Issue 6539, 6782 - Implement support for snippets

lib/snippets.js

Index: lib/snippets.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/lib/snippets.js
@@ -0,0 +1,112 @@
+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-present 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/>.
+ */
+
+"use strict";
+
+const {defaultMatcher} = require("matcher");
+const {RegExpFilter, WhitelistFilter} = require("filterClasses");
+const {extractHostFromFrame, getDecodedHostname,
+       isThirdParty, stringifyURL} = require("url");
+const {checkWhitelisted} = require("whitelisting");
+const {FilterNotifier} = require("filterNotifier");
+const devtools = require("devtools");
+
+const {typeMap} = RegExpFilter;
+
+let library = null;
+let executableCode = new Map();

[Manish Jethani, 2018/03/31 09:36:26]

This cache is not strictly necessary but it would be stupid to generate the
executable code for each call.

+
+fetch(browser.extension.getURL("/snippets.js"), {cache: "no-cache"})
+.then(response => response.text())
+.then(text =>
+{
+  library = text;
+});
+
+function getExecutableCode(snippet)
+{
+  let code = executableCode.get(snippet);
+  if (code)
+    return code;
+
+  code = `
+    "use strict";
+    {
+      let imports = Object.create(null);
+      new Function("exports", ${JSON.stringify(library)})(imports);

[Manish Jethani, 2018/03/31 09:36:26]

So we're loading the snippet library as a function and calling it with an
imports object, which it populates.

+      let key = ${JSON.stringify(snippet)};
+      if (Object.prototype.hasOwnProperty.call(imports, key))

[Manish Jethani, 2018/03/31 09:36:26]

Just to be extra safe it's better to check that the key indeed is in the object
itself and not in the object's prototype chain.

+      {
+        let value = imports[key];
+        if (typeof value == "function")
+          value();
+      }
+    }
+  `;
+
+  executableCode.set(snippet, code);
+  return code;
+}
+
+function injectCode(snippet, tabId, frameId)
+{
+  if (!library)
+    return;
+
+  browser.tabs.executeScript(tabId, {
+    code: getExecutableCode(snippet),
+    frameId,
+    matchAboutBlank: true,
+    runAt: "document_start"
+  });
+}
+
+browser.webNavigation.onCommitted.addListener(details =>
+{
+  // There's a bug in Chrome that causes webNavigation.onCommitted to get
+  // dispatched twice if there's a URL filter present, therefore we must listen
+  // for all URLs and do an explicit check here.
+  if (!/^https?:\/\//.test(details.url))
+    return;
+
+  let url = new URL(details.url);
+  let urlString = stringifyURL(url);
+  let parentFrame = ext.getFrame(details.tabId, details.parentFrameId);
+  let hostname = extractHostFromFrame(parentFrame) || getDecodedHostname(url);
+  let thirdParty = isThirdParty(url, hostname);
+
+  let filter = defaultMatcher.matchesAny(urlString, typeMap.SNIPPET, hostname,
+                                         thirdParty, null, true);
+  if (!filter)
+    return;
+
+  let page = new ext.Page({id: details.tabId, url: details.url});
+  let frame = ext.getFrame(details.tabId, details.frameId);
+
+  if (checkWhitelisted(page, frame))
+    return;
+
+  devtools.logRequest(page, urlString, "SNIPPET", hostname, thirdParty, null,
+                      true, filter);
+  FilterNotifier.emit("filter.hitCount", filter, 0, 0, page);
+
+  if (filter instanceof WhitelistFilter)
+    return;
+
+  for (let snippet of filter.snippets)
+    injectCode(snippet, details.tabId, details.frameId);
+});