erldns

%% Copyright (c) 2012-2020, DNSimple Corporation
%%
%% Permission to use, copy, modify, and/or distribute this software for any
%% purpose with or without fee is hereby granted, provided that the above
%% copyright notice and this permission notice appear in all copies.
%%
%% THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
%% WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
%% MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
%% ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
%% WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
%% ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
%% OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

%% @doc Functions related to TXT record parsing.
-module(erldns_txt).

-include("erldns.hrl").

-export([parse/1]).

-define(MAX_TXT_SIZE, 255).

% Public API

%% @doc Parse a string into a collection of bit strings, each no longer than
%% 255 characters.
-spec parse(binary() | string()) -> [] | [[binary()]].
parse(Binary) when is_binary(Binary) ->
    parse(binary_to_list(Binary));
parse([]) ->
    [];
parse([C | Rest]) ->
    parse_char([C | Rest], C, Rest, [], false).

-spec parse(String :: string(), Rest :: string(), Tokens :: [[binary()]], Escaped :: boolean()) -> [binary()] | [[binary()]].
parse(String, [], [], _) ->
    [split(String)];
parse(_, [], Tokens, _) ->
    Tokens;
parse(String, [C | Rest], Tokens, Escaped) ->
    parse_char(String, C, Rest, Tokens, Escaped).

parse(_, [], Tokens, CurrentToken, true) ->
    % Last character is escaped
    Tokens ++ [CurrentToken];
parse(String, [C | Rest], Tokens, CurrentToken, Escaped) ->
    parse_char(String, C, Rest, Tokens, CurrentToken, Escaped).

%% @doc Do something with the given character. The rules are as follows:
%% * A quote starts/ends a token.
%% * Any other character is considered part of the current token.
-spec parse_char(string(), char(), string(), [string()], boolean()) -> any().
parse_char(String, $", Rest, Tokens, _) ->
    parse(String, Rest, Tokens, [], false);
parse_char(String, _, Rest, Tokens, _) ->
    parse(String, Rest, Tokens, false).

parse_char(String, $", Rest, Tokens, CurrentToken, false) ->
    parse(String, Rest, Tokens ++ [split(CurrentToken)], false);
parse_char(String, $", Rest, Tokens, CurrentToken, true) ->
    parse(String, Rest, Tokens, CurrentToken ++ [$"], false);
parse_char(String, $\\, Rest, Tokens, CurrentToken, false) ->
    parse(String, Rest, Tokens, CurrentToken, true);
parse_char(String, $\\, Rest, Tokens, CurrentToken, true) ->
    parse(String, Rest, Tokens, CurrentToken ++ [$\\], false);
parse_char(String, C, Rest, Tokens, CurrentToken, _) ->
    parse(String, Rest, Tokens, CurrentToken ++ [C], false).

%% @doc Split the given string into a list of bit strings, with each element
%% limited to 255 characters or less.
-spec split(string()) -> [binary()].
split(Data) ->
    split(Data, []).

%% Internal recursive split function.
-spec split(string(), [binary()]) -> [binary()].
split(Data, Parts) ->
    case byte_size(list_to_binary(Data)) > ?MAX_TXT_SIZE of
        true ->
            First = list_to_binary(string:substr(Data, 1, ?MAX_TXT_SIZE)),
            Rest = string:substr(Data, ?MAX_TXT_SIZE + 1),
            case Rest of
                [] ->
                    Parts ++ [First];
                _ ->
                    split(Rest, Parts ++ [First])
            end;
        false ->
            Parts ++ [list_to_binary(Data)]
    end.