LibWeb: Implement <input type=file> behavior

This includes punting on the actual file picker implementation all the
way out to the PageClient. It's likely that some of the real details
should be implemented somewhere closer, like the BrowsingContext or the
Page, but we'll get there.

For now, this allows https://copy.sh/v86 to load the emulation of the
preselected images all the way until it hits a call to
URL.createObjectURL.

Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2022, Adam Hodgen <ant1441@gmail.com>
+ * Copyright (c) 2022, Andrew Kaster <akaster@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -13,11 +14,14 @@
 #include <LibWeb/HTML/EventNames.h>
 #include <LibWeb/HTML/HTMLFormElement.h>
 #include <LibWeb/HTML/HTMLInputElement.h>
+#include <LibWeb/HTML/Scripting/Environments.h>
 #include <LibWeb/Infra/CharacterTypes.h>
 #include <LibWeb/Layout/BlockContainer.h>
 #include <LibWeb/Layout/ButtonBox.h>
 #include <LibWeb/Layout/CheckBox.h>
 #include <LibWeb/Layout/RadioButton.h>
+#include <LibWeb/WebIDL/DOMException.h>
+#include <LibWeb/WebIDL/ExceptionOr.h>
 
 namespace Web::HTML {
 
@@ -44,6 +48,7 @@ void HTMLInputElement::visit_edges(Cell::Visitor& visitor)
     Base::visit_edges(visitor);
     visitor.visit(m_text_node.ptr());
     visitor.visit(m_legacy_pre_activation_behavior_checked_element_in_group.ptr());
+    visitor.visit(m_selected_files);
 }
 
 RefPtr<Layout::Node> HTMLInputElement::create_layout_node(NonnullRefPtr<CSS::StyleProperties> style)
@@ -51,7 +56,7 @@ RefPtr<Layout::Node> HTMLInputElement::create_layout_node(NonnullRefPtr<CSS::Sty
     if (type_state() == TypeAttributeState::Hidden)
         return nullptr;
 
-    if (type_state() == TypeAttributeState::SubmitButton || type_state() == TypeAttributeState::Button || type_state() == TypeAttributeState::ResetButton)
+    if (type_state() == TypeAttributeState::SubmitButton || type_state() == TypeAttributeState::Button || type_state() == TypeAttributeState::ResetButton || type_state() == TypeAttributeState::FileUpload)
         return adopt_ref(*new Layout::ButtonBox(document(), *this, move(style)));
 
     if (type_state() == TypeAttributeState::Checkbox)
@@ -91,6 +96,122 @@ void HTMLInputElement::set_checked_binding(bool checked)
     }
 }
 
+// https://html.spec.whatwg.org/multipage/input.html#dom-input-files
+JS::GCPtr<FileAPI::FileList> HTMLInputElement::files()
+{
+    // On getting, if the IDL attribute applies, it must return a FileList object that represents the current selected files.
+    //  The same object must be returned until the list of selected files changes.
+    // If the IDL attribute does not apply, then it must instead return null.
+    if (m_type != TypeAttributeState::FileUpload)
+        return nullptr;
+
+    if (!m_selected_files)
+        m_selected_files = FileAPI::FileList::create(realm(), {});
+    return m_selected_files;
+}
+
+// https://html.spec.whatwg.org/multipage/input.html#dom-input-files
+void HTMLInputElement::set_files(JS::GCPtr<FileAPI::FileList> files)
+{
+    // 1. If the IDL attribute does not apply or the given value is null, then return.
+    if (m_type != TypeAttributeState::FileUpload || files == nullptr)
+        return;
+
+    // 2. Replace the element's selected files with the given value.
+    m_selected_files = files;
+}
+
+// https://html.spec.whatwg.org/multipage/input.html#update-the-file-selection
+void HTMLInputElement::update_the_file_selection(JS::NonnullGCPtr<FileAPI::FileList> files)
+{
+    // 1. Queue an element task on the user interaction task source given element and the following steps:
+    queue_an_element_task(Task::Source::UserInteraction, [this, files]() mutable {
+        // 1. Update element's selected files so that it represents the user's selection.
+        this->set_files(files.ptr());
+
+        // 2. Fire an event named input at the input element, with the bubbles and composed attributes initialized to true.
+        auto input_event = DOM::Event::create(this->realm(), EventNames::input, { .bubbles = true, .composed = true });
+        this->dispatch_event(*input_event);
+
+        // 3. Fire an event named change at the input element, with the bubbles attribute initialized to true.
+        auto change_event = DOM::Event::create(this->realm(), EventNames::change, { .bubbles = true });
+        this->dispatch_event(*change_event);
+    });
+}
+
+// https://html.spec.whatwg.org/multipage/input.html#show-the-picker,-if-applicable
+static void show_the_picker_if_applicable(HTMLInputElement& element)
+{
+    // To show the picker, if applicable for an input element element:
+
+    // 1. If element's relevant global object does not have transient activation, then return.
+    auto& global_object = relevant_global_object(element);
+    if (!is<HTML::Window>(global_object) || !static_cast<HTML::Window&>(global_object).has_transient_activation())
+        return;
+
+    // FIXME: 2. If element is not mutable, then return.
+
+    // 3. If element's type attribute is in the File Upload state, then run these steps in parallel:
+    if (element.type_state() == HTMLInputElement::TypeAttributeState::FileUpload) {
+        // NOTE: These steps cannot be fully implemented here, and must be done in the PageClient when the response comes back from the PageHost
+
+        // 1. Optionally, wait until any prior execution of this algorithm has terminated.
+        // 2. Display a prompt to the user requesting that the user specify some files.
+        //    If the multiple attribute is not set on element, there must be no more than one file selected; otherwise, any number may be selected.
+        //    Files can be from the filesystem or created on the fly, e.g., a picture taken from a camera connected to the user's device.
+        // 3. Wait for the user to have made their selection.
+        // 4. If the user dismissed the prompt without changing their selection,
+        //    then queue an element task on the user interaction task source given element to fire an event named cancel at element,
+        //    with the bubbles attribute initialized to true.
+        // 5. Otherwise, update the file selection for element.
+
+        bool const multiple = element.has_attribute(HTML::AttributeNames::multiple);
+        auto weak_element = element.make_weak_ptr<DOM::EventTarget>();
+
+        // FIXME: Pass along accept attribute information https://html.spec.whatwg.org/multipage/input.html#attr-input-accept
+        //    The accept attribute may be specified to provide user agents with a hint of what file types will be accepted.
+        element.document().browsing_context()->top_level_browsing_context().page()->client().page_did_request_file_picker(weak_element, multiple);
+        return;
+    }
+
+    // FIXME: show "any relevant user interface" for other type attribute states "in the way [the user agent] normally would"
+
+    // 4. Otherwise, the user agent should show any relevant user interface for selecting a value for element,
+    //    in the way it normally would when the user interacts with the control. (If no such UI applies to element, then this step does nothing.)
+    //    If such a user interface is shown, it must respect the requirements stated in the relevant parts of the specification for how element
+    //    behaves given its type attribute state. (For example, various sections describe restrictions on the resulting value string.)
+    //    This step can have side effects, such as closing other pickers that were previously shown by this algorithm.
+    //    (If this closes a file selection picker, then per the above that will lead to firing either input and change events, or a cancel event.)
+}
+
+// https://html.spec.whatwg.org/multipage/input.html#dom-input-showpicker
+WebIDL::ExceptionOr<void> HTMLInputElement::show_picker()
+{
+    // The showPicker() method steps are:
+
+    // FIXME: 1. If this is not mutable, then throw an "InvalidStateError" DOMException.
+
+    // 2. If this's relevant settings object's origin is not same origin with this's relevant settings object's top-level origin,
+    // and this's type attribute is not in the File Upload state or Color state, then throw a "SecurityError" DOMException.
+    // NOTE: File and Color inputs are exempted from this check for historical reason: their input activation behavior also shows their pickers,
+    //       and has never been guarded by an origin check.
+    if (!relevant_settings_object(*this).origin().is_same_origin(relevant_settings_object(*this).top_level_origin)
+        && m_type != TypeAttributeState::FileUpload && m_type != TypeAttributeState::Color) {
+        return WebIDL::SecurityError::create(realm(), "Cross origin pickers are not allowed"sv);
+    }
+
+    // 3. If this's relevant global object does not have transient activation, then throw a "NotAllowedError" DOMException.
+    // FIXME: The global object we get here should probably not need casted to Window to check for transient activation
+    auto& global_object = relevant_global_object(*this);
+    if (!is<HTML::Window>(global_object) || !static_cast<HTML::Window&>(global_object).has_transient_activation()) {
+        return WebIDL::NotAllowedError::create(realm(), "Too long since user activation to show picker"sv);
+    }
+
+    // 4. Show the picker, if applicable, for this.
+    show_the_picker_if_applicable(*this);
+    return {};
+}
+
 // https://html.spec.whatwg.org/multipage/input.html#input-activation-behavior
 void HTMLInputElement::run_input_activation_behavior()
 {
@@ -121,6 +242,8 @@ void HTMLInputElement::run_input_activation_behavior()
 
         // 3. Submit the form owner from the element.
         form->submit_form(this);
+    } else if (type_state() == TypeAttributeState::FileUpload) {
+        show_the_picker_if_applicable(*this);
     } else {
         dispatch_event(*DOM::Event::create(realm(), EventNames::change));
     }
@@ -147,16 +270,34 @@ void HTMLInputElement::did_edit_text_node(Badge<BrowsingContext>)
     });
 }
 
-// https://html.spec.whatwg.org/multipage/input.html#dom-input-value-value
 String HTMLInputElement::value() const
 {
+    // https://html.spec.whatwg.org/multipage/input.html#dom-input-value-filename
+    if (type_state() == TypeAttributeState::FileUpload) {
+        // NOTE: This "fakepath" requirement is a sad accident of history. See the example in the File Upload state section for more information.
+        // NOTE: Since path components are not permitted in filenames in the list of selected files, the "\fakepath\" cannot be mistaken for a path component.
+        if (m_selected_files && m_selected_files->item(0))
+            return String::formatted("C:\\fakepath\\{}", m_selected_files->item(0)->name());
+        return "C:\\fakepath\\"sv;
+    }
+
+    // https://html.spec.whatwg.org/multipage/input.html#dom-input-value-value
     // Return the current value of the element.
     return m_value;
 }
 
-// https://html.spec.whatwg.org/multipage/input.html#dom-input-value-value
-void HTMLInputElement::set_value(String value)
+WebIDL::ExceptionOr<void> HTMLInputElement::set_value(String value)
 {
+    // https://html.spec.whatwg.org/multipage/input.html#dom-input-value-filename
+    if (type_state() == TypeAttributeState::FileUpload) {
+        // On setting, if the new value is the empty string, empty the list of selected files; otherwise, throw an "InvalidStateError" DOMException.
+        if (value != String::empty())
+            return WebIDL::InvalidStateError::create(realm(), "Setting value of input type file to non-empty string"sv);
+        m_selected_files = nullptr;
+        return {};
+    }
+
+    // https://html.spec.whatwg.org/multipage/input.html#dom-input-value-value
     // 1. Let oldValue be the element's value.
     auto old_value = move(m_value);
 
@@ -174,6 +315,8 @@ void HTMLInputElement::set_value(String value)
     //    text control, unselecting any selected text and resetting the selection direction to "none".
     if (m_text_node && (m_value != old_value))
         m_text_node->set_data(m_value);
+
+    return {};
 }
 
 void HTMLInputElement::create_shadow_tree_if_needed()
@@ -201,7 +344,7 @@ void HTMLInputElement::create_shadow_tree_if_needed()
     auto element = document().create_element(HTML::TagNames::div).release_value();
     element->set_attribute(HTML::AttributeNames::style, "white-space: pre; padding-top: 1px; padding-bottom: 1px; padding-left: 2px; padding-right: 2px");
     m_text_node = heap().allocate<DOM::Text>(realm(), document(), initial_value);
-    m_text_node->set_always_editable(true);
+    m_text_node->set_always_editable(m_type != TypeAttributeState::FileUpload);
     m_text_node->set_owner_input_element({}, *this);
     element->append_child(*m_text_node);
     shadow_root->append_child(move(element));