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/**
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* This file is part of Haketilo.
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*
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* Function: Modifying a web page using the StreamFilter API.
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*
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* Copyright (C) 2018 Giorgio Maone <giorgio@maone.net>
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* Copyright (C) 2021 Wojtek Kosior
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* Redistribution terms are gathered in the `copyright' file.
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*
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* Derived from `bg/ResponseProcessor.js' and `bg/ResponseMetaData.js'
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* in LibreJS.
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*/
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/*
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* IMPORTS_START
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* IMPORT browser
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* IMPORT csp_header_regex
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* IMPORTS_END
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*/
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function validate_encoding(charset)
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{
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try {
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new TextDecoder();
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return charset;
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} catch(e) {
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return undefined;
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}
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}
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function is_content_type_header(header)
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{
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header.name.toLowerCase().trim() === "content-type";
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}
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const charset_reg = /;\s*charset\s*=\s*([\w-]+)/i;
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function properties_from_headers(headers)
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{
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const properties = {};
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for (const header of headers.filter(is_content_type_header)) {
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const match = charset_reg.exec(header.value);
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if (!properties.detected_charset && validate_encoding(match[1]))
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properties.detected_charset = match[1];
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if (/html/i.test(header.value))
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properties.html = true;
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}
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return properties;
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}
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const UTF8_BOM = [0xef, 0xbb, 0xbf];
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const BOMs = [
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[UTF8_BOM, "utf-8"],
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[[0xfe, 0xff], "utf-16be"],
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[[0xff, 0xfe], "utf-16le"]
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];
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function charset_from_BOM(data)
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{
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for (const [BOM, charset] of BOMs) {
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if (BOM.reduce((ac, byte, i) => ac && byte === data[i], true))
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return charset;
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}
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return "";
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}
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const charset_attrs =
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['charset', 'http-equiv="content-type"', 'content*="charset"'];
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const charset_meta_selector =
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charset_attrs.map(a => `head>meta[${a}]`).join(", ");
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function charset_from_meta_tags(doc)
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{
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for (const meta of doc.querySelectorAll(charset_meta_selector)) {
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const maybe_charset = meta.getAttribute("charset");
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if (maybe_charset && validate_encoding(maybe_charset))
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return maybe_charset;
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const match = charset_reg.exec(meta.getAttribute("content"));
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if (match && validate_encoding(match[1]))
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return match[1];
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}
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return undefined;
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}
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function create_decoder(properties, data)
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{
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let charset = charset_from_BOM(data) || properties.detected_charset;
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if (!charset && data.indexOf(0) !== -1) {
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console.debug("Warning: zeroes in bytestream, probable cached encoding mismatch. Trying to decode it as UTF-16.",
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properties);
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return new TextDecoder("utf-16be");
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}
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/* Missing HTTP charset, sniffing in content... */
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/*
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* TODO: I recall there is some standard saying how early in the doc the
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* charset has to be specified. We could process just this part of data.
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*/
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const text = new TextDecoder("latin1").decode(data, {stream: true});
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properties.html = properties.html || /html/i.test(text);
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if (properties.html) {
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const tmp_doc = new DOMParser().parseFromString(text, "text/html");
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charset = charset_from_meta_tags(tmp_doc);
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}
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return new TextDecoder(charset || "latin1");
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}
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function may_define_csp_rules(html)
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{
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const doc = new DOMParser().parseFromString(html, "text/html");
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for (const meta of doc.querySelectorAll("head>meta[http-equiv]")) {
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if (csp_header_regex.test(meta.httpEquiv) && meta.content)
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return true;
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}
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/*
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* Even if no naughty `<meta>' tags were found, subsequent chunk of HTML
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* data could add some. Before we return `false' we need to be sure we
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* reached the start of `<body>' where `<meta>' tags are no longer valid.
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*/
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if (doc.documentElement.nextSibling || doc.body.nextSibling ||
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doc.body.childNodes.length > 1)
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return false;
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if (!doc.body.firstChild)
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return true;
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if (doc.body.firstChild.nodeName !== "#text")
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return false;
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return /^(<\/|&#|.)$/.test(doc.body.firstChild.wholeText);
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}
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function filter_data(properties, event)
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{
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const data = new Uint8Array(event.data);
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let first_chunk = false;
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if (!properties.decoder) {
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first_chunk = true;
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properties.decoder = create_decoder(properties, data);
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properties.encoder = new TextEncoder();
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}
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let decoded = properties.decoder.decode(data);
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/* Force UTF-8, this is the only encoding we can produce. */
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if (first_chunk)
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properties.filter.write(new Uint8Array(UTF8_BOM));
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if (first_chunk && may_define_csp_rules(decoded)) {
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/*
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* HAX! Our content scripts that execute at `document_start' will always
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* run before the first script in the document, but under Mozilla some
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* `<meta>' tags might already be loaded at that point. Here we inject a
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* dummy `<script>' at the beginning (before any `<meta>' tags) that
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* will force `document_start' to happen earlier. This way our content
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* scripts will be able to sanitize `http-equiv' tags with CSP rules
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* that would otherwise stop our injected scripts from executing.
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*
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* As we want to only process HTML files that happen to have naughty
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* `<meta>' tags in `<head>', we use a DOMParser-based heuristic in
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* `may_define_rules()'. We don't do any additional MIME sniffing as it
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* is too unreliable (and our heuristic will likely mark non-HTML files
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* as harmless anyway).
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*/
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const dummy_script = `<script>null</script>`;
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const doctype_decl = /^(\s*<!doctype[^<>"']*>)?/i.exec(decoded)[0];
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decoded = doctype_decl + dummy_script +
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decoded.substring(doctype_decl.length);
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}
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properties.filter.write(properties.encoder.encode(decoded));
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if (properties.decoder.encoding === "utf-8")
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properties.filter.disconnect();
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}
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function apply_stream_filter(details, headers, policy)
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{
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if (!policy.payload)
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return headers;
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const properties = properties_from_headers(headers);
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properties.filter =
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browser.webRequest.filterResponseData(details.requestId);
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properties.filter.ondata = event => filter_data(properties, event);
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properties.filter.onstop = () => properties.filter.close();
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/*
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* In the future we might consider modifying the headers that specify
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* encoding. For now we are not yet doing it, though. However, we
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* prepend the data with UTF-8 BOM which should be enough.
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*/
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return headers;
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}
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/*
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* EXPORTS_START
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* EXPORT apply_stream_filter
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* EXPORTS_END
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*/
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