mirror of
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124 lines
4.5 KiB
C++
124 lines
4.5 KiB
C++
/*
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* Copyright (c) 2022-2023, the SerenityOS developers.
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/Base64.h>
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#include <AK/ByteBuffer.h>
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#include <AK/CharacterTypes.h>
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#include <AK/Error.h>
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#include <AK/StringBuilder.h>
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#include <AK/StringView.h>
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#include <AK/Vector.h>
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#include <LibWeb/Infra/Base64.h>
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#include <LibWeb/Infra/CharacterTypes.h>
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namespace Web::Infra {
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// https://infra.spec.whatwg.org/#forgiving-base64
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ErrorOr<ByteBuffer> decode_forgiving_base64(StringView input)
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{
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// 1. Remove all ASCII whitespace from data.
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// FIXME: It is possible to avoid copying input here, it's just a bit tricky to remove the equal signs
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StringBuilder builder;
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for (auto character : input) {
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if (!is_ascii_whitespace(character))
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TRY(builder.try_append(character));
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}
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auto data = builder.string_view();
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// 2. If data’s code point length divides by 4 leaving no remainder, then:
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if (data.length() % 4 == 0) {
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// If data ends with one or two U+003D (=) code points, then remove them from data.
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if (data.ends_with("=="sv))
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data = data.substring_view(0, data.length() - 2);
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else if (data.ends_with('='))
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data = data.substring_view(0, data.length() - 1);
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}
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// 3. If data’s code point length divides by 4 leaving a remainder of 1, then return failure.
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if (data.length() % 4 == 1)
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return Error::from_string_literal("Invalid input length in forgiving base64 decode");
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// 4. If data contains a code point that is not one of
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// U+002B (+), U+002F (/), ASCII alphanumeric
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// then return failure.
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for (auto point : data) {
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if (point != '+' && point != '/' && !is_ascii_alphanumeric(point))
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return Error::from_string_literal("Invalid character in forgiving base64 decode");
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}
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// 5. Let output be an empty byte sequence.
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// 6. Let buffer be an empty buffer that can have bits appended to it.
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Vector<u8> output;
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u32 buffer = 0;
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auto accumulated_bits = 0;
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auto add_to_buffer = [&](u8 number) {
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VERIFY(number < 64);
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u32 buffer_mask = number;
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if (accumulated_bits == 0)
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buffer_mask <<= 18;
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else if (accumulated_bits == 6)
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buffer_mask <<= 12;
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else if (accumulated_bits == 12)
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buffer_mask <<= 6;
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else if (accumulated_bits == 18)
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buffer_mask <<= 0;
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buffer |= buffer_mask;
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accumulated_bits += 6;
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};
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auto append_bytes = [&]() {
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output.append(static_cast<u8>((buffer & 0xff0000) >> 16));
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output.append(static_cast<u8>((buffer & 0xff00) >> 8));
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output.append(static_cast<u8>(buffer & 0xff));
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buffer = 0;
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accumulated_bits = 0;
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};
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auto alphabet_lookup_table = AK::base64_lookup_table();
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// 7. Let position be a position variable for data, initially pointing at the start of data.
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// 8. While position does not point past the end of data:
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for (auto point : data) {
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// 1. Find the code point pointed to by position in the second column of Table 1: The Base 64 Alphabet of RFC 4648.
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// Let n be the number given in the first cell of the same row. [RFC4648]
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auto n = alphabet_lookup_table[point];
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VERIFY(n >= 0);
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// 2. Append the six bits corresponding to n, most significant bit first, to buffer.
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add_to_buffer(static_cast<u8>(n));
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// 3. buffer has accumulated 24 bits,
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if (accumulated_bits == 24) {
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// interpret them as three 8-bit big-endian numbers.
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// Append three bytes with values equal to those numbers to output, in the same order, and then empty buffer
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append_bytes();
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}
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}
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// 9. If buffer is not empty, it contains either 12 or 18 bits.
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VERIFY(accumulated_bits == 0 || accumulated_bits == 12 || accumulated_bits == 18);
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// If it contains 12 bits, then discard the last four and interpret the remaining eight as an 8-bit big-endian number.
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if (accumulated_bits == 12)
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output.append(static_cast<u8>((buffer & 0xff0000) >> 16));
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// If it contains 18 bits, then discard the last two and interpret the remaining 16 as two 8-bit big-endian numbers.
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// Append the one or two bytes with values equal to those one or two numbers to output, in the same order.
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if (accumulated_bits == 18) {
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output.append(static_cast<u8>((buffer & 0xff0000) >> 16));
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output.append(static_cast<u8>((buffer & 0xff00) >> 8));
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}
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return ByteBuffer::copy(output);
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}
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}
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