Refactor and fix HTTP response filtering to touch only scripts, either external or embedded inside HTML documents and sub-documents.

2 files changed, 192 insertions, 0 deletions

diff --git a/bg/ResponseMetaData.js b/bg/ResponseMetaData.js
new file mode 100644
index 0000000..40ca3f3
--- /dev/null
+++ b/bg/ResponseMetaData.js
@@ -0,0 +1,82 @@
+/**
+* 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/>.
+*/
+
+/**
+  This class parses HTTP response headers to extract both the
+  MIME Content-type and the character set to be used, if specified,
+  to parse textual data through a decoder.
+*/
+
+class ResponseMetaData {
+  constructor(request) {
+    let {responseHeaders} = request;
+    this.headers = {};
+    for (let h of responseHeaders) {
+      if (/^\s*Content-(Type|Disposition)\s*$/i.test(h.name)) {
+        let propertyName =  h.name.split("-")[1].trim();
+        propertyName = `content${propertyName.charAt(0).toUpperCase()}${propertyName.substring(1).toLowerCase()}`;
+        this[propertyName] = h.value;
+        this.headers[propertyName] = h;
+      }
+    }
+    this.forcedUTF8 = false;
+  }
+
+  get charset() {
+    let charset = "";
+    if (this.contentType) {
+      let m = this.contentType.match(/;\s*charset\s*=\s*(\S+)/);
+      if (m) {
+        charset = m[1];
+      }
+    }
+    Object.defineProperty(this, "charset", { value: charset, writable: false, configurable: true });
+    return charset;
+  }
+
+  get isUTF8() {
+    return /^utf-8$/i.test(this.charset);
+  }
+
+  forceUTF8() {
+    if (!(this.forcedUTF8 || this.isUTF8)) {
+      let h = this.headers.contentType;
+      if (h) {
+        h.value = h.value.replace(/;\s*charset\s*=.*|$/, "; charset=utf8");
+        this.forcedUTF8 = true;
+      } // if the header doesn't exist the browser should default to UTF-8 anyway
+    }
+    return this.forcedUTF8;
+  }
+
+  createDecoder() {
+    if (this.charset) {
+      try {
+        return new TextDecoder(this.charset);
+      } catch (e) {
+        console.error(e);
+      }
+    }
+    return new TextDecoder("utf-8");
+  }
+};
+
+module.exports = { ResponseMetaData };
diff --git a/bg/ResponseProcessor.js b/bg/ResponseProcessor.js
new file mode 100644
index 0000000..3f3151b
--- /dev/null
+++ b/bg/ResponseProcessor.js
@@ -0,0 +1,110 @@
+/**
+* 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.js");
+
+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 =
+      request =>  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);
+    }
+  }
+}
+
+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));
+  }
+
+  process(handler) {
+    if (!this.canProcess) return {};
+    let metaData = this.metaData;
+    let {requestId, responseHeaders} = this.request;
+    let filter = browser.webRequest.filterResponseData(requestId);
+    let buffer = [];
+
+    filter.ondata = event => {
+      buffer.push(event.data);
+    };
+
+    filter.onstop = async event => {
+      let decoder = metaData.createDecoder();
+      let params = {stream: true};
+      let text = this.text = buffer.map(
+        chunk => decoder.decode(chunk, params))
+        .join('');
+      let editedText = null;
+      try {
+        let response = {
+          request: this.request,
+          metaData,
+          text,
+        };
+        editedText = await handler(response);
+      } catch(e) {
+        console.error(e);
+      }
+      if (metaData.forcedUTF8 ||
+        editedText !== null && text !== editedText) {
+        // if we changed the charset, the text or both, let's re-encode
+        filter.write(new TextEncoder().encode(editedText));
+      } else {
+        // ... otherwise pass all the raw bytes through
+        for (let chunk of buffer) filter.write(chunk);
+      }
+
+      filter.disconnect();
+    }
+
+    return metaData.forceUTF8() ? {responseHeaders} : {};
+  }
+}
+
+module.exports = { ResponseProcessor };