WebLabels-based license checking implementation.

1 files changed, 87 insertions, 0 deletions

diff --git a/content/externalLicenseChecker.js b/content/externalLicenseChecker.js
new file mode 100644
index 0000000..89f871f
--- /dev/null
+++ b/content/externalLicenseChecker.js
@@ -0,0 +1,87 @@
+/**
+* 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/>.
+*/
+"use strict";
+{
+  let licensedScripts = null;
+    
+  let fetchWebLabels = async (map = new Map()) => {
+    // see https://www.gnu.org/software/librejs/free-your-javascript.html#step3
+    
+    let link = document.querySelector(`link[rel="jslicense"], link[data-jslicense="1"], a[rel="jslicense"], a[data-jslicense="1"]`);
+    if (link) try {
+      let baseURL = link.href;
+      let response = await fetch(baseURL);
+      if (!response.ok) throw `${response.status} ${response.statusText}`;
+      let doc = new DOMParser().parseFromString(
+          await response.text(),
+          "text/html"
+      );
+      let base = doc.querySelector("base");
+      if (base) {
+        base.href = base.href;
+      } else {
+        doc.head.appendChild(doc.createElement("base")).href = baseURL;
+      }
+      let firstURL = parent => parent.querySelector("a").href;
+      let allURLs = parent => Array.map(parent.querySelectorAll("a"), a => a.href);
+      for (let row of doc.querySelectorAll("table#jslicense-labels1 tr")) {
+        let cols = row.querySelectorAll("td");
+        let scriptURL = firstURL(cols[0]);
+        let licenseURLs = allURLs(cols[1]);
+        let sourceURLs = cols[2] ? allURLs(cols[2]) : [];
+        map.set(scriptURL, {scriptURL, licenseURLs, sourceURLs});
+      }
+    } catch (e) {
+      console.error("Error fetching Web Labels at %o", link, e);
+    }
+    return map;
+  }
+  
+  let fetchLicenseInfo = async () => {
+    let map = new Map();
+    
+    // in the fetchXxx methods we add to a map whatever license(s)
+    // URLs and source code references we can find in various formats 
+    // (WebLabels is currently the only implementation), keyed by script URLs.
+    await Promise.all([
+    fetchWebLabels(map),
+    // fetchXmlSpdx(),
+    // fetchTxtSpdx(),
+    // ...
+    ]);
+    return map;
+  }
+  
+  let handlers = {
+    async checkLicensedScript(m) {
+      let {url} = m;
+      if (!licensedScripts) licensedScripts = await fetchLicenseInfo();
+      return licensedScripts.get(url);
+    }
+  }
+
+  browser.runtime.onMessage.addListener(async m => {
+    if (m.action in handlers) {
+      debug("Received message", m);
+      return await handlers[m.action](m);
+    }
+  });
+}