LibWeb/Fetch: Port JS interfaces to new String

Since BodyInit and Headers are tightly coupled to both Request and
Response, I chose to do all of them at once instead of introducing a
bunch of temporary conversion glue code.

13 files changed, 131 insertions, 130 deletions

diff --git a/Userland/Libraries/LibWeb/Bindings/FetchMethod.cpp b/Userland/Libraries/LibWeb/Bindings/FetchMethod.cpp
index 40a9b6de9b..ec57e8007e 100644
--- a/Userland/Libraries/LibWeb/Bindings/FetchMethod.cpp
+++ b/Userland/Libraries/LibWeb/Bindings/FetchMethod.cpp
@@ -24,7 +24,7 @@
 // ```idl
 // #import <Fetch/Request.idl>
 // #import <Fetch/Response.idl>
-// [Exposed=Window]
+// [Exposed=Window, UseNewAKString]
 // interface Dummy {
 //     static Promise<Response> fetch(RequestInfo input, optional RequestInit init = {});
 // };
@@ -55,7 +55,7 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
     if (vm.argument_count() < 1)
         return vm.throw_completion<JS::TypeError>(JS::ErrorType::BadArgCountOne, "fetch");
     auto arg0 = vm.argument(0);
-    auto arg0_to_variant = [&vm, &realm](JS::Value arg0) -> JS::ThrowCompletionOr<Variant<JS::Handle<Request>, DeprecatedString>> {
+    auto arg0_to_variant = [&vm, &realm](JS::Value arg0) -> JS::ThrowCompletionOr<Variant<JS::Handle<Request>, String>> {
         // These might be unused.
         (void)vm;
         (void)realm;
@@ -66,9 +66,9 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
                     return JS::make_handle(static_cast<Request&>(arg0_object));
             }
         }
-        return TRY(arg0.to_deprecated_string(vm));
+        return TRY(arg0.to_string(vm));
     };
-    Variant<JS::Handle<Request>, DeprecatedString> input = TRY(arg0_to_variant(arg0));
+    Variant<JS::Handle<Request>, String> input = TRY(arg0_to_variant(arg0));
     auto arg1 = vm.argument(1);
     if (!arg1.is_nullish() && !arg1.is_object())
         return vm.throw_completion<JS::TypeError>(JS::ErrorType::NotAnObjectOfType, "RequestInit");
@@ -77,7 +77,7 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
     if (arg1.is_object())
         body_property_value = TRY(arg1.as_object().get("body"));
     if (!body_property_value.is_undefined()) {
-        auto body_property_value_to_variant = [&vm, &realm](JS::Value body_property_value) -> JS::ThrowCompletionOr<Variant<JS::Handle<ReadableStream>, JS::Handle<Blob>, JS::Handle<JS::Object>, JS::Handle<URLSearchParams>, DeprecatedString>> {
+        auto body_property_value_to_variant = [&vm, &realm](JS::Value body_property_value) -> JS::ThrowCompletionOr<Variant<JS::Handle<ReadableStream>, JS::Handle<Blob>, JS::Handle<JS::Object>, JS::Handle<URLSearchParams>, String>> {
             // These might be unused.
             (void)vm;
             (void)realm;
@@ -94,9 +94,9 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
                 if (is<JS::ArrayBuffer>(body_property_value_object))
                     return JS::make_handle(body_property_value_object);
             }
-            return TRY(body_property_value.to_deprecated_string(vm));
+            return TRY(body_property_value.to_string(vm));
         };
-        Optional<Variant<JS::Handle<ReadableStream>, JS::Handle<Blob>, JS::Handle<JS::Object>, JS::Handle<URLSearchParams>, DeprecatedString>> body_value;
+        Optional<Variant<JS::Handle<ReadableStream>, JS::Handle<Blob>, JS::Handle<JS::Object>, JS::Handle<URLSearchParams>, String>> body_value;
         if (!body_property_value.is_nullish())
             body_value = TRY(body_property_value_to_variant(body_property_value));
         init.body = body_value;
@@ -161,7 +161,7 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
     if (arg1.is_object())
         headers_property_value = TRY(arg1.as_object().get("headers"));
     if (!headers_property_value.is_undefined()) {
-        auto headers_property_value_to_variant = [&vm, &realm](JS::Value headers_property_value) -> JS::ThrowCompletionOr<Variant<Vector<Vector<DeprecatedString>>, OrderedHashMap<DeprecatedString, DeprecatedString>>> {
+        auto headers_property_value_to_variant = [&vm, &realm](JS::Value headers_property_value) -> JS::ThrowCompletionOr<Variant<Vector<Vector<String>>, OrderedHashMap<String, String>>> {
             // These might be unused.
             (void)vm;
             (void)realm;
@@ -170,7 +170,7 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
                 auto* method = TRY(headers_property_value.get_method(vm, *vm.well_known_symbol_iterator()));
                 if (method) {
                     auto iterator1 = TRY(JS::get_iterator(vm, headers_property_value, JS::IteratorHint::Sync, method));
-                    Vector<Vector<DeprecatedString>> headers_value;
+                    Vector<Vector<String>> headers_value;
                     for (;;) {
                         auto* next1 = TRY(JS::iterator_step(vm, iterator1));
                         if (!next1)
@@ -182,17 +182,15 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
                         if (!iterator_method1)
                             return vm.throw_completion<JS::TypeError>(JS::ErrorType::NotIterable, TRY_OR_THROW_OOM(vm, next_item1.to_string_without_side_effects()));
                         auto iterator2 = TRY(JS::get_iterator(vm, next_item1, JS::IteratorHint::Sync, iterator_method1));
-                        Vector<DeprecatedString> sequence_item1;
+                        Vector<String> sequence_item1;
                         for (;;) {
                             auto* next2 = TRY(JS::iterator_step(vm, iterator2));
                             if (!next2)
                                 break;
                             auto next_item2 = TRY(JS::iterator_value(vm, *next2));
-                            DeprecatedString sequence_item2;
-                            if (next_item2.is_null() && false) {
-                                sequence_item2 = DeprecatedString::empty();
-                            } else {
-                                sequence_item2 = TRY(next_item2.to_deprecated_string(vm));
+                            String sequence_item2;
+                            if (!false || !next_item2.is_null()) {
+                                sequence_item2 = TRY(next_item2.to_string(vm));
                             }
                             sequence_item1.append(sequence_item2);
                         }
@@ -200,25 +198,21 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
                     }
                     return headers_value;
                 }
-                OrderedHashMap<DeprecatedString, DeprecatedString> record_union_type;
+                OrderedHashMap<String, String> record_union_type;
                 auto record_keys1 = TRY(headers_property_value_object.internal_own_property_keys());
                 for (auto& key1 : record_keys1) {
                     auto property_key1 = MUST(JS::PropertyKey::from_value(vm, key1));
                     auto descriptor1 = TRY(headers_property_value_object.internal_get_own_property(property_key1));
                     if (!descriptor1.has_value() || !descriptor1->enumerable.has_value() || !descriptor1->enumerable.value())
                         continue;
-                    DeprecatedString typed_key1;
-                    if (key1.is_null() && false) {
-                        typed_key1 = DeprecatedString::empty();
-                    } else {
-                        typed_key1 = TRY(key1.to_deprecated_string(vm));
+                    String typed_key1;
+                    if (!false || !key1.is_null()) {
+                        typed_key1 = TRY(key1.to_string(vm));
                     }
                     auto value1 = TRY(headers_property_value_object.get(property_key1));
-                    DeprecatedString typed_value1;
-                    if (value1.is_null() && false) {
-                        typed_value1 = DeprecatedString::empty();
-                    } else {
-                        typed_value1 = TRY(value1.to_deprecated_string(vm));
+                    String typed_value1;
+                    if (!false || !value1.is_null()) {
+                        typed_value1 = TRY(value1.to_string(vm));
                     }
                     record_union_type.set(typed_key1, typed_value1);
                 }
@@ -226,7 +220,7 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
             }
             return vm.throw_completion<JS::TypeError>("No union types matched"sv);
         };
-        Optional<Variant<Vector<Vector<DeprecatedString>>, OrderedHashMap<DeprecatedString, DeprecatedString>>> headers_value;
+        Optional<Variant<Vector<Vector<String>>, OrderedHashMap<String, String>>> headers_value;
         if (!headers_property_value.is_nullish())
             headers_value = TRY(headers_property_value_to_variant(headers_property_value));
         init.headers = headers_value;
@@ -235,14 +229,13 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
     if (arg1.is_object())
         integrity_property_value = TRY(arg1.as_object().get("integrity"));
     if (!integrity_property_value.is_undefined()) {
-        DeprecatedString integrity_value;
+        Optional<String> integrity_value;
         if (!integrity_property_value.is_undefined()) {
-            if (integrity_property_value.is_null() && false)
-                integrity_value = DeprecatedString::empty();
-            else
-                integrity_value = TRY(integrity_property_value.to_deprecated_string(vm));
+            if (!false || !integrity_property_value.is_null())
+                integrity_value = TRY(integrity_property_value.to_string(vm));
         }
-        init.integrity = integrity_value;
+        if (integrity_value.has_value())
+            init.integrity = integrity_value.release_value();
     }
     auto keepalive_property_value = JS::js_undefined();
     if (arg1.is_object())
@@ -257,14 +250,13 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
     if (arg1.is_object())
         method_property_value = TRY(arg1.as_object().get("method"));
     if (!method_property_value.is_undefined()) {
-        DeprecatedString method_value;
+        Optional<String> method_value;
         if (!method_property_value.is_undefined()) {
-            if (method_property_value.is_null() && false)
-                method_value = DeprecatedString::empty();
-            else
-                method_value = TRY(method_property_value.to_deprecated_string(vm));
+            if (!false || !method_property_value.is_null())
+                method_value = TRY(method_property_value.to_string(vm));
         }
-        init.method = method_value;
+        if (method_value.has_value())
+            init.method = method_value.release_value();
     }
     auto mode_property_value = JS::js_undefined();
     if (arg1.is_object())
@@ -308,14 +300,13 @@ JS::ThrowCompletionOr<JS::Value> fetch(JS::VM& vm)
     if (arg1.is_object())
         referrer_property_value = TRY(arg1.as_object().get("referrer"));
     if (!referrer_property_value.is_undefined()) {
-        DeprecatedString referrer_value;
+        Optional<String> referrer_value;
         if (!referrer_property_value.is_undefined()) {
-            if (referrer_property_value.is_null() && false)
-                referrer_value = DeprecatedString::empty();
-            else
-                referrer_value = TRY(referrer_property_value.to_deprecated_string(vm));
+            if (!false || !referrer_property_value.is_null())
+                referrer_value = TRY(referrer_property_value.to_string(vm));
         }
-        init.referrer = referrer_value;
+        if (referrer_value.has_value())
+            init.referrer = referrer_value.release_value();
     }
     auto referrer_policy_property_value = JS::js_undefined();
     if (arg1.is_object())
diff --git a/Userland/Libraries/LibWeb/Fetch/Body.cpp b/Userland/Libraries/LibWeb/Fetch/Body.cpp
index 3edc293bf0..8290cf954b 100644
--- a/Userland/Libraries/LibWeb/Fetch/Body.cpp
+++ b/Userland/Libraries/LibWeb/Fetch/Body.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022-2023, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -135,7 +135,7 @@ WebIDL::ExceptionOr<JS::Value> package_data(JS::Realm& realm, ByteBuffer bytes,
         return Infra::parse_json_bytes_to_javascript_value(vm, bytes);
     case PackageDataType::Text:
         // Return the result of running UTF-8 decode on bytes.
-        return JS::PrimitiveString::create(vm, DeprecatedString::copy(bytes));
+        return JS::PrimitiveString::create(vm, TRY_OR_THROW_OOM(vm, String::from_utf8(bytes)));
     default:
         VERIFY_NOT_REACHED();
     }
diff --git a/Userland/Libraries/LibWeb/Fetch/BodyInit.cpp b/Userland/Libraries/LibWeb/Fetch/BodyInit.cpp
index fa60c917bb..8b94dd38bc 100644
--- a/Userland/Libraries/LibWeb/Fetch/BodyInit.cpp
+++ b/Userland/Libraries/LibWeb/Fetch/BodyInit.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022-2023, Linus Groh <linusg@serenityos.org>
  * Copyright (c) 2022, Kenneth Myhra <kennethmyhra@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
@@ -96,10 +96,10 @@ WebIDL::ExceptionOr<Infrastructure::BodyWithType> extract_body(JS::Realm& realm,
             type = TRY_OR_THROW_OOM(vm, ByteBuffer::copy("application/x-www-form-urlencoded;charset=UTF-8"sv.bytes()));
             return {};
         },
-        [&](DeprecatedString const& scalar_value_string) -> WebIDL::ExceptionOr<void> {
-            // NOTE: AK::DeprecatedString is always UTF-8.
+        [&](String const& scalar_value_string) -> WebIDL::ExceptionOr<void> {
+            // NOTE: AK::String is always UTF-8.
             // Set source to the UTF-8 encoding of object.
-            source = scalar_value_string.to_byte_buffer();
+            source = TRY_OR_THROW_OOM(vm, ByteBuffer::copy(scalar_value_string.bytes()));
             // Set type to `text/plain;charset=UTF-8`.
             type = TRY_OR_THROW_OOM(vm, ByteBuffer::copy("text/plain;charset=UTF-8"sv.bytes()));
             return {};
diff --git a/Userland/Libraries/LibWeb/Fetch/BodyInit.h b/Userland/Libraries/LibWeb/Fetch/BodyInit.h
index 27d1648584..f22deb9c7b 100644
--- a/Userland/Libraries/LibWeb/Fetch/BodyInit.h
+++ b/Userland/Libraries/LibWeb/Fetch/BodyInit.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022-2023, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -14,9 +14,9 @@
 namespace Web::Fetch {
 
 // https://fetch.spec.whatwg.org/#bodyinit
-using BodyInit = Variant<JS::Handle<Streams::ReadableStream>, JS::Handle<FileAPI::Blob>, JS::Handle<JS::Object>, JS::Handle<URL::URLSearchParams>, DeprecatedString>;
+using BodyInit = Variant<JS::Handle<Streams::ReadableStream>, JS::Handle<FileAPI::Blob>, JS::Handle<JS::Object>, JS::Handle<URL::URLSearchParams>, String>;
 
-using BodyInitOrReadableBytes = Variant<JS::Handle<Streams::ReadableStream>, JS::Handle<FileAPI::Blob>, JS::Handle<JS::Object>, JS::Handle<URL::URLSearchParams>, DeprecatedString, ReadonlyBytes>;
+using BodyInitOrReadableBytes = Variant<JS::Handle<Streams::ReadableStream>, JS::Handle<FileAPI::Blob>, JS::Handle<JS::Object>, JS::Handle<URL::URLSearchParams>, String, ReadonlyBytes>;
 WebIDL::ExceptionOr<Infrastructure::BodyWithType> safely_extract_body(JS::Realm&, BodyInitOrReadableBytes const&);
 WebIDL::ExceptionOr<Infrastructure::BodyWithType> extract_body(JS::Realm&, BodyInitOrReadableBytes const&, bool keepalive = false);
 
diff --git a/Userland/Libraries/LibWeb/Fetch/Headers.cpp b/Userland/Libraries/LibWeb/Fetch/Headers.cpp
index 7aae86b938..04129a906c 100644
--- a/Userland/Libraries/LibWeb/Fetch/Headers.cpp
+++ b/Userland/Libraries/LibWeb/Fetch/Headers.cpp
@@ -52,7 +52,7 @@ void Headers::visit_edges(JS::Cell::Visitor& visitor)
 }
 
 // https://fetch.spec.whatwg.org/#dom-headers-append
-WebIDL::ExceptionOr<void> Headers::append(DeprecatedString const& name_string, DeprecatedString const& value_string)
+WebIDL::ExceptionOr<void> Headers::append(String const& name_string, String const& value_string)
 {
     auto& vm = this->vm();
 
@@ -66,15 +66,15 @@ WebIDL::ExceptionOr<void> Headers::append(DeprecatedString const& name_string, D
 }
 
 // https://fetch.spec.whatwg.org/#dom-headers-delete
-WebIDL::ExceptionOr<void> Headers::delete_(DeprecatedString const& name_string)
+WebIDL::ExceptionOr<void> Headers::delete_(String const& name_string)
 {
     // The delete(name) method steps are:
-    auto& realm = this->realm();
+    auto& vm = this->vm();
     auto name = name_string.bytes();
 
     // 1. If validating (name, ``) for headers returns false, then return.
     // NOTE: Passing a dummy header value ought not to have any negative repercussions.
-    auto header = TRY_OR_THROW_OOM(realm.vm(), Infrastructure::Header::from_string_pair(name, ""sv));
+    auto header = TRY_OR_THROW_OOM(vm, Infrastructure::Header::from_string_pair(name, ""sv));
     if (!TRY(validate(header)))
         return {};
 
@@ -97,9 +97,10 @@ WebIDL::ExceptionOr<void> Headers::delete_(DeprecatedString const& name_string)
 }
 
 // https://fetch.spec.whatwg.org/#dom-headers-get
-WebIDL::ExceptionOr<DeprecatedString> Headers::get(DeprecatedString const& name_string)
+WebIDL::ExceptionOr<Optional<String>> Headers::get(String const& name_string)
 {
     // The get(name) method steps are:
+    auto& vm = this->vm();
     auto name = name_string.bytes();
 
     // 1. If name is not a header name, then throw a TypeError.
@@ -107,17 +108,16 @@ WebIDL::ExceptionOr<DeprecatedString> Headers::get(DeprecatedString const& name_
         return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Invalid header name"sv };
 
     // 2. Return the result of getting name from this’s header list.
-    auto byte_buffer = TRY_OR_THROW_OOM(vm(), m_header_list->get(name));
-    // FIXME: Teach BindingsGenerator about Optional<DeprecatedString>
-    return byte_buffer.has_value() ? DeprecatedString { byte_buffer->span() } : DeprecatedString {};
+    auto byte_buffer = TRY_OR_THROW_OOM(vm, m_header_list->get(name));
+    return byte_buffer.has_value() ? TRY_OR_THROW_OOM(vm, String::from_utf8(*byte_buffer)) : Optional<String> {};
 }
 
 // https://fetch.spec.whatwg.org/#dom-headers-getsetcookie
-WebIDL::ExceptionOr<Vector<DeprecatedString>> Headers::get_set_cookie()
+WebIDL::ExceptionOr<Vector<String>> Headers::get_set_cookie()
 {
     // The getSetCookie() method steps are:
     auto& vm = this->vm();
-    auto values = Vector<DeprecatedString> {};
+    auto values = Vector<String> {};
 
     // 1. If this’s header list does not contain `Set-Cookie`, then return « ».
     if (!m_header_list->contains("Set-Cookie"sv.bytes()))
@@ -127,13 +127,13 @@ WebIDL::ExceptionOr<Vector<DeprecatedString>> Headers::get_set_cookie()
     //    `Set-Cookie`, in order.
     for (auto const& header : *m_header_list) {
         if (StringView { header.name }.equals_ignoring_case("Set-Cookie"sv))
-            TRY_OR_THROW_OOM(vm, values.try_append(DeprecatedString { header.value.bytes() }));
+            TRY_OR_THROW_OOM(vm, values.try_append(TRY_OR_THROW_OOM(vm, String::from_utf8(header.value))));
     }
     return values;
 }
 
 // https://fetch.spec.whatwg.org/#dom-headers-has
-WebIDL::ExceptionOr<bool> Headers::has(DeprecatedString const& name_string)
+WebIDL::ExceptionOr<bool> Headers::has(String const& name_string)
 {
     // The has(name) method steps are:
     auto name = name_string.bytes();
@@ -147,7 +147,7 @@ WebIDL::ExceptionOr<bool> Headers::has(DeprecatedString const& name_string)
 }
 
 // https://fetch.spec.whatwg.org/#dom-headers-set
-WebIDL::ExceptionOr<void> Headers::set(DeprecatedString const& name_string, DeprecatedString const& value_string)
+WebIDL::ExceptionOr<void> Headers::set(String const& name_string, String const& value_string)
 {
     auto& realm = this->realm();
     auto& vm = realm.vm();
@@ -185,12 +185,11 @@ WebIDL::ExceptionOr<void> Headers::set(DeprecatedString const& name_string, Depr
 // https://webidl.spec.whatwg.org/#es-iterable, Step 4
 JS::ThrowCompletionOr<void> Headers::for_each(ForEachCallback callback)
 {
+    auto& vm = this->vm();
+
     // The value pairs to iterate over are the return value of running sort and combine with this’s header list.
     auto value_pairs_to_iterate_over = [&]() -> JS::ThrowCompletionOr<Vector<Fetch::Infrastructure::Header>> {
-        auto headers_or_error = m_header_list->sort_and_combine();
-        if (headers_or_error.is_error())
-            return vm().throw_completion<JS::InternalError>(JS::ErrorType::NotEnoughMemoryToAllocate);
-        return headers_or_error.release_value();
+        return TRY_OR_THROW_OOM(vm, m_header_list->sort_and_combine());
     };
 
     // 1-5. Are done in the generated wrapper code.
@@ -207,7 +206,7 @@ JS::ThrowCompletionOr<void> Headers::for_each(ForEachCallback callback)
         auto const& pair = pairs[i];
 
         // 2. Invoke idlCallback with « pair’s value, pair’s key, idlObject » and with thisArg as the callback this value.
-        TRY(callback(StringView { pair.name }, StringView { pair.value }));
+        TRY(callback(TRY_OR_THROW_OOM(vm, String::from_utf8(pair.name)), TRY_OR_THROW_OOM(vm, String::from_utf8(pair.value))));
 
         // 3. Set pairs to idlObject’s current list of value pairs to iterate over. (It might have changed.)
         pairs = TRY(value_pairs_to_iterate_over());
@@ -309,20 +308,20 @@ WebIDL::ExceptionOr<void> Headers::fill(HeadersInit const& object)
     // To fill a Headers object headers with a given object object, run these steps:
     return object.visit(
         // 1. If object is a sequence, then for each header of object:
-        [&](Vector<Vector<DeprecatedString>> const& object) -> WebIDL::ExceptionOr<void> {
+        [&](Vector<Vector<String>> const& object) -> WebIDL::ExceptionOr<void> {
             for (auto const& entry : object) {
                 // 1. If header's size is not 2, then throw a TypeError.
                 if (entry.size() != 2)
                     return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Array must contain header key/value pair"sv };
 
                 // 2. Append (header[0], header[1]) to headers.
-                auto header = TRY_OR_THROW_OOM(vm, Infrastructure::Header::from_string_pair(entry[0], entry[1].bytes()));
+                auto header = TRY_OR_THROW_OOM(vm, Infrastructure::Header::from_string_pair(entry[0], entry[1]));
                 TRY(append(move(header)));
             }
             return {};
         },
         // 2. Otherwise, object is a record, then for each key → value of object, append (key, value) to headers.
-        [&](OrderedHashMap<DeprecatedString, DeprecatedString> const& object) -> WebIDL::ExceptionOr<void> {
+        [&](OrderedHashMap<String, String> const& object) -> WebIDL::ExceptionOr<void> {
             for (auto const& entry : object) {
                 auto header = TRY_OR_THROW_OOM(vm, Infrastructure::Header::from_string_pair(entry.key, entry.value));
                 TRY(append(move(header)));
diff --git a/Userland/Libraries/LibWeb/Fetch/Headers.h b/Userland/Libraries/LibWeb/Fetch/Headers.h
index c366b5fcbf..559fe0c3e8 100644
--- a/Userland/Libraries/LibWeb/Fetch/Headers.h
+++ b/Userland/Libraries/LibWeb/Fetch/Headers.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
-#include <AK/DeprecatedString.h>
 #include <AK/HashMap.h>
+#include <AK/String.h>
 #include <AK/Variant.h>
 #include <AK/Vector.h>
 #include <LibJS/Forward.h>
@@ -18,7 +18,7 @@
 
 namespace Web::Fetch {
 
-using HeadersInit = Variant<Vector<Vector<DeprecatedString>>, OrderedHashMap<DeprecatedString, DeprecatedString>>;
+using HeadersInit = Variant<Vector<Vector<String>>, OrderedHashMap<String, String>>;
 
 // https://fetch.spec.whatwg.org/#headers-class
 class Headers final : public Bindings::PlatformObject {
@@ -44,17 +44,17 @@ public:
     void set_guard(Guard guard) { m_guard = guard; }
 
     WebIDL::ExceptionOr<void> fill(HeadersInit const&);
+    WebIDL::ExceptionOr<void> append(Infrastructure::Header);
 
     // JS API functions
-    WebIDL::ExceptionOr<void> append(Infrastructure::Header);
-    WebIDL::ExceptionOr<void> append(DeprecatedString const& name, DeprecatedString const& value);
-    WebIDL::ExceptionOr<void> delete_(DeprecatedString const& name);
-    WebIDL::ExceptionOr<DeprecatedString> get(DeprecatedString const& name);
-    WebIDL::ExceptionOr<Vector<DeprecatedString>> get_set_cookie();
-    WebIDL::ExceptionOr<bool> has(DeprecatedString const& name);
-    WebIDL::ExceptionOr<void> set(DeprecatedString const& name, DeprecatedString const& value);
-
-    using ForEachCallback = Function<JS::ThrowCompletionOr<void>(DeprecatedString const&, DeprecatedString const&)>;
+    WebIDL::ExceptionOr<void> append(String const& name, String const& value);
+    WebIDL::ExceptionOr<void> delete_(String const& name);
+    WebIDL::ExceptionOr<Optional<String>> get(String const& name);
+    WebIDL::ExceptionOr<Vector<String>> get_set_cookie();
+    WebIDL::ExceptionOr<bool> has(String const& name);
+    WebIDL::ExceptionOr<void> set(String const& name, String const& value);
+
+    using ForEachCallback = Function<JS::ThrowCompletionOr<void>(String const&, String const&)>;
     JS::ThrowCompletionOr<void> for_each(ForEachCallback);
 
 private:
diff --git a/Userland/Libraries/LibWeb/Fetch/Headers.idl b/Userland/Libraries/LibWeb/Fetch/Headers.idl
index a495339dd5..43dedffcad 100644
--- a/Userland/Libraries/LibWeb/Fetch/Headers.idl
+++ b/Userland/Libraries/LibWeb/Fetch/Headers.idl
@@ -1,6 +1,6 @@
 typedef (sequence<sequence<ByteString>> or record<ByteString, ByteString>) HeadersInit;
 
-[Exposed=(Window,Worker)]
+[Exposed=(Window,Worker), UseNewAKString]
 interface Headers {
     constructor(optional HeadersInit init);
 
diff --git a/Userland/Libraries/LibWeb/Fetch/Request.cpp b/Userland/Libraries/LibWeb/Fetch/Request.cpp
index a746461137..81d9d218a9 100644
--- a/Userland/Libraries/LibWeb/Fetch/Request.cpp
+++ b/Userland/Libraries/LibWeb/Fetch/Request.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022-2023, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -119,9 +119,9 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<Request>> Request::construct_impl(JS::Realm
     DOM::AbortSignal const* input_signal = nullptr;
 
     // 5. If input is a string, then:
-    if (input.has<DeprecatedString>()) {
+    if (input.has<String>()) {
         // 1. Let parsedURL be the result of parsing input with baseURL.
-        auto parsed_url = URLParser::parse(input.get<DeprecatedString>(), &base_url);
+        auto parsed_url = URLParser::parse(input.get<String>(), &base_url);
 
         // 2. If parsedURL is failure, then throw a TypeError.
         if (!parsed_url.is_valid())
@@ -355,7 +355,7 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<Request>> Request::construct_impl(JS::Realm
 
     // 23. If init["integrity"] exists, then set request’s integrity metadata to it.
     if (init.integrity.has_value())
-        request->set_integrity_metadata(*init.integrity);
+        request->set_integrity_metadata(init.integrity->to_deprecated_string());
 
     // 24. If init["keepalive"] exists, then set request’s keepalive to it.
     if (init.keepalive.has_value())
@@ -373,7 +373,7 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<Request>> Request::construct_impl(JS::Realm
             return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Method must not be one of CONNECT, TRACE, or TRACK"sv };
 
         // 3. Normalize method.
-        method = TRY_OR_THROW_OOM(vm, Infrastructure::normalize_method(method.bytes()));
+        method = TRY_OR_THROW_OOM(vm, String::from_utf8(TRY_OR_THROW_OOM(vm, Infrastructure::normalize_method(method.bytes()))));
 
         // 4. Set request’s method to method.
         request->set_method(MUST(ByteBuffer::copy(method.bytes())));
@@ -424,7 +424,7 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<Request>> Request::construct_impl(JS::Realm
         // 4. If headers is a Headers object, then for each header of its header list, append header to this’s headers.
         if (auto* header_list = headers.get_pointer<JS::NonnullGCPtr<Infrastructure::HeaderList>>()) {
             for (auto& header : *header_list->ptr())
-                TRY(request_object->headers()->append(DeprecatedString::copy(header.name), DeprecatedString::copy(header.value)));
+                TRY(request_object->headers()->append(TRY_OR_THROW_OOM(vm, Infrastructure::Header::from_string_pair(header.name, header.value))));
         }
         // 5. Otherwise, fill this’s headers with headers.
         else {
@@ -457,7 +457,7 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<Request>> Request::construct_impl(JS::Realm
 
         // 4. If type is non-null and this’s headers’s header list does not contain `Content-Type`, then append (`Content-Type`, type) to this’s headers.
         if (type.has_value() && !request_object->headers()->header_list()->contains("Content-Type"sv.bytes()))
-            TRY(request_object->headers()->append("Content-Type"sv, DeprecatedString::copy(type->span())));
+            TRY(request_object->headers()->append(TRY_OR_THROW_OOM(vm, Infrastructure::Header::from_string_pair("Content-Type"sv, type->span()))));
     }
 
     // 37. Let inputOrInitBody be initBody if it is non-null; otherwise inputBody.
@@ -500,17 +500,21 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<Request>> Request::construct_impl(JS::Realm
 }
 
 // https://fetch.spec.whatwg.org/#dom-request-method
-DeprecatedString Request::method() const
+WebIDL::ExceptionOr<String> Request::method() const
 {
+    auto& vm = this->vm();
+
     // The method getter steps are to return this’s request’s method.
-    return DeprecatedString::copy(m_request->method());
+    return TRY_OR_THROW_OOM(vm, String::from_utf8(m_request->method()));
 }
 
 // https://fetch.spec.whatwg.org/#dom-request-url
-DeprecatedString Request::url() const
+WebIDL::ExceptionOr<String> Request::url() const
 {
+    auto& vm = this->vm();
+
     // The url getter steps are to return this’s request’s URL, serialized.
-    return m_request->url().serialize();
+    return TRY_OR_THROW_OOM(vm, String::from_deprecated_string(m_request->url().serialize()));
 }
 
 // https://fetch.spec.whatwg.org/#dom-request-headers
@@ -528,24 +532,25 @@ Bindings::RequestDestination Request::destination() const
 }
 
 // https://fetch.spec.whatwg.org/#dom-request-referrer
-DeprecatedString Request::referrer() const
+WebIDL::ExceptionOr<String> Request::referrer() const
 {
+    auto& vm = this->vm();
     return m_request->referrer().visit(
-        [&](Infrastructure::Request::Referrer const& referrer) {
+        [&](Infrastructure::Request::Referrer const& referrer) -> WebIDL::ExceptionOr<String> {
             switch (referrer) {
             // 1. If this’s request’s referrer is "no-referrer", then return the empty string.
             case Infrastructure::Request::Referrer::NoReferrer:
-                return DeprecatedString::empty();
+                return String {};
             // 2. If this’s request’s referrer is "client", then return "about:client".
             case Infrastructure::Request::Referrer::Client:
-                return DeprecatedString { "about:client"sv };
+                return TRY_OR_THROW_OOM(vm, "about:client"_string);
             default:
                 VERIFY_NOT_REACHED();
             }
         },
-        [&](AK::URL const& url) {
+        [&](AK::URL const& url) -> WebIDL::ExceptionOr<String> {
             // 3. Return this’s request’s referrer, serialized.
-            return url.serialize();
+            return TRY_OR_THROW_OOM(vm, String::from_deprecated_string(url.serialize()));
         });
 }
 
@@ -585,10 +590,12 @@ Bindings::RequestRedirect Request::redirect() const
 }
 
 // https://fetch.spec.whatwg.org/#dom-request-integrity
-DeprecatedString Request::integrity() const
+WebIDL::ExceptionOr<String> Request::integrity() const
 {
+    auto& vm = this->vm();
+
     // The integrity getter steps are to return this’s request’s integrity metadata.
-    return m_request->integrity_metadata();
+    return TRY_OR_THROW_OOM(vm, String::from_deprecated_string(m_request->integrity_metadata()));
 }
 
 // https://fetch.spec.whatwg.org/#dom-request-keepalive
diff --git a/Userland/Libraries/LibWeb/Fetch/Request.h b/Userland/Libraries/LibWeb/Fetch/Request.h
index 55c49611a4..ee9d0709e0 100644
--- a/Userland/Libraries/LibWeb/Fetch/Request.h
+++ b/Userland/Libraries/LibWeb/Fetch/Request.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022-2023, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -19,20 +19,20 @@
 namespace Web::Fetch {
 
 // https://fetch.spec.whatwg.org/#requestinfo
-using RequestInfo = Variant<JS::Handle<Request>, DeprecatedString>;
+using RequestInfo = Variant<JS::Handle<Request>, String>;
 
 // https://fetch.spec.whatwg.org/#requestinit
 struct RequestInit {
-    Optional<DeprecatedString> method;
+    Optional<String> method;
     Optional<HeadersInit> headers;
     Optional<Optional<BodyInit>> body;
-    Optional<DeprecatedString> referrer;
+    Optional<String> referrer;
     Optional<Bindings::ReferrerPolicy> referrer_policy;
     Optional<Bindings::RequestMode> mode;
     Optional<Bindings::RequestCredentials> credentials;
     Optional<Bindings::RequestCache> cache;
     Optional<Bindings::RequestRedirect> redirect;
-    Optional<DeprecatedString> integrity;
+    Optional<String> integrity;
     Optional<bool> keepalive;
     Optional<JS::GCPtr<DOM::AbortSignal>> signal;
     Optional<Bindings::RequestDuplex> duplex;
@@ -78,17 +78,17 @@ public:
     [[nodiscard]] JS::NonnullGCPtr<Infrastructure::Request> request() const { return m_request; }
 
     // JS API functions
-    [[nodiscard]] DeprecatedString method() const;
-    [[nodiscard]] DeprecatedString url() const;
+    [[nodiscard]] WebIDL::ExceptionOr<String> method() const;
+    [[nodiscard]] WebIDL::ExceptionOr<String> url() const;
     [[nodiscard]] JS::NonnullGCPtr<Headers> headers() const;
     [[nodiscard]] Bindings::RequestDestination destination() const;
-    [[nodiscard]] DeprecatedString referrer() const;
+    [[nodiscard]] WebIDL::ExceptionOr<String> referrer() const;
     [[nodiscard]] Bindings::ReferrerPolicy referrer_policy() const;
     [[nodiscard]] Bindings::RequestMode mode() const;
     [[nodiscard]] Bindings::RequestCredentials credentials() const;
     [[nodiscard]] Bindings::RequestCache cache() const;
     [[nodiscard]] Bindings::RequestRedirect redirect() const;
-    [[nodiscard]] DeprecatedString integrity() const;
+    [[nodiscard]] WebIDL::ExceptionOr<String> integrity() const;
     [[nodiscard]] bool keepalive() const;
     [[nodiscard]] bool is_reload_navigation() const;
     [[nodiscard]] bool is_history_navigation() const;
diff --git a/Userland/Libraries/LibWeb/Fetch/Request.idl b/Userland/Libraries/LibWeb/Fetch/Request.idl
index 232d18b394..aae8bc4299 100644
--- a/Userland/Libraries/LibWeb/Fetch/Request.idl
+++ b/Userland/Libraries/LibWeb/Fetch/Request.idl
@@ -6,7 +6,7 @@
 typedef (Request or USVString) RequestInfo;
 
 // https://fetch.spec.whatwg.org/#request
-[Exposed=(Window,Worker)]
+[Exposed=(Window,Worker), UseNewAKString]
 interface Request {
     constructor(RequestInfo input, optional RequestInit init = {});
 
diff --git a/Userland/Libraries/LibWeb/Fetch/Response.cpp b/Userland/Libraries/LibWeb/Fetch/Response.cpp
index 5be3f25759..54e7cf0e79 100644
--- a/Userland/Libraries/LibWeb/Fetch/Response.cpp
+++ b/Userland/Libraries/LibWeb/Fetch/Response.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022-2023, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -168,7 +168,7 @@ JS::NonnullGCPtr<Response> Response::error(JS::VM& vm)
 }
 
 // https://fetch.spec.whatwg.org/#dom-response-redirect
-WebIDL::ExceptionOr<JS::NonnullGCPtr<Response>> Response::redirect(JS::VM& vm, DeprecatedString const& url, u16 status)
+WebIDL::ExceptionOr<JS::NonnullGCPtr<Response>> Response::redirect(JS::VM& vm, String const& url, u16 status)
 {
     auto& realm = *vm.current_realm();
 
@@ -236,12 +236,14 @@ Bindings::ResponseType Response::type() const
 }
 
 // https://fetch.spec.whatwg.org/#dom-response-url
-DeprecatedString Response::url() const
+WebIDL::ExceptionOr<String> Response::url() const
 {
+    auto& vm = this->vm();
+
     // The url getter steps are to return the empty string if this’s response’s URL is null; otherwise this’s response’s URL, serialized with exclude fragment set to true.
     return !m_response->url().has_value()
-        ? DeprecatedString::empty()
-        : m_response->url()->serialize(AK::URL::ExcludeFragment::Yes);
+        ? String {}
+        : TRY_OR_THROW_OOM(vm, String::from_deprecated_string(m_response->url()->serialize(AK::URL::ExcludeFragment::Yes)));
 }
 
 // https://fetch.spec.whatwg.org/#dom-response-redirected
@@ -266,10 +268,12 @@ bool Response::ok() const
 }
 
 // https://fetch.spec.whatwg.org/#dom-response-statustext
-DeprecatedString Response::status_text() const
+WebIDL::ExceptionOr<String> Response::status_text() const
 {
+    auto& vm = this->vm();
+
     // The statusText getter steps are to return this’s response’s status message.
-    return DeprecatedString::copy(m_response->status_message());
+    return TRY_OR_THROW_OOM(vm, String::from_utf8(m_response->status_message()));
 }
 
 // https://fetch.spec.whatwg.org/#dom-response-headers
diff --git a/Userland/Libraries/LibWeb/Fetch/Response.h b/Userland/Libraries/LibWeb/Fetch/Response.h
index 516a680c6c..4ae12d7624 100644
--- a/Userland/Libraries/LibWeb/Fetch/Response.h
+++ b/Userland/Libraries/LibWeb/Fetch/Response.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022-2023, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -21,7 +21,7 @@ namespace Web::Fetch {
 // https://fetch.spec.whatwg.org/#responseinit
 struct ResponseInit {
     u16 status;
-    DeprecatedString status_text;
+    String status_text;
     Optional<HeadersInit> headers;
 };
 
@@ -46,14 +46,14 @@ public:
 
     // JS API functions
     [[nodiscard]] static JS::NonnullGCPtr<Response> error(JS::VM&);
-    [[nodiscard]] static WebIDL::ExceptionOr<JS::NonnullGCPtr<Response>> redirect(JS::VM&, DeprecatedString const& url, u16 status);
-    [[nodiscard]] static WebIDL::ExceptionOr<JS::NonnullGCPtr<Response>> json(JS::VM&, JS::Value data, ResponseInit const& init = {});
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<Response>> redirect(JS::VM&, String const& url, u16 status);
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<Response>> json(JS::VM&, JS::Value data, ResponseInit const& init = {});
     [[nodiscard]] Bindings::ResponseType type() const;
-    [[nodiscard]] DeprecatedString url() const;
+    [[nodiscard]] WebIDL::ExceptionOr<String> url() const;
     [[nodiscard]] bool redirected() const;
     [[nodiscard]] u16 status() const;
     [[nodiscard]] bool ok() const;
-    [[nodiscard]] DeprecatedString status_text() const;
+    [[nodiscard]] WebIDL::ExceptionOr<String> status_text() const;
     [[nodiscard]] JS::NonnullGCPtr<Headers> headers() const;
     [[nodiscard]] WebIDL::ExceptionOr<JS::NonnullGCPtr<Response>> clone() const;
 
diff --git a/Userland/Libraries/LibWeb/Fetch/Response.idl b/Userland/Libraries/LibWeb/Fetch/Response.idl
index 467f7f18bb..e73be7df90 100644
--- a/Userland/Libraries/LibWeb/Fetch/Response.idl
+++ b/Userland/Libraries/LibWeb/Fetch/Response.idl
@@ -2,7 +2,7 @@
 #import <Fetch/BodyInit.idl>
 #import <Fetch/Headers.idl>
 
-[Exposed=(Window,Worker)]
+[Exposed=(Window,Worker), UseNewAKString]
 interface Response {
     constructor(optional BodyInit? body = null, optional ResponseInit init = {});