layout/

replaced.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 https://mozilla.org/MPL/2.0/. */

use app_units::{Au, MAX_AU};
use base::id::{BrowsingContextId, PipelineId};
use data_url::DataUrl;
use embedder_traits::ViewportDetails;
use euclid::{Scale, Size2D};
use html5ever::local_name;
use layout_api::wrapper_traits::ThreadSafeLayoutNode;
use layout_api::{IFrameSize, LayoutImageDestination, SVGElementData};
use malloc_size_of_derive::MallocSizeOf;
use net_traits::image_cache::{Image, ImageOrMetadataAvailable, VectorImage};
use script::layout_dom::ServoThreadSafeLayoutNode;
use selectors::Element;
use servo_arc::Arc as ServoArc;
use style::Zero;
use style::attr::AttrValue;
use style::computed_values::object_fit::T as ObjectFit;
use style::logical_geometry::{Direction, WritingMode};
use style::properties::{ComputedValues, StyleBuilder};
use style::rule_cache::RuleCacheConditions;
use style::servo::url::ComputedUrl;
use style::stylesheets::container_rule::ContainerSizeQuery;
use style::values::CSSFloat;
use style::values::computed::image::Image as ComputedImage;
use style::values::computed::{Content, Context, ToComputedValue};
use style::values::generics::counters::{GenericContentItem, GenericContentItems};
use url::Url;
use webrender_api::ImageKey;

use crate::cell::ArcRefCell;
use crate::context::{LayoutContext, LayoutImageCacheResult};
use crate::dom::NodeExt;
use crate::fragment_tree::{
    BaseFragment, BaseFragmentInfo, CollapsedBlockMargins, Fragment, IFrameFragment, ImageFragment,
};
use crate::geom::{LogicalVec2, PhysicalPoint, PhysicalRect, PhysicalSize};
use crate::layout_box_base::{CacheableLayoutResult, LayoutBoxBase};
use crate::sizing::{
    ComputeInlineContentSizes, InlineContentSizesResult, LazySize, SizeConstraint,
};
use crate::style_ext::{AspectRatio, Clamp, ComputedValuesExt, LayoutStyle};
use crate::{ConstraintSpace, ContainingBlock};

#[derive(Debug, MallocSizeOf)]
pub(crate) struct ReplacedContents {
    pub kind: ReplacedContentKind,
    natural_size: NaturalSizes,
    base_fragment_info: BaseFragmentInfo,
}

/// The natural dimensions of a replaced element, including a height, width, and
/// aspect ratio.
///
/// * Raster images always have an natural width and height, with 1 image pixel = 1px.
///   The natural ratio should be based on dividing those.
///   See <https://github.com/w3c/csswg-drafts/issues/4572> for the case where either is zero.
///   PNG specifically disallows this but I (SimonSapin) am not sure about other formats.
///
/// * Form controls have both natural width and height **but no natural ratio**.
///   See <https://github.com/w3c/csswg-drafts/issues/1044> and
///   <https://drafts.csswg.org/css-images/#natural-dimensions> “In general, […]”
///
/// * For SVG, see <https://svgwg.org/svg2-draft/coords.html#SizingSVGInCSS>
///   and again <https://github.com/w3c/csswg-drafts/issues/4572>.
///
/// * IFrames do not have natural width and height or natural ratio according
///   to <https://drafts.csswg.org/css-images/#intrinsic-dimensions>.
#[derive(Debug, MallocSizeOf)]
pub(crate) struct NaturalSizes {
    pub width: Option<Au>,
    pub height: Option<Au>,
    pub ratio: Option<CSSFloat>,
}

impl NaturalSizes {
    pub(crate) fn from_width_and_height(width: f32, height: f32) -> Self {
        // https://drafts.csswg.org/css-images/#natural-aspect-ratio:
        // "If an object has a degenerate natural aspect ratio (at least one part being
        // zero or infinity), it is treated as having no natural aspect ratio.""
        let ratio = if width.is_normal() && height.is_normal() {
            Some(width / height)
        } else {
            None
        };

        Self {
            width: Some(Au::from_f32_px(width)),
            height: Some(Au::from_f32_px(height)),
            ratio,
        }
    }

    pub(crate) fn from_natural_size_in_dots(natural_size_in_dots: PhysicalSize<f64>) -> Self {
        // FIXME: should 'image-resolution' (when implemented) be used *instead* of
        // `script::dom::htmlimageelement::ImageRequest::current_pixel_density`?
        // https://drafts.csswg.org/css-images-4/#the-image-resolution
        let dppx = 1.0;
        let width = natural_size_in_dots.width as f32 / dppx;
        let height = natural_size_in_dots.height as f32 / dppx;
        Self::from_width_and_height(width, height)
    }

    pub(crate) fn empty() -> Self {
        Self {
            width: None,
            height: None,
            ratio: None,
        }
    }
}

#[derive(Debug, MallocSizeOf)]
pub(crate) struct CanvasInfo {
    pub source: Option<ImageKey>,
}

#[derive(Debug, MallocSizeOf)]
pub(crate) struct IFrameInfo {
    pub pipeline_id: PipelineId,
    pub browsing_context_id: BrowsingContextId,
}

#[derive(Debug, MallocSizeOf)]
pub(crate) struct VideoInfo {
    pub image_key: webrender_api::ImageKey,
}

#[derive(Debug, MallocSizeOf)]
pub(crate) enum ReplacedContentKind {
    Image(Option<Image>, bool /* showing_broken_image_icon */),
    IFrame(IFrameInfo),
    Canvas(CanvasInfo),
    Video(Option<VideoInfo>),
    SVGElement(Option<VectorImage>),
    Audio,
}

impl ReplacedContents {
    pub fn for_element(
        node: ServoThreadSafeLayoutNode<'_>,
        context: &LayoutContext,
    ) -> Option<Self> {
        if let Some(ref data_attribute_string) = node.as_typeless_object_with_data_attribute() {
            if let Some(url) = try_to_parse_image_data_url(data_attribute_string) {
                return Self::from_image_url(
                    node,
                    context,
                    &ComputedUrl::Valid(ServoArc::new(url)),
                );
            }
        }

        let (kind, natural_size) = {
            if let Some((image, natural_size_in_dots)) = node.as_image() {
                if let Some(content_image) = Self::from_content_property(node, context) {
                    return Some(content_image);
                }
                (
                    ReplacedContentKind::Image(image, node.showing_broken_image_icon()),
                    NaturalSizes::from_natural_size_in_dots(natural_size_in_dots),
                )
            } else if let Some((canvas_info, natural_size_in_dots)) = node.as_canvas() {
                (
                    ReplacedContentKind::Canvas(canvas_info),
                    NaturalSizes::from_natural_size_in_dots(natural_size_in_dots),
                )
            } else if let Some((pipeline_id, browsing_context_id)) = node.as_iframe() {
                (
                    ReplacedContentKind::IFrame(IFrameInfo {
                        pipeline_id,
                        browsing_context_id,
                    }),
                    NaturalSizes::empty(),
                )
            } else if let Some((image_key, natural_size_in_dots)) = node.as_video() {
                (
                    ReplacedContentKind::Video(image_key.map(|key| VideoInfo { image_key: key })),
                    natural_size_in_dots
                        .map_or_else(NaturalSizes::empty, NaturalSizes::from_natural_size_in_dots),
                )
            } else if let Some(svg_data) = node.as_svg() {
                Self::svg_kind_size(svg_data, context, node)?
            } else if node
                .as_html_element()
                .is_some_and(|element| element.has_local_name(&local_name!("audio")))
            {
                let natural_size = NaturalSizes {
                    width: None,
                    // 40px is the height of the controls.
                    // See /components/script/resources/media-controls.css
                    height: Some(Au::from_px(40)),
                    ratio: None,
                };
                (ReplacedContentKind::Audio, natural_size)
            } else {
                return Self::from_content_property(node, context);
            }
        };

        if let ReplacedContentKind::Image(Some(Image::Raster(ref image)), _) = kind {
            context
                .image_resolver
                .handle_animated_image(node.opaque(), image.clone());
        }

        Some(Self {
            kind,
            natural_size,
            base_fragment_info: node.into(),
        })
    }

    fn svg_kind_size(
        svg_data: SVGElementData,
        context: &LayoutContext,
        node: ServoThreadSafeLayoutNode<'_>,
    ) -> Option<(ReplacedContentKind, NaturalSizes)> {
        let rule_cache_conditions = &mut RuleCacheConditions::default();

        let parent_style = node.style(&context.style_context);
        let style_builder = StyleBuilder::new(
            context.style_context.stylist.device(),
            Some(context.style_context.stylist),
            Some(&parent_style),
            None,
            None,
            false,
        );

        let to_computed_context = Context::new(
            style_builder,
            context.style_context.quirks_mode(),
            rule_cache_conditions,
            ContainerSizeQuery::none(),
        );

        let attr_to_computed = |attr_val: &AttrValue| {
            if let AttrValue::Length(_, length) = attr_val {
                length.to_computed_value(&to_computed_context)
            } else {
                None
            }
        };
        let width = svg_data.width.and_then(attr_to_computed);
        let height = svg_data.height.and_then(attr_to_computed);

        let ratio = if let (Some(width), Some(height)) = (width, height) {
            if !width.is_zero() && !height.is_zero() {
                Some(width.px() / height.px())
            } else {
                None
            }
        } else {
            svg_data.ratio_from_view_box()
        };

        let natural_size = NaturalSizes {
            width: width.map(|w| Au::from_f32_px(w.px())),
            height: height.map(|h| Au::from_f32_px(h.px())),
            ratio,
        };

        let svg_source = match svg_data.source {
            None => {
                // The SVGSVGElement is not yet serialized, so we add it to a list
                // and hand it over to script to peform the serialization.
                context
                    .image_resolver
                    .queue_svg_element_for_serialization(node);
                return None;
            },
            Some(Err(_)) => {
                // Don't attempt to serialize if previous attempt had errored.
                return None;
            },
            Some(Ok(svg_source)) => svg_source,
        };

        let result = context
            .image_resolver
            .get_cached_image_for_url(
                node.opaque(),
                svg_source,
                LayoutImageDestination::BoxTreeConstruction,
            )
            .ok();

        let vector_image = result.map(|result| match result {
            Image::Vector(mut vector_image) => {
                vector_image.svg_id = Some(svg_data.svg_id);
                vector_image
            },
            _ => unreachable!("SVG element can't contain a raster image."),
        });

        Some((ReplacedContentKind::SVGElement(vector_image), natural_size))
    }

    fn from_content_property(
        node: ServoThreadSafeLayoutNode<'_>,
        context: &LayoutContext,
    ) -> Option<Self> {
        // If the `content` property is a single image URL, non-replaced boxes
        // and images get replaced with the given image.
        if let Content::Items(GenericContentItems { items, .. }) =
            node.style(&context.style_context).clone_content()
        {
            if let [GenericContentItem::Image(image)] = items.as_slice() {
                // Invalid images are treated as zero-sized.
                return Some(
                    Self::from_image(node, context, image)
                        .unwrap_or_else(|| Self::zero_sized_invalid_image(node)),
                );
            }
        }
        None
    }

    pub fn from_image_url(
        node: ServoThreadSafeLayoutNode<'_>,
        context: &LayoutContext,
        image_url: &ComputedUrl,
    ) -> Option<Self> {
        if let ComputedUrl::Valid(image_url) = image_url {
            let (image, width, height) = match context.image_resolver.get_or_request_image_or_meta(
                node.opaque(),
                image_url.clone().into(),
                LayoutImageDestination::BoxTreeConstruction,
            ) {
                LayoutImageCacheResult::DataAvailable(img_or_meta) => match img_or_meta {
                    ImageOrMetadataAvailable::ImageAvailable { image, .. } => {
                        if let Image::Raster(image) = &image {
                            context
                                .image_resolver
                                .handle_animated_image(node.opaque(), image.clone());
                        }
                        let metadata = image.metadata();
                        (
                            Some(image.clone()),
                            metadata.width as f32,
                            metadata.height as f32,
                        )
                    },
                    ImageOrMetadataAvailable::MetadataAvailable(metadata, _id) => {
                        (None, metadata.width as f32, metadata.height as f32)
                    },
                },
                LayoutImageCacheResult::Pending | LayoutImageCacheResult::LoadError => return None,
            };

            return Some(Self {
                kind: ReplacedContentKind::Image(image, false /* showing_broken_image_icon */),
                natural_size: NaturalSizes::from_width_and_height(width, height),
                base_fragment_info: node.into(),
            });
        }
        None
    }

    pub fn from_image(
        element: ServoThreadSafeLayoutNode<'_>,
        context: &LayoutContext,
        image: &ComputedImage,
    ) -> Option<Self> {
        match image {
            ComputedImage::Url(image_url) => Self::from_image_url(element, context, image_url),
            _ => None, // TODO
        }
    }

    pub(crate) fn zero_sized_invalid_image(node: ServoThreadSafeLayoutNode<'_>) -> Self {
        Self {
            kind: ReplacedContentKind::Image(None, false /* showing_broken_image_icon */),
            natural_size: NaturalSizes::from_width_and_height(0., 0.),
            base_fragment_info: node.into(),
        }
    }

    #[inline]
    fn is_broken_image(&self) -> bool {
        matches!(self.kind, ReplacedContentKind::Image(_, true))
    }

    #[inline]
    fn content_size(
        &self,
        axis: Direction,
        preferred_aspect_ratio: Option<AspectRatio>,
        get_size_in_opposite_axis: &dyn Fn() -> SizeConstraint,
        get_fallback_size: &dyn Fn() -> Au,
    ) -> Au {
        let Some(ratio) = preferred_aspect_ratio else {
            return get_fallback_size();
        };
        let transfer = |size| ratio.compute_dependent_size(axis, size);
        match get_size_in_opposite_axis() {
            SizeConstraint::Definite(size) => transfer(size),
            SizeConstraint::MinMax(min_size, max_size) => get_fallback_size()
                .clamp_between_extremums(transfer(min_size), max_size.map(transfer)),
        }
    }

    fn calculate_fragment_rect(
        &self,
        style: &ServoArc<ComputedValues>,
        size: PhysicalSize<Au>,
    ) -> (PhysicalSize<Au>, PhysicalRect<Au>) {
        if let ReplacedContentKind::Image(Some(Image::Raster(image)), true) = &self.kind {
            let size = Size2D::new(
                Au::from_f32_px(image.metadata.width as f32),
                Au::from_f32_px(image.metadata.height as f32),
            )
            .min(size);
            return (PhysicalSize::zero(), size.into());
        }

        let natural_size = PhysicalSize::new(
            self.natural_size.width.unwrap_or(size.width),
            self.natural_size.height.unwrap_or(size.height),
        );

        let object_fit_size = self.natural_size.ratio.map_or(size, |width_over_height| {
            let preserve_aspect_ratio_with_comparison =
                |size: PhysicalSize<Au>, comparison: fn(&Au, &Au) -> bool| {
                    let candidate_width = size.height.scale_by(width_over_height);
                    if comparison(&candidate_width, &size.width) {
                        return PhysicalSize::new(candidate_width, size.height);
                    }

                    let candidate_height = size.width.scale_by(1. / width_over_height);
                    debug_assert!(comparison(&candidate_height, &size.height));
                    PhysicalSize::new(size.width, candidate_height)
                };

            match style.clone_object_fit() {
                ObjectFit::Fill => size,
                ObjectFit::Contain => preserve_aspect_ratio_with_comparison(size, PartialOrd::le),
                ObjectFit::Cover => preserve_aspect_ratio_with_comparison(size, PartialOrd::ge),
                ObjectFit::None => natural_size,
                ObjectFit::ScaleDown => {
                    preserve_aspect_ratio_with_comparison(size.min(natural_size), PartialOrd::le)
                },
            }
        });

        let object_position = style.clone_object_position();
        let horizontal_position = object_position
            .horizontal
            .to_used_value(size.width - object_fit_size.width);
        let vertical_position = object_position
            .vertical
            .to_used_value(size.height - object_fit_size.height);

        let object_position = PhysicalPoint::new(horizontal_position, vertical_position);
        (
            object_fit_size,
            PhysicalRect::new(object_position, object_fit_size),
        )
    }

    pub fn make_fragments(
        &self,
        layout_context: &LayoutContext,
        style: &ServoArc<ComputedValues>,
        size: PhysicalSize<Au>,
    ) -> Vec<Fragment> {
        let (object_fit_size, rect) = self.calculate_fragment_rect(style, size);
        let clip = PhysicalRect::new(PhysicalPoint::origin(), size);

        let mut base = BaseFragment::new(self.base_fragment_info, style.clone().into(), rect);
        match &self.kind {
            ReplacedContentKind::Image(image, showing_broken_image_icon) => image
                .as_ref()
                .and_then(|image| match image {
                    Image::Raster(raster_image) => raster_image.id,
                    Image::Vector(vector_image) => {
                        let scale = layout_context.style_context.device_pixel_ratio();
                        let width = object_fit_size.width.scale_by(scale.0).to_px();
                        let height = object_fit_size.height.scale_by(scale.0).to_px();
                        let size = Size2D::new(width, height);
                        let tag = self.base_fragment_info.tag?;
                        layout_context
                            .image_resolver
                            .rasterize_vector_image(
                                vector_image.id,
                                size,
                                tag.node,
                                vector_image.svg_id.clone(),
                            )
                            .and_then(|i| i.id)
                    },
                })
                .map(|image_key| {
                    Fragment::Image(ArcRefCell::new(ImageFragment {
                        base,
                        clip,
                        image_key: Some(image_key),
                        showing_broken_image_icon: *showing_broken_image_icon,
                    }))
                })
                .into_iter()
                .collect(),
            ReplacedContentKind::Video(video) => {
                vec![Fragment::Image(ArcRefCell::new(ImageFragment {
                    base,
                    clip,
                    image_key: video.as_ref().map(|video| video.image_key),
                    showing_broken_image_icon: false,
                }))]
            },
            ReplacedContentKind::IFrame(iframe) => {
                let size = Size2D::new(rect.size.width.to_f32_px(), rect.size.height.to_f32_px());
                let hidpi_scale_factor = layout_context.style_context.device_pixel_ratio();

                layout_context.iframe_sizes.lock().insert(
                    iframe.browsing_context_id,
                    IFrameSize {
                        browsing_context_id: iframe.browsing_context_id,
                        pipeline_id: iframe.pipeline_id,
                        viewport_details: ViewportDetails {
                            size,
                            hidpi_scale_factor: Scale::new(hidpi_scale_factor.0),
                        },
                    },
                );
                vec![Fragment::IFrame(ArcRefCell::new(IFrameFragment {
                    base,
                    pipeline_id: iframe.pipeline_id,
                }))]
            },
            ReplacedContentKind::Canvas(canvas_info) => {
                if self.natural_size.width == Some(Au::zero()) ||
                    self.natural_size.height == Some(Au::zero())
                {
                    return vec![];
                }

                let Some(image_key) = canvas_info.source else {
                    return vec![];
                };

                vec![Fragment::Image(ArcRefCell::new(ImageFragment {
                    base,
                    clip,
                    image_key: Some(image_key),
                    showing_broken_image_icon: false,
                }))]
            },
            ReplacedContentKind::SVGElement(vector_image) => {
                let Some(vector_image) = vector_image else {
                    return vec![];
                };

                // TODO: This is incorrect if the SVG has a viewBox.
                base.rect = PhysicalSize::new(
                    vector_image
                        .metadata
                        .width
                        .try_into()
                        .map_or(MAX_AU, Au::from_px),
                    vector_image
                        .metadata
                        .height
                        .try_into()
                        .map_or(MAX_AU, Au::from_px),
                )
                .into();

                let scale = layout_context.style_context.device_pixel_ratio();
                let raster_size = Size2D::new(
                    base.rect.size.width.scale_by(scale.0).to_px(),
                    base.rect.size.height.scale_by(scale.0).to_px(),
                );

                let tag = self.base_fragment_info.tag.unwrap();
                layout_context
                    .image_resolver
                    .rasterize_vector_image(
                        vector_image.id,
                        raster_size,
                        tag.node,
                        vector_image.svg_id.clone(),
                    )
                    .and_then(|image| image.id)
                    .map(|image_key| {
                        Fragment::Image(ArcRefCell::new(ImageFragment {
                            base,
                            clip,
                            image_key: Some(image_key),
                            showing_broken_image_icon: false,
                        }))
                    })
                    .into_iter()
                    .collect()
            },
            ReplacedContentKind::Audio => vec![],
        }
    }

    pub(crate) fn preferred_aspect_ratio(
        &self,
        style: &ComputedValues,
        padding_border_sums: &LogicalVec2<Au>,
    ) -> Option<AspectRatio> {
        if matches!(self.kind, ReplacedContentKind::Audio) {
            // This isn't specified, but other browsers don't support `aspect-ratio` on `<audio>`.
            // See <https://phabricator.services.mozilla.com/D118245>
            return None;
        }
        if self.is_broken_image() {
            // This isn't specified, but when an image is broken, we should prefer to the aspect
            // ratio from the style, rather than the aspect ratio from the broken image icon.
            // Note that the broken image icon *does* affect the content size of the image
            // though as we want the image to be as big as the icon if the size was not specified
            // in the style.
            style.preferred_aspect_ratio(None, padding_border_sums)
        } else {
            style.preferred_aspect_ratio(self.natural_size.ratio, padding_border_sums)
        }
    }

    /// The inline size that would result from combining the natural size
    /// and the default object size, but disregarding the specified size.
    /// <https://drafts.csswg.org/css-images-3/#natural-dimensions>
    /// <https://drafts.csswg.org/css-images-3/#default-object-size>
    /// <https://drafts.csswg.org/css-images-3/#specified-size>
    pub(crate) fn fallback_inline_size(&self, writing_mode: WritingMode) -> Au {
        if writing_mode.is_horizontal() {
            self.natural_size.width.unwrap_or_else(|| Au::from_px(300))
        } else {
            self.natural_size.height.unwrap_or_else(|| Au::from_px(150))
        }
    }

    /// The block size that would result from combining the natural size
    /// and the default object size, but disregarding the specified size.
    /// <https://drafts.csswg.org/css-images-3/#natural-dimensions>
    /// <https://drafts.csswg.org/css-images-3/#default-object-size>
    /// <https://drafts.csswg.org/css-images-3/#specified-size>
    pub(crate) fn fallback_block_size(&self, writing_mode: WritingMode) -> Au {
        if writing_mode.is_horizontal() {
            self.natural_size.height.unwrap_or_else(|| Au::from_px(150))
        } else {
            self.natural_size.width.unwrap_or_else(|| Au::from_px(300))
        }
    }

    #[inline]
    pub(crate) fn layout_style<'a>(&self, base: &'a LayoutBoxBase) -> LayoutStyle<'a> {
        LayoutStyle::Default(&base.style)
    }

    pub(crate) fn layout(
        &self,
        layout_context: &LayoutContext,
        containing_block_for_children: &ContainingBlock,
        preferred_aspect_ratio: Option<AspectRatio>,
        base: &LayoutBoxBase,
        lazy_block_size: &LazySize,
    ) -> CacheableLayoutResult {
        let writing_mode = base.style.writing_mode;
        let inline_size = containing_block_for_children.size.inline;
        let content_block_size = self.content_size(
            Direction::Block,
            preferred_aspect_ratio,
            &|| SizeConstraint::Definite(inline_size),
            &|| self.fallback_block_size(writing_mode),
        );
        let size = LogicalVec2 {
            inline: inline_size,
            block: lazy_block_size.resolve(|| content_block_size),
        }
        .to_physical_size(writing_mode);
        CacheableLayoutResult {
            baselines: Default::default(),
            collapsible_margins_in_children: CollapsedBlockMargins::zero(),
            content_block_size,
            content_inline_size_for_table: None,
            // The result doesn't depend on `containing_block_for_children.size.block`,
            // but it depends on `lazy_block_size`, which is probably tied to that.
            depends_on_block_constraints: true,
            fragments: self.make_fragments(layout_context, &base.style, size),
            specific_layout_info: None,
        }
    }
}

impl ComputeInlineContentSizes for ReplacedContents {
    fn compute_inline_content_sizes(
        &self,
        _: &LayoutContext,
        constraint_space: &ConstraintSpace,
    ) -> InlineContentSizesResult {
        let inline_content_size = self.content_size(
            Direction::Inline,
            constraint_space.preferred_aspect_ratio,
            &|| constraint_space.block_size,
            &|| self.fallback_inline_size(constraint_space.style.writing_mode),
        );
        InlineContentSizesResult {
            sizes: inline_content_size.into(),
            depends_on_block_constraints: constraint_space.preferred_aspect_ratio.is_some(),
        }
    }
}

fn try_to_parse_image_data_url(string: &str) -> Option<Url> {
    if !string.starts_with("data:") {
        return None;
    }
    let data_url = DataUrl::process(string).ok()?;
    let mime_type = data_url.mime_type();
    if mime_type.type_ != "image" {
        return None;
    }

    // TODO: Find a better way to test for supported image formats. Currently this type of check is
    // repeated several places in Servo, but should be centralized somehow.
    if !matches!(
        mime_type.subtype.as_str(),
        "png" | "jpeg" | "gif" | "webp" | "bmp" | "ico"
    ) {
        return None;
    }

    Url::parse(string).ok()
}