utilize Pattern Tree to decide the policy to use and modify HTTP response headers according to that policy

This commit also enhances the build script so that preprocessor conditionals can now use operators '&&' and '||'.
The features being developed are not yet included in the actual Haketilo build.
Some of the new source files contain similar functionality to other ones already existing in the source tree. At some point the latter will be removed.

1 files changed, 189 insertions, 0 deletions

diff --git a/background/webrequest.js b/background/webrequest.js
new file mode 100644
index 0000000..e32947a
--- /dev/null
+++ b/background/webrequest.js
@@ -0,0 +1,189 @@
+/**
+ * This file is part of Haketilo.
+ *
+ * Function: Modify HTTP traffic usng webRequest API.
+ *
+ * Copyright (C) 2021 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 this code in a
+ * proprietary program, I am not going to enforce this in court.
+ */
+
+#IMPORT common/indexeddb.js        AS haketilodb
+#IF MOZILLA
+#IMPORT background/stream_filter.js
+#ENDIF
+
+#FROM common/browser.js IMPORT browser
+#FROM common/misc.js    IMPORT is_privileged_url, csp_header_regex
+#FROM common/policy.js  IMPORT decide_policy
+
+#FROM background/patterns_query_manager.js IMPORT tree
+
+let secret;
+
+let default_allow = false;
+
+async function track_default_allow()
+{
+    const set_val = ch => default_allow = (ch.new_val || {}).value;
+    const [tracking, settings] = await haketilodb.track.settings(set_val);
+    for (const setting of settings) {
+	if (setting.name === "default_allow")
+	    default_allow = setting.value;
+    }
+}
+
+function on_headers_received(details)
+{
+    const url = details.url;
+    if (is_privileged_url(details.url))
+	return;
+
+    let headers = details.responseHeaders;
+
+    const policy = decide_policy(tree, details.url, default_allow, secret);
+    if (policy.allow)
+	return;
+
+    if (policy.payload)
+	headers = headers.filter(h => !csp_header_regex.test(h.name));
+
+    headers.push({name: "Content-Security-Policy", value: policy.csp});
+
+#IF MOZILLA
+    let skip = false;
+    for (const header of headers) {
+	if (header.name.toLowerCase().trim() !== "content-disposition")
+	    continue;
+
+	if (/^\s*attachment\s*(;.*)$/i.test(header.value)) {
+		skip = true;
+	} else {
+	    skip = false;
+	    break;
+	}
+    }
+    skip = skip || (details.statusCode >= 300 && details.statusCode < 400);
+
+    if (!skip)
+	headers = stream_filter.apply(details, headers, policy);
+#ENDIF
+
+    return {responseHeaders: headers};
+}
+
+#IF CHROMIUM && MV2
+const request_url_regex = /^[^?]*\?url=(.*)$/;
+const redirect_url_template = browser.runtime.getURL("dummy") + "?settings=";
+
+function on_before_request(details)
+{
+    /*
+     * Content script will make a synchronous XmlHttpRequest to extension's
+     * `dummy` file to query settings for given URL. We smuggle that
+     * information in query parameter of the URL we redirect to.
+     * A risk of fingerprinting arises if a page with script execution allowed
+     * guesses the dummy file URL and makes an AJAX call to it. It is currently
+     * a problem in ManifestV2 Chromium-family port of Haketilo because Chromium
+     * uses predictable URLs for web-accessible resources. We plan to fix it in
+     * the future ManifestV3 port.
+     */
+    if (details.type !== "xmlhttprequest")
+	return {cancel: true};
+
+#IF DEBUG
+    console.debug(`Settings queried using XHR for '${details.url}'.`);
+#ENDIF
+
+    /*
+     * request_url should be of the following format:
+     *     <url_for_extension's_dummy_file>?url=<valid_urlencoded_url>
+     */
+    const match = request_url_regex.exec(details.url);
+    if (match) {
+	const queried_url = decodeURIComponent(match[1]);
+
+	if (details.initiator && !queried_url.startsWith(details.initiator)) {
+	    console.warn(`Blocked suspicious query of '${url}' by '${details.initiator}'. This might be the result of page fingerprinting the browser.`);
+	    return {cancel: true};
+	}
+
+	const policy = decide_policy(tree, details.url, default_allow, secret);
+	if (!policy.error) {
+	    const encoded_policy = encodeURIComponent(JSON.stringify(policy));
+	    return {redirectUrl: redirect_url_template + encoded_policy};
+	}
+    }
+
+    console.warn(`Bad request! Expected ${browser.runtime.getURL("dummy")}?url=<valid_urlencoded_url>. Got ${request_url}. This might be the result of page fingerprinting the browser.`);
+
+    return {cancel: true};
+}
+
+const all_types = [
+    "main_frame", "sub_frame", "stylesheet", "script", "image", "font",
+    "object", "xmlhttprequest", "ping", "csp_report", "media", "websocket",
+    "other", "main_frame", "sub_frame"
+];
+#ENDIF
+
+async function start(secret_)
+{
+    secret = secret_;
+
+#IF CHROMIUM
+    const extra_opts = ["blocking", "extraHeaders"];
+#ELSE
+    const extra_opts = ["blocking"];
+#ENDIF
+
+    browser.webRequest.onHeadersReceived.addListener(
+	on_headers_received,
+	{urls: ["<all_urls>"], types: ["main_frame", "sub_frame"]},
+	extra_opts.concat("responseHeaders")
+    );
+
+#IF CHROMIUM && MV2
+    browser.webRequest.onBeforeRequest.addListener(
+	on_before_request,
+	{urls: [browser.runtime.getURL("dummy") + "*"], types: all_types},
+	extra_opts
+    );
+#ENDIF
+
+    await track_default_allow();
+}
+#EXPORT start