serialize and deserialize entire Response object when relaying fetch() calls to other contexts using sendMessage

1 files changed, 30 insertions, 25 deletions

diff --git a/background/CORS_bypass_server.js b/background/CORS_bypass_server.js
index 9805d41..d15db54 100644
--- a/background/CORS_bypass_server.js
+++ b/background/CORS_bypass_server.js
@@ -2,7 +2,7 @@
  * 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.
+ *           requests through this background script using one-off messages.
  *
  * Copyright (C) 2022 Wojtek Kosior <koszko@koszko.org>
  *
@@ -43,35 +43,40 @@
  */
 
 #FROM common/browser.js IMPORT browser
+#FROM common/misc.js    IMPORT uint8_to_hex, error_data_jsonifiable
 
-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;
-    }
+/*
+ * In this file we implement a fetch()-from-background-script service. Code in
+ * other parts of the extension shall call sendMessage() with arguments to
+ * fetch() and code here will call fetch() with those arguments and send back
+ * the response.
+ *
+ * We have to convert the Response from fetch() into a JSON-ifiable value and
+ * then convert it back (using Response() constructor) due (among others) the
+ * limitations of Chromium's messaging API:
+ * https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Chrome_incompatibilities#data_cloning_algorithm
+ *
+ * We also catch possible errors from fetch() (e.g. in case of an invalid URL)
+ * and send their data in JSON-ifiable form so that the error object can be
+ * later re-created.
+ */
+
+/* Make it possible to serialize Response object. */
+async function response_data_jsonifiable(response) {
+    return {
+	status:     response.status,
+	statusText: response.statusText,
+	headers:    [...response.headers.entries()],
+	body:       uint8_to_hex(new Uint8Array(await response.arrayBuffer()))
+    };
 }
 
-async function perform_download(fetch_data, respond_cb) {
+async function perform_download(fetch_data) {
     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;
+	const response = await fetch(fetch_data.url, fetch_data.init);
+	return response_data_jsonifiable(response);
     } catch(e) {
-	return {error: "" + e};
+	return {error: error_data_jsonifiable(e)};
     }
 }