ClipboardReader class (#854)

* Create ClipboardReader class

* Use ClipboardReader in Backend

* Update ClipboardMonitor to use ClipboardReader

* Replace _onApiClipboardImageGet call

* Assign clipboard reader browser

1 files changed, 148 insertions, 0 deletions

diff --git a/ext/bg/js/clipboard-reader.js b/ext/bg/js/clipboard-reader.js
new file mode 100644
index 00000000..66cf0c25
--- /dev/null
+++ b/ext/bg/js/clipboard-reader.js
@@ -0,0 +1,148 @@
+/*
+ * Copyright (C) 2020  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/>.
+ */
+
+/**
+ * Class which can read text and images from the clipboard.
+ */
+class ClipboardReader {
+    /**
+     * Creates a new instances of a clipboard reader.
+     * @param document The Document object to be used, or null for no support.
+     * @param pasteTargetSelector The selector for the paste target element.
+     * @param imagePasteTargetSelector The selector for the image paste target element.
+     */
+    constructor({document=null, pasteTargetSelector=null, imagePasteTargetSelector=null}) {
+        this._document = document;
+        this._browser = null;
+        this._pasteTarget = null;
+        this._pasteTargetSelector = pasteTargetSelector;
+        this._imagePasteTarget = null;
+        this._imagePasteTargetSelector = imagePasteTargetSelector;
+    }
+
+    /**
+     * Gets the browser being used.
+     */
+    get browser() {
+        return this._browser;
+    }
+
+    /**
+     * Assigns the browser being used.
+     */
+    set browser(value) {
+        this._browser = value;
+    }
+
+    /**
+     * Gets the text in the clipboard.
+     * @returns A string containing the clipboard text.
+     * @throws Error if not supported.
+     */
+    async getText() {
+        /*
+        Notes:
+            document.execCommand('paste') doesn't work on Firefox.
+            This may be a bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1603985
+            Therefore, navigator.clipboard.readText() is used on Firefox.
+
+            navigator.clipboard.readText() can't be used in Chrome for two reasons:
+            * Requires page to be focused, else it rejects with an exception.
+            * When the page is focused, Chrome will request clipboard permission, despite already
+              being an extension with clipboard permissions. It effectively asks for the
+              non-extension permission for clipboard access.
+        */
+        if (this._isFirefox()) {
+            return await navigator.clipboard.readText();
+        }
+
+        const document = this._document;
+        if (document === null) {
+            throw new Error('Not supported');
+        }
+
+        let target = this._pasteTarget;
+        if (target === null) {
+            target = document.querySelector(this._pasteTargetSelector);
+            if (target === null) {
+                throw new Error('Clipboard paste target does not exist');
+            }
+            this._pasteTarget = target;
+        }
+
+        target.value = '';
+        target.focus();
+        document.execCommand('paste');
+        const result = target.value;
+        target.value = '';
+        return (typeof result === 'string' ? result : '');
+    }
+
+    /**
+     * Gets the first image in the clipboard.
+     * @returns A string containing a data URL of the image file, or null if no image was found.
+     * @throws Error if not supported.
+     */
+    async getImage() {
+        // See browser-specific notes in getText
+        if (this._isFirefox()) {
+            if (typeof navigator.clipboard !== 'undefined' && typeof navigator.clipboard.read === 'function') {
+                // This function is behind the flag: dom.events.asyncClipboard.dataTransfer
+                const {files} = await navigator.clipboard.read();
+                if (files.length === 0) { return null; }
+                const result = await this._readFileAsDataURL(files[0]);
+                return result;
+            }
+        }
+
+        const document = this._document;
+        if (document === null) {
+            throw new Error('Not supported');
+        }
+
+        let target = this._imagePasteTarget;
+        if (target === null) {
+            target = document.querySelector(this._imagePasteTargetSelector);
+            if (target === null) {
+                throw new Error('Clipboard paste target does not exist');
+            }
+            this._imagePasteTarget = target;
+        }
+
+        target.focus();
+        document.execCommand('paste');
+        const image = target.querySelector('img[src^="data:"]');
+        const result = (image !== null ? image.getAttribute('src') : null);
+        target.textContent = '';
+        return result;
+    }
+
+    // Private
+
+    _isFirefox() {
+        return (this._browser === 'firefox' || this._browser === 'firefox-mobile');
+    }
+
+    _readFileAsDataURL(file) {
+        return new Promise((resolve, reject) => {
+            const reader = new FileReader();
+            reader.onload = () => resolve(reader.result);
+            reader.onerror = () => reject(reader.error);
+            reader.readAsDataURL(file);
+        });
+    }
+}