%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2007-2013. 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%
%%
%% Description: Implements base 64 encode and decode. See RFC4648.
-module(base64).
-export([encode/1, decode/1, mime_decode/1,
encode_to_string/1, decode_to_string/1, mime_decode_to_string/1]).
%%-------------------------------------------------------------------------
%% The following type is a subtype of string() for return values
%% of (some) functions of this module.
%%-------------------------------------------------------------------------
-type ascii_string() :: [1..127].
%%-------------------------------------------------------------------------
%% encode_to_string(ASCII) -> Base64String
%% ASCII - string() | binary()
%% Base64String - string()
%%
%% Description: Encodes a plain ASCII string (or binary) into base64.
%%-------------------------------------------------------------------------
-spec encode_to_string(Data) -> Base64String when
Data :: string() | binary(),
Base64String :: ascii_string().
encode_to_string(Bin) when is_binary(Bin) ->
encode_to_string(binary_to_list(Bin));
encode_to_string(List) when is_list(List) ->
encode_l(List).
%%-------------------------------------------------------------------------
%% encode(ASCII) -> Base64
%% ASCII - string() | binary()
%% Base64 - binary()
%%
%% Description: Encodes a plain ASCII string (or binary) into base64.
%%-------------------------------------------------------------------------
-spec encode(Data) -> Base64 when
Data :: string() | binary(),
Base64 :: binary().
encode(Bin) when is_binary(Bin) ->
encode_binary(Bin);
encode(List) when is_list(List) ->
list_to_binary(encode_l(List)).
-spec encode_l(string()) -> ascii_string().
encode_l([]) ->
[];
encode_l([A]) ->
[b64e(A bsr 2),
b64e((A band 3) bsl 4), $=, $=];
encode_l([A,B]) ->
[b64e(A bsr 2),
b64e(((A band 3) bsl 4) bor (B bsr 4)),
b64e((B band 15) bsl 2), $=];
encode_l([A,B,C|Ls]) ->
BB = (A bsl 16) bor (B bsl 8) bor C,
[b64e(BB bsr 18),
b64e((BB bsr 12) band 63),
b64e((BB bsr 6) band 63),
b64e(BB band 63) | encode_l(Ls)].
encode_binary(Bin) ->
Split = 3*(byte_size(Bin) div 3),
<<Main0:Split/binary,Rest/binary>> = Bin,
Main = << <<(b64e(C)):8>> || <<C:6>> <= Main0 >>,
case Rest of
<<A:6,B:6,C:4>> ->
<<Main/binary,(b64e(A)):8,(b64e(B)):8,(b64e(C bsl 2)):8,$=:8>>;
<<A:6,B:2>> ->
<<Main/binary,(b64e(A)):8,(b64e(B bsl 4)):8,$=:8,$=:8>>;
<<>> ->
Main
end.
%%-------------------------------------------------------------------------
%% mime_decode(Base64) -> ASCII
%% decode(Base64) -> ASCII
%% Base64 - string() | binary()
%% ASCII - binary()
%%
%% Description: Decodes an base64 encoded string to plain ASCII.
%% mime_decode strips away all characters not Base64 before converting,
%% whereas decode crashes if an illegal character is found
%%-------------------------------------------------------------------------
-spec decode(Base64) -> Data when
Base64 :: string() | binary(),
Data :: binary().
decode(Bin) when is_binary(Bin) ->
decode_binary(<<>>, Bin);
decode(List) when is_list(List) ->
list_to_binary(decode_l(List)).
-spec mime_decode(Base64) -> Data when
Base64 :: string() | binary(),
Data :: binary().
mime_decode(Bin) when is_binary(Bin) ->
mime_decode_binary(<<>>, Bin);
mime_decode(List) when is_list(List) ->
mime_decode(list_to_binary(List)).
-spec decode_l(string()) -> string().
decode_l(List) ->
L = strip_spaces(List, []),
decode(L, []).
-spec mime_decode_l(string()) -> string().
mime_decode_l(List) ->
L = strip_illegal(List, [], 0),
decode(L, []).
%%-------------------------------------------------------------------------
%% mime_decode_to_string(Base64) -> ASCII
%% decode_to_string(Base64) -> ASCII
%% Base64 - string() | binary()
%% ASCII - binary()
%%
%% Description: Decodes an base64 encoded string to plain ASCII.
%% mime_decode strips away all characters not Base64 before converting,
%% whereas decode crashes if an illegal character is found
%%-------------------------------------------------------------------------
-spec decode_to_string(Base64) -> DataString when
Base64 :: string() | binary(),
DataString :: string().
decode_to_string(Bin) when is_binary(Bin) ->
decode_to_string(binary_to_list(Bin));
decode_to_string(List) when is_list(List) ->
decode_l(List).
-spec mime_decode_to_string(Base64) -> DataString when
Base64 :: string() | binary(),
DataString :: string().
mime_decode_to_string(Bin) when is_binary(Bin) ->
mime_decode_to_string(binary_to_list(Bin));
mime_decode_to_string(List) when is_list(List) ->
mime_decode_l(List).
%% One-based decode map.
-define(DECODE_MAP,
{bad,bad,bad,bad,bad,bad,bad,bad,ws,ws,bad,bad,ws,bad,bad, %1-15
bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad, %16-31
ws,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,62,bad,bad,bad,63, %32-47
52,53,54,55,56,57,58,59,60,61,bad,bad,bad,eq,bad,bad, %48-63
bad,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,
15,16,17,18,19,20,21,22,23,24,25,bad,bad,bad,bad,bad,
bad,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,
41,42,43,44,45,46,47,48,49,50,51,bad,bad,bad,bad,bad,
bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,
bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,
bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,
bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,
bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,
bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,
bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,
bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad,bad}).
decode_binary(Result0, <<C:8,T0/bits>>) ->
case element(C, ?DECODE_MAP) of
bad ->
erlang:error({badarg,C});
ws ->
decode_binary(Result0, T0);
eq ->
case strip_ws(T0) of
<<$=:8,T/binary>> ->
<<>> = strip_ws(T),
Split = byte_size(Result0) - 1,
<<Result:Split/bytes,_:4>> = Result0,
Result;
T ->
<<>> = strip_ws(T),
Split = byte_size(Result0) - 1,
<<Result:Split/bytes,_:2>> = Result0,
Result
end;
Bits ->
decode_binary(<<Result0/bits,Bits:6>>, T0)
end;
decode_binary(Result, <<>>) ->
true = is_binary(Result),
Result.
%% Skipping pad character if not at end of string. Also liberal about
%% excess padding and skipping of other illegal (non-base64 alphabet)
%% characters. See section 3.3 of RFC4648
mime_decode_binary(Result, <<0:8,T/bits>>) ->
mime_decode_binary(Result, T);
mime_decode_binary(Result0, <<C:8,T/bits>>) ->
case element(C, ?DECODE_MAP) of
Bits when is_integer(Bits) ->
mime_decode_binary(<<Result0/bits,Bits:6>>, T);
eq ->
case tail_contains_more(T, false) of
{<<>>, Eq} ->
%% No more valid data.
case bit_size(Result0) rem 8 of
0 ->
%% '====' is not uncommon.
Result0;
4 when Eq ->
%% enforce at least one more '=' only ignoring illegals and spacing
Split = byte_size(Result0) - 1,
<<Result:Split/bytes,_:4>> = Result0,
Result;
2 ->
%% remove 2 bits
Split = byte_size(Result0) - 1,
<<Result:Split/bytes,_:2>> = Result0,
Result
end;
{More, _} ->
%% More valid data, skip the eq as invalid
mime_decode_binary(Result0, More)
end;
_ ->
mime_decode_binary(Result0, T)
end;
mime_decode_binary(Result, <<>>) ->
true = is_binary(Result),
Result.
decode([], A) -> A;
decode([$=,$=,C2,C1|Cs], A) ->
Bits2x6 = (b64d(C1) bsl 18) bor (b64d(C2) bsl 12),
Octet1 = Bits2x6 bsr 16,
decode(Cs, [Octet1|A]);
decode([$=,C3,C2,C1|Cs], A) ->
Bits3x6 = (b64d(C1) bsl 18) bor (b64d(C2) bsl 12)
bor (b64d(C3) bsl 6),
Octet1 = Bits3x6 bsr 16,
Octet2 = (Bits3x6 bsr 8) band 16#ff,
decode(Cs, [Octet1,Octet2|A]);
decode([C4,C3,C2,C1| Cs], A) ->
Bits4x6 = (b64d(C1) bsl 18) bor (b64d(C2) bsl 12)
bor (b64d(C3) bsl 6) bor b64d(C4),
Octet1 = Bits4x6 bsr 16,
Octet2 = (Bits4x6 bsr 8) band 16#ff,
Octet3 = Bits4x6 band 16#ff,
decode(Cs, [Octet1,Octet2,Octet3|A]).
%%%========================================================================
%%% Internal functions
%%%========================================================================
strip_spaces([], A) -> A;
strip_spaces([$\s|Cs], A) -> strip_spaces(Cs, A);
strip_spaces([$\t|Cs], A) -> strip_spaces(Cs, A);
strip_spaces([$\r|Cs], A) -> strip_spaces(Cs, A);
strip_spaces([$\n|Cs], A) -> strip_spaces(Cs, A);
strip_spaces([C|Cs], A) -> strip_spaces(Cs, [C | A]).
strip_ws(<<$\t,T/binary>>) ->
strip_ws(T);
strip_ws(<<$\n,T/binary>>) ->
strip_ws(T);
strip_ws(<<$\r,T/binary>>) ->
strip_ws(T);
strip_ws(<<$\s,T/binary>>) ->
strip_ws(T);
strip_ws(T) -> T.
%% Skipping pad character if not at end of string. Also liberal about
%% excess padding and skipping of other illegal (non-base64 alphabet)
%% characters. See section 3.3 of RFC4648
strip_illegal([], A, _Cnt) ->
A;
strip_illegal([0|Cs], A, Cnt) ->
strip_illegal(Cs, A, Cnt);
strip_illegal([C|Cs], A, Cnt) ->
case element(C, ?DECODE_MAP) of
bad ->
strip_illegal(Cs, A, Cnt);
ws ->
strip_illegal(Cs, A, Cnt);
eq ->
case {tail_contains_more(Cs, false), Cnt rem 4} of
{{[], _}, 0} ->
A; %% Ignore extra =
{{[], true}, 2} ->
[$=|[$=|A]]; %% 'XX=='
{{[], _}, 3} ->
[$=|A]; %% 'XXX='
{{[H|T], _}, _} ->
%% more data, skip equals
strip_illegal(T, [H|A], Cnt+1)
end;
_ ->
strip_illegal(Cs, [C|A], Cnt+1)
end.
%% Search the tail for more valid data and remember if we saw
%% another equals along the way.
tail_contains_more([], Eq) ->
{[], Eq};
tail_contains_more(<<>>, Eq) ->
{<<>>, Eq};
tail_contains_more([C|T]=More, Eq) ->
case element(C, ?DECODE_MAP) of
bad ->
tail_contains_more(T, Eq);
ws ->
tail_contains_more(T, Eq);
eq ->
tail_contains_more(T, true);
_ ->
{More, Eq}
end;
tail_contains_more(<<C:8,T/bits>> =More, Eq) ->
case element(C, ?DECODE_MAP) of
bad ->
tail_contains_more(T, Eq);
ws ->
tail_contains_more(T, Eq);
eq ->
tail_contains_more(T, true);
_ ->
{More, Eq}
end.
%% accessors
b64e(X) ->
element(X+1,
{$A, $B, $C, $D, $E, $F, $G, $H, $I, $J, $K, $L, $M, $N,
$O, $P, $Q, $R, $S, $T, $U, $V, $W, $X, $Y, $Z,
$a, $b, $c, $d, $e, $f, $g, $h, $i, $j, $k, $l, $m, $n,
$o, $p, $q, $r, $s, $t, $u, $v, $w, $x, $y, $z,
$0, $1, $2, $3, $4, $5, $6, $7, $8, $9, $+, $/}).
b64d(X) ->
b64d_ok(element(X, ?DECODE_MAP)).
b64d_ok(I) when is_integer(I) -> I.
