net: Start reducing number of IPCs channels used for fetch with a FetchThread (#33863)

Instead of creating a `ROUTER` for each fetch, create a fetch thread
which handles all incoming and outcoming fetch requests. Now messages
involving fetches carry a "request id" which indicates which fetch is
being addressed by the message. This greatly reduces the number of file
descriptors used by fetch.

In addition, the interface for kicking off fetches is simplified when
using the `Listener` with `Document`s and the `GlobalScope`.

This does not fix all leaked file descriptors / mach ports, but greatly
eliminates the number used. Now tests can be run without limiting
procesess on modern macOS systems.

Followup work:

1. There are more instances where fetch is done using the old method.
   Some of these require more changes in order to be converted to the
   `FetchThread` approach.
2. Eliminate usage of IPC channels when doing redirects.
3. Also eliminate the IPC channel used for cancel handling.
4. This change opens up the possiblity of controlling the priority of
   fetch requests.

Fixes #29834.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/htmlscriptelement.rs

@@ -18,12 +18,11 @@ use dom_struct::dom_struct;
 use encoding_rs::Encoding;
 use html5ever::{local_name, namespace_url, ns, LocalName, Prefix};
 use ipc_channel::ipc;
-use ipc_channel::router::ROUTER;
 use js::jsval::UndefinedValue;
 use js::rust::{transform_str_to_source_text, CompileOptionsWrapper, HandleObject, Stencil};
 use net_traits::http_status::HttpStatus;
 use net_traits::request::{
-    CorsSettings, CredentialsMode, Destination, ParserMetadata, RequestBuilder,
+    CorsSettings, CredentialsMode, Destination, ParserMetadata, RequestBuilder, RequestId,
 };
 use net_traits::{
     FetchMetadata, FetchResponseListener, Metadata, NetworkError, ResourceFetchTiming,
@@ -351,11 +350,13 @@ struct ClassicContext {
 }
 
 impl FetchResponseListener for ClassicContext {
-    fn process_request_body(&mut self) {} // TODO(KiChjang): Perhaps add custom steps to perform fetch here?
+    // TODO(KiChjang): Perhaps add custom steps to perform fetch here?
+    fn process_request_body(&mut self, _: RequestId) {}
 
-    fn process_request_eof(&mut self) {} // TODO(KiChjang): Perhaps add custom steps to perform fetch here?
+    // TODO(KiChjang): Perhaps add custom steps to perform fetch here?
+    fn process_request_eof(&mut self, _: RequestId) {}
 
-    fn process_response(&mut self, metadata: Result<FetchMetadata, NetworkError>) {
+    fn process_response(&mut self, _: RequestId, metadata: Result<FetchMetadata, NetworkError>) {
         self.metadata = metadata.ok().map(|meta| match meta {
             FetchMetadata::Unfiltered(m) => m,
             FetchMetadata::Filtered { unsafe_, .. } => unsafe_,
@@ -383,7 +384,7 @@ impl FetchResponseListener for ClassicContext {
         };
     }
 
-    fn process_response_chunk(&mut self, mut chunk: Vec<u8>) {
+    fn process_response_chunk(&mut self, _: RequestId, mut chunk: Vec<u8>) {
         if self.status.is_ok() {
             self.data.append(&mut chunk);
         }
@@ -392,7 +393,11 @@ impl FetchResponseListener for ClassicContext {
     /// <https://html.spec.whatwg.org/multipage/#fetch-a-classic-script>
     /// step 4-9
     #[allow(unsafe_code)]
-    fn process_response_eof(&mut self, response: Result<ResourceFetchTiming, NetworkError>) {
+    fn process_response_eof(
+        &mut self,
+        _: RequestId,
+        response: Result<ResourceFetchTiming, NetworkError>,
+    ) {
         let (source_text, final_url) = match (response.as_ref(), self.status.as_ref()) {
             (Err(err), _) | (_, Err(err)) => {
                 // Step 6, response is an error.
@@ -538,9 +543,8 @@ fn fetch_a_classic_script(
     options: ScriptFetchOptions,
     character_encoding: &'static Encoding,
 ) {
-    let doc = document_from_node(script);
-
     // Step 1, 2.
+    let doc = document_from_node(script);
     let request = script_fetch_request(
         url.clone(),
         cors_setting,
@@ -548,10 +552,11 @@ fn fetch_a_classic_script(
         script.global().pipeline_id(),
         options.clone(),
     );
+    let request = doc.prepare_request(request);
 
     // TODO: Step 3, Add custom steps to perform fetch
 
-    let context = Arc::new(Mutex::new(ClassicContext {
+    let context = ClassicContext {
         elem: Trusted::new(script),
         kind,
         character_encoding,
@@ -561,26 +566,8 @@ fn fetch_a_classic_script(
         status: Ok(()),
         fetch_options: options,
         resource_timing: ResourceFetchTiming::new(ResourceTimingType::Resource),
-    }));
-
-    let (action_sender, action_receiver) = ipc::channel().unwrap();
-    let (task_source, canceller) = doc
-        .window()
-        .task_manager()
-        .networking_task_source_with_canceller();
-    let listener = NetworkListener {
-        context,
-        task_source,
-        canceller: Some(canceller),
     };
-
-    ROUTER.add_route(
-        action_receiver.to_opaque(),
-        Box::new(move |message| {
-            listener.notify_fetch(message.to().unwrap());
-        }),
-    );
-    doc.fetch_async(LoadType::Script(url), request, action_sender);
+    doc.fetch(LoadType::Script(url), request, context);
 }
 
 impl HTMLScriptElement {