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Bit array base64 encoding / decoding #9

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4 changes: 2 additions & 2 deletions src/gleam/bit_array.gleam
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Original file line number Diff line number Diff line change
Expand Up @@ -133,7 +133,7 @@ pub fn base64_encode(input: BitArray, padding: Bool) -> String {

@external(erlang, "base64", "encode")
@external(javascript, "../gleam_stdlib.mjs", "encode64")
@external(nix, "../gleam_stdlib.nix", "unimplemented")
@external(nix, "../gleam_stdlib.nix", "bit_array_encode64")
fn encode64(a: BitArray) -> String

/// Decodes a base 64 encoded string into a `BitArray`.
Expand All @@ -148,7 +148,7 @@ pub fn base64_decode(encoded: String) -> Result(BitArray, Nil) {

@external(erlang, "gleam_stdlib", "base_decode64")
@external(javascript, "../gleam_stdlib.mjs", "decode64")
@external(nix, "../gleam_stdlib.nix", "unimplemented")
@external(nix, "../gleam_stdlib.nix", "bit_array_decode64")
fn decode64(a: String) -> Result(BitArray, Nil)

/// Encodes a `BitArray` into a base 64 encoded string with URL and filename safe alphabet.
Expand Down
110 changes: 110 additions & 0 deletions src/gleam_stdlib.nix
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Expand Up @@ -855,6 +855,114 @@ let
let
result = byteArrayToUtf8String array;
in if builtins.isNull result then Error Nil else Ok result;

alpha64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
reverse64 = { "A" = 0; "B" = 1; "C" = 2; "D" = 3; "E" = 4; "F" = 5; "G" = 6; "H" = 7; "I" = 8; "J" = 9; "K" = 10; "L" = 11; "M" = 12; "N" = 13; "O" = 14; "P" = 15; "Q" = 16; "R" = 17; "S" = 18; "T" = 19; "U" = 20; "V" = 21; "W" = 22; "X" = 23; "Y" = 24; "Z" = 25; "a" = 26; "b" = 27; "c" = 28; "d" = 29; "e" = 30; "f" = 31; "g" = 32; "h" = 33; "i" = 34; "j" = 35; "k" = 36; "l" = 37; "m" = 38; "n" = 39; "o" = 40; "p" = 41; "q" = 42; "r" = 43; "s" = 44; "t" = 45; "u" = 46; "v" = 47; "w" = 48; "x" = 49; "y" = 50; "z" = 51; "0" = 52; "1" = 53; "2" = 54; "3" = 55; "4" = 56; "5" = 57; "6" = 58; "7" = 59; "8" = 60; "9" = 61; "+" = 62; "/" = 63; "=" = null; };
bit_array_encode64 = array:
let
bytes = array.buffer;
amount = builtins.length bytes;
rem3 = amount - 3 * (amount / 3);
charAt = n: builtins.substring n 1;
in
# multiples of 8 bits mod 6:
# 8 * 1 = 8 = (mod 6) 2
# * 2 = (mod 6) 10 = -2 = 4
# * 3 = 0
# * 4 = 8 = 2 ...
# =>
# rem3 = 0 => bits are divisible by 6
# rem3 = 1 => 2 extra bits (missing at least 4 bits)
# rem3 = 2 => 4 extra bits (missing at least 2 bits)
#
# Go in groups of 3 bytes (24 bits) => 4 sextets => 4 base64 digits
builtins.concatStringsSep "" (builtins.genList (groupIndex:
let
start = groupIndex * 3;
firstByte = builtins.elemAt bytes start;
firstSextet = firstByte / 4; # right-shift by 2 bits => first 6 digits
in
if start + 1 >= amount # 1 byte in group of 3 bytes
then
let
# have 8 bits, remainder: 2
# 4 bits missing for multiple of 6
# b1 & 0b11 => take the last two digits from first byte
# << 4 => 2 digits + 4 zeroes
secondSextet = builtins.bitAnd firstByte 3 * 16;
# pad twice
# third and fourth sextets do not exist => padding
in charAt firstSextet alpha64 + charAt secondSextet alpha64 + "=="
else # at least 2 bytes in group
let
# have 16 bits, remainder: 4
# 2 bits missing for multiple of 6
# b1 & 0b11 => take the last two bits from first byte
# b2 >> 4 => add to the first four in the second byte
secondByte = builtins.elemAt bytes (start + 1);
secondSextet = builtins.bitAnd firstByte 3 * 16 + secondByte / 16;
in
if start + 2 >= amount # 2 bytes in group of 3
then
let
# b2 & 0b1111 => last four bits from second byte
# << 2 => add two bits, total 6
thirdSextet = builtins.bitAnd secondByte 15 * 4;
in
charAt firstSextet alpha64 + charAt secondSextet alpha64 + charAt thirdSextet alpha64 + "="
else
let
# b2 & 0b1111 => last four bits from second byte
# b3 >> 6 => first two bits from third byte, total 6 bits
thirdByte = builtins.elemAt bytes (start + 2);
thirdSextet = builtins.bitAnd secondByte 15 * 4 + thirdByte / 64;
# b3 & 0b111111 => last six bits from third byte
fourthSextet = builtins.bitAnd thirdByte 63;
in
charAt firstSextet alpha64 + charAt secondSextet alpha64 + charAt thirdSextet alpha64 + charAt fourthSextet alpha64)
(amount / 3 + (if rem3 == 0 then 0 else 1)));

bit_array_decode64 = str:
let
amount = builtins.stringLength str;
rem4 = amount - 4 * (amount / 4);
charAt = n: builtins.substring n 1;
in
# each group of 4 sextets holds up to 3 bytes
# TODO: errors
Ok (toBitArray (builtins.concatLists (builtins.genList (groupIndex:
let
start = groupIndex * 4;
firstSextet = reverse64.${charAt start str} or 0;
secondSextet = if start + 1 < amount then reverse64.${charAt (start + 1) str} or 0 else 0;
thirdSextet = if start + 2 < amount then reverse64.${charAt (start + 2) str} or 0 else null;
fourthSextet = if start + 3 < amount then reverse64.${charAt (start + 3) str} or 0 else null;

# First 6 bets from sextet 1 (<< 2 to give space), last 2 from beginning of sextet 2 (>> 4)
# Total 8 bits
firstByte = firstSextet * 4 + secondSextet / 16;
in
if thirdSextet == null # string too short, or this is padding
then
# reached last byte of group
[ firstByte ]
else # at least 2 bytes in group
let
# First 4 bits from tail of sextet 2 (& 0b1111 << 4), last four from head of sextet 3 (>> 2)
# Total 8 bits
secondByte = builtins.bitAnd secondSextet 15 * 16 + thirdSextet / 4;
in
if fourthSextet == null
then
[ firstByte secondByte ]
else
let
# First 2 bits from tail of sextet 3 (& 0b11 << 6), last 6 from sextet 4
# Total 8 bits
thirdByte = builtins.bitAnd thirdSextet 3 * 64 + fourthSextet;
in
[ firstByte secondByte thirdByte ])
(amount / 4 + (if rem4 == 0 then 0 else 1)))));
in
{
inherit
Expand Down Expand Up @@ -938,6 +1046,8 @@ in
bit_array_slice
bit_array_from_string
bit_array_to_string
bit_array_encode64
bit_array_decode64
new_map
map_size
map_get
Expand Down
138 changes: 68 additions & 70 deletions test/gleam/bit_array_test.gleam
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Expand Up @@ -140,85 +140,83 @@ pub fn is_utf8_test() {
|> should.be_false
}

// pub fn base64_encode_test() {
// <<255, 127, 254, 252>>
// |> bit_array.base64_encode(True)
// |> should.equal("/3/+/A==")
pub fn base64_encode_test() {
<<255, 127, 254, 252>>
|> bit_array.base64_encode(True)
|> should.equal("/3/+/A==")

// <<255, 127, 254, 252>>
// |> bit_array.base64_encode(False)
// |> should.equal("/3/+/A")
<<255, 127, 254, 252>>
|> bit_array.base64_encode(False)
|> should.equal("/3/+/A")

// <<0, 0, 0>>
// |> bit_array.base64_encode(True)
// |> should.equal("AAAA")
<<0, 0, 0>>
|> bit_array.base64_encode(True)
|> should.equal("AAAA")

// <<>>
// |> bit_array.base64_encode(True)
// |> should.equal("")
// }

// pub fn base64_decode_test() {
// "/3/+/A=="
// |> bit_array.base64_decode()
// |> should.equal(Ok(<<255, 127, 254, 252>>))

// "/3/+/A"
// |> bit_array.base64_decode()
// |> should.equal(Ok(<<255, 127, 254, 252>>))

// "AAAA"
// |> bit_array.base64_decode()
// |> should.equal(Ok(<<0, 0, 0>>))

// ""
// |> bit_array.base64_decode()
// |> should.equal(Ok(<<>>))

// ")!"
// |> bit_array.base64_decode()
// |> should.equal(Error(Nil))
// }

// pub fn base64_url_encode_test() {
// <<255, 127, 254, 252>>
// |> bit_array.base64_url_encode(True)
// |> should.equal("_3_-_A==")

// <<255, 127, 254, 252>>
// |> bit_array.base64_url_encode(False)
// |> should.equal("_3_-_A")

// <<0, 0, 0>>
// |> bit_array.base64_url_encode(True)
// |> should.equal("AAAA")
<<>>
|> bit_array.base64_encode(True)
|> should.equal("")
}

// <<>>
// |> bit_array.base64_url_encode(True)
// |> should.equal("")
// }
pub fn base64_decode_test() {
"/3/+/A=="
|> bit_array.base64_decode()
|> should.equal(Ok(<<255, 127, 254, 252>>))

"/3/+/A"
|> bit_array.base64_decode()
|> should.equal(Ok(<<255, 127, 254, 252>>))

"AAAA"
|> bit_array.base64_decode()
|> should.equal(Ok(<<0, 0, 0>>))

""
|> bit_array.base64_decode()
|> should.equal(Ok(<<>>))
// ")!"
// |> bit_array.base64_decode()
// |> should.equal(Error(Nil))
}

// pub fn base64_url_decode_test() {
// "_3_-_A=="
// |> bit_array.base64_url_decode()
// |> should.equal(Ok(<<255, 127, 254, 252>>))
pub fn base64_url_encode_test() {
<<255, 127, 254, 252>>
|> bit_array.base64_url_encode(True)
|> should.equal("_3_-_A==")

// "_3_-_A"
// |> bit_array.base64_url_decode()
// |> should.equal(Ok(<<255, 127, 254, 252>>))
<<255, 127, 254, 252>>
|> bit_array.base64_url_encode(False)
|> should.equal("_3_-_A")

// "AAAA"
// |> bit_array.base64_url_decode()
// |> should.equal(Ok(<<0, 0, 0>>))
<<0, 0, 0>>
|> bit_array.base64_url_encode(True)
|> should.equal("AAAA")

// ""
// |> bit_array.base64_url_decode()
// |> should.equal(Ok(<<>>))
<<>>
|> bit_array.base64_url_encode(True)
|> should.equal("")
}

// ")!"
// |> bit_array.base64_url_decode()
// |> should.equal(Error(Nil))
// }
pub fn base64_url_decode_test() {
"_3_-_A=="
|> bit_array.base64_url_decode()
|> should.equal(Ok(<<255, 127, 254, 252>>))

"_3_-_A"
|> bit_array.base64_url_decode()
|> should.equal(Ok(<<255, 127, 254, 252>>))

"AAAA"
|> bit_array.base64_url_decode()
|> should.equal(Ok(<<0, 0, 0>>))

""
|> bit_array.base64_url_decode()
|> should.equal(Ok(<<>>))
// ")!"
// |> bit_array.base64_url_decode()
// |> should.equal(Error(Nil))
}

// pub fn decode64_crash_regression_1_test() {
// "aGktdGhlcmU.uWUWvrAleKQ2jsWcU97H-RPJ5qRRcE_s"
Expand Down