Split out shared networking code into net_traits crate

Fixes #4476

components/net_traits/local_image_cache.rs

@@ -0,0 +1,170 @@
+/* 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/. */
+
+/*!
+An adapter for ImageCacheTask that does local caching to avoid
+extra message traffic, it also avoids waiting on the same image
+multiple times and thus triggering reflows multiple times.
+*/
+
+use image_cache_task::{ImageResponseMsg, ImageCacheTask, Msg};
+use url::Url;
+
+use std::borrow::ToOwned;
+use std::collections::HashMap;
+use std::collections::hash_map::Entry::{Occupied, Vacant};
+use std::sync::mpsc::{channel, Receiver};
+use util::task::spawn_named;
+
+pub trait ImageResponder<NodeAddress: Send> {
+    fn respond(&self) -> Box<Fn(ImageResponseMsg, NodeAddress)+Send>;
+}
+
+pub struct LocalImageCache<NodeAddress> {
+    image_cache_task: ImageCacheTask,
+    round_number: uint,
+    on_image_available: Option<Box<ImageResponder<NodeAddress>+Send>>,
+    state_map: HashMap<Url, ImageState>
+}
+
+impl<NodeAddress: Send> LocalImageCache<NodeAddress> {
+    pub fn new(image_cache_task: ImageCacheTask) -> LocalImageCache<NodeAddress> {
+        LocalImageCache {
+            image_cache_task: image_cache_task,
+            round_number: 1,
+            on_image_available: None,
+            state_map: HashMap::new()
+        }
+    }
+}
+
+#[derive(Clone)]
+struct ImageState {
+    prefetched: bool,
+    decoded: bool,
+    last_request_round: uint,
+    last_response: ImageResponseMsg
+}
+
+impl<NodeAddress: Send + 'static> LocalImageCache<NodeAddress> {
+    /// The local cache will only do a single remote request for a given
+    /// URL in each 'round'. Layout should call this each time it begins
+    pub fn next_round(&mut self, on_image_available: Box<ImageResponder<NodeAddress> + Send>) {
+        self.round_number += 1;
+        self.on_image_available = Some(on_image_available);
+    }
+
+    pub fn prefetch(&mut self, url: &Url) {
+        {
+            let state = self.get_state(url);
+            if state.prefetched {
+                return
+            }
+
+            state.prefetched = true;
+        }
+
+        self.image_cache_task.send(Msg::Prefetch((*url).clone()));
+    }
+
+    pub fn decode(&mut self, url: &Url) {
+        {
+            let state = self.get_state(url);
+            if state.decoded {
+                return
+            }
+            state.decoded = true;
+        }
+
+        self.image_cache_task.send(Msg::Decode((*url).clone()));
+    }
+
+    // FIXME: Should return a Future
+    pub fn get_image(&mut self, node_address: NodeAddress, url: &Url) -> Receiver<ImageResponseMsg> {
+        {
+            let round_number = self.round_number;
+            let state = self.get_state(url);
+
+            // Save the previous round number for comparison
+            let last_round = state.last_request_round;
+            // Set the current round number for this image
+            state.last_request_round = round_number;
+
+            match state.last_response {
+                ImageResponseMsg::ImageReady(ref image) => {
+                    let (chan, port) = channel();
+                    chan.send(ImageResponseMsg::ImageReady(image.clone())).unwrap();
+                    return port;
+                }
+                ImageResponseMsg::ImageNotReady => {
+                    if last_round == round_number {
+                        let (chan, port) = channel();
+                        chan.send(ImageResponseMsg::ImageNotReady).unwrap();
+                        return port;
+                    } else {
+                        // We haven't requested the image from the
+                        // remote cache this round
+                    }
+                }
+                ImageResponseMsg::ImageFailed => {
+                    let (chan, port) = channel();
+                    chan.send(ImageResponseMsg::ImageFailed).unwrap();
+                    return port;
+                }
+            }
+        }
+
+        let (response_chan, response_port) = channel();
+        self.image_cache_task.send(Msg::GetImage((*url).clone(), response_chan));
+
+        let response = response_port.recv().unwrap();
+        match response {
+            ImageResponseMsg::ImageNotReady => {
+                // Need to reflow when the image is available
+                // FIXME: Instead we should be just passing a Future
+                // to the caller, then to the display list. Finally,
+                // the compositor should be responsible for waiting
+                // on the image to load and triggering layout
+                let image_cache_task = self.image_cache_task.clone();
+                assert!(self.on_image_available.is_some());
+                let on_image_available =
+                    self.on_image_available.as_ref().unwrap().respond();
+                let url = (*url).clone();
+                spawn_named("LocalImageCache".to_owned(), move || {
+                    let (response_chan, response_port) = channel();
+                    image_cache_task.send(Msg::WaitForImage(url, response_chan));
+                    on_image_available(response_port.recv().unwrap(), node_address);
+                });
+            }
+            _ => ()
+        }
+
+        // Put a copy of the response in the cache
+        let response_copy = match response {
+            ImageResponseMsg::ImageReady(ref image) => ImageResponseMsg::ImageReady(image.clone()),
+            ImageResponseMsg::ImageNotReady => ImageResponseMsg::ImageNotReady,
+            ImageResponseMsg::ImageFailed => ImageResponseMsg::ImageFailed
+        };
+        self.get_state(url).last_response = response_copy;
+
+        let (chan, port) = channel();
+        chan.send(response).unwrap();
+        return port;
+    }
+
+    fn get_state<'a>(&'a mut self, url: &Url) -> &'a mut ImageState {
+        match self.state_map.entry((*url).clone()) {
+            Occupied(entry) => entry.into_mut(),
+            Vacant(entry) =>
+                entry.insert(ImageState {
+                    prefetched: false,
+                    decoded: false,
+                    last_request_round: 0,
+                    last_response: ImageResponseMsg::ImageNotReady,
+                })
+        }
+    }
+}
+
+