3 files changed, 131 insertions, 20 deletions
diff --git a/ext/js/background/backend.js b/ext/js/background/backend.js
index f5cbb349..308ae4d5 100644
--- a/ext/js/background/backend.js
+++ b/ext/js/background/backend.js
@@ -58,16 +58,18 @@ class Backend {
         this._anki = new AnkiConnect();
         this._mecab = new Mecab();
 
-        this._clipboardReader = {
-            getText: this._getTextOffscreen.bind(this)
-        };
-        if (!chrome || !chrome.offscreen) {
+        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({
@@ -227,6 +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 {
@@ -566,21 +571,6 @@ class Backend {
         return this._clipboardReader.getText(false);
     }
 
-    async _getTextOffscreen(useRichText) {
-        await this._setupOffscreenDocument();
-        return new Promise((resolve, reject) => {
-            const callback = (response) => {
-                try {
-                    resolve(this._getMessageResponseResult(response));
-                } catch (error) {
-                    reject(error);
-                }
-            };
-
-            chrome.runtime.sendMessage({action: 'clipboardGetOffscreen', params: {useRichText}}, callback);
-        });
-    }
-
     async _onApiGetDisplayTemplatesHtml() {
         return await this._fetchAsset('/display-templates.html');
     }
@@ -1634,6 +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);
@@ -2244,6 +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') {
@@ -2300,7 +2312,7 @@ class Backend {
         this._creatingOffscreen = chrome.offscreen.createDocument({
             url: 'offscreen.html',
             reasons: ['CLIPBOARD'],
-            justification: 'reason for needing the document'
+            justification: 'Access to the clipboard'
         });
         await this._creatingOffscreen;
         this._creatingOffscreen = null;
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');
+    }
+}