Everywhere: Hoist the Libraries folder to the top-level

Author: https://github.com/trflynn89
Commit: 93712b24bf
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2256
Reviewed-by: https://github.com/sideshowbarker

Libraries/LibJS/Runtime/Uint8Array.cpp

@@ -0,0 +1,842 @@
+/*
+ * Copyright (c) 2024, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Base64.h>
+#include <AK/StringBuilder.h>
+#include <AK/StringUtils.h>
+#include <LibJS/Runtime/Temporal/AbstractOperations.h>
+#include <LibJS/Runtime/TypedArray.h>
+#include <LibJS/Runtime/Uint8Array.h>
+#include <LibJS/Runtime/VM.h>
+#include <LibJS/Runtime/ValueInlines.h>
+
+namespace JS {
+
+void Uint8ArrayConstructorHelpers::initialize(Realm& realm, Object& constructor)
+{
+    auto& vm = constructor.vm();
+
+    static constexpr u8 attr = Attribute::Writable | Attribute::Configurable;
+    constructor.define_native_function(realm, vm.names.fromBase64, from_base64, 1, attr);
+    constructor.define_native_function(realm, vm.names.fromHex, from_hex, 1, attr);
+}
+
+void Uint8ArrayPrototypeHelpers::initialize(Realm& realm, Object& prototype)
+{
+    auto& vm = prototype.vm();
+
+    static constexpr u8 attr = Attribute::Writable | Attribute::Configurable;
+    prototype.define_native_function(realm, vm.names.toBase64, to_base64, 0, attr);
+    prototype.define_native_function(realm, vm.names.toHex, to_hex, 0, attr);
+    prototype.define_native_function(realm, vm.names.setFromBase64, set_from_base64, 1, attr);
+    prototype.define_native_function(realm, vm.names.setFromHex, set_from_hex, 1, attr);
+}
+
+static ThrowCompletionOr<Alphabet> parse_alphabet(VM& vm, Object& options)
+{
+    // Let alphabet be ? Get(opts, "alphabet").
+    auto alphabet = TRY(options.get(vm.names.alphabet));
+
+    // If alphabet is undefined, set alphabet to "base64".
+    if (alphabet.is_undefined())
+        return Alphabet::Base64;
+
+    // If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
+    if (alphabet.is_string()) {
+        if (alphabet.as_string().utf8_string_view() == "base64"sv)
+            return Alphabet::Base64;
+        if (alphabet.as_string().utf8_string_view() == "base64url"sv)
+            return Alphabet::Base64URL;
+    }
+
+    return vm.throw_completion<TypeError>(ErrorType::OptionIsNotValidValue, alphabet, "alphabet"sv);
+}
+
+static ThrowCompletionOr<LastChunkHandling> parse_last_chunk_handling(VM& vm, Object& options)
+{
+    // Let lastChunkHandling be ? Get(opts, "lastChunkHandling").
+    auto last_chunk_handling = TRY(options.get(vm.names.lastChunkHandling));
+
+    // If lastChunkHandling is undefined, set lastChunkHandling to "loose".
+    if (last_chunk_handling.is_undefined())
+        return LastChunkHandling::Loose;
+
+    // If lastChunkHandling is not one of "loose", "strict", or "stop-before-partial", throw a TypeError exception.
+    if (last_chunk_handling.is_string()) {
+        if (last_chunk_handling.as_string().utf8_string_view() == "loose"sv)
+            return LastChunkHandling::Loose;
+        if (last_chunk_handling.as_string().utf8_string_view() == "strict"sv)
+            return LastChunkHandling::Strict;
+        if (last_chunk_handling.as_string().utf8_string_view() == "stop-before-partial"sv)
+            return LastChunkHandling::StopBeforePartial;
+    }
+
+    return vm.throw_completion<TypeError>(ErrorType::OptionIsNotValidValue, last_chunk_handling, "lastChunkHandling"sv);
+}
+
+// 1 Uint8Array.prototype.toBase64 ( [ options ] ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-uint8array.prototype.tobase64
+JS_DEFINE_NATIVE_FUNCTION(Uint8ArrayPrototypeHelpers::to_base64)
+{
+    auto options_value = vm.argument(0);
+
+    // 1. Let O be the this value.
+    // 2. Perform ? ValidateUint8Array(O).
+    auto typed_array = TRY(validate_uint8_array(vm));
+
+    // 3. Let opts be ? GetOptionsObject(options).
+    auto* options = TRY(Temporal::get_options_object(vm, options_value));
+
+    // 4. Let alphabet be ? Get(opts, "alphabet").
+    // 5. If alphabet is undefined, set alphabet to "base64".
+    // 6. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
+    auto alphabet = TRY(parse_alphabet(vm, *options));
+
+    // 7. Let omitPadding be ToBoolean(? Get(opts, "omitPadding")).
+    auto omit_padding_value = TRY(options->get(vm.names.omitPadding)).to_boolean();
+    auto omit_padding = omit_padding_value ? AK::OmitPadding::Yes : AK::OmitPadding::No;
+
+    // 8. Let toEncode be ? GetUint8ArrayBytes(O).
+    auto to_encode = TRY(get_uint8_array_bytes(vm, typed_array));
+
+    String out_ascii;
+
+    // 9. If alphabet is "base64", then
+    if (alphabet == Alphabet::Base64) {
+        // a. Let outAscii be the sequence of code points which results from encoding toEncode according to the base64
+        //    encoding specified in section 4 of RFC 4648. Padding is included if and only if omitPadding is false.
+        out_ascii = MUST(encode_base64(to_encode, omit_padding));
+    }
+    // 10. Else,
+    else {
+        // a. Assert: alphabet is "base64url".
+        // b. Let outAscii be the sequence of code points which results from encoding toEncode according to the base64url
+        //    encoding specified in section 5 of RFC 4648. Padding is included if and only if omitPadding is false.
+        out_ascii = MUST(encode_base64url(to_encode, omit_padding));
+    }
+
+    // 11. Return CodePointsToString(outAscii).
+    return PrimitiveString::create(vm, move(out_ascii));
+}
+
+// 2 Uint8Array.prototype.toHex ( ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-uint8array.prototype.tobase64
+JS_DEFINE_NATIVE_FUNCTION(Uint8ArrayPrototypeHelpers::to_hex)
+{
+    // 1. Let O be the this value.
+    // 2. Perform ? ValidateUint8Array(O).
+    auto typed_array = TRY(validate_uint8_array(vm));
+
+    // 3. Let toEncode be ? GetUint8ArrayBytes(O).
+    auto to_encode = TRY(get_uint8_array_bytes(vm, typed_array));
+
+    // 4. Let out be the empty String.
+    StringBuilder out;
+
+    // 5. For each byte byte of toEncode, do
+    for (auto byte : to_encode.bytes()) {
+        // a. Let hex be Number::toString(𝔽(byte), 16).
+        // b. Set hex to StringPad(hex, 2, "0", START).
+        // c. Set out to the string-concatenation of out and hex.
+        out.appendff("{:02x}", byte);
+    }
+
+    // 6. Return out.
+    return PrimitiveString::create(vm, MUST(out.to_string()));
+}
+
+// 3 Uint8Array.fromBase64 ( string [ , options ] ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-uint8array.frombase64
+JS_DEFINE_NATIVE_FUNCTION(Uint8ArrayConstructorHelpers::from_base64)
+{
+    auto& realm = *vm.current_realm();
+
+    auto string_value = vm.argument(0);
+    auto options_value = vm.argument(1);
+
+    // 1. If string is not a String, throw a TypeError exception.
+    if (!string_value.is_string())
+        return vm.throw_completion<TypeError>(ErrorType::NotAString, string_value);
+
+    // 2. Let opts be ? GetOptionsObject(options).
+    auto* options = TRY(Temporal::get_options_object(vm, options_value));
+
+    // 3. Let alphabet be ? Get(opts, "alphabet").
+    // 4. If alphabet is undefined, set alphabet to "base64".
+    // 5. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
+    auto alphabet = TRY(parse_alphabet(vm, *options));
+
+    // 6. Let lastChunkHandling be ? Get(opts, "lastChunkHandling").
+    // 7. If lastChunkHandling is undefined, set lastChunkHandling to "loose".
+    // 8. If lastChunkHandling is not one of "loose", "strict", or "stop-before-partial", throw a TypeError exception.
+    auto last_chunk_handling = TRY(parse_last_chunk_handling(vm, *options));
+
+    // 9. Let result be FromBase64(string, alphabet, lastChunkHandling).
+    auto result = JS::from_base64(vm, string_value.as_string().utf8_string_view(), alphabet, last_chunk_handling);
+
+    // 10. If result.[[Error]] is not none, then
+    if (result.error.has_value()) {
+        // a. Throw result.[[Error]].
+        return result.error.release_value();
+    }
+
+    // 11. Let resultLength be the length of result.[[Bytes]].
+    auto result_length = result.bytes.size();
+
+    // 12. Let ta be ? AllocateTypedArray("Uint8Array", %Uint8Array%, "%Uint8Array.prototype%", resultLength).
+    auto typed_array = TRY(Uint8Array::create(realm, result_length));
+
+    // 13. Set the value at each index of ta.[[ViewedArrayBuffer]].[[ArrayBufferData]] to the value at the corresponding
+    //     index of result.[[Bytes]].
+    auto& array_buffer_data = typed_array->viewed_array_buffer()->buffer();
+
+    for (size_t index = 0; index < result_length; ++index)
+        array_buffer_data[index] = result.bytes[index];
+
+    // 14. Return ta.
+    return typed_array;
+}
+
+// 4 Uint8Array.prototype.setFromBase64 ( string [ , options ] ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-uint8array.prototype.setfrombase64
+JS_DEFINE_NATIVE_FUNCTION(Uint8ArrayPrototypeHelpers::set_from_base64)
+{
+    auto& realm = *vm.current_realm();
+
+    auto string_value = vm.argument(0);
+    auto options_value = vm.argument(1);
+
+    // 1. Let into be the this value.
+    // 2. Perform ? ValidateUint8Array(into).
+    auto into = TRY(validate_uint8_array(vm));
+
+    // 3. If string is not a String, throw a TypeError exception.
+    if (!string_value.is_string())
+        return vm.throw_completion<TypeError>(ErrorType::NotAString, string_value);
+
+    // 4. Let opts be ? GetOptionsObject(options).
+    auto* options = TRY(Temporal::get_options_object(vm, options_value));
+
+    // 5. Let alphabet be ? Get(opts, "alphabet").
+    // 6. If alphabet is undefined, set alphabet to "base64".
+    // 7. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
+    auto alphabet = TRY(parse_alphabet(vm, *options));
+
+    // 8. Let lastChunkHandling be ? Get(opts, "lastChunkHandling").
+    // 9. If lastChunkHandling is undefined, set lastChunkHandling to "loose".
+    // 10. If lastChunkHandling is not one of "loose", "strict", or "stop-before-partial", throw a TypeError exception.
+    auto last_chunk_handling = TRY(parse_last_chunk_handling(vm, *options));
+
+    // 11. Let taRecord be MakeTypedArrayWithBufferWitnessRecord(into, seq-cst).
+    auto typed_array_record = make_typed_array_with_buffer_witness_record(into, ArrayBuffer::Order::SeqCst);
+
+    // 12. If IsTypedArrayOutOfBounds(taRecord) is true, throw a TypeError exception.
+    if (is_typed_array_out_of_bounds(typed_array_record))
+        return vm.throw_completion<TypeError>(ErrorType::BufferOutOfBounds, "TypedArray"sv);
+
+    // 13. Let byteLength be TypedArrayLength(taRecord).
+    auto byte_length = typed_array_length(typed_array_record);
+
+    // 14. Let result be FromBase64(string, alphabet, lastChunkHandling, byteLength).
+    auto result = JS::from_base64(vm, string_value.as_string().utf8_string_view(), alphabet, last_chunk_handling, byte_length);
+
+    // 15. Let bytes be result.[[Bytes]].
+    auto bytes = move(result.bytes);
+
+    // 16. Let written be the length of bytes.
+    auto written = bytes.size();
+
+    // 17. NOTE: FromBase64 does not invoke any user code, so the ArrayBuffer backing into cannot have been detached or shrunk.
+    // 18. Assert: written ≤ byteLength.
+    VERIFY(written <= byte_length);
+
+    // 19. Perform SetUint8ArrayBytes(into, bytes).
+    set_uint8_array_bytes(into, bytes);
+
+    // 20. If result.[[Error]] is not none, then
+    if (result.error.has_value()) {
+        // a. Throw result.[[Error]].
+        return result.error.release_value();
+    }
+
+    // 21. Let resultObject be OrdinaryObjectCreate(%Object.prototype%).
+    auto result_object = Object::create(realm, realm.intrinsics().object_prototype());
+
+    // 22. Perform ! CreateDataPropertyOrThrow(resultObject, "read", 𝔽(result.[[Read]])).
+    MUST(result_object->create_data_property(vm.names.read, Value { result.read }));
+
+    // 23. Perform ! CreateDataPropertyOrThrow(resultObject, "written", 𝔽(written)).
+    MUST(result_object->create_data_property(vm.names.written, Value { written }));
+
+    // 24. Return resultObject.
+    return result_object;
+}
+
+// 5 Uint8Array.fromHex ( string ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-uint8array.fromhex
+JS_DEFINE_NATIVE_FUNCTION(Uint8ArrayConstructorHelpers::from_hex)
+{
+    auto& realm = *vm.current_realm();
+
+    auto string_value = vm.argument(0);
+
+    // 1. If string is not a String, throw a TypeError exception.
+    if (!string_value.is_string())
+        return vm.throw_completion<TypeError>(ErrorType::NotAString, string_value);
+
+    // 2. Let result be FromHex(string).
+    auto result = JS::from_hex(vm, string_value.as_string().utf8_string_view());
+
+    // 3. If result.[[Error]] is not none, then
+    if (result.error.has_value()) {
+        // a. Throw result.[[Error]].
+        return result.error.release_value();
+    }
+
+    // 4. Let resultLength be the length of result.[[Bytes]].
+    auto result_length = result.bytes.size();
+
+    // 5. Let ta be ? AllocateTypedArray("Uint8Array", %Uint8Array%, "%Uint8Array.prototype%", resultLength).
+    auto typed_array = TRY(Uint8Array::create(realm, result_length));
+
+    // 6. Set the value at each index of ta.[[ViewedArrayBuffer]].[[ArrayBufferData]] to the value at the corresponding
+    //    index of result.[[Bytes]].
+    auto& array_buffer_data = typed_array->viewed_array_buffer()->buffer();
+
+    for (size_t index = 0; index < result_length; ++index)
+        array_buffer_data[index] = result.bytes[index];
+
+    // 7. Return ta.
+    return typed_array;
+}
+
+// 6 Uint8Array.prototype.setFromHex ( string ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-uint8array.prototype.setfromhex
+JS_DEFINE_NATIVE_FUNCTION(Uint8ArrayPrototypeHelpers::set_from_hex)
+{
+    auto& realm = *vm.current_realm();
+
+    auto string_value = vm.argument(0);
+
+    // 1. Let into be the this value.
+    // 2. Perform ? ValidateUint8Array(into).
+    auto into = TRY(validate_uint8_array(vm));
+
+    // 3. If string is not a String, throw a TypeError exception.
+    if (!string_value.is_string())
+        return vm.throw_completion<TypeError>(ErrorType::NotAString, string_value);
+
+    // 4. Let taRecord be MakeTypedArrayWithBufferWitnessRecord(into, seq-cst).
+    auto typed_array_record = make_typed_array_with_buffer_witness_record(into, ArrayBuffer::Order::SeqCst);
+
+    // 5. If IsTypedArrayOutOfBounds(taRecord) is true, throw a TypeError exception.
+    if (is_typed_array_out_of_bounds(typed_array_record))
+        return vm.throw_completion<TypeError>(ErrorType::BufferOutOfBounds, "TypedArray"sv);
+
+    // 6. Let byteLength be TypedArrayLength(taRecord).
+    auto byte_length = typed_array_length(typed_array_record);
+
+    // 7. Let result be FromHex(string, byteLength).
+    auto result = JS::from_hex(vm, string_value.as_string().utf8_string_view(), byte_length);
+
+    // 8. Let bytes be result.[[Bytes]].
+    auto bytes = move(result.bytes);
+
+    // 9. Let written be the length of bytes.
+    auto written = bytes.size();
+
+    // 10. NOTE: FromHex does not invoke any user code, so the ArrayBuffer backing into cannot have been detached or shrunk.
+    // 11. Assert: written ≤ byteLength.
+    VERIFY(written <= byte_length);
+
+    // 12. Perform SetUint8ArrayBytes(into, bytes).
+    set_uint8_array_bytes(into, bytes);
+
+    // 13. If result.[[Error]] is not none, then
+    if (result.error.has_value()) {
+        // a. Throw result.[[Error]].
+        return result.error.release_value();
+    }
+
+    // 14. Let resultObject be OrdinaryObjectCreate(%Object.prototype%).
+    auto result_object = Object::create(realm, realm.intrinsics().object_prototype());
+
+    // 15. Perform ! CreateDataPropertyOrThrow(resultObject, "read", 𝔽(result.[[Read]])).
+    MUST(result_object->create_data_property(vm.names.read, Value { result.read }));
+
+    // 16. Perform ! CreateDataPropertyOrThrow(resultObject, "written", 𝔽(written)).
+    MUST(result_object->create_data_property(vm.names.written, Value { written }));
+
+    // 17. Return resultObject.
+    return result_object;
+}
+
+// 7 ValidateUint8Array ( ta ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-validateuint8array
+ThrowCompletionOr<NonnullGCPtr<TypedArrayBase>> validate_uint8_array(VM& vm)
+{
+    auto this_object = TRY(vm.this_value().to_object(vm));
+
+    // 1. Perform ? RequireInternalSlot(ta, [[TypedArrayName]]).
+    if (!this_object->is_typed_array())
+        return vm.throw_completion<TypeError>(ErrorType::NotAnObjectOfType, "Uint8Array");
+
+    auto& typed_array = static_cast<TypedArrayBase&>(*this_object.ptr());
+
+    // 2. If ta.[[TypedArrayName]] is not "Uint8Array", throw a TypeError exception.
+    if (typed_array.kind() != TypedArrayBase::Kind::Uint8Array)
+        return vm.throw_completion<TypeError>(ErrorType::NotAnObjectOfType, "Uint8Array");
+
+    // 3. Return UNUSED.
+    return typed_array;
+}
+
+// 8 GetUint8ArrayBytes ( ta ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-getuint8arraybytes
+ThrowCompletionOr<ByteBuffer> get_uint8_array_bytes(VM& vm, TypedArrayBase const& typed_array)
+{
+    // 1. Let buffer be ta.[[ViewedArrayBuffer]].
+    // 2. Let taRecord be MakeTypedArrayWithBufferWitnessRecord(ta, SEQ-CST).
+    auto typed_array_record = make_typed_array_with_buffer_witness_record(typed_array, ArrayBuffer::Order::SeqCst);
+
+    // 3. If IsTypedArrayOutOfBounds(taRecord) is true, throw a TypeError exception.
+    if (is_typed_array_out_of_bounds(typed_array_record))
+        return vm.throw_completion<TypeError>(ErrorType::BufferOutOfBounds, "TypedArray"sv);
+
+    // 4. Let len be TypedArrayLength(taRecord).
+    auto length = typed_array_length(typed_array_record);
+
+    // 5. Let byteOffset be ta.[[ByteOffset]].
+    auto byte_offset = typed_array.byte_offset();
+
+    // 6. Let bytes be a new empty List.
+    ByteBuffer bytes;
+
+    // 7. Let index be 0.
+    // 8. Repeat, while index < len,
+    for (u32 index = 0; index < length; ++index) {
+        // a. Let byteIndex be byteOffset + index.
+        auto byte_index = byte_offset + index;
+
+        // b. Let byte be ℝ(GetValueFromBuffer(buffer, byteIndex, UINT8, true, UNORDERED)).
+        auto byte = typed_array.get_value_from_buffer(byte_index, ArrayBuffer::Order::Unordered);
+
+        // c. Append byte to bytes.
+        bytes.append(MUST(byte.to_u8(vm)));
+
+        // d. Set index to index + 1.
+    }
+
+    // 9. Return bytes.
+    return bytes;
+}
+
+// 9 SetUint8ArrayBytes ( into, bytes ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-writeuint8arraybytes
+void set_uint8_array_bytes(TypedArrayBase& into, ReadonlyBytes bytes)
+{
+    // 1. Let offset be into.[[ByteOffset]].
+    auto offset = into.byte_offset();
+
+    // 2. Let len be the length of bytes.
+    auto length = bytes.size();
+
+    // 3. Let index be 0.
+    // 4. Repeat, while index < len,
+    for (u32 index = 0; index < length; ++index) {
+        // a. Let byte be bytes[index].
+        auto byte = bytes[index];
+
+        // b. Let byteIndexInBuffer be index + offset.
+        auto byte_index_in_buffer = index + offset;
+
+        // c. Perform SetValueInBuffer(into.[[ViewedArrayBuffer]], byteIndexInBuffer, uint8, 𝔽(byte), true, unordered).
+        into.set_value_in_buffer(byte_index_in_buffer, Value { byte }, ArrayBuffer::Order::Unordered);
+
+        // d. Set index to index + 1.
+    }
+}
+
+// 10.1 SkipAsciiWhitespace ( string, index ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-skipasciiwhitespace
+static size_t skip_ascii_whitespace(StringView string, size_t index)
+{
+    // 1. Let length be the length of string.
+    auto length = string.length();
+
+    // 2. Repeat, while index < length,
+    while (index < length) {
+        // a. Let char be the code unit at index index of string.
+        auto ch = string[index];
+
+        // b. If char is neither 0x0009 (TAB), 0x000A (LF), 0x000C (FF), 0x000D (CR), nor 0x0020 (SPACE), then
+        if (ch != '\t' && ch != '\n' && ch != '\f' && ch != '\r' && ch != ' ') {
+            // i. Return index.
+            return index;
+        }
+
+        // c. Set index to index + 1.
+        ++index;
+    }
+
+    // 3. Return index.
+    return index;
+}
+
+// 10.2 DecodeBase64Chunk ( chunk [ , throwOnExtraBits ] ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-frombase64
+static ThrowCompletionOr<ByteBuffer> decode_base64_chunk(VM& vm, StringBuilder& chunk, Optional<bool> throw_on_extra_bits = {})
+{
+    // 1. Let chunkLength be the length of chunk.
+    auto chunk_length = chunk.length();
+
+    // 2. If chunkLength is 2, then
+    if (chunk_length == 2) {
+        // a. Set chunk to the string-concatenation of chunk and "AA".
+        chunk.append("AA"sv);
+    }
+    // 3. Else if chunkLength is 3, then
+    else if (chunk_length == 3) {
+        // a. Set chunk to the string-concatenation of chunk and "A".
+        chunk.append("A"sv);
+    }
+    // 4. Else,
+    else {
+        // a. Assert: chunkLength is 4.
+        VERIFY(chunk_length == 4);
+    }
+
+    // 5. Let byteSequence be the unique sequence of 3 bytes resulting from decoding chunk as base64 (such that applying
+    //    the base64 encoding specified in section 4 of RFC 4648 to byteSequence would produce chunk).
+    // 6. Let bytes be a List whose elements are the elements of byteSequence, in order.
+    auto bytes = MUST(decode_base64(chunk.string_view()));
+
+    // 7. If chunkLength is 2, then
+    if (chunk_length == 2) {
+        // a. Assert: throwOnExtraBits is present.
+        VERIFY(throw_on_extra_bits.has_value());
+
+        // b. If throwOnExtraBits is true and bytes[1] ≠ 0, then
+        if (*throw_on_extra_bits && bytes[1] != 0) {
+            // i. Throw a SyntaxError exception.
+            return vm.throw_completion<SyntaxError>("Extra bits found at end of chunk"sv);
+        }
+
+        // c. Return « bytes[0] ».
+        return MUST(bytes.slice(0, 1));
+    }
+
+    // 8. Else if chunkLength is 3, then
+    if (chunk_length == 3) {
+        // a. Assert: throwOnExtraBits is present.
+        VERIFY(throw_on_extra_bits.has_value());
+
+        // b. If throwOnExtraBits is true and bytes[2] ≠ 0, then
+        if (*throw_on_extra_bits && bytes[2] != 0) {
+            // i. Throw a SyntaxError exception.
+            return vm.throw_completion<SyntaxError>("Extra bits found at end of chunk"sv);
+        }
+
+        // c. Return « bytes[0], bytes[1] ».
+        return MUST(bytes.slice(0, 2));
+    }
+
+    // 9. Else,
+    //     a. Return bytes.
+    return bytes;
+}
+
+// 10.3 FromBase64 ( string, alphabet, lastChunkHandling [ , maxLength ] ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-frombase64
+DecodeResult from_base64(VM& vm, StringView string, Alphabet alphabet, LastChunkHandling last_chunk_handling, Optional<size_t> max_length)
+{
+    // FIXME: We can only use simdutf when the last-chunk-handling parameter is "loose". Upstream is planning to implement
+    //        the remaining options. When that is complete, we should be able to remove the slow implementation below. See:
+    //        https://github.com/simdutf/simdutf/issues/440
+    if (last_chunk_handling == LastChunkHandling::Loose) {
+        auto output = MUST(ByteBuffer::create_uninitialized(max_length.value_or_lazy_evaluated([&]() {
+            return AK::size_required_to_decode_base64(string);
+        })));
+
+        auto result = alphabet == Alphabet::Base64
+            ? AK::decode_base64_into(string, output)
+            : AK::decode_base64url_into(string, output);
+
+        if (result.is_error()) {
+            auto error = vm.throw_completion<SyntaxError>(result.error().error.string_literal());
+            return { .read = result.error().valid_input_bytes, .bytes = move(output), .error = move(error) };
+        }
+
+        return { .read = result.value(), .bytes = move(output), .error = {} };
+    }
+
+    // 1. If maxLength is not present, then
+    if (!max_length.has_value()) {
+        // a. Let maxLength be 2**53 - 1.
+        max_length = MAX_ARRAY_LIKE_INDEX;
+
+        // b. NOTE: Because the input is a string, the length of strings is limited to 2**53 - 1 characters, and the
+        //    output requires no more bytes than the input has characters, this limit can never be reached. However, it
+        //    is editorially convenient to use a finite value here.
+    }
+
+    // 2. NOTE: The order of validation and decoding in the algorithm below is not observable. Implementations are
+    //    encouraged to perform them in whatever order is most efficient, possibly interleaving validation with decoding,
+    //    as long as the behaviour is observably equivalent.
+
+    // 3. If maxLength is 0, then
+    if (max_length == 0uz) {
+        // a. Return the Record { [[Read]]: 0, [[Bytes]]: « », [[Error]]: none }.
+        return { .read = 0, .bytes = {}, .error = {} };
+    }
+
+    // 4. Let read be 0.
+    size_t read = 0;
+
+    // 5. Let bytes be « ».
+    ByteBuffer bytes;
+
+    // 6. Let chunk be the empty String.
+    StringBuilder chunk;
+
+    // 7. Let chunkLength be 0.
+    size_t chunk_length = 0;
+
+    // 8. Let index be 0.
+    size_t index = 0;
+
+    // 9. Let length be the length of string.
+    auto length = string.length();
+
+    // 10. Repeat,
+    while (true) {
+        // a. Set index to SkipAsciiWhitespace(string, index).
+        index = skip_ascii_whitespace(string, index);
+
+        // b. If index = length, then
+        if (index == length) {
+            // i. If chunkLength > 0, then
+            if (chunk_length > 0) {
+                // 1. If lastChunkHandling is "stop-before-partial", then
+                if (last_chunk_handling == LastChunkHandling::StopBeforePartial) {
+                    // a. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: none }.
+                    return { .read = read, .bytes = move(bytes), .error = {} };
+                }
+                // 2. Else if lastChunkHandling is "loose", then
+                else if (last_chunk_handling == LastChunkHandling::Loose) {
+                    VERIFY_NOT_REACHED();
+                }
+                // 3. Else,
+                else {
+                    // a. Assert: lastChunkHandling is "strict".
+                    VERIFY(last_chunk_handling == LastChunkHandling::Strict);
+
+                    // b. Let error be a new SyntaxError exception.
+                    auto error = vm.throw_completion<SyntaxError>("Invalid trailing data"sv);
+
+                    // c. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
+                    return { .read = read, .bytes = move(bytes), .error = move(error) };
+                }
+            }
+
+            // ii. Return the Record { [[Read]]: length, [[Bytes]]: bytes, [[Error]]: none }.
+            return { .read = length, .bytes = move(bytes), .error = {} };
+        }
+
+        // c. Let char be the substring of string from index to index + 1.
+        auto ch = string[index];
+
+        // d. Set index to index + 1.
+        ++index;
+
+        // e. If char is "=", then
+        if (ch == '=') {
+            // i. If chunkLength < 2, then
+            if (chunk_length < 2) {
+                // 1. Let error be a new SyntaxError exception.
+                auto error = vm.throw_completion<SyntaxError>("Unexpected padding character"sv);
+
+                // 2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
+                return { .read = read, .bytes = move(bytes), .error = move(error) };
+            }
+
+            // ii. Set index to SkipAsciiWhitespace(string, index).
+            index = skip_ascii_whitespace(string, index);
+
+            // iii. If chunkLength = 2, then
+            if (chunk_length == 2) {
+                // 1. If index = length, then
+                if (index == length) {
+                    // a. If lastChunkHandling is "stop-before-partial", then
+                    if (last_chunk_handling == LastChunkHandling::StopBeforePartial) {
+                        // i. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: none }.
+                        return { .read = read, .bytes = move(bytes), .error = {} };
+                    }
+
+                    // b. Let error be a new SyntaxError exception.
+                    auto error = vm.throw_completion<SyntaxError>("Incomplete number of padding characters"sv);
+
+                    // c. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
+                    return { .read = read, .bytes = move(bytes), .error = move(error) };
+                }
+
+                // 2. Set char to the substring of string from index to index + 1.
+                ch = string[index];
+
+                // 3. If char is "=", then
+                if (ch == '=') {
+                    // a. Set index to SkipAsciiWhitespace(string, index + 1).
+                    index = skip_ascii_whitespace(string, index + 1);
+                }
+            }
+
+            // iv. If index < length, then
+            if (index < length) {
+                // 1. Let error be a new SyntaxError exception.
+                auto error = vm.throw_completion<SyntaxError>("Unexpected padding character"sv);
+
+                // 2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
+                return { .read = read, .bytes = move(bytes), .error = move(error) };
+            }
+
+            // v. If lastChunkHandling is "strict", let throwOnExtraBits be true.
+            // vi. Else, let throwOnExtraBits be false.
+            auto throw_on_extra_bits = last_chunk_handling == LastChunkHandling::Strict;
+
+            // vii. Let decodeResult be Completion(DecodeBase64Chunk(chunk, throwOnExtraBits)).
+            auto decode_result = decode_base64_chunk(vm, chunk, throw_on_extra_bits);
+
+            // viii. If decodeResult is an abrupt completion, then
+            if (decode_result.is_error()) {
+                // 1. Let error be decodeResult.[[Value]].
+                auto error = decode_result.release_error();
+
+                // 2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
+                return { .read = read, .bytes = move(bytes), .error = move(error) };
+            }
+
+            // ix. Set bytes to the list-concatenation of bytes and ! decodeResult.
+            bytes.append(decode_result.release_value());
+
+            // x. Return the Record { [[Read]]: length, [[Bytes]]: bytes, [[Error]]: none }.
+            return { .read = length, .bytes = move(bytes), .error = {} };
+        }
+
+        // f. If alphabet is "base64url", then
+        if (alphabet == Alphabet::Base64URL) {
+            // i. If char is either "+" or "/", then
+            if (ch == '+' || ch == '/') {
+                // 1. Let error be a new SyntaxError exception.
+                auto error = vm.throw_completion<SyntaxError>(MUST(String::formatted("Invalid character '{}'"sv, ch)));
+
+                // 2. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
+                return { .read = read, .bytes = move(bytes), .error = move(error) };
+            }
+            // ii. Else if char is "-", then
+            else if (ch == '-') {
+                // 1. Set char to "+".
+                ch = '+';
+            }
+            // iii. Else if char is "_", then
+            else if (ch == '_') {
+                // 1. Set char to "/".
+                ch = '/';
+            }
+        }
+
+        // g. If the sole code unit of char is not an element of the standard base64 alphabet, then
+        static constexpr auto standard_base64_alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"sv;
+
+        if (!standard_base64_alphabet.contains(ch)) {
+            // i. Let error be a new SyntaxError exception.
+            auto error = vm.throw_completion<SyntaxError>(MUST(String::formatted("Invalid character '{}'"sv, ch)));
+
+            // ii. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
+            return { .read = read, .bytes = move(bytes), .error = move(error) };
+        }
+
+        // h. Let remaining be maxLength - the length of bytes.
+        auto remaining = *max_length - bytes.size();
+
+        // i. If remaining = 1 and chunkLength = 2, or if remaining = 2 and chunkLength = 3, then
+        if ((remaining == 1 && chunk_length == 2) || (remaining == 2 && chunk_length == 3)) {
+            // i. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: none }.
+            return { .read = read, .bytes = move(bytes), .error = {} };
+        }
+
+        // j. Set chunk to the string-concatenation of chunk and char.
+        chunk.append(ch);
+
+        // k. Set chunkLength to the length of chunk.
+        chunk_length = chunk.length();
+
+        // l. If chunkLength = 4, then
+        if (chunk_length == 4) {
+            // i. Set bytes to the list-concatenation of bytes and ! DecodeBase64Chunk(chunk).
+            bytes.append(MUST(decode_base64_chunk(vm, chunk)));
+
+            // ii. Set chunk to the empty String.
+            chunk.clear();
+
+            // iii. Set chunkLength to 0.
+            chunk_length = 0;
+
+            // iv. Set read to index.
+            read = index;
+
+            // v. If the length of bytes = maxLength, then
+            if (bytes.size() == max_length) {
+                // 1. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: none }.
+                return { .read = read, .bytes = move(bytes), .error = {} };
+            }
+        }
+    }
+}
+
+// 10.4 FromHex ( string [ , maxLength ] ), https://tc39.es/proposal-arraybuffer-base64/spec/#sec-fromhex
+DecodeResult from_hex(VM& vm, StringView string, Optional<size_t> max_length)
+{
+    // 1. If maxLength is not present, let maxLength be 2**53 - 1.
+    if (!max_length.has_value())
+        max_length = MAX_ARRAY_LIKE_INDEX;
+
+    // 2. Let length be the length of string.
+    auto length = string.length();
+
+    // 3. Let bytes be « ».
+    ByteBuffer bytes;
+
+    // 4. Let read be 0.
+    size_t read = 0;
+
+    // 5. If length modulo 2 is not 0, then
+    if (length % 2 != 0) {
+        // a. Let error be a new SyntaxError exception.
+        auto error = vm.throw_completion<SyntaxError>("Hex string must have an even length"sv);
+
+        // b. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
+        return { .read = read, .bytes = move(bytes), .error = move(error) };
+    }
+
+    // 6. Repeat, while read < length and the length of bytes < maxLength,
+    while (read < length && bytes.size() < *max_length) {
+        // a. Let hexits be the substring of string from read to read + 2.
+        auto hexits = string.substring_view(read, 2);
+
+        // d. Let byte be the integer value represented by hexits in base-16 notation, using the letters A-F and a-f
+        //    for digits with values 10 through 15.
+        // NOTE: We do this early so that we don't have to effectively parse hexits twice.
+        auto byte = AK::StringUtils::convert_to_uint_from_hex<u8>(hexits, AK::TrimWhitespace::No);
+
+        // b. If hexits contains any code units which are not in "0123456789abcdefABCDEF", then
+        if (!byte.has_value()) {
+            // i. Let error be a new SyntaxError exception.
+            auto error = vm.throw_completion<SyntaxError>("Hex string must only contain hex characters"sv);
+
+            // ii. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: error }.
+            return { .read = read, .bytes = move(bytes), .error = move(error) };
+        }
+
+        // c. Set read to read + 2.
+        read += 2;
+
+        // e. Append byte to bytes.
+        bytes.append(*byte);
+    }
+
+    // 7. Return the Record { [[Read]]: read, [[Bytes]]: bytes, [[Error]]: none }.
+    return { .read = read, .bytes = move(bytes), .error = {} };
+}
+
+}