Issue 3375 - Issue reporter: move screenshot creation into the content process

lib/child/dataCollector.js

Index: lib/child/dataCollector.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/lib/child/dataCollector.js
@@ -0,0 +1,112 @@
+/*
+ * 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/>.
+ */
+
+/**
+ * @fileOverview Collects some data for a content window, to be attached to
+ * issue reports.
+ */
+
+"use strict";
+
+let {Services} = Cu.import("resource://gre/modules/Services.jsm", {});
+let {Task} = Cu.import("resource://gre/modules/Task.jsm", {});
+
+let {Utils} = require("utils");
+
+addMessageListener("AdblockPlus:CollectData", onCollectData);
+onShutdown.add(() => {
+  removeMessageListener("AdblockPlus:CollectData", onCollectData);
+});
+
+function onCollectData(message)
+{
+  let {outerWindowID, screenshotWidth, responseID} = message.data;
+
+  function success(data)
+  {
+    sendAsyncMessage("AdblockPlus:CollectDataResponse", {
+      responseID,
+      data
+    });
+  }
+
+  function error(e)
+  {
+    Cu.reportError(e);
+    sendAsyncMessage("AdblockPlus:CollectDataResponse", {
+      responseID,
+      data: null
+    });
+  }
+
+  let window = Services.wm.getOuterWindowWithId(outerWindowID);
+  if (window)
+  {
+    Task.spawn(function*()
+    {
+      let data = {};
+      data.screenshot = yield createScreenshot(window, screenshotWidth);
+      return data;
+    }).then(success, error);
+  }
+}
+
+function* createScreenshot(window, screenshotWidth)
+{
+  let canvas = window.document.createElement("canvas");
+  canvas.width = screenshotWidth;
+
+  let context = canvas.getContext("2d");
+  let wndWidth = window.document.documentElement.scrollWidth;
+  let wndHeight = window.document.documentElement.scrollHeight;
+
+  // Copy scaled screenshot of the webpage, according to the specified width.
+
+  // Gecko doesn't like sizes more than 64k, restrict to 30k to be on the safe side.
+  // Also, make sure height is at most five times the width to keep image size down.
+  let copyWidth = Math.min(wndWidth, 30000);
+  let copyHeight = Math.min(wndHeight, 30000, copyWidth * 5);
+  let copyX = Math.max(Math.min(window.scrollX - copyWidth / 2, wndWidth - copyWidth), 0);
+  let copyY = Math.max(Math.min(window.scrollY - copyHeight / 2, wndHeight - copyHeight), 0);
+
+  let scalingFactor = screenshotWidth / copyWidth;
+  canvas.height = copyHeight * scalingFactor;
+
+  context.save();
+  context.scale(scalingFactor, scalingFactor);
+  context.drawWindow(window, copyX, copyY, copyWidth, copyHeight, "rgb(255,255,255)");
+  context.restore();
+
+  // Reduce colors
+  let pixelData = context.getImageData(0, 0, canvas.width, canvas.height);
+  let max = pixelData.width * pixelData.height * 4;
+  let mapping = [0x00,  0x55,  0xAA,  0xFF];
+  for (let i = 0; i < max; i++)
+  {
+    pixelData.data[i] = mapping[pixelData.data[i] >> 6];
+
+    if (i % 5000 == 0)
+    {
+      // Take a break every 5000 bytes to prevent browser hangs
+      yield new Promise((resolve, reject) => Utils.runAsync(resolve));
+    }
+  }
+
+  // Convert the data into an image URL
+  context.putImageData(pixelData, 0, 0);
+  return canvas.toDataURL("image/png");
+}