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/**
* GNU LibreJS - A browser add-on to block nonfree nontrivial JavaScript.
*
* Copyright (C) 2018 Giorgio Maone <giorgio@maone.net>
* Copyright (C) 2022 Yuchen Pei <id@ypei.org>
*
* This file is part of GNU LibreJS.
*
* GNU LibreJS 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.
*
* GNU LibreJS 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.
*
* You should have received a copy of the GNU General Public License
* along with GNU LibreJS. If not, see <http://www.gnu.org/licenses/>.
*/
/**
An abstraction layer over the StreamFilter API, allowing its clients to process
only the "interesting" HTML and script requests and leaving the other alone
*/
const { ResponseMetaData } = require('./ResponseMetaData');
const listeners = new WeakMap();
const webRequestEvent = browser.webRequest.onHeadersReceived;
// Some hardcoded return values for the onHeadersReceived callback.
const BLOCKING_RESPONSES = {
ACCEPT: {}, // Do nothing
REJECT: { cancel: true }, // Cancel the request. See docs of BlockingResponse
};
class ResponseProcessor {
static install(handler, types = ['main_frame', 'sub_frame', 'script']) {
if (listeners.has(handler)) return false;
const listener =
async request => await new ResponseTextFilter(request).process(handler);
listeners.set(handler, listener);
webRequestEvent.addListener(
listener,
{ urls: ['<all_urls>'], types },
['blocking', 'responseHeaders']
);
return true;
}
static uninstall(handler) {
const listener = listeners.get(handler);
if (listener) {
webRequestEvent.removeListener(listener);
}
}
}
class ResponseTextFilter {
constructor(request) {
this.request = request;
const { type, statusCode } = request;
const md = this.metaData = new ResponseMetaData(request);
this.canProcess = // we want to process html documents and scripts only
(statusCode < 300 || statusCode >= 400) && // skip redirections
!md.disposition && // skip forced downloads
(type === 'script' || /\bhtml\b/i.test(md.contentType));
}
async process(handler) {
if (!this.canProcess) return BlockingResponses.ACCEPT;
const { metaData, request } = this;
const response = { request, metaData }; // we keep it around allowing callbacks to store state
if (typeof handler.pre !== 'function' || typeof handler.post !== 'function') {
throw new Error('handler should have a pre and post function.');
}
// If can determine without checking and filtering response
// payload then return.
const res = await handler.pre(response);
if (res) return res;
const { requestId } = request;
// create a filter to modify response data, see
// Mozilla/Add-ons/WebExtensions/API/webRequest/filterResponseData
const filter = browser.webRequest.filterResponseData(requestId);
let buffer = [];
filter.ondata = event => {
buffer.push(event.data);
};
filter.onstop = async _ => {
// concatenate chunks
const size = buffer.reduce((sum, chunk) => sum + chunk.byteLength, 0)
let allBytes = new Uint8Array(size);
let pos = 0;
for (const chunk of buffer) {
allBytes.set(new Uint8Array(chunk), pos);
pos += chunk.byteLength;
}
buffer = null; // allow garbage collection
if (allBytes.indexOf(0) !== -1) {
console.debug('Warning: zeroes in bytestream, probable cached encoding mismatch.', request);
if (request.type === 'script') {
console.debug('It\'s a script, trying to refetch it.');
response.text = await (await fetch(request.url, { cache: 'reload', credentials: 'include' })).text();
} else {
console.debug('It\'s a %s, trying to decode it as UTF-16.', request.type);
response.text = new TextDecoder('utf-16be').decode(allBytes, { stream: true });
}
} else {
response.text = metaData.decode(allBytes);
}
let editedText = null;
try {
editedText = await handler.post(response);
} catch (e) {
console.error(e);
}
if (editedText !== null && editedText !== response.text) {
// we changed the content, let's re-encode
const encoded = new TextEncoder().encode(editedText);
// pre-pending the UTF-8 BOM will force the charset per HTML 5 specs
allBytes = new Uint8Array(encoded.byteLength + 3);
allBytes.set(ResponseMetaData.UTF8BOM, 0); // UTF-8 BOM
allBytes.set(encoded, 3);
}
filter.write(allBytes);
filter.close();
}
// Accepting the filtered payload.
return BLOCKING_RESPONSES.ACCEPT;
}
}
module.exports = { ResponseProcessor, BLOCKING_RESPONSES };
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