Haketilo

 * Copyright (C) 2021, 2022 Wojtek Kosior <koszko@koszko.org>

#IMPORT common/indexeddb.js AS haketilodb

#FROM common/misc.js    IMPORT is_privileged_url, csp_header_regex, \

                               sha256_async AS sha256

#IF MOZILLA

/*

 * Under Mozilla-based browsers, responses are cached together with headers as

 * they appear *after* modifications by Haketilo. This means Haketilo's CSP

 * script-blocking headers might be present in responses loaded from cache. In

 * the meantime the user might have changes Haketilo settings to instead allow

 * the scripts on the page in question. This causes a problem and creates the

 * need to somehow restore the response headers to the state in which they

 * arrived from the server.

 * To cope with this, Haketilo will inject some additional headers with private

 * data. Those will include a hard-to-guess value derived from extension's

 * internal ID. It is assumed the internal ID has a longer lifetime than cached

 * responses.

 */

const settings_page_url = browser.runtime.getURL("html/settings.html");

const header_prefix_prom = sha256(settings_page_url)

      .then(hash => `X-Haketilo-${hash}`);

/*

 * Mozilla, unlike Chrome, allows webRequest callbacks to return promises. Here

 * we leverage that to be able to use asynchronous sha256 computation.

 */

async function on_headers_received(details) {

#IF NEVER

} /* Help auto-indent in editors. */

#ENDIF

#ELSE

function on_headers_received(details) {

#ENDIF

#IF MOZILLA

    const prefix = await header_prefix_prom;

    /*

     * We assume that the original CSP headers of a response are always

     * preserved under names of the form:

     *     X-Haketilo-<some_secret>-<original_name>

     * In some cases the original response may contain no CSP headers. To still

     * be able to tell whether the headers we were provided were modified by

     * Haketilo in the past, all modifications are accompanied by addition of an

     * extra header with name:

     *     X-Haketilo-<some_secret>

     */

    const restore_old_headers = details.fromCache &&

	  !!headers.filter(h => h.name === prefix).length;

    if (restore_old_headers) {

	const restored_headers = [];

	for (const h of headers) {

	    if (csp_header_regex.test(h.name) || h.name === prefix)

		continue;

	    if (h.name.startsWith(prefix)) {

		restored_headers.push({

		    name:  h.name.substring(prefix.length + 1),

		    value: h.value

		});

	    } else {

		restored_headers.push(h);

	    }

	}

	headers = restored_headers;

    }

#ENDIF

    if (!policy.allow) {

#IF MOZILLA

	const to_append = [{name: prefix, value: ":)"}];

	for (const h of headers.filter(h => csp_header_regex.test(h.name))) {

	    if (!policy.payload)

		to_append.push(Object.assign({}, h));

	    h.name = `${prefix}-${h.name}`;

	}

	headers.push(...to_append);

#ELSE

	if (policy.payload)

	    headers = headers.filter(h => !csp_header_regex.test(h.name));

#ENDIF

	headers.push({name: "Content-Security-Policy", value: policy.csp});

    }

    /*

     * When page is meant to be viewed in the browser, use streamFilter to

     * inject a dummy <script> at the very beginning of it. This <script>

     * will cause extension's content scripts to run before page's first <meta>

     * tag is rendered so that they can prevent CSP rules inside <meta> tags

     * from blocking the payload we want to inject.

     */

    let use_stream_filter = !!policy.payload;

    if (use_stream_filter) {

	for (const header of headers) {

	    if (header.name.toLowerCase().trim() !== "content-disposition")

		continue;

	    if (/^\s*attachment\s*(;.*)$/i.test(header.value)) {

		use_stream_filter = false;

	    } else {

		use_stream_filter = true;

		break;

	    }

    use_stream_filter = use_stream_filter &&

	(details.statusCode < 300 || details.statusCode >= 400);

    if (use_stream_filter)