htmlimageelement.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 app_units::{Au, AU_PER_PX};
use cssparser::{Parser, ParserInput};
use document_loader::{LoadType, LoadBlocker};
use dom::activation::Activatable;
use dom::attr::Attr;
use dom::bindings::cell::DomRefCell;
use dom::bindings::codegen::Bindings::DOMRectBinding::DOMRectBinding::DOMRectMethods;
use dom::bindings::codegen::Bindings::ElementBinding::ElementBinding::ElementMethods;
use dom::bindings::codegen::Bindings::HTMLImageElementBinding;
use dom::bindings::codegen::Bindings::HTMLImageElementBinding::HTMLImageElementMethods;
use dom::bindings::codegen::Bindings::MouseEventBinding::MouseEventMethods;
use dom::bindings::codegen::Bindings::NodeBinding::NodeBinding::NodeMethods;
use dom::bindings::codegen::Bindings::WindowBinding::WindowMethods;
use dom::bindings::error::Fallible;
use dom::bindings::inheritance::Castable;
use dom::bindings::refcounted::Trusted;
use dom::bindings::reflector::DomObject;
use dom::bindings::root::{DomRoot, LayoutDom, MutNullableDom};
use dom::bindings::str::DOMString;
use dom::document::Document;
use dom::element::{AttributeMutation, Element, RawLayoutElementHelpers};
use dom::element::{reflect_cross_origin_attribute, set_cross_origin_attribute};
use dom::event::{Event, EventBubbles, EventCancelable};
use dom::eventtarget::EventTarget;
use dom::htmlareaelement::HTMLAreaElement;
use dom::htmlelement::HTMLElement;
use dom::htmlformelement::{FormControl, HTMLFormElement};
use dom::htmlmapelement::HTMLMapElement;
use dom::htmlpictureelement::HTMLPictureElement;
use dom::htmlsourceelement::HTMLSourceElement;
use dom::mouseevent::MouseEvent;
use dom::node::{Node, NodeDamage, document_from_node, window_from_node};
use dom::progressevent::ProgressEvent;
use dom::values::UNSIGNED_LONG_MAX;
use dom::virtualmethods::VirtualMethods;
use dom::window::Window;
use dom_struct::dom_struct;
use euclid::Point2D;
use html5ever::{LocalName, Prefix};
use ipc_channel::ipc;
use ipc_channel::router::ROUTER;
use microtask::{Microtask, MicrotaskRunnable};
use mime::{Mime, TopLevel};
use net_traits::{FetchResponseListener, FetchMetadata, NetworkError, FetchResponseMsg};
use net_traits::image::base::{Image, ImageMetadata};
use net_traits::image_cache::{CanRequestImages, ImageCache, ImageOrMetadataAvailable};
use net_traits::image_cache::{ImageResponder, ImageResponse, ImageState, PendingImageId};
use net_traits::image_cache::UsePlaceholder;
use net_traits::request::RequestInit;
use network_listener::{NetworkListener, PreInvoke};
use num_traits::ToPrimitive;
use script_thread::ScriptThread;
use servo_url::ServoUrl;
use servo_url::origin::ImmutableOrigin;
use std::cell::{Cell, RefMut};
use std::char;
use std::collections::HashSet;
use std::default::Default;
use std::i32;
use std::sync::{Arc, Mutex};
use style::attr::{AttrValue, LengthOrPercentageOrAuto, parse_double, parse_length, parse_unsigned_integer};
use style::context::QuirksMode;
use style::media_queries::MediaList;
use style::parser::ParserContext;
use style::str::is_ascii_digit;
use style::stylesheets::{CssRuleType, Origin};
use style::values::specified::{AbsoluteLength, source_size_list::SourceSizeList};
use style::values::specified::length::{Length, NoCalcLength};
use style_traits::ParsingMode;
use task_source::{TaskSource, TaskSourceName};


enum ParseState {
    InDescriptor,
    InParens,
    AfterDescriptor,
}

pub struct SourceSet {
    image_sources: Vec<ImageSource>,
    source_size: SourceSizeList,
}

impl SourceSet {
    fn new() -> SourceSet {
        SourceSet {
            image_sources: Vec::new(),
            source_size: SourceSizeList::empty(),
        }
    }
}

#[derive(Clone, Debug, PartialEq)]
pub struct ImageSource {
    pub url: String,
    pub descriptor: Descriptor,
}

#[derive(Clone, Debug, PartialEq)]
pub struct Descriptor {
    pub wid: Option<u32>,
    pub den: Option<f64>,
}

#[derive(Clone, Copy, JSTraceable, MallocSizeOf)]
#[allow(dead_code)]
enum State {
    Unavailable,
    PartiallyAvailable,
    CompletelyAvailable,
    Broken,
}

#[derive(Clone, Copy, JSTraceable, MallocSizeOf)]
enum ImageRequestPhase {
    Pending,
    Current
}
#[derive(JSTraceable, MallocSizeOf)]
#[must_root]
struct ImageRequest {
    state: State,
    parsed_url: Option<ServoUrl>,
    source_url: Option<DOMString>,
    blocker: Option<LoadBlocker>,
    #[ignore_malloc_size_of = "Arc"]
    image: Option<Arc<Image>>,
    metadata: Option<ImageMetadata>,
    final_url: Option<ServoUrl>,
    current_pixel_density: Option<f64>,
}
#[dom_struct]
pub struct HTMLImageElement {
    htmlelement: HTMLElement,
    image_request: Cell<ImageRequestPhase>,
    current_request: DomRefCell<ImageRequest>,
    pending_request: DomRefCell<ImageRequest>,
    form_owner: MutNullableDom<HTMLFormElement>,
    generation: Cell<u32>,
    #[ignore_malloc_size_of = "SourceSet"]
    source_set: DomRefCell<SourceSet>,
    last_selected_source: DomRefCell<Option<DOMString>>,
}

impl HTMLImageElement {
    pub fn get_url(&self) -> Option<ServoUrl> {
        self.current_request.borrow().parsed_url.clone()
    }
}

/// The context required for asynchronously loading an external image.
struct ImageContext {
    /// Reference to the script thread image cache.
    image_cache: Arc<ImageCache>,
    /// Indicates whether the request failed, and why
    status: Result<(), NetworkError>,
    /// The cache ID for this request.
    id: PendingImageId,
}

impl FetchResponseListener for ImageContext {
    fn process_request_body(&mut self) {}
    fn process_request_eof(&mut self) {}

    fn process_response(&mut self, metadata: Result<FetchMetadata, NetworkError>) {
        self.image_cache.notify_pending_response(
            self.id,
            FetchResponseMsg::ProcessResponse(metadata.clone()));

        let metadata = metadata.ok().map(|meta| {
            match meta {
                FetchMetadata::Unfiltered(m) => m,
                FetchMetadata::Filtered { unsafe_, .. } => unsafe_
            }
        });

        let status_code = metadata.as_ref().and_then(|m| {
            m.status.as_ref().map(|&(code, _)| code)
        }).unwrap_or(0);

        self.status = match status_code {
            0 => Err(NetworkError::Internal("No http status code received".to_owned())),
            200...299 => Ok(()), // HTTP ok status codes
            _ => Err(NetworkError::Internal(format!("HTTP error code {}", status_code)))
        };
    }

    fn process_response_chunk(&mut self, payload: Vec<u8>) {
        if self.status.is_ok() {
            self.image_cache.notify_pending_response(
                self.id,
                FetchResponseMsg::ProcessResponseChunk(payload));
        }
    }

    fn process_response_eof(&mut self, response: Result<(), NetworkError>) {
        self.image_cache.notify_pending_response(
            self.id,
            FetchResponseMsg::ProcessResponseEOF(response));
    }
}

impl PreInvoke for ImageContext {}

impl HTMLImageElement {
    /// Update the current image with a valid URL.
    fn fetch_image(&self, img_url: &ServoUrl) {
        fn add_cache_listener_for_element(image_cache: Arc<ImageCache>,
                                          id: PendingImageId,
                                          elem: &HTMLImageElement) {
            let trusted_node = Trusted::new(elem);
            let (responder_sender, responder_receiver) = ipc::channel().unwrap();

            let window = window_from_node(elem);
            let task_source = window.networking_task_source();
            let task_canceller = window.task_canceller(TaskSourceName::Networking);
            let generation = elem.generation.get();
            ROUTER.add_route(responder_receiver.to_opaque(), Box::new(move |message| {
                debug!("Got image {:?}", message);
                // Return the image via a message to the script thread, which marks
                // the element as dirty and triggers a reflow.
                let element = trusted_node.clone();
                let image = message.to().unwrap();
                // FIXME(nox): Why are errors silenced here?
                let _ = task_source.queue_with_canceller(
                    task!(process_image_response: move || {
                        let element = element.root();
                        // Ignore any image response for a previous request that has been discarded.
                        if generation == element.generation.get() {
                            element.process_image_response(image);
                        }
                    }),
                    &task_canceller,
                );
            }));

            image_cache.add_listener(id, ImageResponder::new(responder_sender, id));
        }

        let window = window_from_node(self);
        let image_cache = window.image_cache();
        let response =
            image_cache.find_image_or_metadata(img_url.clone().into(),
                                               UsePlaceholder::Yes,
                                               CanRequestImages::Yes);
        match response {
            Ok(ImageOrMetadataAvailable::ImageAvailable(image, url)) => {
                self.process_image_response(ImageResponse::Loaded(image, url));
            }

            Ok(ImageOrMetadataAvailable::MetadataAvailable(m)) => {
                self.process_image_response(ImageResponse::MetadataLoaded(m));
            }

            Err(ImageState::Pending(id)) => {
                add_cache_listener_for_element(image_cache.clone(), id, self);
            }

            Err(ImageState::LoadError) => {
                self.process_image_response(ImageResponse::None);
            }

            Err(ImageState::NotRequested(id)) => {
                add_cache_listener_for_element(image_cache, id, self);
                self.fetch_request(img_url, id);
            }
        }
    }

    fn fetch_request(&self, img_url: &ServoUrl, id: PendingImageId) {
        let document = document_from_node(self);
        let window = window_from_node(self);

        let context = Arc::new(Mutex::new(ImageContext {
            image_cache: window.image_cache(),
            status: Ok(()),
            id: id,
        }));

        let (action_sender, action_receiver) = ipc::channel().unwrap();
        let listener = NetworkListener {
            context: context,
            task_source: window.networking_task_source(),
            canceller: Some(window.task_canceller(TaskSourceName::Networking)),
        };
        ROUTER.add_route(action_receiver.to_opaque(), Box::new(move |message| {
            listener.notify_fetch(message.to().unwrap());
        }));

        let request = RequestInit {
            url: img_url.clone(),
            origin: document.origin().immutable().clone(),
            pipeline_id: Some(document.global().pipeline_id()),
            .. RequestInit::default()
        };

        // This is a background load because the load blocker already fulfills the
        // purpose of delaying the document's load event.
        document.loader_mut().fetch_async_background(request, action_sender);
    }

    // Steps common to when an image has been loaded.
    fn handle_loaded_image(&self, image: Arc<Image>, url: ServoUrl) {
        self.current_request.borrow_mut().metadata = Some(ImageMetadata {
            height: image.height,
            width: image.width
        });
        self.current_request.borrow_mut().final_url = Some(url);
        self.current_request.borrow_mut().image = Some(image);
        self.current_request.borrow_mut().state = State::CompletelyAvailable;
        LoadBlocker::terminate(&mut self.current_request.borrow_mut().blocker);
        // Mark the node dirty
        self.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
    }

    /// Step 24 of https://html.spec.whatwg.org/multipage/#update-the-image-data
    fn process_image_response(&self, image: ImageResponse) {
        // TODO: Handle multipart/x-mixed-replace
        let (trigger_image_load, trigger_image_error) = match (image, self.image_request.get()) {
            (ImageResponse::Loaded(image, url), ImageRequestPhase::Current) => {
                self.handle_loaded_image(image, url);
                (true, false)
            },
            (ImageResponse::PlaceholderLoaded(image, url), ImageRequestPhase::Current) => {
                self.handle_loaded_image(image, url);
                (false, true)
            },
            (ImageResponse::Loaded(image, url), ImageRequestPhase::Pending) => {
                self.abort_request(State::Unavailable, ImageRequestPhase::Pending);
                self.image_request.set(ImageRequestPhase::Current);
                self.handle_loaded_image(image, url);
                (true, false)
            },
            (ImageResponse::PlaceholderLoaded(image, url), ImageRequestPhase::Pending) => {
                self.abort_request(State::Unavailable, ImageRequestPhase::Pending);
                self.image_request.set(ImageRequestPhase::Current);
                self.handle_loaded_image(image, url);
                (false, true)
            },
            (ImageResponse::MetadataLoaded(meta), ImageRequestPhase::Current) => {
                self.current_request.borrow_mut().state = State::PartiallyAvailable;
                self.current_request.borrow_mut().metadata = Some(meta);
                (false, false)
            },
            (ImageResponse::MetadataLoaded(_), ImageRequestPhase::Pending) => {
                self.pending_request.borrow_mut().state = State::PartiallyAvailable;
                (false, false)
            },
            (ImageResponse::None, ImageRequestPhase::Current) => {
                self.abort_request(State::Broken, ImageRequestPhase::Current);
                (false, true)
            },
            (ImageResponse::None, ImageRequestPhase::Pending) => {
                self.abort_request(State::Broken, ImageRequestPhase::Current);
                self.abort_request(State::Broken, ImageRequestPhase::Pending);
                self.image_request.set(ImageRequestPhase::Current);
                (false, true)
            },
        };

        // Fire image.onload and loadend
        if trigger_image_load {
            // TODO: https://html.spec.whatwg.org/multipage/#fire-a-progress-event-or-event
            self.upcast::<EventTarget>().fire_event(atom!("load"));
            self.upcast::<EventTarget>().fire_event(atom!("loadend"));
        }

        // Fire image.onerror
        if trigger_image_error {
            self.upcast::<EventTarget>().fire_event(atom!("error"));
            self.upcast::<EventTarget>().fire_event(atom!("loadend"));
        }

        // Trigger reflow
        let window = window_from_node(self);
        window.add_pending_reflow();
    }

    /// <https://html.spec.whatwg.org/multipage/#abort-the-image-request>
    fn abort_request(&self, state: State, request: ImageRequestPhase) {
        let mut request = match request {
            ImageRequestPhase::Current => self.current_request.borrow_mut(),
            ImageRequestPhase::Pending => self.pending_request.borrow_mut(),
        };
        LoadBlocker::terminate(&mut request.blocker);
        request.state = state;
        request.image = None;
        request.metadata = None;
    }

    /// <https://html.spec.whatwg.org/multipage/#update-the-source-set>
    fn update_source_set(&self) {
        // Step 1
        *self.source_set.borrow_mut() = SourceSet::new();

        // Step 2
        let elem = self.upcast::<Element>();
        let parent = elem.upcast::<Node>().GetParentElement();
        let nodes;
        let elements = match parent.as_ref() {
            Some(p) => {
                if p.is::<HTMLPictureElement>() {
                    nodes = p.upcast::<Node>().children();
                    nodes.filter_map(DomRoot::downcast::<Element>)
                        .map(|n| DomRoot::from_ref(&*n)).collect()
                } else {
                    vec![DomRoot::from_ref(&*elem)]
                }
            }
            None => {
                vec![DomRoot::from_ref(&*elem)]
            }
        };

        // Step 3
        let width = match elem.get_attribute(&ns!(), &local_name!("width")) {
            Some(x) => {
                match parse_length(&x.value()) {
                    LengthOrPercentageOrAuto::Length(x) =>{
                        let abs_length = AbsoluteLength::Px(x.to_f32_px());
                        Some(Length::NoCalc(NoCalcLength::Absolute(abs_length)))
                    },
                    _ => None
                }
            },
            None => None
        };

        // Step 4
        for element in &elements {
            // Step 4.1
            if *element == DomRoot::from_ref(&*elem) {
                let mut source_set = SourceSet::new();
                // Step 4.1.1
                if let Some(x) = element.get_attribute(&ns!(), &local_name!("srcset")) {
                    source_set.image_sources = parse_a_srcset_attribute(&x.value());
                }

                // Step 4.1.2
                if let Some(x) = element.get_attribute(&ns!(), &local_name!("sizes")) {
                    source_set.source_size =
                        parse_a_sizes_attribute(DOMString::from_string(x.value().to_string()));
                }

                // Step 4.1.3
                let src_attribute = element.get_string_attribute(&local_name!("src"));
                let is_src_empty = src_attribute.is_empty();
                let no_density_source_of_1 = source_set.image_sources.iter()
                                                .all(|source| source.descriptor.den != Some(1.));
                let no_width_descriptor = source_set.image_sources.iter()
                                            .all(|source| source.descriptor.wid.is_none());
                if !is_src_empty && no_density_source_of_1 && no_width_descriptor {
                    source_set.image_sources.push(ImageSource {
                        url: src_attribute.to_string(),
                        descriptor: Descriptor { wid: None, den: None }
                    })
                }

                // Step 4.1.4
                self.normalise_source_densities(&mut source_set, width);

                // Step 4.1.5
                *self.source_set.borrow_mut() = source_set;

                // Step 4.1.6
                return;
            }
            // Step 4.2
            if !element.is::<HTMLSourceElement>() {
                continue;
            }

            // Step 4.3 - 4.4
            let mut source_set = SourceSet::new();
            match element.get_attribute(&ns!(), &local_name!("srcset")) {
                Some(x) => {
                    source_set.image_sources = parse_a_srcset_attribute(&x.value());
                }
                _ => continue
            }

            // Step 4.5
            if source_set.image_sources.is_empty() {
                continue;
            }

            // Step 4.6
            if let Some(x) = element.get_attribute(&ns!(), &local_name!("media")) {
                if !self.matches_environment(x.value().to_string()) {
                    continue;
                }
            }

            // Step 4.7
            if let Some(x) = element.get_attribute(&ns!(), &local_name!("sizes")) {
                source_set.source_size =
                    parse_a_sizes_attribute(DOMString::from_string(x.value().to_string()));
            }

            // Step 4.8
            if let Some(x) = element.get_attribute(&ns!(), &local_name!("type")) {
                // TODO Handle unsupported mime type
                let mime = x.value().parse::<Mime>();
                match mime {
                    Ok(m) =>
                        match m {
                            Mime(TopLevel::Image, _, _) => (),
                            _ => continue
                        },
                    _ => continue
                }
            }

            // Step 4.9
            self.normalise_source_densities(&mut source_set, width);

            // Step 4.10
            *self.source_set.borrow_mut() = source_set;
            return;
        }
    }

    fn evaluate_source_size_list(&self, source_size_list: &mut SourceSizeList, _width: Option<Length>) -> Au {
        let document = document_from_node(self);
        let device = document.device();
        if !device.is_some() {
            return Au(1);
        }
        let quirks_mode = document.quirks_mode();
        //FIXME https://github.com/whatwg/html/issues/3832
        source_size_list.evaluate(&device.unwrap(), quirks_mode)
    }

    /// https://html.spec.whatwg.org/multipage/#matches-the-environment
    fn matches_environment(&self, media_query: String) -> bool {
        let document = document_from_node(self);
        let device = document.device();
        if !device.is_some() {
            return false;
        }
        let quirks_mode = document.quirks_mode();
        let document_url = &document.url();
        let context = ParserContext::new(
            Origin::Author,
            document_url,
            Some(CssRuleType::Style),
            ParsingMode::all(),
            quirks_mode,
            None,
        );
        let mut parserInput = ParserInput::new(&media_query);
        let mut parser = Parser::new(&mut parserInput);
        let media_list = MediaList::parse(&context, &mut parser);
        media_list.evaluate(&device.unwrap(), quirks_mode)
    }

    /// <https://html.spec.whatwg.org/multipage/#normalise-the-source-densities>
    fn normalise_source_densities(&self, source_set: &mut SourceSet, width: Option<Length>) {
        // Step 1
        let mut source_size = &mut source_set.source_size;

        // Find source_size_length for Step 2.2
        let source_size_length = self.evaluate_source_size_list(&mut source_size, width);

        // Step 2
        for imgsource in &mut source_set.image_sources {
            // Step 2.1
            if imgsource.descriptor.den.is_some() {
                continue;
            }
            // Step 2.2
            if imgsource.descriptor.wid.is_some() {
                let wid = imgsource.descriptor.wid.unwrap();
                imgsource.descriptor.den = Some(wid as f64 / source_size_length.to_f64_px());
            } else {
                //Step 2.3
                imgsource.descriptor.den = Some(1 as f64);
            }
        };
    }

    /// <https://html.spec.whatwg.org/multipage/#select-an-image-source>
    fn select_image_source(&self) -> Option<(DOMString, f32)> {
        // Step 1, 3
        self.update_source_set();
        let source_set = &*self.source_set.borrow_mut();
        let len = source_set.image_sources.len();

        // Step 2
        if len == 0 {
            return None;
        }

        // Step 4
        let mut repeat_indices = HashSet::new();
        for outer_index in 0..len {
            if repeat_indices.contains(&outer_index) {
                continue;
            }
            let imgsource = &source_set.image_sources[outer_index];
            let pixel_density = imgsource.descriptor.den.unwrap();
            for inner_index in (outer_index + 1)..len {
                let imgsource2 = &source_set.image_sources[inner_index];
                if pixel_density == imgsource2.descriptor.den.unwrap() {
                    repeat_indices.insert(inner_index);
                }
            }
        }

        let mut max = (0f64, 0);
        let img_sources = &mut vec![];
        for (index, image_source) in source_set.image_sources.iter().enumerate() {
            if repeat_indices.contains(&index) {
                continue;
            }
            let den = image_source.descriptor.den.unwrap();
            if max.0 < den {
                max = (den, img_sources.len());
            }
            img_sources.push(image_source);
        }

        // Step 5
        let mut best_candidate = max;
        let device = document_from_node(self).device();
        if let Some(device) = device {
            let device_den = device.device_pixel_ratio().get() as f64;
            for (index, image_source) in img_sources.iter().enumerate() {
                let current_den = image_source.descriptor.den.unwrap();
                if current_den < best_candidate.0 && current_den >= device_den {
                    best_candidate = (current_den, index);
                }
            }
        }
        let selected_source = img_sources.remove(best_candidate.1).clone();
        Some((DOMString::from_string(selected_source.url), selected_source.descriptor.den.unwrap() as f32))
    }

    fn init_image_request(&self,
                          request: &mut RefMut<ImageRequest>,
                          url: &ServoUrl,
                          src: &DOMString) {
        request.parsed_url = Some(url.clone());
        request.source_url = Some(src.clone());
        request.image = None;
        request.metadata = None;
        let document = document_from_node(self);
        LoadBlocker::terminate(&mut request.blocker);
        request.blocker = Some(LoadBlocker::new(&*document, LoadType::Image(url.clone())));
    }

    /// Step 12 of html.spec.whatwg.org/multipage/#update-the-image-data
    fn prepare_image_request(&self, url: &ServoUrl, src: &DOMString) {
        match self.image_request.get() {
            ImageRequestPhase::Pending => {
                if let Some(pending_url) = self.pending_request.borrow().parsed_url.clone() {
                    // Step 12.1
                    if pending_url == *url {
                        return
                    }
                }
            },
            ImageRequestPhase::Current => {
                let mut current_request = self.current_request.borrow_mut();
                let mut pending_request = self.pending_request.borrow_mut();
                // step 12.4, create a new "image_request"
                match (current_request.parsed_url.clone(), current_request.state) {
                    (Some(parsed_url), State::PartiallyAvailable) => {
                        // Step 12.2
                        if parsed_url == *url {
                            // 12.3 abort pending request
                            pending_request.image = None;
                            pending_request.parsed_url = None;
                            LoadBlocker::terminate(&mut pending_request.blocker);
                            // TODO: queue a task to restart animation, if restart-animation is set
                            return
                        }
                        self.image_request.set(ImageRequestPhase::Pending);
                        self.init_image_request(&mut pending_request, &url, &src);
                    },
                    (_, State::Broken) | (_, State::Unavailable) => {
                        // Step 12.5
                        self.init_image_request(&mut current_request, &url, &src);
                    },
                    (_, _) => {
                        // step 12.6
                        self.image_request.set(ImageRequestPhase::Pending);
                        self.init_image_request(&mut pending_request, &url, &src);
                    },
                }
            }
        }
        self.fetch_image(&url);
    }

    /// Step 8-12 of html.spec.whatwg.org/multipage/#update-the-image-data
    fn update_the_image_data_sync_steps(&self) {
        let document = document_from_node(self);
        let window = document.window();
        let task_source = window.dom_manipulation_task_source();
        let this = Trusted::new(self);
        let src = match self.select_image_source() {
            Some(src) => {
                // Step 8.
                // TODO: Handle pixel density.
                src.0
            },
            None => {
                // Step 9.
                // FIXME(nox): Why are errors silenced here?
                let _ = task_source.queue(
                    task!(image_null_source_error: move || {
                        let this = this.root();
                        {
                            let mut current_request =
                                this.current_request.borrow_mut();
                            current_request.source_url = None;
                            current_request.parsed_url = None;
                        }
                        if this.upcast::<Element>().has_attribute(&local_name!("src")) {
                            this.upcast::<EventTarget>().fire_event(atom!("error"));
                        }
                        // FIXME(nox): According to the spec, setting the current
                        // request to the broken state is done prior to queuing a
                        // task, why is this here?
                        this.abort_request(State::Broken, ImageRequestPhase::Current);
                        this.abort_request(State::Broken, ImageRequestPhase::Pending);
                    }),
                    window.upcast(),
                );
                return;
            },
        };
        // Step 10.
        let target = Trusted::new(self.upcast::<EventTarget>());
        // FIXME(nox): Why are errors silenced here?
        let _ = task_source.queue(
            task!(fire_progress_event: move || {
                let target = target.root();

                let event = ProgressEvent::new(
                    &target.global(),
                    atom!("loadstart"),
                    EventBubbles::DoesNotBubble,
                    EventCancelable::NotCancelable,
                    false,
                    0,
                    0,
                );
                event.upcast::<Event>().fire(&target);
            }),
            window.upcast(),
        );
        // Step 11
        let base_url = document.base_url();
        let parsed_url = base_url.join(&src);
        match parsed_url {
            Ok(url) => {
                    // Step 12
                self.prepare_image_request(&url, &src);
            },
            Err(_) => {
                // Step 11.1-11.5.
                let src = String::from(src);
                // FIXME(nox): Why are errors silenced here?
                let _ = task_source.queue(
                    task!(image_selected_source_error: move || {
                        let this = this.root();
                        {
                            let mut current_request =
                                this.current_request.borrow_mut();
                            current_request.source_url = Some(src.into());
                        }
                        this.upcast::<EventTarget>().fire_event(atom!("error"));
                        this.upcast::<EventTarget>().fire_event(atom!("loadend"));

                        // FIXME(nox): According to the spec, setting the current
                        // request to the broken state is done prior to queuing a
                        // task, why is this here?
                        this.abort_request(State::Broken, ImageRequestPhase::Current);
                        this.abort_request(State::Broken, ImageRequestPhase::Pending);
                    }),
                    window.upcast(),
                );
            }
        }
    }

    /// <https://html.spec.whatwg.org/multipage/#update-the-image-data>
    fn update_the_image_data(&self) {
        let document = document_from_node(self);
        let window = document.window();
        let elem = self.upcast::<Element>();
        let src = elem.get_string_attribute(&local_name!("src"));
        let base_url = document.base_url();

        // https://html.spec.whatwg.org/multipage/#reacting-to-dom-mutations
        // Always first set the current request to unavailable,
        // ensuring img.complete is false.
        {
            let mut current_request = self.current_request.borrow_mut();
            current_request.state = State::Unavailable;
        }

        if !document.is_active() {
            // Step 1 (if the document is inactive)
            // TODO: use GlobalScope::enqueue_microtask,
            // to queue micro task to come back to this algorithm
        }
        // Step 2 abort if user-agent does not supports images
        // NOTE: Servo only supports images, skipping this step

        // Step 3, 4
        let mut selected_source = None;
        let mut pixel_density = None;
        let src_set = elem.get_string_attribute(&local_name!("srcset"));
        let is_parent_picture = elem.upcast::<Node>().GetParentElement()
            .map_or(false, |p| p.is::<HTMLPictureElement>());
        if src_set.is_empty() && !is_parent_picture && !src.is_empty() {
            selected_source = Some(src.clone());
            pixel_density = Some(1 as f64);
        };

        // Step 5
        *self.last_selected_source.borrow_mut() = selected_source.clone();

        // Step 6, check the list of available images
        if !selected_source.as_ref().map_or(false, |source| source.is_empty()) {
            if let Ok(img_url) = base_url.join(&src) {
                let image_cache = window.image_cache();
                let response = image_cache.find_image_or_metadata(img_url.clone().into(),
                                                                  UsePlaceholder::No,
                                                                  CanRequestImages::No);
                if let Ok(ImageOrMetadataAvailable::ImageAvailable(image, url)) = response {
                    // Step 6.3
                    let metadata = ImageMetadata { height: image.height, width: image.width };
                    // Step 6.3.2 abort requests
                    self.abort_request(State::CompletelyAvailable, ImageRequestPhase::Current);
                    self.abort_request(State::CompletelyAvailable, ImageRequestPhase::Pending);
                    let mut current_request = self.current_request.borrow_mut();
                    current_request.final_url = Some(url);
                    current_request.image = Some(image.clone());
                    current_request.metadata = Some(metadata);
                    // Step 6.3.6
                    current_request.current_pixel_density = pixel_density;
                    let this = Trusted::new(self);
                    let src = String::from(src);
                    let _ = window.dom_manipulation_task_source().queue(
                        task!(image_load_event: move || {
                            let this = this.root();
                            {
                                let mut current_request =
                                    this.current_request.borrow_mut();
                                current_request.parsed_url = Some(img_url);
                                current_request.source_url = Some(src.into());
                            }
                            // TODO: restart animation, if set.
                            this.upcast::<EventTarget>().fire_event(atom!("load"));
                        }),
                        window.upcast(),
                    );
                    return;
                }
            }
        }
        // step 7, await a stable state.
        self.generation.set(self.generation.get() + 1);
        let task = ImageElementMicrotask::StableStateUpdateImageDataTask {
            elem: DomRoot::from_ref(self),
            generation: self.generation.get(),
        };
        ScriptThread::await_stable_state(Microtask::ImageElement(task));
    }

    fn new_inherited(local_name: LocalName, prefix: Option<Prefix>, document: &Document) -> HTMLImageElement {
        HTMLImageElement {
            htmlelement: HTMLElement::new_inherited(local_name, prefix, document),
            image_request: Cell::new(ImageRequestPhase::Current),
            current_request: DomRefCell::new(ImageRequest {
                state: State::Unavailable,
                parsed_url: None,
                source_url: None,
                image: None,
                metadata: None,
                blocker: None,
                final_url: None,
                current_pixel_density: None,
            }),
            pending_request: DomRefCell::new(ImageRequest {
                state: State::Unavailable,
                parsed_url: None,
                source_url: None,
                image: None,
                metadata: None,
                blocker: None,
                final_url: None,
                current_pixel_density: None,
            }),
            form_owner: Default::default(),
            generation: Default::default(),
            source_set: DomRefCell::new(SourceSet::new()),
            last_selected_source: DomRefCell::new(None),
        }
    }

    #[allow(unrooted_must_root)]
    pub fn new(local_name: LocalName,
               prefix: Option<Prefix>,
               document: &Document) -> DomRoot<HTMLImageElement> {
        Node::reflect_node(Box::new(HTMLImageElement::new_inherited(local_name, prefix, document)),
                           document,
                           HTMLImageElementBinding::Wrap)
    }

    pub fn Image(window: &Window,
                 width: Option<u32>,
                 height: Option<u32>) -> Fallible<DomRoot<HTMLImageElement>> {
        let document = window.Document();
        let image = HTMLImageElement::new(local_name!("img"), None, &document);
        if let Some(w) = width {
            image.SetWidth(w);
        }
        if let Some(h) = height {
            image.SetHeight(h);
        }

        Ok(image)
    }
    pub fn areas(&self) -> Option<Vec<DomRoot<HTMLAreaElement>>> {
        let elem = self.upcast::<Element>();
        let usemap_attr = elem.get_attribute(&ns!(), &local_name!("usemap"))?;

        let value = usemap_attr.value();

        if value.len() == 0 || !value.is_char_boundary(1) {
            return None
        }

        let (first, last) = value.split_at(1);

        if first != "#" || last.len() == 0 {
            return None
        }

        let useMapElements = document_from_node(self).upcast::<Node>()
                                .traverse_preorder()
                                .filter_map(DomRoot::downcast::<HTMLMapElement>)
                                .find(|n| n.upcast::<Element>().get_string_attribute(&LocalName::from("name")) == last);

        useMapElements.map(|mapElem| mapElem.get_area_elements())
    }

    pub fn get_origin(&self) -> Option<ImmutableOrigin> {
        match self.current_request.borrow_mut().final_url {
            Some(ref url) => Some(url.origin()),
            None => None
        }
    }

}

#[derive(JSTraceable, MallocSizeOf)]
pub enum ImageElementMicrotask {
    StableStateUpdateImageDataTask {
        elem: DomRoot<HTMLImageElement>,
        generation: u32,
    }
}

impl MicrotaskRunnable for ImageElementMicrotask {
    fn handler(&self) {
        match self {
            &ImageElementMicrotask::StableStateUpdateImageDataTask { ref elem, ref generation } => {
                // Step 7 of https://html.spec.whatwg.org/multipage/#update-the-image-data,
                // stop here if other instances of this algorithm have been scheduled
                if elem.generation.get() == *generation {
                    elem.update_the_image_data_sync_steps();
                }
            },
        }
    }
}

pub trait LayoutHTMLImageElementHelpers {
    #[allow(unsafe_code)]
    unsafe fn image(&self) -> Option<Arc<Image>>;

    #[allow(unsafe_code)]
    unsafe fn image_url(&self) -> Option<ServoUrl>;

    fn get_width(&self) -> LengthOrPercentageOrAuto;
    fn get_height(&self) -> LengthOrPercentageOrAuto;
}

impl LayoutHTMLImageElementHelpers for LayoutDom<HTMLImageElement> {
    #[allow(unsafe_code)]
    unsafe fn image(&self) -> Option<Arc<Image>> {
        (*self.unsafe_get()).current_request.borrow_for_layout().image.clone()
    }

    #[allow(unsafe_code)]
    unsafe fn image_url(&self) -> Option<ServoUrl> {
        (*self.unsafe_get()).current_request.borrow_for_layout().parsed_url.clone()
    }

    #[allow(unsafe_code)]
    fn get_width(&self) -> LengthOrPercentageOrAuto {
        unsafe {
            (*self.upcast::<Element>().unsafe_get())
                .get_attr_for_layout(&ns!(), &local_name!("width"))
                .map(AttrValue::as_dimension)
                .cloned()
                .unwrap_or(LengthOrPercentageOrAuto::Auto)
        }
    }

    #[allow(unsafe_code)]
    fn get_height(&self) -> LengthOrPercentageOrAuto {
        unsafe {
            (*self.upcast::<Element>().unsafe_get())
                .get_attr_for_layout(&ns!(), &local_name!("height"))
                .map(AttrValue::as_dimension)
                .cloned()
                .unwrap_or(LengthOrPercentageOrAuto::Auto)
        }
    }
}

//https://html.spec.whatwg.org/multipage/#parse-a-sizes-attribute
pub fn parse_a_sizes_attribute(value: DOMString) -> SourceSizeList {
    let mut input = ParserInput::new(&value);
    let mut parser = Parser::new(&mut input);
    let url = ServoUrl::parse("about:blank").unwrap();
    let context = ParserContext::new(
        Origin::Author,
        &url,
        Some(CssRuleType::Style),
        ParsingMode::empty(),
        QuirksMode::NoQuirks,
        None,
    );
    SourceSizeList::parse(&context, &mut parser)
}

impl HTMLImageElementMethods for HTMLImageElement {
    // https://html.spec.whatwg.org/multipage/#dom-img-alt
    make_getter!(Alt, "alt");
    // https://html.spec.whatwg.org/multipage/#dom-img-alt
    make_setter!(SetAlt, "alt");

    // https://html.spec.whatwg.org/multipage/#dom-img-src
    make_url_getter!(Src, "src");

    // https://html.spec.whatwg.org/multipage/#dom-img-src
    make_setter!(SetSrc, "src");

    // https://html.spec.whatwg.org/multipage/#dom-img-crossOrigin
    fn GetCrossOrigin(&self) -> Option<DOMString> {
        reflect_cross_origin_attribute(self.upcast::<Element>())
    }

    // https://html.spec.whatwg.org/multipage/#dom-img-crossOrigin
    fn SetCrossOrigin(&self, value: Option<DOMString>) {
        set_cross_origin_attribute(self.upcast::<Element>(), value);
    }

    // https://html.spec.whatwg.org/multipage/#dom-img-usemap
    make_getter!(UseMap, "usemap");
    // https://html.spec.whatwg.org/multipage/#dom-img-usemap
    make_setter!(SetUseMap, "usemap");

    // https://html.spec.whatwg.org/multipage/#dom-img-ismap
    make_bool_getter!(IsMap, "ismap");
    // https://html.spec.whatwg.org/multipage/#dom-img-ismap
    make_bool_setter!(SetIsMap, "ismap");

    // https://html.spec.whatwg.org/multipage/#dom-img-width
    fn Width(&self) -> u32 {
        let node = self.upcast::<Node>();
        match node.bounding_content_box() {
            Some(rect) => rect.size.width.to_px() as u32,
            None => self.NaturalWidth(),
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-img-width
    fn SetWidth(&self, value: u32) {
        image_dimension_setter(self.upcast(), local_name!("width"), value);
    }

    // https://html.spec.whatwg.org/multipage/#dom-img-height
    fn Height(&self) -> u32 {
        let node = self.upcast::<Node>();
        match node.bounding_content_box() {
            Some(rect) => rect.size.height.to_px() as u32,
            None => self.NaturalHeight(),
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-img-height
    fn SetHeight(&self, value: u32) {
        image_dimension_setter(self.upcast(), local_name!("height"), value);
    }

    // https://html.spec.whatwg.org/multipage/#dom-img-naturalwidth
    fn NaturalWidth(&self) -> u32 {
        let ref metadata = self.current_request.borrow().metadata;

        match *metadata {
            Some(ref metadata) => metadata.width,
            None => 0,
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-img-naturalheight
    fn NaturalHeight(&self) -> u32 {
        let ref metadata = self.current_request.borrow().metadata;

        match *metadata {
            Some(ref metadata) => metadata.height,
            None => 0,
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-img-complete
    fn Complete(&self) -> bool {
        let elem = self.upcast::<Element>();
        // TODO: take srcset into account
        if !elem.has_attribute(&local_name!("src")) {
            return true
        }
        let src = elem.get_string_attribute(&local_name!("src"));
        if src.is_empty() {
            return true
        }
        let request = self.current_request.borrow();
        let request_state = request.state;
        match request_state {
            State::CompletelyAvailable | State::Broken => return true,
            State::PartiallyAvailable | State::Unavailable => return false,
        }
    }

    // https://html.spec.whatwg.org/multipage/#dom-img-currentsrc
    fn CurrentSrc(&self) -> DOMString {
        let ref url = self.current_request.borrow().parsed_url;
        match *url {
            Some(ref url) => DOMString::from_string(url.clone().into_string()),
            None => DOMString::from(""),
        }
    }

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

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

    // https://html.spec.whatwg.org/multipage/#dom-img-align
    make_getter!(Align, "align");

    // https://html.spec.whatwg.org/multipage/#dom-img-align
    make_setter!(SetAlign, "align");

    // https://html.spec.whatwg.org/multipage/#dom-img-hspace
    make_uint_getter!(Hspace, "hspace");

    // https://html.spec.whatwg.org/multipage/#dom-img-hspace
    make_uint_setter!(SetHspace, "hspace");

    // https://html.spec.whatwg.org/multipage/#dom-img-vspace
    make_uint_getter!(Vspace, "vspace");

    // https://html.spec.whatwg.org/multipage/#dom-img-vspace
    make_uint_setter!(SetVspace, "vspace");

    // https://html.spec.whatwg.org/multipage/#dom-img-longdesc
    make_getter!(LongDesc, "longdesc");

    // https://html.spec.whatwg.org/multipage/#dom-img-longdesc
    make_setter!(SetLongDesc, "longdesc");

    // https://html.spec.whatwg.org/multipage/#dom-img-border
    make_getter!(Border, "border");

    // https://html.spec.whatwg.org/multipage/#dom-img-border
    make_setter!(SetBorder, "border");
}

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

    fn adopting_steps(&self, old_doc: &Document) {
        self.super_type().unwrap().adopting_steps(old_doc);
        self.update_the_image_data();
    }

    fn attribute_mutated(&self, attr: &Attr, mutation: AttributeMutation) {
        self.super_type().unwrap().attribute_mutated(attr, mutation);
        match attr.local_name() {
            &local_name!("src") => self.update_the_image_data(),
            _ => {},
        }
    }

    fn parse_plain_attribute(&self, name: &LocalName, value: DOMString) -> AttrValue {
        match name {
            &local_name!("name") => AttrValue::from_atomic(value.into()),
            &local_name!("width") | &local_name!("height") => AttrValue::from_dimension(value.into()),
            &local_name!("hspace") | &local_name!("vspace") => AttrValue::from_u32(value.into(), 0),
            _ => self.super_type().unwrap().parse_plain_attribute(name, value),
        }
    }

    fn handle_event(&self, event: &Event) {
        if event.type_() != atom!("click") {
            return
        }

       let area_elements = self.areas();
       let elements = match area_elements {
           Some(x) => x,
           None => return,
       };

       // Fetch click coordinates
       let mouse_event = match event.downcast::<MouseEvent>() {
           Some(x) => x,
           None => return,
       };

       let point = Point2D::new(mouse_event.ClientX().to_f32().unwrap(),
                                mouse_event.ClientY().to_f32().unwrap());
       let bcr = self.upcast::<Element>().GetBoundingClientRect();
       let bcr_p = Point2D::new(bcr.X() as f32, bcr.Y() as f32);

       // Walk HTMLAreaElements
       for element in elements {
           let shape = element.get_shape_from_coords();
           let shp = match shape {
               Some(x) => x.absolute_coords(bcr_p),
               None => return,
           };
           if shp.hit_test(&point) {
               element.activation_behavior(event, self.upcast());
               return
           }
       }
    }
}

impl FormControl for HTMLImageElement {
    fn form_owner(&self) -> Option<DomRoot<HTMLFormElement>> {
        self.form_owner.get()
    }

    fn set_form_owner(&self, form: Option<&HTMLFormElement>) {
        self.form_owner.set(form);
    }

    fn to_element<'a>(&'a self) -> &'a Element {
        self.upcast::<Element>()
    }

    fn is_listed(&self) -> bool {
        false
    }
}

fn image_dimension_setter(element: &Element, attr: LocalName, value: u32) {
    // This setter is a bit weird: the IDL type is unsigned long, but it's parsed as
    // a dimension for rendering.
    let value = if value > UNSIGNED_LONG_MAX {
        0
    } else {
        value
    };

    // FIXME: There are probably quite a few more cases of this. This is the
    // only overflow that was hitting on automation, but we should consider what
    // to do in the general case case.
    //
    // See <https://github.com/servo/app_units/issues/22>
    let pixel_value = if value > (i32::MAX / AU_PER_PX) as u32 {
        0
    } else {
        value
    };

    let dim = LengthOrPercentageOrAuto::Length(Au::from_px(pixel_value as i32));
    let value = AttrValue::Dimension(value.to_string(), dim);
    element.set_attribute(&attr, value);
}

/// Collect sequence of code points
pub fn collect_sequence_characters<F>(s: &str, predicate: F) -> (&str, &str)
    where F: Fn(&char) -> bool
{
    for (i, ch) in s.chars().enumerate() {
        if !predicate(&ch) {
            return (&s[0..i], &s[i..])
        }
    }

    return (s, "");
}

/// Parse an `srcset` attribute - https://html.spec.whatwg.org/multipage/#parsing-a-srcset-attribute.
pub fn parse_a_srcset_attribute(input: &str) -> Vec<ImageSource> {
    let mut url_len = 0;
    let mut candidates: Vec<ImageSource> = vec![];
    while url_len < input.len() {
        let position = &input[url_len..];
        let (spaces, position) = collect_sequence_characters(position, |c| *c == ',' || char::is_whitespace(*c));
        // add the length of the url that we parse to advance the start index
        let space_len = spaces.char_indices().count();
        url_len += space_len;
        if position.is_empty() {
            return candidates;
        }
        let (url, spaces) = collect_sequence_characters(position, |c| !char::is_whitespace(*c));
        // add the counts of urls that we parse to advance the start index
        url_len += url.chars().count();
        let comma_count = url.chars().rev().take_while(|c| *c == ',').count();
        let url: String = url.chars().take(url.chars().count() - comma_count).collect();
        // add 1 to start index, for the comma
        url_len += comma_count + 1;
        let (space, position) = collect_sequence_characters(spaces, |c| char::is_whitespace(*c));
        let space_len = space.len();
        url_len += space_len;
        let mut descriptors = Vec::new();
        let mut current_descriptor = String::new();
        let mut state = ParseState::InDescriptor;
        let mut char_stream = position.chars().enumerate();
        let mut buffered: Option<(usize, char)> = None;
        loop {
            let next_char = buffered.take().or_else(|| char_stream.next());
            if next_char.is_some() {
                url_len += 1;
            }
            match state {
                ParseState::InDescriptor => {
                    match next_char {
                        Some((_, ' ')) => {
                            if !current_descriptor.is_empty() {
                                descriptors.push(current_descriptor.clone());
                                current_descriptor = String::new();
                                state = ParseState::AfterDescriptor;
                            }
                            continue;
                        }
                        Some((_, ',')) => {
                            if !current_descriptor.is_empty() {
                                descriptors.push(current_descriptor.clone());
                            }
                            break;
                        }
                        Some((_, c @ '(')) => {
                            current_descriptor.push(c);
                            state = ParseState::InParens;
                            continue;
                        }
                        Some((_, c)) => {
                            current_descriptor.push(c);
                        }
                        None => {
                            if !current_descriptor.is_empty() {
                                descriptors.push(current_descriptor.clone());
                            }
                            break;
                        }
                    }
                }
                ParseState::InParens => {
                    match next_char {
                        Some((_, c @ ')')) => {
                            current_descriptor.push(c);
                            state = ParseState::InDescriptor;
                            continue;
                        }
                        Some((_, c)) => {
                            current_descriptor.push(c);
                            continue;
                        }
                        None => {
                            if !current_descriptor.is_empty() {
                                descriptors.push(current_descriptor.clone());
                            }
                            break;
                        }
                    }
                }
                ParseState::AfterDescriptor => {
                    match next_char {
                        Some((_, ' ')) => {
                            state = ParseState::AfterDescriptor;
                            continue;
                        }
                        Some((idx, c)) => {
                            state = ParseState::InDescriptor;
                            buffered = Some((idx, c));
                            continue;
                        }
                        None => {
                            if !current_descriptor.is_empty() {
                                descriptors.push(current_descriptor.clone());
                            }
                            break;
                        }
                    }
                }
            }
        }

        let mut error = false;
        let mut width: Option<u32> = None;
        let mut density: Option<f64> = None;
        let mut future_compat_h: Option<u32> = None;
        for descriptor in descriptors {
            let (digits, remaining) = collect_sequence_characters(&descriptor, |c| is_ascii_digit(c) || *c == '.');
            let valid_non_negative_integer = parse_unsigned_integer(digits.chars());
            let has_w = remaining == "w";
            let valid_floating_point = parse_double(digits);
            let has_x = remaining == "x";
            let has_h = remaining == "h";
            if valid_non_negative_integer.is_ok() && has_w {
                let result = valid_non_negative_integer;
                error = result.is_err();
                if width.is_some() || density.is_some() {
                    error = true;
                }
                if let Ok(w) = result {
                    width = Some(w);
                }
            } else if valid_floating_point.is_ok() && has_x {
                let result = valid_floating_point;
                error = result.is_err();
                if width.is_some() || density.is_some() || future_compat_h.is_some() {
                    error = true;
                }
                if let Ok(x) = result {
                    density = Some(x);
                }
            } else if valid_non_negative_integer.is_ok() && has_h {
                let result = valid_non_negative_integer;
                error = result.is_err();
                if density.is_some() || future_compat_h.is_some() {
                    error = true;
                }
                if let Ok(h) = result {
                    future_compat_h = Some(h);
                }
            } else {
                error = true;
            }
        }
        if future_compat_h.is_some() && width.is_none() {
            error = true;
        }
        if !error {
            let descriptor = Descriptor { wid: width, den: density };
            let image_source = ImageSource { url: url, descriptor: descriptor };
            candidates.push(image_source);
        }
    }
    candidates
}