facilitate making CORS-agnostic requests through background script

1 files changed, 90 insertions, 0 deletions

diff --git a/background/CORS_bypass_server.js b/background/CORS_bypass_server.js
new file mode 100644
index 0000000..cbed945
--- /dev/null
+++ b/background/CORS_bypass_server.js
@@ -0,0 +1,90 @@
+/**
+ * This file is part of Haketilo.
+ *
+ * Function: Allow other parts of the extension to bypass CORS by routing their
+ *           request through this background script using one-off messages.
+ *
+ * Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
+ *
+ * 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.
+ *
+ * As additional permission under GNU GPL version 3 section 7, you
+ * may distribute forms of that code without the copy of the GNU
+ * GPL normally required by section 4, provided you include this
+ * license notice and, in case of non-source distribution, a URL
+ * through which recipients can access the Corresponding Source.
+ * If you modify file(s) with this exception, you may extend this
+ * exception to your version of the file(s), but you are not
+ * obligated to do so. If you do not wish to do so, delete this
+ * exception statement from your version.
+ *
+ * As a special exception to the GPL, any HTML file which merely
+ * makes function calls to this code, and for that purpose
+ * includes it by reference shall be deemed a separate work for
+ * copyright law purposes. If you modify this code, you may extend
+ * this exception to your version of the code, but you are not
+ * obligated to do so. If you do not wish to do so, delete this
+ * exception statement from your version.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * I, Wojtek Kosior, thereby promise not to sue for violation of this file's
+ * license. Although I request that you do not make use of this code in a
+ * proprietary program, I am not going to enforce this in court.
+ */
+
+#FROM common/browser.js IMPORT browser
+
+async function get_prop(object, prop, result_object, call_prop=false) {
+    try {
+	result_object[prop] = call_prop ? (await object[prop]()) : object[prop];
+    } catch(e) {
+	result_object[`error-${prop}`] = "" + e;
+    }
+}
+
+async function perform_download(fetch_data, respond_cb) {
+    try {
+	const response = await fetch(fetch_data.url);
+	const result = {};
+
+	for (const prop of (fetch_data.to_get || []))
+	    get_prop(response, prop, result);
+
+	const to_call = (fetch_data.to_call || []);
+	const promises = [];
+	for (let i = 0; i < to_call.length; i++) {
+	    const response_to_use = i === to_call.length - 1 ?
+		response : response.clone();
+	    promises.push(get_prop(response_to_use, to_call[i], result, true));
+	}
+
+	await Promise.all(promises);
+	return result;
+    } catch(e) {
+	return {error: "" + e};
+    }
+}
+
+function on_CORS_bypass_request([type, fetch_data], sender, respond_cb) {
+    if (type !== "CORS_bypasss")
+	return;
+
+    perform_download(fetch_data).then(respond_cb);
+
+    return true;
+}
+
+function start() {
+    browser.runtime.onMessage.addListener(on_CORS_bypass_request);
+}
+#EXPORT start