LibWeb: Implement Headers.getSetCookie()

This is a normative change in the Fetch spec.
See: e4d3480

This also implements the changes to the 'sort and combine' algorithm,
which now treats "set-cookie" headers differently, and is exposed to JS
via the Headers' iterator.

Passes all 21 WPT tests :^)
http://wpt.live/fetch/api/headers/header-setcookie.any.html

Userland/Libraries/LibWeb/Fetch/Headers.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
  */
@@ -112,6 +112,26 @@ WebIDL::ExceptionOr<DeprecatedString> Headers::get(DeprecatedString const& name_
     return byte_buffer.has_value() ? DeprecatedString { byte_buffer->span() } : DeprecatedString {};
 }
 
+// https://fetch.spec.whatwg.org/#dom-headers-getsetcookie
+WebIDL::ExceptionOr<Vector<DeprecatedString>> Headers::get_set_cookie()
+{
+    // The getSetCookie() method steps are:
+    auto& vm = this->vm();
+    auto values = Vector<DeprecatedString> {};
+
+    // 1. If this’s header list does not contain `Set-Cookie`, then return « ».
+    if (!m_header_list->contains("Set-Cookie"sv.bytes()))
+        return values;
+
+    // 2. Return the values of all headers in this’s header list whose name is a byte-case-insensitive match for
+    //    `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() }));
+    }
+    return values;
+}
+
 // https://fetch.spec.whatwg.org/#dom-headers-has
 WebIDL::ExceptionOr<bool> Headers::has(DeprecatedString const& name_string)
 {

Userland/Libraries/LibWeb/Fetch/Headers.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
  */
@@ -50,6 +50,7 @@ public:
     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);
 

Userland/Libraries/LibWeb/Fetch/Headers.idl

@@ -7,6 +7,7 @@ interface Headers {
     undefined append(ByteString name, ByteString value);
     undefined delete(ByteString name);
     ByteString? get(ByteString name);
+    sequence<ByteString> getSetCookie();
     boolean has(ByteString name);
     undefined set(ByteString name, ByteString value);
     iterable<ByteString, ByteString>;

Userland/Libraries/LibWeb/Fetch/Infrastructure/HTTP/Headers.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>
  * Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
  *
@@ -257,22 +257,40 @@ ErrorOr<Vector<Header>> HeaderList::sort_and_combine() const
 
     // 2. Let names be the result of convert header names to a sorted-lowercase set with all the names of the headers in list.
     Vector<ReadonlyBytes> names_list;
+    TRY(names_list.try_ensure_capacity(size()));
     for (auto const& header : *this)
-        names_list.append(header.name);
+        names_list.unchecked_append(header.name);
     auto names = TRY(convert_header_names_to_a_sorted_lowercase_set(names_list));
 
     // 3. For each name of names:
     for (auto& name : names) {
-        // 1. Let value be the result of getting name from list.
-        // 2. Assert: value is not null.
-        auto value = TRY(get(name)).value();
+        // 1. If name is `set-cookie`, then:
+        if (name == "set-cookie"sv.bytes()) {
+            // 1. Let values be a list of all values of headers in list whose name is a byte-case-insensitive match for name, in order.
+            // 2. For each value of values:
+            for (auto const& [header_name, value] : *this) {
+                if (StringView { header_name }.equals_ignoring_case(name)) {
+                    // 1. Append (name, value) to headers.
+                    auto header = TRY(Header::from_string_pair(name, value));
+                    TRY(headers.try_append(move(header)));
+                }
+            }
+        }
+        // 2. Otherwise:
+        else {
+            // 1. Let value be the result of getting name from list.
+            auto value = TRY(get(name));
 
-        // 3. Append (name, value) to headers.
-        auto header = Infrastructure::Header {
-            .name = move(name),
-            .value = move(value),
-        };
-        headers.append(move(header));
+            // 2. Assert: value is not null.
+            VERIFY(value.has_value());
+
+            // 3. Append (name, value) to headers.
+            auto header = Header {
+                .name = move(name),
+                .value = value.release_value(),
+            };
+            TRY(headers.try_append(move(header)));
+        }
     }
 
     // 4. Return headers.