[WIP Prototype] ES6 https://html.spec.whatwg.org/#fetch-a-single-module-script implementation

third_party/WebKit/Source/core/dom/ModuleMap.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/dom/ModuleMap.h"
+
+#include "bindings/core/v8/ScriptController.h"
+#include "bindings/core/v8/V8PerIsolateData.h"
+#include "core/fetch/ResourceFetcher.h"
+#include "platform/network/mime/MIMETypeRegistry.h"
+#include "wtf/AutoReset.h"
+#include <v8.h>
+
+namespace blink {
+
+ModuleLoaderClient::~ModuleLoaderClient() {}
+
+void ModuleLoaderClient::catchUpToLatestStateIfNeeded(
+    ModuleLoaderState latestState) {
+  if (m_state == ModuleLoaderState::Finished)
+    return;
+  if (latestState == ModuleLoaderState::Finished) {
+    notifyFinished();
+    m_state = latestState;
+  }
+}
+
+ModuleLoader::ModuleLoader(const KURL& url, ScriptController* scriptController)
+    : m_url(url), m_scriptController(scriptController) {}
+
+ModuleLoader::~ModuleLoader() {}
+
+void ModuleLoader::advanceState(ModuleLoaderState newState) {
+  switch (m_state) {
+    case ModuleLoaderState::Initial:
+      DCHECK_EQ(newState, ModuleLoaderState::Fetching);
+      break;
+    case ModuleLoaderState::Fetching:
+      DCHECK_EQ(newState, ModuleLoaderState::Finished);
+      break;
+    case ModuleLoaderState::Finished:
+    default:
+      NOTREACHED();
+  }
+
+  m_state = newState;
+
+  notifyAndFlushPendingClients();
+}
+
+ModuleLoader* ModuleLoader::fetch(const KURL& url,
+                                  ScriptController* scriptController,
+                                  ResourceFetcher* fetcher) {
+  ModuleLoader* loader = new ModuleLoader(url, scriptController);
+  loader->fetchInternal(fetcher);
+  return loader;
+}
+
+void ModuleLoader::fetchInternal(ResourceFetcher* fetcher) {
+  // Step 4. Set moduleMap[url] to "fetching".
+  advanceState(ModuleLoaderState::Fetching);
+
+  // Step 5. Let request be a new request whose url is url, destination is
+  // destination, type is "script", mode is "cors", credentials mode is
+  // credentials mode, cryptographic nonce metadata is cryptographic nonce,
+  // parser metadata is parser state, referrer is referrer, and client is
+  // fetch
+  // client settings object.
+  FetchRequest request(ResourceRequest(m_url), "module");
+  // request.setDefer(FetchRequest::LazyLoad); //? always async -> defer?
+  Member<ScriptResource> resource = ScriptResource::fetch(request, fetcher);
+  setResource(resource);
+
+  // Step 6. If the caller specified custom steps to perform the fetch,
+  // perform
+  // them on request, setting the is top-level flag if the top-level module
+  // fetch flag is set. Return from this algorithm, and when the custom
+  // perform
+  // the fetch steps complete with response response, run the remaining steps.
+  // Otherwise, fetch request. Return from this algorithm, and run the
+  // remaining
+  // steps as part of the fetch's process response for the response response.
+  // Note: response is always CORS-same-origin.
+
+  // TODO(kouhei): I don't know what Step 6 means. ScriptLoader seems to
+  // ignore
+  // the step?
+}
+
+bool ModuleLoader::wasModuleLoadSuccessful(Resource* resource) {
+  // Implements conditions in Step 7 of
+  // https://html.spec.whatwg.org/#fetch-a-single-module-script
+
+  // - response's type is "error"
+  if (resource->errorOccurred())
+    return false;
+
+  const auto& response = resource->response();
+  // - response's status is not an ok status
+  if (response.isHTTP() &&
+      (response.httpStatusCode() < 200 || response.httpStatusCode() >= 300)) {
+    return false;
+  }
+
+  // The result of extracting a MIME type from response's header list
+  // (ignoring parameters) is not a JavaScript MIME type
+  // Note: For historical reasons, fetching a classic script does not include
+  // MIME type checking. In contrast, module scripts will fail to load if they
+  // are not of a correct MIME type.
+  if (!MIMETypeRegistry::isSupportedJavaScriptMIMEType(response.mimeType()))
+    return false;
+
+  return true;
+}
+
+void ModuleLoader::notifyFinished(Resource*) {
+  printf("notifyFinished!\n");
+
+  // Note: "conditions" referred in Step 7 is implemented in
+  // wasModuleLoadSuccessful().
+  // Step 7. If any of the following conditions are met, set moduleMap[url] to
+  // null, asynchronously complete this algorithm with null, and abort these
+  // steps.
+  if (!wasModuleLoadSuccessful(resource())) {
+    printf("notifyFinished but load was not successful\n");
+
+    m_wasLoadSuccessful = false;
+    advanceState(ModuleLoaderState::Finished);
+    setResource(nullptr);
+    return;
+  }
+
+  // Step 8. Let source text be the result of UTF-8 decoding response's body.
+  String script = resource()->script();
+  printf("fetched script: %s\n", script.utf8().data());
+
+  // Step 9. Let module script be the result of creating a module script given
+  // source text, module map settings object, response's url, cryptographic
+  // nonce, parser state, and credentials mode.
+
+  // TODO(kouhei): post a task to compile module?
+  m_scriptModule = m_scriptController->compileModule(script, m_url.getString());
+  m_wasLoadSuccessful = !m_scriptModule.isNull();
+  advanceState(ModuleLoaderState::Finished);
+  setResource(nullptr);
+}
+
+void ModuleLoader::addClient(ModuleLoaderClient* newClient) {
+  DCHECK(!m_pendingClients.contains(newClient));
+  DCHECK(!m_clients.contains(newClient));
+  newClient->setLoader(this);
+  m_pendingClients.add(newClient);
+
+  notifyAndFlushPendingClients();
+}
+
+void ModuleLoader::notifyAndFlushPendingClients() {
+  if (m_isFlushingPendingClients) {
+    // This notifyAndFlushPendingClients call was reentrant.
+    // Defer to first notifyAndFlushPendingClients to do the job.
+    return;
+  }
+
+  AutoReset<bool> forbidClientModificationScope(&m_isFlushingPendingClients,
+                                                true);
+
+  if (m_lastClientNotifiedState != m_state) {
+    // if m_state has changed since last update, put all m_clients back into
+    // m_pendingClients so that they catchUpToLatestStateIfNeeded()
+    m_pendingClients.swap(m_clients);
+    while (!m_clients.isEmpty()) {
+      m_pendingClients.add(m_clients.takeAny());
+    }
+
+    m_lastClientNotifiedState = m_state;
+  }
+
+  while (!m_pendingClients.isEmpty()) {
+    // Iterate on copy as m_pendingClients may be added in the notification
+    // loop.
+    HeapHashSet<Member<ModuleLoaderClient>> clientsToCatchUp;
+    clientsToCatchUp.swap(m_pendingClients);
+    for (const auto& client : clientsToCatchUp) {
+      client->catchUpToLatestStateIfNeeded(m_state);
+    }
+
+    // Caught up clients do not have any notifications to receive after the
+    // load is finished.
+    if (hasFinished())
+      continue;
+
+    while (!clientsToCatchUp.isEmpty())
+      m_clients.add(clientsToCatchUp.takeAny());
+  }
+}
+
+DEFINE_TRACE(ModuleLoader) {
+  visitor->trace(m_scriptController);
+  visitor->trace(m_pendingClients);
+  visitor->trace(m_clients);
+  ResourceOwner<ScriptResource>::trace(visitor);
+}
+
+ModuleMap::ModuleMap(ScriptController* scriptController,
+                     ResourceFetcher* fetcher)
+    : m_scriptController(scriptController), m_fetcher(fetcher) {
+  DCHECK(m_scriptController);
+  DCHECK(m_fetcher);
+}
+
+void ModuleMap::fetchSingle(const KURL& url, ModuleLoaderClient* client) {
+  printf("ModuleMap::fetch(%s)\n", url.getString().utf8().data());
+
+  MapImpl::AddResult result = m_map.set(url, nullptr);
+  Member<ModuleLoader>& loaderEntry = result.storedValue->value;
+  if (!result.isNewEntry) {
+    printf("not new entry\n");
+
+    // - If moduleMap[url] is "fetching", wait (in parallel) until that
+    // loaderEntry's value changes, then proceed to the next step.
+    // - If moduleMap[url] exists, asynchronously complete this algorithm
+    // with moduleMap[url], and abort these steps.
+    loaderEntry->addClient(client);

[dominicc (has gone to gerrit), 2016/12/13 07:45:29]

I think this design has to be careful with the transition from loading, to map
entry.

I wonder if it would be more robust if the map entry was what handled having
multiple readers pile up against it, instead of the loader? If you used a double
linked list of these readers, notifying them would probably be pretty simple?

Then the loader can have one and only one client. That happens to be all you
need for the inline module script case for example. And in the named module
script, the module map (entry) would be the one and only client.

WDYT?

[kouhei (in TOK), 2016/12/15 04:56:27]

I'd like to discuss this offline (probably need a whiteboard)

+    return;
+  }
+
+  ModuleLoader* loader =
+      ModuleLoader::fetch(url, m_scriptController.get(), m_fetcher.get());
+
+  // Step 10. Set moduleMap[url] to module script, and asynchronously complete
+  // this algorithm with module script.
+  loaderEntry = loader;
+  loaderEntry->addClient(client);
+}
+
+DEFINE_TRACE(ModuleMap) {
+  visitor->trace(m_map);
+  visitor->trace(m_scriptController);
+  visitor->trace(m_fetcher);
+}
+
+}  // namespace blink