aboutsummaryrefslogtreecommitdiff
path: root/bg/ResponseProcessor.js
blob: 0340a6f43dc27facc4d9c24eaa721887d67732a4 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
/**
* 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 } = request;
    let filter = browser.webRequest.filterResponseData(requestId);
    let buffer = [];

    filter.ondata = event => {
      buffer.push(event.data);
    };

    filter.onstop = async unused => {
      // concatenate chunks
      let size = buffer.reduce((sum, chunk) => 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 && editedText.indexOf('/* LibreJS: script accepted') !== 0) {
        // 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 };