Issue 1853 - Moved filter generation into background page

lib/filterComposer.js

Index: lib/filterComposer.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/lib/filterComposer.js
@@ -0,0 +1,122 @@
+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-2015 Eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus 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 Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+let {getDecodedHostname, stringifyURL} = require("url");
+
+function escapeChar(chr)
+{
+  let code = chr.charCodeAt(0);
+
+  // Control characters and leading digits must be escaped based on
+  // their char code in CSS. Moreover, curly brackets aren't allowed
+  // in elemhide filters, and therefore must be escaped based on their
+  // char code as well.
+  if (code <= 0x1F || code == 0x7F || /[\d\{\}]/.test(chr))
+    return "\\" + code.toString(16) + " ";
+
+  return "\\" + chr;
+}
+
+/**
+ * Escapes a token (e.g. tag, id, class or attribute) to be used in CSS selectors.
+ *
+ * @param {string} s
+ * @return {string}
+ */
+function escapeCSS(s)
+{
+  return s.replace(/^[\d\-]|[^\w\-\u0080-\uFFFF]/g, escapeChar);
+}
+exports.escapeCSS = escapeCSS;
+
+/**
+ * Quotes a string to be used as attribute value in CSS selectors.
+ *
+ * @param {string} value
+ * @return {string}
+ */
+function quoteCSS(value)
+{
+  return '"' + value.replace(/["\\\{\}\x00-\x1F\x7F]/g, escapeChar) + '"';
+}
+exports.quoteCSS = quoteCSS;
+
+function canBlockURL(url)
+{
+  return url.protocol == "http:" || url.protocol == "https:";
+}
+
+/**
+ * Generates filters to block an element.
+ *
+ * @param {string}   tagName  The element's tag name
+ * @param {string}   [src]    The element's "src" attribute
+ * @param {string}   [id]     The element's "id" attribute
+ * @param {string}   [style]  The element's "style" attribute
+ * @param {string[]} classes  The classes given by the element's "class" attribute
+ * @param {string[]} urls     The URLs considered when loading the element
+ * @param {URL}      baseURL  The URL of the document containing the element
+ *
+ * @return {object} An object holding the list of generated filters and
+ *                  the list of CSS selectors for the included element
+ *                  hiding filters: {filters: [...], selectors: [...]}
+ */
+function composeFilters(tagName, id, src, style, classes, urls, baseURL)
+{
+  // Add a blocking filter for each HTTP(S) URL associated with the element
+  let filters = [];
+  for (let url of urls)
+  {
+    let urlObj = new URL(url, baseURL);
+    if (canBlockURL(urlObj))
+    {
+      let filter = stringifyURL(urlObj).replace(/^[\w\-]+:\/+(?:www\.)?/, "||");
+
+      if (filters.indexOf(filter) == -1)
+        filters.push(filter);
+    }
+  }
+
+  // Generate CSS selectors based on the element's "id" and "class" attribute
+  let selectors = [];
+  if (id)
+    selectors.push("#" + escapeCSS(id));
+  if (classes.length > 0)
+    selectors.push(classes.map(c => "." + escapeCSS(c)).join(""));
+
+  // If there is a "src" attribute, specifiying a URL that we can't block,
+  // generate a CSS selector matching the "src" attribute
+  if (src && !canBlockURL(new URL(src, baseURL)))
+    selectors.push(escapeCSS(tagName) + "[src=" + quoteCSS(src) + "]");
+
+  // As last resort, if there is a "style" attribute, and we couldn't generate
+  // any filters so far, generate a CSS selector matching the "style" attribute
+  if (style && selectors.length == 0 && filters.length == 0)
+    selectors.push(escapeCSS(tagName) + "[style=" + quoteCSS(style) + "]");
+
+  // Add an element hiding filter for each generated CSS selector
+  if (selectors.length > 0)
+  {
+    let domain = getDecodedHostname(baseURL).replace(/^www\./, "");
+
+    for (let selector of selectors)
+      filters.push(domain + "##" + selector);
+  }
+
+  return {filters: filters, selectors: selectors};
+}
+exports.composeFilters = composeFilters;