Haketilo

/**

 * This file is part of Haketilo.

 *

 * Function: Injecting policy to page by modifying HTTP headers.

 *

 * Copyright (C) 2021, Wojtek Kosior

 * Copyright (C) 2021, jahoti

 *

 * 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.

 */

/*

 * IMPORTS_START

 * IMPORT sign_data

 * IMPORT extract_signed

 * IMPORT make_csp_rule

 * IMPORT csp_header_regex

 * IMPORTS_END

 */

function inject_csp_headers(headers, policy)

{

    let csp_headers;

    let old_signature;

    let haketilo_header;

    for (const header of headers.filter(h => h.name === "x-haketilo")) {

	/* x-haketilo header has format: <signature>_0_<data> */

	const match = /^([^_]+)_(0_.*)$/.exec(header.value);

	if (!match)

	    continue;

	const result = extract_signed(...match.slice(1, 3));

	if (result.fail)

	    continue;

	/* This should succeed - it's our self-produced valid JSON. */

	const old_data = JSON.parse(decodeURIComponent(result.data));

	/* Confirmed- it's the originals, smuggled in! */

	csp_headers = old_data.csp_headers;

	old_signature = old_data.policy_sig;

	haketilo_header = header;

	break;

    }

    if (policy.has_payload) {

	csp_headers = [];

	const non_csp_headers = [];

	const header_list =

	      h => csp_header_regex.test(h) ? csp_headers : non_csp_headers;

	headers.forEach(h => header_list(h.name).push(h));

	headers = non_csp_headers;

    } else {

	headers.push(...csp_headers || []);

    }

    if (!haketilo_header) {

	haketilo_header = {name: "x-haketilo"};

	headers.push(haketilo_header);

    }

    if (old_signature)

	headers = headers.filter(h => h.value.search(old_signature) === -1);

    const policy_str = encodeURIComponent(JSON.stringify(policy));

    const signed_policy = sign_data(policy_str, new Date().getTime());

    const later_30sec = new Date(new Date().getTime() + 30000).toGMTString();

    headers.push({

	name: "Set-Cookie",

	value: `haketilo-${signed_policy.join("=")}; Expires=${later_30sec};`

    });

    /*

     * Smuggle in the signature and the original CSP headers for future use.

     * These are signed with a time of 0, as it's not clear there is a limit on

     * how long Firefox might retain headers in the cache.

     */

    let haketilo_data = {csp_headers, policy_sig: signed_policy[0]};

    haketilo_data = encodeURIComponent(JSON.stringify(haketilo_data));

    haketilo_header.value = sign_data(haketilo_data, 0).join("_");

    if (!policy.allow) {

	headers.push({

	    name: "content-security-policy",

	    value: make_csp_rule(policy)

	});

    }

    return headers;

}

/*

 * EXPORTS_START

 * EXPORT inject_csp_headers

 * EXPORTS_END

 */