Ever wanted to encode a string in Base64? Can't be bothered with those bloated Text to Base64 websites? Too elegant for those overrated "terminals" or whatever? Now you can encode strings in Base64 straight in luau with TYPES!

base64_type.luau

--!strict
--!optimize 2
--!native

type function Base64(user_type)
	if not user_type:is("singleton") then
		error(`provided type is not a singleton: {user_type.tag}`)
	end

	local value = tostring(user_type:value() :: string)
	local buff = buffer.fromstring(value)

	local PADDING_CHARACTER = 61
	local ALPHABET_INDEX = buffer.create(64) do
		local Characters = {
			65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80,
			81, 82, 83, 84, 85, 86, 87, 88, 89, 90,
			97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112,
			113, 114, 115, 116, 117, 118, 119, 120, 121, 122,
			48, 49, 50, 51, 52, 53, 54, 55, 56, 57,
			43, 47 
		}

		for Index = 0, 63 do
			buffer.writeu8(ALPHABET_INDEX, Index, Characters[Index + 1])
		end
	end

	local DIRECT_LOOKUP = buffer.create(256) do
		for Index = 0, 255 do
			buffer.writeu8(DIRECT_LOOKUP, Index, buffer.readu8(ALPHABET_INDEX, bit32.band(Index, 63)))
		end
	end

	local DECODE_TABLE = buffer.create(256) do
		for Index = 0, 255 do
			buffer.writeu8(DECODE_TABLE, Index, 255)
		end

		for Index = 65, 90 do
			buffer.writeu8(DECODE_TABLE, Index, Index - 65)
		end

		for Index = 97, 122 do
			buffer.writeu8(DECODE_TABLE, Index, Index - 97 + 26)
		end

		for Index = 48, 57 do
			buffer.writeu8(DECODE_TABLE, Index, Index - 48 + 52)
		end

		buffer.writeu8(DECODE_TABLE, 43, 62)
		buffer.writeu8(DECODE_TABLE, 47, 63)
	end

	local Padding = PADDING_CHARACTER
	local InputLength = buffer.len(buff)
	local Chunks = math.ceil(InputLength / 3)
	local OutputLength = Chunks * 4
	local Output = buffer.create(OutputLength)

	local Lookup = DIRECT_LOOKUP

	local DoubleChunks = math.floor((Chunks - 1) / 2)
	for ChunkIndex = 1, DoubleChunks do
		local InputIndex = (ChunkIndex - 1) * 6
		local OutputIndex = (ChunkIndex - 1) * 8

		local Word1 = bit32.byteswap(buffer.readu32(buff, InputIndex))
		local Octet1_1 = bit32.rshift(Word1, 26)
		local Octet1_2 = bit32.rshift(Word1, 20)
		local Octet1_3 = bit32.rshift(Word1, 14)
		local Octet1_4 = bit32.rshift(Word1, 8)

		local Word2 = bit32.byteswap(buffer.readu32(buff, InputIndex + 3))
		local Octet2_1 = bit32.rshift(Word2, 26)
		local Octet2_2 = bit32.rshift(Word2, 20)
		local Octet2_3 = bit32.rshift(Word2, 14)
		local Octet2_4 = bit32.rshift(Word2, 8)

		buffer.writeu32(Output, OutputIndex, bit32.bor(
			buffer.readu8(Lookup, bit32.band(Octet1_1, 255)),
			buffer.readu8(Lookup, bit32.band(Octet1_2, 255)) * 256,
			buffer.readu8(Lookup, bit32.band(Octet1_3, 255)) * 65536,
			buffer.readu8(Lookup, bit32.band(Octet1_4, 255)) * 16777216
			))

		buffer.writeu32(Output, OutputIndex + 4, bit32.bor(
			buffer.readu8(Lookup, bit32.band(Octet2_1, 255)),
			buffer.readu8(Lookup, bit32.band(Octet2_2, 255)) * 256,
			buffer.readu8(Lookup, bit32.band(Octet2_3, 255)) * 65536,
			buffer.readu8(Lookup, bit32.band(Octet2_4, 255)) * 16777216
			))
	end

	local ProcessedChunks = DoubleChunks * 2
	if ProcessedChunks < Chunks - 1 then
		local InputIndex = ProcessedChunks * 3
		local OutputIndex = ProcessedChunks * 4

		local Word = bit32.byteswap(buffer.readu32(buff, InputIndex))
		local Octet1 = bit32.rshift(Word, 26)
		local Octet2 = bit32.rshift(Word, 20)
		local Octet3 = bit32.rshift(Word, 14)
		local Octet4 = bit32.rshift(Word, 8)

		buffer.writeu32(Output, OutputIndex, bit32.bor(
			buffer.readu8(Lookup, bit32.band(Octet1, 255)),
			buffer.readu8(Lookup, bit32.band(Octet2, 255)) * 256,
			buffer.readu8(Lookup, bit32.band(Octet3, 255)) * 65536,
			buffer.readu8(Lookup, bit32.band(Octet4, 255)) * 16777216
			))
	end

	if InputLength > 0 then
		local TotalProcessedChunks = DoubleChunks * 2 + (ProcessedChunks < Chunks - 1 and 1 or 0)
		local ProcessedBytes = TotalProcessedChunks * 3
		local RemainingBytes = InputLength - ProcessedBytes
		local LastOutputIndex = OutputLength - 4

		if RemainingBytes == 3 then
			if ProcessedBytes + 4 <= InputLength then
				local Word = bit32.byteswap(buffer.readu32(buff, ProcessedBytes))
				local Octet1 = bit32.rshift(Word, 26)
				local Octet2 = bit32.rshift(Word, 20)
				local Octet3 = bit32.rshift(Word, 14)
				local Octet4 = bit32.rshift(Word, 8)

				buffer.writeu32(Output, LastOutputIndex, bit32.bor(
					buffer.readu8(Lookup, bit32.band(Octet1, 255)),
					buffer.readu8(Lookup, bit32.band(Octet2, 255)) * 256,
					buffer.readu8(Lookup, bit32.band(Octet3, 255)) * 65536,
					buffer.readu8(Lookup, bit32.band(Octet4, 255)) * 16777216
					))
			else
				local Byte1 = buffer.readu8(buff, ProcessedBytes)
				local Byte2 = buffer.readu8(buff, ProcessedBytes + 1)
				local Byte3 = buffer.readu8(buff, ProcessedBytes + 2)
				local Combined = bit32.bor(bit32.lshift(Byte1, 16), bit32.lshift(Byte2, 8), Byte3)

				local Octet1 = bit32.rshift(Combined, 18)
				local Octet2 = bit32.band(bit32.rshift(Combined, 12), 63)
				local Octet3 = bit32.band(bit32.rshift(Combined, 6), 63)
				local Octet4 = bit32.band(Combined, 63)

				buffer.writeu32(Output, LastOutputIndex, bit32.bor(
					buffer.readu8(Lookup, Octet1),
					buffer.readu8(Lookup, Octet2) * 256,
					buffer.readu8(Lookup, Octet3) * 65536,
					buffer.readu8(Lookup, Octet4) * 16777216
					))
			end

		elseif RemainingBytes == 2 then
			local Byte1 = buffer.readu8(buff, ProcessedBytes)
			local Byte2 = buffer.readu8(buff, ProcessedBytes + 1)
			local Combined = bit32.bor(bit32.lshift(Byte1, 16), bit32.lshift(Byte2, 8))

			local Octet1 = bit32.rshift(Combined, 18)
			local Octet2 = bit32.rshift(Combined, 12)
			local Octet3 = bit32.rshift(Combined, 6)

			buffer.writeu32(Output, LastOutputIndex, bit32.bor(
				buffer.readu8(Lookup, bit32.band(Octet1, 255)),
				buffer.readu8(Lookup, bit32.band(Octet2, 255)) * 256,
				buffer.readu8(Lookup, bit32.band(Octet3, 255)) * 65536,
				Padding * 16777216
				))

		elseif RemainingBytes == 1 then
			local Byte1 = buffer.readu8(buff, ProcessedBytes)
			local Combined = bit32.lshift(Byte1, 16)

			local Octet1 = bit32.rshift(Combined, 18)
			local Octet2 = bit32.rshift(Combined, 12)

			buffer.writeu32(Output, LastOutputIndex, bit32.bor(
				buffer.readu8(Lookup, bit32.band(Octet1, 255)),
				buffer.readu8(Lookup, bit32.band(Octet2, 255)) * 256,
				Padding * 65536,
				Padding * 16777216
				))
		end
	end

	return types.singleton(buffer.tostring(Output))
end

-- Example Usage:
local Encoded: Base64<"This is a test string"> = "" -- Press tab for autocompletion!
-- Do note that autocompletion will *not* work with Fragment Autocomplete

Awesome!