erltls

-module(erltls_record).

-include("erltls.hrl").

-export([
    get_protocol_record_header_size/1,
    read_next_record/4,
    is_dtls/1
]).

-define(RC_HEADER_SIZE_TLS, 5).
-define(RC_HEADER_SIZE_DTLS, 13).
-define(MAX_TLS_RECORD_LENGHT, 16384).
-define(VALIDATE_PACKET_LENGTH(Length), Length =< ?MAX_TLS_RECORD_LENGHT).

read_next_record(TcpSocket, IsDtls, RecordHeaderSize, Timeout) ->
    case gen_tcp:recv(TcpSocket, RecordHeaderSize, Timeout) of
        {ok, RecordHeaderPacket} ->
            case get_record_header_info(IsDtls, RecordHeaderPacket) of
                {ok, Type, FgLength} ->
                    case validate_record(Type, FgLength) of
                        true ->
                            case gen_tcp:recv(TcpSocket, FgLength, Timeout) of
                                {ok, PacketFragment} ->
                                    {ok, Type,  <<RecordHeaderPacket/binary, PacketFragment/binary>>};
                                Error ->
                                    Error
                            end;
                        _ ->
                            {error, invalid_tls_frame}
                    end;
                Error ->
                    Error
            end;
        Error ->
            Error
    end.

% dtls header: type:uint8(21 - alert) {major:uint8 minor:uint8} epoch:uint16 sequence_number:uint48 length:uint16
% tls header:  type:uint8(21 - alert) {major:uint8 minor:uint8} length:uint16

get_record_header_info(IsDtls, HeaderBytes) ->
    case IsDtls of
        false ->
            <<Type:8/integer, _MaV:8/integer, _MiV:8/integer, FgLength:16/integer, _Rest/binary>> = HeaderBytes,
            {ok, Type, FgLength};
        _ ->
            <<Type:8/integer, _MaV:8/integer, _MiV:8/integer, _Epoch:16/integer, _Seq:48/integer, FgLength:16/integer, _Rest/binary>> = HeaderBytes,
            {ok, Type, FgLength}
    end.

get_protocol_record_header_size(dtlsv1) ->
    ?RC_HEADER_SIZE_DTLS;
get_protocol_record_header_size('dtlsv1.2') ->
    ?RC_HEADER_SIZE_DTLS;
get_protocol_record_header_size(_Protocol) ->
    ?RC_HEADER_SIZE_TLS.

validate_record(Type, Length) ->
    case Type of
        ?SSL_RECORD_HANDSHAKE ->
            ?VALIDATE_PACKET_LENGTH(Length);
        ?SSL_RECORD_ALERT ->
            ?VALIDATE_PACKET_LENGTH(Length);
        ?SSL_RECORD_CHANGE_CIPHER_SPEC ->
            ?VALIDATE_PACKET_LENGTH(Length);
        ?SSL_RECORD_APP_DATA ->
            ?VALIDATE_PACKET_LENGTH(Length);
        _ ->
            false
    end.

is_dtls(dtlsv1) ->
    true;
is_dtls('dtlsv1.2') ->
    true;
is_dtls(_) ->
    false.