Make script thread initiate requests for images needed by layout.

In support of this goal, the layout thread collects information about
CSS images that are missing image data and hands it off to the script
thread after layout completes. The script thread stores a list of
nodes that will need to be reflowed after the associated network
request is complete. The script thread ensures that the nodes are
not GCed while a request is ongoing, which the layout thread is
incapable of guaranteeing.

The image cache's API has also been redesigned in support of this
work. No network requests are made by the new image cache, since it
does not possess the document-specific information necessary to
initiate them. Instead, there is now a single, synchronous
query operation that optionally reserves a slot when a cache
entry for a URL cannot be found. This reserved slot is then
the responsibility of the queryer to populate with the contents
of the network response for the URL once it is complete. Any
subsequent queries for the same URL will be informed that the
response is pending until that occurs.

The changes to layout also remove the synchronous image loading
code path, which means that reftests now test the same code
that non-test binaries execute. The decision to take a screenshot
now considers whether there are any outstanding image
requests for layout in order to avoid intermittent failures in
reftests that use CSS images.

1 files changed, 176 insertions, 12 deletions

diff --git a/components/script/dom/htmlimageelement.rs b/components/script/dom/htmlimageelement.rs
index ec9f2e1ec80..e762675bc70 100644
--- a/components/script/dom/htmlimageelement.rs
+++ b/components/script/dom/htmlimageelement.rs
@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use app_units::{Au, AU_PER_PX};
+use document_loader::{LoadType, LoadBlocker};
 use dom::activation::Activatable;
 use dom::attr::Attr;
 use dom::bindings::cell::DOMRefCell;
@@ -16,6 +17,7 @@ use dom::bindings::error::Fallible;
 use dom::bindings::inheritance::Castable;
 use dom::bindings::js::{LayoutJS, Root};
 use dom::bindings::refcounted::Trusted;
+use dom::bindings::reflector::DomObject;
 use dom::bindings::str::DOMString;
 use dom::document::Document;
 use dom::element::{AttributeMutation, Element, RawLayoutElementHelpers};
@@ -34,13 +36,17 @@ use euclid::point::Point2D;
 use html5ever_atoms::LocalName;
 use ipc_channel::ipc;
 use ipc_channel::router::ROUTER;
+use net_traits::{FetchResponseListener, FetchMetadata, Metadata, NetworkError};
 use net_traits::image::base::{Image, ImageMetadata};
-use net_traits::image_cache_thread::{ImageResponder, ImageResponse};
+use net_traits::image_cache_thread::{ImageResponder, ImageResponse, PendingImageId, ImageState};
+use net_traits::image_cache_thread::{UsePlaceholder, ImageOrMetadataAvailable};
+use net_traits::request::{RequestInit, Type as RequestType};
+use network_listener::{NetworkListener, PreInvoke};
 use num_traits::ToPrimitive;
 use script_thread::Runnable;
 use servo_url::ServoUrl;
 use std::i32;
-use std::sync::Arc;
+use std::sync::{Arc, Mutex};
 use style::attr::{AttrValue, LengthOrPercentageOrAuto};
 use task_source::TaskSource;
 
@@ -53,10 +59,12 @@ enum State {
     Broken,
 }
 #[derive(JSTraceable, HeapSizeOf)]
+#[must_root]
 struct ImageRequest {
     state: State,
     parsed_url: Option<ServoUrl>,
     source_url: Option<DOMString>,
+    blocker: Option<LoadBlocker>,
     #[ignore_heap_size_of = "Arc"]
     image: Option<Arc<Image>>,
     metadata: Option<ImageMetadata>,
@@ -74,6 +82,64 @@ impl HTMLImageElement {
     }
 }
 
+struct ImageRequestRunnable {
+    element: Trusted<HTMLImageElement>,
+    img_url: ServoUrl,
+    id: PendingImageId,
+}
+
+impl ImageRequestRunnable {
+    fn new(element: Trusted<HTMLImageElement>,
+           img_url: ServoUrl,
+           id: PendingImageId)
+           -> ImageRequestRunnable {
+        ImageRequestRunnable {
+            element: element,
+            img_url: img_url,
+            id: id,
+        }
+    }
+}
+
+impl Runnable for ImageRequestRunnable {
+    fn handler(self: Box<Self>) {
+        let this = *self;
+        let trusted_node = this.element.clone();
+        let element = this.element.root();
+
+        let document = document_from_node(&*element);
+        let window = window_from_node(&*element);
+
+        let context = Arc::new(Mutex::new(ImageContext {
+            elem: trusted_node,
+            data: vec!(),
+            metadata: None,
+            url: this.img_url.clone(),
+            status: Ok(()),
+            id: this.id,
+        }));
+
+        let (action_sender, action_receiver) = ipc::channel().unwrap();
+        let listener = NetworkListener {
+            context: context,
+            task_source: window.networking_task_source(),
+            wrapper: Some(window.get_runnable_wrapper()),
+        };
+        ROUTER.add_route(action_receiver.to_opaque(), box move |message| {
+            listener.notify_fetch(message.to().unwrap());
+        });
+
+        let request = RequestInit {
+            url: this.img_url.clone(),
+            origin: document.url().clone(),
+            type_: RequestType::Image,
+            pipeline_id: Some(document.global().pipeline_id()),
+            .. RequestInit::default()
+        };
+
+        document.fetch_async(LoadType::Image(this.img_url), request, action_sender);
+    }
+}
 
 struct ImageResponseHandlerRunnable {
     element: Trusted<HTMLImageElement>,
@@ -122,23 +188,83 @@ impl Runnable for ImageResponseHandlerRunnable {
             element.upcast::<EventTarget>().fire_event(atom!("error"));
         }
 
+        LoadBlocker::terminate(&mut element.current_request.borrow_mut().blocker);
+
         // Trigger reflow
         let window = window_from_node(&*document);
         window.add_pending_reflow();
     }
 }
 
+/// The context required for asynchronously loading an external image.
+struct ImageContext {
+    /// The element that initiated the request.
+    elem: Trusted<HTMLImageElement>,
+    /// The response body received to date.
+    data: Vec<u8>,
+    /// The response metadata received to date.
+    metadata: Option<Metadata>,
+    /// The initial URL requested.
+    url: ServoUrl,
+    /// 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.metadata = metadata.ok().map(|meta| match meta {
+            FetchMetadata::Unfiltered(m) => m,
+            FetchMetadata::Filtered { unsafe_, .. } => unsafe_
+        });
+
+        let status_code = self.metadata.as_ref().and_then(|m| {
+            match m.status {
+                Some((c, _)) => Some(c),
+                _ => None,
+            }
+        }).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, mut payload: Vec<u8>) {
+        if self.status.is_ok() {
+            self.data.append(&mut payload);
+        }
+    }
+
+    fn process_response_eof(&mut self, _response: Result<(), NetworkError>) {
+        let elem = self.elem.root();
+        let document = document_from_node(&*elem);
+        let window = document.window();
+        let image_cache = window.image_cache_thread();
+        image_cache.store_complete_image_bytes(self.id, self.data.clone());
+        document.finish_load(LoadType::Image(self.url.clone()));
+    }
+}
+
+impl PreInvoke for ImageContext {}
+
 impl HTMLImageElement {
     /// Makes the local `image` member match the status of the `src` attribute and starts
     /// prefetching the image. This method must be called after `src` is changed.
     fn update_image(&self, value: Option<(DOMString, ServoUrl)>) {
         let document = document_from_node(self);
         let window = document.window();
-        let image_cache = window.image_cache_thread();
         match value {
             None => {
                 self.current_request.borrow_mut().parsed_url = None;
                 self.current_request.borrow_mut().source_url = None;
+                LoadBlocker::terminate(&mut self.current_request.borrow_mut().blocker);
                 self.current_request.borrow_mut().image = None;
             }
             Some((src, base_url)) => {
@@ -147,22 +273,57 @@ impl HTMLImageElement {
                     self.current_request.borrow_mut().parsed_url = Some(img_url.clone());
                     self.current_request.borrow_mut().source_url = Some(src);
 
+                    LoadBlocker::terminate(&mut self.current_request.borrow_mut().blocker);
+                    self.current_request.borrow_mut().blocker =
+                        Some(LoadBlocker::new(&*document, LoadType::Image(img_url.clone())));
+
                     let trusted_node = Trusted::new(self);
                     let (responder_sender, responder_receiver) = ipc::channel().unwrap();
                     let task_source = window.networking_task_source();
                     let wrapper = window.get_runnable_wrapper();
+                    let img_url_cloned = img_url.clone();
+                    let trusted_node_clone = trusted_node.clone();
                     ROUTER.add_route(responder_receiver.to_opaque(), box move |message| {
                         // Return the image via a message to the script thread, which marks the element
                         // as dirty and triggers a reflow.
-                        let image_response = message.to().unwrap();
-                        let runnable = box ImageResponseHandlerRunnable::new(
-                            trusted_node.clone(), image_response);
-                        let _ = task_source.queue_with_wrapper(runnable, &wrapper);
+                        let runnable = ImageResponseHandlerRunnable::new(
+                            trusted_node_clone.clone(), message.to().unwrap());
+                        let _ = task_source.queue_with_wrapper(box runnable, &wrapper);
                     });
 
-                    image_cache.request_image_and_metadata(img_url.into(),
-                                              window.image_cache_chan(),
-                                              Some(ImageResponder::new(responder_sender)));
+                    let image_cache = window.image_cache_thread();
+                    let response =
+                        image_cache.find_image_or_metadata(img_url_cloned.into(), UsePlaceholder::Yes);
+                    match response {
+                        Ok(ImageOrMetadataAvailable::ImageAvailable(image)) => {
+                            let event = box ImageResponseHandlerRunnable::new(
+                                trusted_node, ImageResponse::Loaded(image));
+                            event.handler();
+                        }
+
+                        Ok(ImageOrMetadataAvailable::MetadataAvailable(m)) => {
+                            let event = box ImageResponseHandlerRunnable::new(
+                                trusted_node, ImageResponse::MetadataLoaded(m));
+                            event.handler();
+                        }
+
+                        Err(ImageState::Pending(id)) => {
+                            image_cache.add_listener(id, ImageResponder::new(responder_sender, id));
+                        }
+
+                        Err(ImageState::LoadError) => {
+                            let event = box ImageResponseHandlerRunnable::new(
+                                trusted_node, ImageResponse::None);
+                            event.handler();
+                        }
+
+                        Err(ImageState::NotRequested(id)) => {
+                            image_cache.add_listener(id, ImageResponder::new(responder_sender, id));
+                            let runnable = box ImageRequestRunnable::new(
+                                Trusted::new(self), img_url, id);
+                            runnable.handler();
+                        }
+                    }
                 } else {
                     // https://html.spec.whatwg.org/multipage/#update-the-image-data
                     // Step 11 (error substeps)
@@ -202,6 +363,7 @@ impl HTMLImageElement {
             }
         }
     }
+
     fn new_inherited(local_name: LocalName, prefix: Option<DOMString>, document: &Document) -> HTMLImageElement {
         HTMLImageElement {
             htmlelement: HTMLElement::new_inherited(local_name, prefix, document),
@@ -210,14 +372,16 @@ impl HTMLImageElement {
                 parsed_url: None,
                 source_url: None,
                 image: None,
-                metadata: None
+                metadata: None,
+                blocker: None,
             }),
             pending_request: DOMRefCell::new(ImageRequest {
                 state: State::Unavailable,
                 parsed_url: None,
                 source_url: None,
                 image: None,
-                metadata: None
+                metadata: None,
+                blocker: None,
             }),
         }
     }