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/**
* GNU LibreJS - A browser add-on to block nonfree nontrivial JavaScript.
*
* Copyright (C) 2018 Giorgio Maone <giorgio@maone.net>
*
* 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
*/
let {ResponseMetaData} = require("./ResponseMetaData");
let listeners = new WeakMap();
let webRequestEvent = browser.webRequest.onHeadersReceived;
class ResponseProcessor {
static install(handler, types = ["main_frame", "sub_frame", "script"]) {
if (listeners.has(handler)) return false;
let 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) {
let listener = listeners.get(handler);
if (listener) {
webRequestEvent.removeListener(listener);
}
}
}
Object.assign(ResponseProcessor, {
// control flow values to be returned by handler.pre() callbacks
ACCEPT: {},
REJECT: {cancel: true},
CONTINUE: null
});
class ResponseTextFilter {
constructor(request) {
this.request = request;
let {type, statusCode} = request;
let 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 ResponseProcessor.ACCEPT;
let {metaData, request} = this;
let response = {request, metaData}; // we keep it around allowing callbacks to store state
if (typeof handler.pre === "function") {
let res = await handler.pre(response);
if (res) return res;
if (handler.post) handler = handler.post;
if (typeof handler !== "function") return ResponseProcessor.ACCEPT;
}
let {requestId, responseHeaders} = request;
let filter = browser.webRequest.filterResponseData(requestId);
let buffer = [];
filter.ondata = event => {
buffer.push(event.data);
};
filter.onstop = async event => {
// concatenate chunks
let size = buffer.reduce((sum, chunk, n) => sum + chunk.byteLength, 0)
let allBytes = new Uint8Array(size);
let pos = 0;
for (let 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(response);
} catch(e) {
console.error(e);
}
if (editedText !== null) {
// we changed the content, let's re-encode
let 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();
}
return ResponseProcessor.ACCEPT;
}
}
module.exports = { ResponseProcessor };
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