version record from a version atom
%% or vice versa.
%%--------------------------------------------------------------------
protocol_version_name('tlsv1.3') ->
    ?TLS_1_3;
protocol_version_name('tlsv1.2') ->
    ?TLS_1_2;
protocol_version_name('tlsv1.1') ->
    ?TLS_1_1;
protocol_version_name(tlsv1) ->
    ?TLS_1_0;
protocol_version_name(sslv3) ->
    ?SSL_3_0;
protocol_version_name(sslv2) -> %% Backwards compatibility
    ?SSL_2_0.

%%--------------------------------------------------------------------
-spec protocol_version(tls_version()) -> tls_atom_version().
%%
%% Description: Creates a protocol version record from a version atom
%% or vice versa.
%%--------------------------------------------------------------------

protocol_version(?TLS_1_3) ->
    'tlsv1.3';
protocol_version(?TLS_1_2) ->
    'tlsv1.2';
protocol_version(?TLS_1_1) ->
    'tlsv1.1';
protocol_version(?TLS_1_0) ->
    tlsv1;
protocol_version(?SSL_3_0) ->
    sslv3.
%%--------------------------------------------------------------------
-spec lowest_protocol_version(tls_version(), tls_version()) -> tls_version().
%%     
%% Description: Lowes protocol version of two given versions 
%%--------------------------------------------------------------------
lowest_protocol_version(Version1, Version2) when ?TLS_LT(Version1, Version2) ->
    Version1;
lowest_protocol_version(_, Version2) ->
    Version2.

%%--------------------------------------------------------------------
-spec lowest_protocol_version([tls_version()]) -> tls_version().
%%     
%% Description: Lowest protocol version present in a list
%%--------------------------------------------------------------------
lowest_protocol_version(Versions) ->
    check_protocol_version(Versions, fun lowest_protocol_version/2).

%%--------------------------------------------------------------------
-spec highest_protocol_version([tls_version()]) -> tls_version().
%%     
%% Description: Highest protocol version present in a list
%%--------------------------------------------------------------------
highest_protocol_version(Versions) ->
    check_protocol_version(Versions, fun highest_protocol_version/2).


check_protocol_version([], Fun) -> check_protocol_version(supported_protocol_versions(), Fun);
check_protocol_version([Ver | Versions], Fun) -> lists:foldl(Fun, Ver, Versions).

%%--------------------------------------------------------------------
-spec highest_protocol_version(tls_version(), tls_version()) -> tls_version().
%%     
%% Description: Highest protocol version of two given versions 
%%--------------------------------------------------------------------
highest_protocol_version(Version1, Version2) when ?TLS_GT(Version1, Version2) ->
    Version1;
highest_protocol_version(_, Version2) ->
    Version2.

%%--------------------------------------------------------------------
-spec is_higher(V1 :: tls_version(), V2::tls_version()) -> boolean().
%%     
%% Description: Is V1 > V2
%%--------------------------------------------------------------------
is_higher(V1, V2) when ?TLS_GT(V1, V2) ->
    true;
is_higher(_, _) ->
    false.


%%--------------------------------------------------------------------
-spec supported_protocol_versions() -> [tls_version()].					 
%%
%% Description: Protocol versions supported
%%--------------------------------------------------------------------
supported_protocol_versions() ->
    Fun = fun(Version) ->
		  protocol_version_name(Version)
	  end,
    case application:get_env(ssl, protocol_version) of
	undefined ->
	    lists:map(Fun, supported_protocol_versions([]));
	{ok, []} ->
	    lists:map(Fun, supported_protocol_versions([]));
	{ok, Vsns} when is_list(Vsns) ->
	    Versions = lists:filter(fun is_acceptable_version/1, lists:map(Fun, Vsns)),
	    supported_protocol_versions(Versions);
	{ok, Vsn} ->
	    Versions = lists:filter(fun is_acceptable_version/1, [Fun(Vsn)]),
	    supported_protocol_versions(Versions)
    end.

supported_protocol_versions([]) ->
    Vsns = sufficient_support(?ALL_SUPPORTED_VERSIONS),
    application:set_env(ssl, protocol_version, Vsns),
    Vsns;

supported_protocol_versions([_|_] = Vsns) ->
    sufficient_support(Vsns).

sufficient_crypto_support(Version) ->
    sufficient_crypto_support(crypto:supports(), Version).

sufficient_crypto_support(CryptoSupport, Version) when Version == 'tlsv1';
                                                       Version == 'tlsv1.1' ->
    Hashes =  proplists:get_value(hashs, CryptoSupport),
    PKeys =  proplists:get_value(public_keys, CryptoSupport),
    proplists:get_bool(sha, Hashes) 
        andalso
        proplists:get_bool(md5, Hashes) 
        andalso 
        proplists:get_bool(aes_cbc, proplists:get_value(ciphers, CryptoSupport)) 
        andalso
          (proplists:get_bool(ecdsa, PKeys) orelse proplists:get_bool(rsa, PKeys) orelse proplists:get_bool(dss, PKeys)) 
        andalso
          (proplists:get_bool(ecdh, PKeys) orelse proplists:get_bool(dh, PKeys));

sufficient_crypto_support(CryptoSupport, 'tlsv1.2') ->
    PKeys =  proplists:get_value(public_keys, CryptoSupport),
    (proplists:get_bool(sha256, proplists:get_value(hashs, CryptoSupport)))
        andalso 
          (proplists:get_bool(aes_cbc, proplists:get_value(ciphers, CryptoSupport)))
        andalso
          (proplists:get_bool(ecdsa, PKeys) orelse proplists:get_bool(rsa, PKeys) orelse proplists:get_bool(dss, PKeys)) 
        andalso
          (proplists:get_bool(ecdh, PKeys) orelse proplists:get_bool(dh, PKeys));

%%  A TLS-compliant application MUST implement the TLS_AES_128_GCM_SHA256
%%  [GCM] cipher suite and SHOULD implement the TLS_AES_256_GCM_SHA384
%%  [GCM] and TLS_CHACHA20_POLY1305_SHA256 [RFC8439] cipher suites (see
%%  Appendix B.4).
%%
%%  A TLS-compliant application MUST support digital signatures with
%%  rsa_pkcs1_sha256 (for certificates), rsa_pss_rsae_sha256 (for
%%  CertificateVerify and certificates), and ecdsa_secp256r1_sha256.  A
%%  TLS-compliant application MUST support key exchange with secp256r1
%%  (NIST P-256) and SHOULD support key exchange with X25519 [RFC7748].
sufficient_crypto_support(CryptoSupport, 'tlsv1.3') ->
    Fun = fun({Group, Algorithm}) ->
                  is_algorithm_supported(CryptoSupport, Group, Algorithm)
          end,
   %% Minimum requirement check
   L = [{ciphers, aes_gcm},                %% TLS_AES_*_GCM_*
         {hashs, sha256},                   %% TLS_AES_128_GCM_SHA256
         {rsa_opts, rsa_pkcs1_padding},     %% rsa_pkcs1_sha256
         {rsa_opts, rsa_pkcs1_pss_padding}, %% rsa_pss_*
         {public_keys, ecdh},
         {public_keys, rsa},
         {public_keys, ecdsa},
         {curves, secp256r1}               %% key exchange with secp256r1
        ],
    lists:all(Fun, L);
sufficient_crypto_support(CryptoSupport, Version) ->
    sufficient_crypto_support(CryptoSupport, protocol_version(Version)).


is_algorithm_supported(CryptoSupport, Group, Algorithm) ->
    proplists:get_bool(Algorithm, proplists:get_value(Group, CryptoSupport)).

-spec is_acceptable_version(tls_version()) -> boolean().
is_acceptable_version(Version)
  when ?TLS_1_X(Version) ->
    true;
is_acceptable_version(_) ->
    false.

-spec is_acceptable_version(tls_version(), Supported :: [tls_version()]) -> boolean().
is_acceptable_version(Version, Versions) ->
    ?TLS_1_X(Version) andalso lists:member(Version, Versions).

-spec hello_version([tls_version()]) -> tls_version().
hello_version([Highest|_]) when ?TLS_GTE(Highest, ?TLS_1_2) ->
    ?TLS_1_2;
hello_version(Versions) ->
    lowest_protocol_version(Versions).

split_iovec([], _) ->
    [];
split_iovec(Data, MaximumFragmentLength) ->
    {Part,Rest} = split_iovec(Data, MaximumFragmentLength, []),
    [Part|split_iovec(Rest, MaximumFragmentLength)].

%%--------------------------------------------------------------------
%%% Internal functions
%%--------------------------------------------------------------------
initial_connection_state(ConnectionEnd, MaxEarlyDataSize) ->
    #{security_parameters => ssl_record:initial_security_params(ConnectionEnd),
      sequence_number => 0,
      cipher_state  => undefined,
      mac_secret  => undefined,
      early_data => #{pending_early_data_size => MaxEarlyDataSize,
                      trial_decryption => false,
                      early_data_accepted => false
                     },
      reneg => #{secure_renegotiation => undefined,
                 client_verify_data => undefined,
                 server_verify_data => undefined}
     }.

%% Used by logging to recreate the received bytes
build_tls_record(#ssl_tls{type = Type, version = Version, fragment = Fragment}) ->
    Length = byte_size(Fragment),
    {MajVer, MinVer} = Version,
    <<?BYTE(Type),?BYTE(MajVer),?BYTE(MinVer),?UINT16(Length), Fragment/binary>>.


parse_tls_records(Versions, Q, MaxFragLen, Downgrade, undefined) ->
    decode_tls_records(Versions, Q, MaxFragLen, Downgrade, [], undefined, undefined, undefined);
parse_tls_records(Versions, Q, MaxFragLen, Downgrade, #ssl_tls{type = Type, version = Version, fragment = Length}) ->
    decode_tls_records(Versions, Q, MaxFragLen, Downgrade, [], Type, Version, Length).

%% Generic code path
decode_tls_records(Versions, {_,Size,_} = Q0, MaxFragLen, Downgrade, Acc, undefined, _Version, _Length) ->
    if
        5 =< Size ->
            {<<?BYTE(Type),?BYTE(MajVer),?BYTE(MinVer), ?UINT16(Length)>>, Q} = binary_from_front(5, Q0),
            %% TODO: convert the MajVer and MinVer to corresponding macro
            Version = {MajVer,MinVer},
            validate_tls_records_type(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length);
        3 =< Size ->
            {<<?BYTE(Type),?BYTE(MajVer),?BYTE(MinVer)>>, Q} = binary_from_front(3, Q0),
            Version = {MajVer,MinVer},
            validate_tls_records_type(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, undefined);
        1 =< Size ->
            {<<?BYTE(Type)>>, Q} = binary_from_front(1, Q0),
            validate_tls_records_type(Versions, Q, MaxFragLen, Downgrade, Acc, Type, undefined, undefined);
        true ->
            validate_tls_records_type(Versions, Q0, MaxFragLen, Downgrade, Acc, undefined, undefined, undefined)
    end;
decode_tls_records(Versions, {_,Size,_} = Q0, MaxFragLen, Downgrade, Acc, Type, undefined, _Length) ->
    if
        4 =< Size ->
            {<<?BYTE(MajVer),?BYTE(MinVer), ?UINT16(Length)>>, Q} = binary_from_front(4, Q0),
            Version = {MajVer,MinVer},
            validate_tls_record_version(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length);
        2 =< Size ->
            {<<?BYTE(MajVer),?BYTE(MinVer)>>, Q} = binary_from_front(2, Q0),
            Version = {MajVer,MinVer},
            validate_tls_record_version(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, undefined);
        true ->
            validate_tls_record_version(Versions, Q0, MaxFragLen, Downgrade, Acc, Type, undefined, undefined)
    end;
decode_tls_records(Versions, {_,Size,_} = Q0, MaxFragLen, Downgrade, Acc, Type, Version, undefined) ->
    if
        2 =< Size ->
            {<<?UINT16(Length)>>, Q} = binary_from_front(2, Q0),
            validate_tls_record_length(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length);
        true ->
            validate_tls_record_length(Versions, Q0, MaxFragLen, Downgrade, Acc, Type, Version, undefined)
    end;
decode_tls_records(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length) ->
    validate_tls_record_length(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length).


%% TODO: separate validation logic from modification of the record
validate_tls_records_type(_Versions, Q, _MaxFragLen, _Downgrade, Acc, undefined, _Version, _Length) ->
    {lists:reverse(Acc),
     {undefined, Q}};
validate_tls_records_type(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length) when ?KNOWN_RECORD_TYPE(Type) ->
    validate_tls_record_version(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length);
validate_tls_records_type(_Versions, _Q, _MaxFragLen, _Downgrade, _Acc, Type, _Version, _Length) ->
    %% Not ?KNOWN_RECORD_TYPE(Type)
    ?ALERT_REC(?FATAL, ?UNEXPECTED_MESSAGE, {unsupported_record_type, Type}).


validate_tls_record_version(_Versions, Q, _MaxFragLen, _Downgrade, Acc, Type, undefined, _Length) ->
    {lists:reverse(Acc),
     {#ssl_tls{type = Type, version = undefined, fragment = undefined}, Q}};
validate_tls_record_version(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length) when is_list(Versions) ->
    case is_acceptable_version(Version, Versions) of
        true ->
            validate_tls_record_length(Versions, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length);
        false ->
            ?ALERT_REC(?FATAL, ?BAD_RECORD_MAC, {unsupported_version, Version})
    end;
validate_tls_record_version(?TLS_1_3 = Version, Q, MaxFragLen,
                            Downgrade, Acc, Type, ?TLS_1_2 = OuterVersion, Length) ->
    validate_tls_record_length(Version, Q, MaxFragLen, Downgrade, Acc, Type, OuterVersion, Length);
validate_tls_record_version(Version, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length) ->
    %% Exact version match
    validate_tls_record_length(Version, Q, MaxFragLen, Downgrade, Acc, Type, Version, Length);
validate_tls_record_version(_Versions, _Q, _MaxFragLen, _Downgrade, _Acc, _Type, Version, _Length) ->
    ?ALERT_REC(?FATAL, ?BAD_RECORD_MAC, {unsupported_version, Version}).


validate_tls_record_length(_Versions, Q, _MaxFragLen, _Downgrade, Acc, Type, Version, undefined) ->
    {lists:reverse(Acc),
     {#ssl_tls{type = Type, version = Version, fragment = undefined}, Q}};
validate_tls_record_length(Versions, {_,Size0,_} = Q0, MaxFragLen,
                           Downgrade, Acc, Type, Version, Length) ->
    Max = if is_integer(MaxFragLen) ->
                  MaxFragLen + ?MAX_PADDING_LENGTH + ?MAX_MAC_LENGTH;
             true ->
                  max_len(Versions)
          end,
    if
        Length =< Max ->
            if
                Length =< Size0 ->
                    %% Complete record
                    {Fragment, Q} = binary_from_front(Length, Q0),
                    Record = #ssl_tls{type = Type, version = Version, fragment = Fragment},
                    ssl_logger:debug(get(log_level), inbound, 'record', Record),
                    case Downgrade of
                        {_Pid, _From} ->
                            %% parse only single record for downgrade scenario, buffer remaining data
                            {[Record], {undefined, Q}};
                        _ ->
                            decode_tls_records(Versions, Q, MaxFragLen, Downgrade, [Record|Acc], undefined, undefined, undefined)
                    end;
                true ->
                    {lists:reverse(Acc),
                     {#ssl_tls{type = Type, version = Version, fragment = Length}, Q0}}
            end;
        true ->
            ?ALERT_REC(?FATAL, ?RECORD_OVERFLOW)
    end.


binary_from_front(0, Q) ->
    {<<>>, Q};
binary_from_front(SplitSize, {Front,Size,Rear}) when SplitSize =< Size ->
    binary_from_front(SplitSize, Front, Size, Rear, []).
%%
%% SplitSize > 0 and there is at least SplitSize bytes buffered in Front and Rear
binary_from_front(SplitSize, [], Size, Rear, Acc) ->
    case Rear of
        %% Avoid lists:reverse/1 for simple cases.
        %% Case clause for [] to avoid infinite loop.
        [_] ->
            binary_from_front(SplitSize, Rear, Size, [], Acc);
        [Bin2,Bin1] ->
            binary_from_front(SplitSize, [Bin1,Bin2], Size, [], Acc);
        [Bin3,Bin2,Bin1] ->
            binary_from_front(SplitSize, [Bin1,Bin2,Bin3], Size, [], Acc);
        [_,_,_|_] ->
            binary_from_front(SplitSize, lists:reverse(Rear), Size, [], Acc)
    end;
binary_from_front(SplitSize, [Bin|Front], Size, Rear, []) ->
    %% Optimize the frequent case when the accumulator is empty
    BinSize = byte_size(Bin),
    if
        SplitSize < BinSize ->
            {RetBin, Rest} = erlang:split_binary(Bin, SplitSize),
            {RetBin, {[Rest|Front],Size - SplitSize,Rear}};
        BinSize < SplitSize ->
            binary_from_front(SplitSize - BinSize, Front, Size, Rear, [Bin]);
        true -> % Perfect fit
            {Bin, {Front,Size - SplitSize,Rear}}
    end;
binary_from_front(SplitSize, [Bin|Front], Size, Rear, Acc) ->
    BinSize = byte_size(Bin),
    if
        SplitSize < BinSize ->
            {Last, Rest} = erlang:split_binary(Bin, SplitSize),
            RetBin = iolist_to_binary(lists:reverse(Acc, [Last])),
            {RetBin, {[Rest|Front],Size - byte_size(RetBin),Rear}};
        BinSize < SplitSize ->
            binary_from_front(SplitSize - BinSize, Front, Size, Rear, [Bin|Acc]);
        true -> % Perfect fit
            RetBin = iolist_to_binary(lists:reverse(Acc, [Bin])),
            {RetBin, {Front,Size - byte_size(RetBin),Rear}}
    end.

%%--------------------------------------------------------------------
encode_plain_text(Type, Version, Data, ConnectionStates0) ->
    {[CipherText],ConnectionStates} = encode_fragments(Type, Version, [Data], ConnectionStates0),
    {CipherText,ConnectionStates}.
%%--------------------------------------------------------------------
encode_fragments(Type, Version, Data,
                 #{current_write := #{cipher_state := CipherS,
                                      sequence_number := Seq}} = ConnectionStates) ->
    encode_fragments(Type, Version, Data, ConnectionStates, CipherS, Seq, []).
%%
encode_fragments(_Type, _Version, [], #{current_write := WriteS} = CS,
                 CipherS, Seq, CipherFragments) ->
    {lists:reverse(CipherFragments),
     CS#{current_write := WriteS#{cipher_state := CipherS, sequence_number := Seq}}};
encode_fragments(Type, Version, [Text|Data],
                 #{current_write :=
                       #{security_parameters :=
                             #security_parameters{cipher_type = ?AEAD,
                                                  bulk_cipher_algorithm = BCAlg} = SecPars}} = CS,
                 CipherS0, Seq, CipherFragments) ->
    SeqBin = <<?UINT64(Seq)>>,
    CipherS1 = ssl_record:nonce_seed(BCAlg, SeqBin, CipherS0),
    {MajVer, MinVer} = Version,
    VersionBin = <<?BYTE(MajVer), ?BYTE(MinVer)>>,
    StartAdditionalData = <<SeqBin/binary, ?BYTE(Type), VersionBin/binary>>,
    {CipherFragment,CipherS} = ssl_record:cipher_aead(Version, Text, CipherS1,
                                                      StartAdditionalData, SecPars),
    Length = byte_size(CipherFragment),
    CipherHeader = <<?BYTE(Type), VersionBin/binary, ?UINT16(Length)>>,
    encode_fragments(Type, Version, Data, CS, CipherS, Seq + 1,
                     [[CipherHeader, CipherFragment] | CipherFragments]);
encode_fragments(Type, Version, [Text|Data],
                 #{current_write :=
                       #{security_parameters :=
                             #security_parameters{mac_algorithm = MacAlgorithm} = SecPars,
                         mac_secret := MacSecret}} = CS,
                 CipherS0, Seq, CipherFragments) ->
    MacHash = ssl_cipher:calc_mac_hash(Type, Version, Text, MacAlgorithm, MacSecret, Seq),
    {CipherFragment,CipherS} = ssl_record:cipher(Version, Text, CipherS0, MacHash, SecPars),
    Length = byte_size(CipherFragment),
    {MajVer, MinVer} = Version,
    CipherHeader = <<?BYTE(Type), ?BYTE(MajVer), ?BYTE(MinVer), ?UINT16(Length)>>,
    encode_fragments(Type, Version, Data, CS, CipherS, Seq + 1,
                     [[CipherHeader, CipherFragment] | CipherFragments]).


%%--------------------------------------------------------------------

%% 1/n-1 splitting countermeasure Rizzo/Duong-Beast, RC4 ciphers are
%% not vulnerable to this attack.
split_iovec(Data, ?TLS_1_0, BCA, one_n_minus_one, MaxLength)
  when BCA =/= ?RC4 ->
    {Part, RestData} = split_iovec(Data, 1, []),
    [Part|split_iovec(RestData, MaxLength)];
%% 0/n splitting countermeasure for clients that are incompatible with 1/n-1
%% splitting.
split_iovec(Data, ?TLS_1_0, BCA, zero_n, MaxLength)
  when BCA =/= ?RC4 ->
    {Part, RestData} = split_iovec(Data, 0, []),
    [Part|split_iovec(RestData, MaxLength)];
split_iovec(Data, _Version, _BCA, _BeatMitigation, MaxLength) ->
    split_iovec(Data, MaxLength).

split_iovec([Bin|Data] = Bin_Data, SplitSize, Acc) ->
    BinSize = byte_size(Bin),
    if
        BinSize =< SplitSize ->
            split_iovec(Data, SplitSize - BinSize, [Bin|Acc]);
        SplitSize == 0 ->
            {lists:reverse(Acc), Bin_Data};
        SplitSize < BinSize ->
            {Last, Rest} = erlang:split_binary(Bin, SplitSize),
            {lists:reverse(Acc, [Last]), [Rest|Data]}
    end;
split_iovec([], _SplitSize, Acc) ->
    {lists:reverse(Acc),[]}.

%%--------------------------------------------------------------------


max_len([?TLS_1_3|_])->
    ?TLS13_MAX_CIPHER_TEXT_LENGTH;
max_len(?TLS_1_3)->
    ?TLS13_MAX_CIPHER_TEXT_LENGTH;
max_len(_) ->
    ?MAX_CIPHER_TEXT_LENGTH.

sufficient_support(Versions) ->
    CryptoSupport = crypto:supports(),
    [Ver ||  Ver <- Versions, sufficient_crypto_support(CryptoSupport, Ver)].

