4 files changed, 174 insertions, 7 deletions
diff --git a/ext/js/background/backend.js b/ext/js/background/backend.js
index 565f4abf..308ae4d5 100644
--- a/ext/js/background/backend.js
+++ b/ext/js/background/backend.js
@@ -57,12 +57,21 @@ class Backend {
         });
         this._anki = new AnkiConnect();
         this._mecab = new Mecab();
-        this._clipboardReader = new ClipboardReader({
-            // eslint-disable-next-line no-undef
-            document: (typeof document === 'object' && document !== null ? document : null),
-            pasteTargetSelector: '#clipboard-paste-target',
-            richContentPasteTargetSelector: '#clipboard-rich-content-paste-target'
-        });
+
+        if (!chrome.offscreen) {
+            this._clipboardReader = new ClipboardReader({
+                // eslint-disable-next-line no-undef
+                document: (typeof document === 'object' && document !== null ? document : null),
+                pasteTargetSelector: '#clipboard-paste-target',
+                richContentPasteTargetSelector: '#clipboard-rich-content-paste-target'
+            });
+        } else {
+            this._clipboardReader = {
+                getText: this._getTextOffscreen.bind(this),
+                getImage: this._getImageOffscreen.bind(this)
+            };
+        }
+
         this._clipboardMonitor = new ClipboardMonitor({
             japaneseUtil: this._japaneseUtil,
             clipboardReader: this._clipboardReader
@@ -97,6 +106,8 @@ class Backend {
         this._permissions = null;
         this._permissionsUtil = new PermissionsUtil();
 
+        this._creatingOffscreen = null;
+
         this._messageHandlers = new Map([
             ['requestBackendReadySignal',    {async: false, contentScript: true,  handler: this._onApiRequestBackendReadySignal.bind(this)}],
             ['optionsGet',                   {async: false, contentScript: true,  handler: this._onApiOptionsGet.bind(this)}],
@@ -218,6 +229,9 @@ class Backend {
 
             await this._requestBuilder.prepare();
             await this._environment.prepare();
+            if (chrome.offscreen) {
+                await this._setupOffscreenDocument();
+            }
             this._clipboardReader.browser = this._environment.getInfo().browser;
 
             try {
@@ -1610,6 +1624,20 @@ class Backend {
         return await (json ? response.json() : response.text());
     }
 
+    _sendMessagePromise(...args) {
+        return new Promise((resolve, reject) => {
+            const callback = (response) => {
+                try {
+                    resolve(this._getMessageResponseResult(response));
+                } catch (error) {
+                    reject(error);
+                }
+            };
+
+            chrome.runtime.sendMessage(...args, callback);
+        });
+    }
+
     _sendMessageIgnoreResponse(...args) {
         const callback = () => this._checkLastError(chrome.runtime.lastError);
         chrome.runtime.sendMessage(...args, callback);
@@ -2220,6 +2248,14 @@ class Backend {
         return results;
     }
 
+    async _getTextOffscreen(useRichText) {
+        return this._sendMessagePromise({action: 'clipboardGetTextOffscreen', params: {useRichText}});
+    }
+
+    async _getImageOffscreen() {
+        return this._sendMessagePromise({action: 'clipboardGetImageOffscreen'});
+    }
+
     _onApiOpenCrossFramePort({targetTabId, targetFrameId}, sender) {
         const sourceTabId = (sender && sender.tab ? sender.tab.id : null);
         if (typeof sourceTabId !== 'number') {
@@ -2262,4 +2298,36 @@ class Backend {
 
         return {targetTabId, targetFrameId};
     }
+
+    // https://developer.chrome.com/docs/extensions/reference/offscreen/
+    async _setupOffscreenDocument() {
+        if (await this._hasOffscreenDocument()) {
+            return;
+        }
+        if (this._creatingOffscreen) {
+            await this._creatingOffscreen;
+            return;
+        }
+
+        this._creatingOffscreen = chrome.offscreen.createDocument({
+            url: 'offscreen.html',
+            reasons: ['CLIPBOARD'],
+            justification: 'Access to the clipboard'
+        });
+        await this._creatingOffscreen;
+        this._creatingOffscreen = null;
+    }
+    async _hasOffscreenDocument() {
+        const offscreenUrl = chrome.runtime.getURL('offscreen.html');
+        if (!chrome.runtime.getContexts) { // chrome version <116
+            const matchedClients = await clients.matchAll();
+            return await matchedClients.some((client) => client.url === offscreenUrl);
+        }
+
+        const contexts = await chrome.runtime.getContexts({
+            contextTypes: ['OFFSCREEN_DOCUMENT'],
+            documentUrls: [offscreenUrl]
+        });
+        return !!contexts.length;
+    }
 }
diff --git a/ext/js/background/offscreen-main.js b/ext/js/background/offscreen-main.js
new file mode 100644
index 00000000..808e7766
--- /dev/null
+++ b/ext/js/background/offscreen-main.js
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ * Copyright (C) 2020-2022  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* global
+ * Offscreen
+ */
+
+(() => {
+    new Offscreen();
+})();
diff --git a/ext/js/background/offscreen.js b/ext/js/background/offscreen.js
new file mode 100644
index 00000000..bc41d189
--- /dev/null
+++ b/ext/js/background/offscreen.js
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ * Copyright (C) 2016-2022  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* global
+ * ClipboardReader
+ */
+
+/**
+ * This class controls the core logic of the extension, including API calls
+ * and various forms of communication between browser tabs and external applications.
+ */
+class Offscreen {
+    /**
+     * Creates a new instance.
+     */
+    constructor() {
+        this._clipboardReader = new ClipboardReader({
+            // eslint-disable-next-line no-undef
+            document: (typeof document === 'object' && document !== null ? document : null),
+            pasteTargetSelector: '#clipboard-paste-target',
+            richContentPasteTargetSelector: '#clipboard-rich-content-paste-target'
+        });
+
+        this._messageHandlers = new Map([
+            ['clipboardGetTextOffscreen',                 {async: true,  contentScript: true,  handler: this._getTextHandler.bind(this)}],
+            ['clipboardGetImageOffscreen',                 {async: true,  contentScript: true,  handler: this._getImageHandler.bind(this)}]
+        ]);
+
+        const onMessage = this._onMessage.bind(this);
+        chrome.runtime.onMessage.addListener(onMessage);
+    }
+
+    _getTextHandler({useRichText}) {
+        return this._clipboardReader.getText(useRichText);
+    }
+
+    _getImageHandler() {
+        return this._clipboardReader.getImage();
+    }
+
+    _onMessage({action, params}, sender, callback) {
+        const messageHandler = this._messageHandlers.get(action);
+        if (typeof messageHandler === 'undefined') { return false; }
+        this._validatePrivilegedMessageSender(sender);
+
+        return invokeMessageHandler(messageHandler, params, callback, sender);
+    }
+
+    _validatePrivilegedMessageSender(sender) {
+        let {url} = sender;
+        if (typeof url === 'string' && yomichan.isExtensionUrl(url)) { return; }
+        const {tab} = url;
+        if (typeof tab === 'object' && tab !== null) {
+            ({url} = tab);
+            if (typeof url === 'string' && yomichan.isExtensionUrl(url)) { return; }
+        }
+        throw new Error('Invalid message sender');
+    }
+}
diff --git a/ext/js/display/search-display-controller.js b/ext/js/display/search-display-controller.js
index 25d9d6c2..5a271e05 100644
--- a/ext/js/display/search-display-controller.js
+++ b/ext/js/display/search-display-controller.js
@@ -44,7 +44,7 @@ class SearchDisplayController {
         this._clipboardMonitor = new ClipboardMonitor({
             japaneseUtil,
             clipboardReader: {
-                getText: async () => (await yomichan.api.clipboardGet())
+                getText: yomichan.api.clipboardGet.bind(yomichan.api)
             }
         });
         this._messageHandlers = new Map();