servo/components/script/dom/htmlformelement.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

use dom::bindings::codegen::Bindings::BlobBinding::BlobMethods;
use dom::bindings::codegen::Bindings::DocumentBinding::DocumentMethods;
use dom::bindings::codegen::Bindings::EventBinding::EventMethods;
use dom::bindings::codegen::Bindings::HTMLButtonElementBinding::HTMLButtonElementMethods;
use dom::bindings::codegen::Bindings::HTMLFormControlsCollectionBinding::HTMLFormControlsCollectionMethods;
use dom::bindings::codegen::Bindings::HTMLFormElementBinding;
use dom::bindings::codegen::Bindings::HTMLFormElementBinding::HTMLFormElementMethods;
use dom::bindings::codegen::Bindings::HTMLInputElementBinding::HTMLInputElementMethods;
use dom::bindings::codegen::Bindings::HTMLTextAreaElementBinding::HTMLTextAreaElementMethods;
use dom::bindings::conversions::DerivedFrom;
use dom::bindings::inheritance::{Castable, ElementTypeId, HTMLElementTypeId, NodeTypeId};
use dom::bindings::js::{MutNullableJS, Root};
use dom::bindings::refcounted::Trusted;
use dom::bindings::reflector::DomObject;
use dom::bindings::str::DOMString;
use dom::blob::Blob;
use dom::document::Document;
use dom::element::Element;
use dom::eventtarget::EventTarget;
use dom::file::File;
use dom::globalscope::GlobalScope;
use dom::htmlbuttonelement::HTMLButtonElement;
use dom::htmlcollection::CollectionFilter;
use dom::htmldatalistelement::HTMLDataListElement;
use dom::htmlelement::HTMLElement;
use dom::htmlfieldsetelement::HTMLFieldSetElement;
use dom::htmlformcontrolscollection::HTMLFormControlsCollection;
use dom::htmlinputelement::HTMLInputElement;
use dom::htmlobjectelement::HTMLObjectElement;
use dom::htmloutputelement::HTMLOutputElement;
use dom::htmlselectelement::HTMLSelectElement;
use dom::htmltextareaelement::HTMLTextAreaElement;
use dom::node::{Node, document_from_node, window_from_node};
use dom::validitystate::ValidationFlags;
use dom::virtualmethods::VirtualMethods;
use encoding::EncodingRef;
use encoding::all::UTF_8;
use encoding::label::encoding_from_whatwg_label;
use html5ever_atoms::LocalName;
use hyper::header::{Charset, ContentDisposition, ContentType, DispositionParam, DispositionType};
use hyper::method::Method;
use msg::constellation_msg::PipelineId;
use rand::random;
use script_thread::{MainThreadScriptMsg, Runnable};
use script_traits::LoadData;
use std::borrow::ToOwned;
use std::cell::Cell;
use std::sync::mpsc::Sender;
use style::attr::AttrValue;
use style::str::split_html_space_chars;
use task_source::TaskSource;

#[derive(JSTraceable, PartialEq, Clone, Copy, HeapSizeOf)]
pub struct GenerationId(u32);

#[dom_struct]
pub struct HTMLFormElement {
    htmlelement: HTMLElement,
    marked_for_reset: Cell<bool>,
    elements: MutNullableJS<HTMLFormControlsCollection>,
    generation_id: Cell<GenerationId>
}

impl HTMLFormElement {
    fn new_inherited(local_name: LocalName,
                     prefix: Option<DOMString>,
                     document: &Document) -> HTMLFormElement {
        HTMLFormElement {
            htmlelement: HTMLElement::new_inherited(local_name, prefix, document),
            marked_for_reset: Cell::new(false),
            elements: Default::default(),
            generation_id: Cell::new(GenerationId(0))
        }
    }

    #[allow(unrooted_must_root)]
    pub fn new(local_name: LocalName,
               prefix: Option<DOMString>,
               document: &Document) -> Root<HTMLFormElement> {
        Node::reflect_node(box HTMLFormElement::new_inherited(local_name, prefix, document),
                           document,
                           HTMLFormElementBinding::Wrap)
    }

    pub fn generation_id(&self) -> GenerationId {
        self.generation_id.get()
    }
}

impl HTMLFormElementMethods for HTMLFormElement {
    // https://html.spec.whatwg.org/multipage/#dom-form-acceptcharset
    make_getter!(AcceptCharset, "accept-charset");

    // https://html.spec.whatwg.org/multipage/#dom-form-acceptcharset
    make_setter!(SetAcceptCharset, "accept-charset");

    // https://html.spec.whatwg.org/multipage/#dom-fs-action
    make_string_or_document_url_getter!(Action, "action");

    // https://html.spec.whatwg.org/multipage/#dom-fs-action
    make_setter!(SetAction, "action");

    // https://html.spec.whatwg.org/multipage/#dom-form-autocomplete
    make_enumerated_getter!(Autocomplete, "autocomplete", "on", "off");

    // https://html.spec.whatwg.org/multipage/#dom-form-autocomplete
    make_setter!(SetAutocomplete, "autocomplete");

    // https://html.spec.whatwg.org/multipage/#dom-fs-enctype
    make_enumerated_getter!(Enctype,
                            "enctype",
                            "application/x-www-form-urlencoded",
                            "text/plain" | "multipart/form-data");

    // https://html.spec.whatwg.org/multipage/#dom-fs-enctype
    make_setter!(SetEnctype, "enctype");

    // https://html.spec.whatwg.org/multipage/#dom-fs-encoding
    fn Encoding(&self) -> DOMString {
        self.Enctype()
    }

    // https://html.spec.whatwg.org/multipage/#dom-fs-encoding
    fn SetEncoding(&self, value: DOMString) {
        self.SetEnctype(value)
    }

    // https://html.spec.whatwg.org/multipage/#dom-fs-method
    make_enumerated_getter!(Method, "method", "get", "post" | "dialog");

    // https://html.spec.whatwg.org/multipage/#dom-fs-method
    make_setter!(SetMethod, "method");

    // https://html.spec.whatwg.org/multipage/#dom-form-name
    make_getter!(Name, "name");

    // https://html.spec.whatwg.org/multipage/#dom-form-name
    make_atomic_setter!(SetName, "name");

    // https://html.spec.whatwg.org/multipage/#dom-fs-novalidate
    make_bool_getter!(NoValidate, "novalidate");

    // https://html.spec.whatwg.org/multipage/#dom-fs-novalidate
    make_bool_setter!(SetNoValidate, "novalidate");

    // https://html.spec.whatwg.org/multipage/#dom-fs-target
    make_getter!(Target, "target");

    // https://html.spec.whatwg.org/multipage/#dom-fs-target
    make_setter!(SetTarget, "target");

    // https://html.spec.whatwg.org/multipage/#the-form-element:concept-form-submit
    fn Submit(&self) {
        self.submit(SubmittedFrom::FromForm, FormSubmitter::FormElement(self));
    }

    // https://html.spec.whatwg.org/multipage/#dom-form-reset
    fn Reset(&self) {
        self.reset(ResetFrom::FromForm);
    }

    // https://html.spec.whatwg.org/multipage/#dom-form-elements
    fn Elements(&self) -> Root<HTMLFormControlsCollection> {
        if let Some(elements) = self.elements.get() {
            return elements;
        }

        #[derive(JSTraceable, HeapSizeOf)]
        struct ElementsFilter {
            form: Root<HTMLFormElement>
        }
        impl CollectionFilter for ElementsFilter {
            fn filter<'a>(&self, elem: &'a Element, _root: &'a Node) -> bool {
                let form_owner = match elem.upcast::<Node>().type_id() {
                    NodeTypeId::Element(ElementTypeId::HTMLElement(t)) => {
                        match t {
                            HTMLElementTypeId::HTMLButtonElement => {
                                elem.downcast::<HTMLButtonElement>().unwrap().form_owner()
                            }
                            HTMLElementTypeId::HTMLFieldSetElement => {
                                elem.downcast::<HTMLFieldSetElement>().unwrap().form_owner()
                            }
                            HTMLElementTypeId::HTMLInputElement => {
                                let input_elem = elem.downcast::<HTMLInputElement>().unwrap();
                                if input_elem.type_() == atom!("image") {
                                    return false;
                                }
                                input_elem.form_owner()
                            }
                            HTMLElementTypeId::HTMLObjectElement => {
                                elem.downcast::<HTMLObjectElement>().unwrap().form_owner()
                            }
                            HTMLElementTypeId::HTMLOutputElement => {
                                elem.downcast::<HTMLOutputElement>().unwrap().form_owner()
                            }
                            HTMLElementTypeId::HTMLSelectElement => {
                                elem.downcast::<HTMLSelectElement>().unwrap().form_owner()
                            }
                            HTMLElementTypeId::HTMLTextAreaElement => {
                                elem.downcast::<HTMLTextAreaElement>().unwrap().form_owner()
                            }
                            _ => {
                                debug_assert!(!elem.downcast::<HTMLElement>().unwrap().is_listed_element() ||
                                              elem.local_name() == &local_name!("keygen"));
                                return false;
                            }
                        }
                    }
                    _ => return false,
                };

                match form_owner {
                    Some(form_owner) => form_owner == self.form,
                    None => false,
                }
            }
        }
        let filter = box ElementsFilter { form: Root::from_ref(self) };
        let window = window_from_node(self);
        let elements = HTMLFormControlsCollection::new(&window, self.upcast(), filter);
        self.elements.set(Some(&elements));
        elements
    }

    // https://html.spec.whatwg.org/multipage/#dom-form-length
    fn Length(&self) -> u32 {
        self.Elements().Length() as u32
    }

    // https://html.spec.whatwg.org/multipage/#dom-form-item
    fn IndexedGetter(&self, index: u32) -> Option<Root<Element>> {
        let elements = self.Elements();
        elements.IndexedGetter(index)
    }
}

#[derive(Copy, Clone, HeapSizeOf, PartialEq)]
pub enum SubmittedFrom {
    FromForm,
    NotFromForm
}

#[derive(Copy, Clone, HeapSizeOf)]
pub enum ResetFrom {
    FromForm,
    NotFromForm
}


impl HTMLFormElement {
    // https://html.spec.whatwg.org/multipage/#picking-an-encoding-for-the-form
    fn pick_encoding(&self) -> EncodingRef {
        // Step 2
        if self.upcast::<Element>().has_attribute(&local_name!("accept-charset")) {
            // Substep 1
            let input = self.upcast::<Element>().get_string_attribute(&local_name!("accept-charset"));

            // Substep 2, 3, 4
            let mut candidate_encodings = split_html_space_chars(&*input).filter_map(encoding_from_whatwg_label);

            // Substep 5, 6
            return candidate_encodings.next().unwrap_or(UTF_8);
        }

        // Step 1, 3
        document_from_node(self).encoding()
    }

    // https://html.spec.whatwg.org/multipage/#text/plain-encoding-algorithm
    fn encode_plaintext(&self, form_data: &mut Vec<FormDatum>) -> String {
        // Step 1
        let mut result = String::new();

        // Step 2
        let encoding = self.pick_encoding();

        // Step 3
        let charset = &*encoding.whatwg_name().unwrap();

        for entry in form_data.iter_mut() {
            // Step 4, 5
            let value = entry.replace_value(charset);

            // Step 6
            result.push_str(&*format!("{}={}\r\n", entry.name, value));
        }

        // Step 7
        result
    }

    /// [Form submission](https://html.spec.whatwg.org/multipage/#concept-form-submit)
    pub fn submit(&self, submit_method_flag: SubmittedFrom, submitter: FormSubmitter) {
        // Step 1
        let doc = document_from_node(self);
        let base = doc.base_url();
        // TODO: Handle browsing contexts (Step 2, 3)
        // Step 4
        if submit_method_flag == SubmittedFrom::NotFromForm &&
           !submitter.no_validate(self)
        {
            if self.interactive_validation().is_err() {
                // TODO: Implement event handlers on all form control elements
                self.upcast::<EventTarget>().fire_event(atom!("invalid"));
                return;
            }
        }
        // Step 5
        if submit_method_flag == SubmittedFrom::NotFromForm {
            let event = self.upcast::<EventTarget>()
                .fire_bubbling_cancelable_event(atom!("submit"));
            if event.DefaultPrevented() {
                return;
            }
        }
        // Step 6
        let mut form_data = self.get_form_dataset(Some(submitter));

        // Step 7
        let encoding = self.pick_encoding();

        // Step 8
        let mut action = submitter.action();

        // Step 9
        if action.is_empty() {
            action = DOMString::from(base.as_str());
        }
        // Step 10-11
        let action_components = match base.join(&action) {
            Ok(url) => url,
            Err(_) => return
        };
        // Step 12-15
        let scheme = action_components.scheme().to_owned();
        let enctype = submitter.enctype();
        let method = submitter.method();
        let _target = submitter.target();
        // TODO: Handle browsing contexts, partially loaded documents (step 16-17)

        let mut load_data = LoadData::new(action_components, doc.get_referrer_policy(), Some(doc.url()));

        // Step 18
        match (&*scheme, method) {
            (_, FormMethod::FormDialog) => {
                // TODO: Submit dialog
                // https://html.spec.whatwg.org/multipage/#submit-dialog
            }
            // https://html.spec.whatwg.org/multipage/#submit-mutate-action
            ("http", FormMethod::FormGet) | ("https", FormMethod::FormGet) | ("data", FormMethod::FormGet) => {
                load_data.headers.set(ContentType::form_url_encoded());
                self.mutate_action_url(&mut form_data, load_data, encoding);
            }
            // https://html.spec.whatwg.org/multipage/#submit-body
            ("http", FormMethod::FormPost) | ("https", FormMethod::FormPost) => {
                load_data.method = Method::Post;
                self.submit_entity_body(&mut form_data, load_data, enctype, encoding);
            }
            // https://html.spec.whatwg.org/multipage/#submit-get-action
            ("file", _) | ("about", _) | ("data", FormMethod::FormPost) |
            ("ftp", _) | ("javascript", _) => {
                self.plan_to_navigate(load_data);
            }
            ("mailto", FormMethod::FormPost) => {
                // TODO: Mail as body
                // https://html.spec.whatwg.org/multipage/#submit-mailto-body
            }
            ("mailto", FormMethod::FormGet) => {
                // TODO: Mail with headers
                // https://html.spec.whatwg.org/multipage/#submit-mailto-headers
            }
            _ => return,
        }
    }

    // https://html.spec.whatwg.org/multipage/#submit-mutate-action
    fn mutate_action_url(&self, form_data: &mut Vec<FormDatum>, mut load_data: LoadData, encoding: EncodingRef) {
        let charset = &*encoding.whatwg_name().unwrap();

        if let Some(ref mut url) = load_data.url.as_mut_url() {
            url.query_pairs_mut().clear()
               .encoding_override(Some(self.pick_encoding()))
               .extend_pairs(form_data.into_iter()
                                      .map(|field| (field.name.clone(), field.replace_value(charset))));
        }

        self.plan_to_navigate(load_data);
    }

    // https://html.spec.whatwg.org/multipage/#submit-body
    fn submit_entity_body(&self, form_data: &mut Vec<FormDatum>, mut load_data: LoadData,
                          enctype: FormEncType, encoding: EncodingRef) {
        let boundary = generate_boundary();
        let bytes = match enctype {
            FormEncType::UrlEncoded => {
                let charset = &*encoding.whatwg_name().unwrap();
                load_data.headers.set(ContentType::form_url_encoded());


                if let Some(ref mut url) = load_data.url.as_mut_url() {
                    url.query_pairs_mut().clear()
                       .encoding_override(Some(self.pick_encoding()))
                       .extend_pairs(form_data.into_iter()
                       .map(|field| (field.name.clone(), field.replace_value(charset))));
                }

                load_data.url.query().unwrap_or("").to_string().into_bytes()
            }
            FormEncType::FormDataEncoded => {
                let mime = mime!(Multipart / FormData; Boundary =(&boundary));
                load_data.headers.set(ContentType(mime));
                encode_multipart_form_data(form_data, boundary, encoding)
            }
            FormEncType::TextPlainEncoded => {
                load_data.headers.set(ContentType(mime!(Text / Plain)));
                self.encode_plaintext(form_data).into_bytes()
            }
        };

        load_data.data = Some(bytes);
        self.plan_to_navigate(load_data);
    }

    /// [Planned navigation](https://html.spec.whatwg.org/multipage/#planned-navigation)
    fn plan_to_navigate(&self, load_data: LoadData) {
        let window = window_from_node(self);

        // Step 1
        // Each planned navigation runnable is tagged with a generation ID, and
        // before the runnable is handled, it first checks whether the HTMLFormElement's
        // generation ID is the same as its own generation ID.
        let GenerationId(prev_id) = self.generation_id.get();
        self.generation_id.set(GenerationId(prev_id + 1));

        // Step 2
        let nav = box PlannedNavigation {
            load_data: load_data,
            pipeline_id: window.upcast::<GlobalScope>().pipeline_id(),
            script_chan: window.main_thread_script_chan().clone(),
            generation_id: self.generation_id.get(),
            form: Trusted::new(self)
        };

        // Step 3
        window.dom_manipulation_task_source().queue(nav, window.upcast()).unwrap();
    }

    /// Interactively validate the constraints of form elements
    /// https://html.spec.whatwg.org/multipage/#interactively-validate-the-constraints
    fn interactive_validation(&self) -> Result<(), ()> {
        // Step 1-3
        let _unhandled_invalid_controls = match self.static_validation() {
            Ok(()) => return Ok(()),
            Err(err) => err
        };
        // TODO: Report the problems with the constraints of at least one of
        //       the elements given in unhandled invalid controls to the user
        // Step 4
        Err(())
    }

    /// Statitically validate the constraints of form elements
    /// https://html.spec.whatwg.org/multipage/#statically-validate-the-constraints
    fn static_validation(&self) -> Result<(), Vec<FormSubmittableElement>> {
        let node = self.upcast::<Node>();
        // FIXME(#3553): This is an incorrect way of getting controls owned by the
        //               form, refactor this when html5ever's form owner PR lands
        // Step 1-3
        let invalid_controls = node.traverse_preorder().filter_map(|field| {
            if let Some(el) = field.downcast::<Element>() {
                if el.disabled_state() {
                    None
                } else {
                    let validatable = match el.as_maybe_validatable() {
                        Some(v) => v,
                        None => return None
                    };
                    if !validatable.is_instance_validatable() {
                        None
                    } else if validatable.validate(ValidationFlags::empty()) {
                        None
                    } else {
                        Some(FormSubmittableElement::from_element(&el))
                    }
                }
            } else {
                None
            }
        }).collect::<Vec<FormSubmittableElement>>();
        // Step 4
        if invalid_controls.is_empty() { return Ok(()); }
        // Step 5-6
        let unhandled_invalid_controls = invalid_controls.into_iter().filter_map(|field| {
            let event = field.as_event_target()
                .fire_cancelable_event(atom!("invalid"));
            if !event.DefaultPrevented() { return Some(field); }
            None
        }).collect::<Vec<FormSubmittableElement>>();
        // Step 7
        Err(unhandled_invalid_controls)
    }

    /// https://html.spec.whatwg.org/multipage/#constructing-the-form-data-set
    /// Steps range from 1 to 3
    fn get_unclean_dataset(&self, submitter: Option<FormSubmitter>) -> Vec<FormDatum> {
        let node = self.upcast::<Node>();
        // FIXME(#3553): This is an incorrect way of getting controls owned
        //               by the form, but good enough until html5ever lands
        let mut data_set = Vec::new();
        for child in node.traverse_preorder() {
            // Step 3.1: The field element is disabled.
            match child.downcast::<Element>() {
                Some(el) if !el.disabled_state() => (),
                _ => continue,
            }

            // Step 3.1: The field element has a datalist element ancestor.
            if child.ancestors()
                    .any(|a| Root::downcast::<HTMLDataListElement>(a).is_some()) {
                continue;
            }
            if let NodeTypeId::Element(ElementTypeId::HTMLElement(element)) = child.type_id() {
                match element {
                    HTMLElementTypeId::HTMLInputElement => {
                        let input = child.downcast::<HTMLInputElement>().unwrap();

                        data_set.append(&mut input.form_datums(submitter));
                    }
                    HTMLElementTypeId::HTMLButtonElement => {
                        let button = child.downcast::<HTMLButtonElement>().unwrap();
                        if let Some(datum) = button.form_datum(submitter) {
                            data_set.push(datum);
                        }
                    }
                    HTMLElementTypeId::HTMLObjectElement => {
                        // Unimplemented
                        ()
                    }
                    HTMLElementTypeId::HTMLSelectElement => {
                        let select = child.downcast::<HTMLSelectElement>().unwrap();
                        select.push_form_data(&mut data_set);
                    }
                    HTMLElementTypeId::HTMLTextAreaElement => {
                        let textarea = child.downcast::<HTMLTextAreaElement>().unwrap();
                        let name = textarea.Name();
                        if !name.is_empty() {
                            data_set.push(FormDatum {
                                ty: textarea.Type(),
                                name: name,
                                value: FormDatumValue::String(textarea.Value())
                            });
                        }
                    }
                    _ => ()
                }
            }
        }
        data_set
        // TODO: Handle `dirnames` (needs directionality support)
        //       https://html.spec.whatwg.org/multipage/#the-directionality
    }

    /// https://html.spec.whatwg.org/multipage/#constructing-the-form-data-set
    pub fn get_form_dataset(&self, submitter: Option<FormSubmitter>) -> Vec<FormDatum> {
        fn clean_crlf(s: &str) -> DOMString {
            // Step 4
            let mut buf = "".to_owned();
            let mut prev = ' ';
            for ch in s.chars() {
                match ch {
                    '\n' if prev != '\r' => {
                        buf.push('\r');
                        buf.push('\n');
                    },
                    '\n' => {
                        buf.push('\n');
                    },
                    // This character isn't LF but is
                    // preceded by CR
                    _ if prev == '\r' => {
                        buf.push('\r');
                        buf.push('\n');
                        buf.push(ch);
                    },
                    _ => buf.push(ch)
                };
                prev = ch;
            }
            // In case the last character was CR
            if prev == '\r' {
                buf.push('\n');
            }
            DOMString::from(buf)
        }

        // Step 1-3
        let mut ret = self.get_unclean_dataset(submitter);
        // Step 4
        for datum in &mut ret {
            match &*datum.ty {
                "file" | "textarea" => (), // TODO
                _ => {
                    datum.name = clean_crlf(&datum.name);
                    datum.value = FormDatumValue::String(clean_crlf(match datum.value {
                        FormDatumValue::String(ref s) => s,
                        FormDatumValue::File(_) => unreachable!()
                    }));
                }
            }
        };
        // Step 5
        ret
    }

    pub fn reset(&self, _reset_method_flag: ResetFrom) {
        // https://html.spec.whatwg.org/multipage/#locked-for-reset
        if self.marked_for_reset.get() {
            return;
        } else {
            self.marked_for_reset.set(true);
        }

        let event = self.upcast::<EventTarget>()
            .fire_bubbling_cancelable_event(atom!("reset"));
        if event.DefaultPrevented() {
            return;
        }

        // TODO: This is an incorrect way of getting controls owned
        //       by the form, but good enough until html5ever lands
        for child in self.upcast::<Node>().traverse_preorder() {
            match child.type_id() {
                NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLInputElement)) => {
                    child.downcast::<HTMLInputElement>().unwrap().reset();
                }
                // TODO HTMLKeygenElement unimplemented
                //NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLKeygenElement)) => {
                //    // Unimplemented
                //    {}
                //}
                NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLSelectElement)) => {
                    child.downcast::<HTMLSelectElement>().unwrap().reset();
                }
                NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLTextAreaElement)) => {
                    child.downcast::<HTMLTextAreaElement>().unwrap().reset();
                }
                NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLOutputElement)) => {
                    // Unimplemented
                    {}
                }
                _ => {}
            }
        };
        self.marked_for_reset.set(false);
    }

}

#[derive(JSTraceable, HeapSizeOf, Clone)]
pub enum FormDatumValue {
    File(Root<File>),
    String(DOMString)
}

#[derive(HeapSizeOf, JSTraceable, Clone)]
pub struct FormDatum {
    pub ty: DOMString,
    pub name: DOMString,
    pub value: FormDatumValue
}

impl FormDatum {
    pub fn replace_value(&self, charset: &str) -> String {
        if self.name == "_charset_" && self.ty == "hidden" {
            return charset.to_string();
        }

        match self.value {
            FormDatumValue::File(ref f) => String::from(f.name().clone()),
            FormDatumValue::String(ref s) => String::from(s.clone()),
        }
    }
}

#[derive(Copy, Clone, HeapSizeOf)]
pub enum FormEncType {
    TextPlainEncoded,
    UrlEncoded,
    FormDataEncoded
}

#[derive(Copy, Clone, HeapSizeOf)]
pub enum FormMethod {
    FormGet,
    FormPost,
    FormDialog
}

#[derive(HeapSizeOf)]
pub enum FormSubmittableElement {
    ButtonElement(Root<HTMLButtonElement>),
    InputElement(Root<HTMLInputElement>),
    // TODO: HTMLKeygenElement unimplemented
    // KeygenElement(&'a HTMLKeygenElement),
    ObjectElement(Root<HTMLObjectElement>),
    SelectElement(Root<HTMLSelectElement>),
    TextAreaElement(Root<HTMLTextAreaElement>),
}

impl FormSubmittableElement {
    fn as_event_target(&self) -> &EventTarget {
        match *self {
            FormSubmittableElement::ButtonElement(ref button) => button.upcast(),
            FormSubmittableElement::InputElement(ref input) => input.upcast(),
            FormSubmittableElement::ObjectElement(ref object) => object.upcast(),
            FormSubmittableElement::SelectElement(ref select) => select.upcast(),
            FormSubmittableElement::TextAreaElement(ref textarea) => textarea.upcast()
        }
    }

    fn from_element(element: &Element) -> FormSubmittableElement {
        if let Some(input) = element.downcast::<HTMLInputElement>() {
            FormSubmittableElement::InputElement(Root::from_ref(&input))
        }
        else if let Some(input) = element.downcast::<HTMLButtonElement>() {
            FormSubmittableElement::ButtonElement(Root::from_ref(&input))
        }
        else if let Some(input) = element.downcast::<HTMLObjectElement>() {
            FormSubmittableElement::ObjectElement(Root::from_ref(&input))
        }
        else if let Some(input) = element.downcast::<HTMLSelectElement>() {
            FormSubmittableElement::SelectElement(Root::from_ref(&input))
        }
        else if let Some(input) = element.downcast::<HTMLTextAreaElement>() {
            FormSubmittableElement::TextAreaElement(Root::from_ref(&input))
        } else {
            unreachable!()
        }
    }
}

#[derive(Copy, Clone, HeapSizeOf)]
pub enum FormSubmitter<'a> {
    FormElement(&'a HTMLFormElement),
    InputElement(&'a HTMLInputElement),
    ButtonElement(&'a HTMLButtonElement)
    // TODO: image submit, etc etc
}

impl<'a> FormSubmitter<'a> {
    fn action(&self) -> DOMString {
        match *self {
            FormSubmitter::FormElement(form) => form.Action(),
            FormSubmitter::InputElement(input_element) => {
                input_element.get_form_attribute(&local_name!("formaction"),
                                                 |i| i.FormAction(),
                                                 |f| f.Action())
            },
            FormSubmitter::ButtonElement(button_element) => {
                button_element.get_form_attribute(&local_name!("formaction"),
                                                  |i| i.FormAction(),
                                                  |f| f.Action())
            }
        }
    }

    fn enctype(&self) -> FormEncType {
        let attr = match *self {
            FormSubmitter::FormElement(form) => form.Enctype(),
            FormSubmitter::InputElement(input_element) => {
                input_element.get_form_attribute(&local_name!("formenctype"),
                                                 |i| i.FormEnctype(),
                                                 |f| f.Enctype())
            },
            FormSubmitter::ButtonElement(button_element) => {
                button_element.get_form_attribute(&local_name!("formenctype"),
                                                  |i| i.FormEnctype(),
                                                  |f| f.Enctype())
            }
        };
        match &*attr {
            "multipart/form-data" => FormEncType::FormDataEncoded,
            "text/plain" => FormEncType::TextPlainEncoded,
            // https://html.spec.whatwg.org/multipage/#attr-fs-enctype
            // urlencoded is the default
            _ => FormEncType::UrlEncoded
        }
    }

    fn method(&self) -> FormMethod {
        let attr = match *self {
            FormSubmitter::FormElement(form) => form.Method(),
            FormSubmitter::InputElement(input_element) => {
                input_element.get_form_attribute(&local_name!("formmethod"),
                                                 |i| i.FormMethod(),
                                                 |f| f.Method())
            },
            FormSubmitter::ButtonElement(button_element) => {
                button_element.get_form_attribute(&local_name!("formmethod"),
                                                  |i| i.FormMethod(),
                                                  |f| f.Method())
            }
        };
        match &*attr {
            "dialog" => FormMethod::FormDialog,
            "post" => FormMethod::FormPost,
            _ => FormMethod::FormGet
        }
    }

    fn target(&self) -> DOMString {
        match *self {
            FormSubmitter::FormElement(form) => form.Target(),
            FormSubmitter::InputElement(input_element) => {
                input_element.get_form_attribute(&local_name!("formtarget"),
                                                 |i| i.FormTarget(),
                                                 |f| f.Target())
            },
            FormSubmitter::ButtonElement(button_element) => {
                button_element.get_form_attribute(&local_name!("formtarget"),
                                                  |i| i.FormTarget(),
                                                  |f| f.Target())
            }
        }
    }

    fn no_validate(&self, _form_owner: &HTMLFormElement) -> bool {
        match *self {
            FormSubmitter::FormElement(form) => form.NoValidate(),
            FormSubmitter::InputElement(input_element) => {
                input_element.get_form_boolean_attribute(&local_name!("formnovalidate"),
                                                 |i| i.FormNoValidate(),
                                                 |f| f.NoValidate())
            }
            FormSubmitter::ButtonElement(button_element) => {
                button_element.get_form_boolean_attribute(&local_name!("formnovalidate"),
                                                  |i| i.FormNoValidate(),
                                                  |f| f.NoValidate())
            }
        }
    }
}

pub trait FormControl: DerivedFrom<Element> + DomObject {
    // FIXME: This is wrong (https://github.com/servo/servo/issues/3553)
    //        but we need html5ever to do it correctly
    fn form_owner(&self) -> Option<Root<HTMLFormElement>> {
        // https://html.spec.whatwg.org/multipage/#reset-the-form-owner
        let elem = self.to_element();
        let owner = elem.get_string_attribute(&local_name!("form"));
        if !owner.is_empty() {
            let doc = document_from_node(elem);
            let owner = doc.GetElementById(owner);
            if let Some(ref o) = owner {
                let maybe_form = o.downcast::<HTMLFormElement>();
                if maybe_form.is_some() {
                    return maybe_form.map(Root::from_ref);
                }
            }
        }
        elem.upcast::<Node>().ancestors().filter_map(Root::downcast).next()
    }

    fn get_form_attribute<InputFn, OwnerFn>(&self,
                                            attr: &LocalName,
                                            input: InputFn,
                                            owner: OwnerFn)
                                            -> DOMString
        where InputFn: Fn(&Self) -> DOMString,
              OwnerFn: Fn(&HTMLFormElement) -> DOMString
    {
        if self.to_element().has_attribute(attr) {
            input(self)
        } else {
            self.form_owner().map_or(DOMString::new(), |t| owner(&t))
        }
    }

    fn get_form_boolean_attribute<InputFn, OwnerFn>(&self,
                                            attr: &LocalName,
                                            input: InputFn,
                                            owner: OwnerFn)
                                            -> bool
        where InputFn: Fn(&Self) -> bool,
              OwnerFn: Fn(&HTMLFormElement) -> bool
    {
        if self.to_element().has_attribute(attr) {
            input(self)
        } else {
            self.form_owner().map_or(false, |t| owner(&t))
        }
    }

    fn to_element(&self) -> &Element {
        self.upcast()
    }

    // XXXKiChjang: Implement these on inheritors
    // fn candidate_for_validation(&self) -> bool;
    // fn satisfies_constraints(&self) -> bool;
}

impl VirtualMethods for HTMLFormElement {
    fn super_type(&self) -> Option<&VirtualMethods> {
        Some(self.upcast::<HTMLElement>() as &VirtualMethods)
    }

    fn parse_plain_attribute(&self, name: &LocalName, value: DOMString) -> AttrValue {
        match name {
            &local_name!("name") => AttrValue::from_atomic(value.into()),
            _ => self.super_type().unwrap().parse_plain_attribute(name, value),
        }
    }
}

struct PlannedNavigation {
    load_data: LoadData,
    pipeline_id: PipelineId,
    script_chan: Sender<MainThreadScriptMsg>,
    generation_id: GenerationId,
    form: Trusted<HTMLFormElement>
}

impl Runnable for PlannedNavigation {
    fn name(&self) -> &'static str { "PlannedNavigation" }

    fn handler(self: Box<PlannedNavigation>) {
        if self.generation_id == self.form.root().generation_id.get() {
            let script_chan = self.script_chan.clone();
            script_chan.send(MainThreadScriptMsg::Navigate(self.pipeline_id, self.load_data, false)).unwrap();
        }
    }
}


// https://html.spec.whatwg.org/multipage/#multipart/form-data-encoding-algorithm
pub fn encode_multipart_form_data(form_data: &mut Vec<FormDatum>,
                                  boundary: String, encoding: EncodingRef) -> Vec<u8> {
    // Step 1
    let mut result = vec![];

    // Step 2
    let charset = &*encoding.whatwg_name().unwrap_or("UTF-8");

    // Step 3
    for entry in form_data.iter_mut() {
        // 3.1
        if entry.name == "_charset_" && entry.ty == "hidden" {
            entry.value = FormDatumValue::String(DOMString::from(charset.clone()));
        }
        // TODO: 3.2

        // Step 4
        // https://tools.ietf.org/html/rfc7578#section-4
        // NOTE(izgzhen): The encoding here expected by most servers seems different from
        // what spec says (that it should start with a '\r\n').
        let mut boundary_bytes = format!("--{}\r\n", boundary).into_bytes();
        result.append(&mut boundary_bytes);
        let mut content_disposition = ContentDisposition {
            disposition: DispositionType::Ext("form-data".to_owned()),
            parameters: vec![DispositionParam::Ext("name".to_owned(), String::from(entry.name.clone()))]
        };

        match entry.value {
            FormDatumValue::String(ref s) => {
                let mut bytes = format!("Content-Disposition: {}\r\n\r\n{}",
                                        content_disposition, s).into_bytes();
                result.append(&mut bytes);
            }
            FormDatumValue::File(ref f) => {
                content_disposition.parameters.push(
                    DispositionParam::Filename(Charset::Ext(String::from(charset.clone())),
                                               None,
                                               f.name().clone().into()));
                // https://tools.ietf.org/html/rfc7578#section-4.4
                let content_type = ContentType(f.upcast::<Blob>().Type()
                                                .parse().unwrap_or(mime!(Text / Plain)));
                let mut type_bytes = format!("Content-Disposition: {}\r\ncontent-type: {}\r\n\r\n",
                                             content_disposition,
                                             content_type).into_bytes();
                result.append(&mut type_bytes);

                let mut bytes = f.upcast::<Blob>().get_bytes().unwrap_or(vec![]);

                result.append(&mut bytes);
            }
        }
    }

    let mut boundary_bytes = format!("\r\n--{}--", boundary).into_bytes();
    result.append(&mut boundary_bytes);

    result
}

// https://tools.ietf.org/html/rfc7578#section-4.1
pub fn generate_boundary() -> String {
    let i1 = random::<u32>();
    let i2 = random::<u32>();

    format!("---------------------------{0}{1}", i1, i2)
}