1 files changed, 118 insertions, 0 deletions
diff --git a/toolkit/components/translations/actors/TranslationsChild.sys.mjs b/toolkit/components/translations/actors/TranslationsChild.sys.mjs
new file mode 100644
index 0000000000..a3f8d15c85
--- /dev/null
+++ b/toolkit/components/translations/actors/TranslationsChild.sys.mjs
@@ -0,0 +1,118 @@
+/* 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/. */
+
+const lazy = {};
+ChromeUtils.defineESModuleGetters(lazy, {
+  TranslationsDocument:
+    "chrome://global/content/translations/translations-document.sys.mjs",
+  LRUCache:
+    "chrome://global/content/translations/translations-document.sys.mjs",
+  LanguageDetector:
+    "resource://gre/modules/translation/LanguageDetector.sys.mjs",
+});
+
+/**
+ * This file is extremely sensitive to memory size and performance!
+ */
+export class TranslationsChild extends JSWindowActorChild {
+  /**
+   * @type {TranslationsDocument | null}
+   */
+  #translatedDoc = null;
+
+  /**
+   * This cache is shared across TranslationsChild instances. This means
+   * that it will be shared across multiple page loads in the same origin.
+   * @type {LRUCache | null}
+   */
+  static #translationsCache = null;
+
+  handleEvent(event) {
+    switch (event.type) {
+      case "DOMContentLoaded":
+        this.sendAsyncMessage("Translations:ReportLangTags", {
+          documentElementLang: this.document.documentElement.lang,
+        });
+        break;
+    }
+  }
+
+  addProfilerMarker(message) {
+    ChromeUtils.addProfilerMarker(
+      "TranslationsChild",
+      { innerWindowId: this.contentWindow.windowGlobalChild.innerWindowId },
+      message
+    );
+  }
+
+  async receiveMessage({ name, data }) {
+    switch (name) {
+      case "Translations:TranslatePage": {
+        if (this.#translatedDoc?.translator.engineStatus === "error") {
+          this.#translatedDoc.destroy();
+          this.#translatedDoc = null;
+        }
+
+        if (this.#translatedDoc) {
+          console.error("This page was already translated.");
+          return undefined;
+        }
+
+        const { fromLanguage, toLanguage, port, translationsStart } = data;
+        if (
+          !TranslationsChild.#translationsCache ||
+          !TranslationsChild.#translationsCache.matches(
+            fromLanguage,
+            toLanguage
+          )
+        ) {
+          TranslationsChild.#translationsCache = new lazy.LRUCache(
+            fromLanguage,
+            toLanguage
+          );
+        }
+
+        this.#translatedDoc = new lazy.TranslationsDocument(
+          this.document,
+          fromLanguage,
+          toLanguage,
+          this.contentWindow.windowGlobalChild.innerWindowId,
+          port,
+          () => this.sendAsyncMessage("Translations:RequestPort"),
+          translationsStart,
+          () => this.docShell.now(),
+          TranslationsChild.#translationsCache
+        );
+
+        return undefined;
+      }
+      case "Translations:GetDocumentElementLang":
+        return this.document.documentElement.lang;
+      case "Translations:IdentifyLanguage": {
+        // Wait for idle callback as the page will be more settled if it has
+        // dynamic content, like on a React app.
+        if (this.contentWindow) {
+          await new Promise(resolve => {
+            this.contentWindow.requestIdleCallback(resolve);
+          });
+        }
+
+        try {
+          return lazy.LanguageDetector.detectLanguageFromDocument(
+            this.document
+          );
+        } catch (error) {
+          return null;
+        }
+      }
+      case "Translations:AcquirePort": {
+        this.addProfilerMarker("Acquired a port, resuming translations");
+        this.#translatedDoc.translator.acquirePort(data.port);
+        return undefined;
+      }
+      default:
+        throw new Error("Unknown message.", name);
+    }
+  }
+}