Implementing download updates stream.

downloads/observer.js

@@ -0,0 +1,145 @@
+"use strict";
+
+const { components: { Constructor: CC } } = require("chrome");
+const dowloadManager = CC("@mozilla.org/download-manager;1",
+                          "nsIDownloadManager")();
+const unload = require("unload");
+
+
+/**
+ * Returns normalized, JSON serializeable version of given `nsIDownload`.
+ * @see https://developer.mozilla.org/en/XPCOM_Interface_Reference/nsIDownload
+ * @param {nsIDownload} download
+ * @returns {JSON}
+ */
+function Download(download) {
+  let { id, displayName, amountTransferred, percentComplete, state, MIMEInfo,
+        referrer, size, source, speed, startTime, target } = download;
+
+  return {
+    /**
+     * The ID by which the download is identified uniquely in the database
+     * @type {Number}
+     */
+    id: id,
+    /**
+     * A user-readable description of the transfer.
+     * @type {String}
+     */
+    description: String(displayName),
+    /**
+     * The number of bytes downloaded so far.
+     * @type {Number}
+     */
+    transferred: amountTransferred,
+    /**
+     * The total size of the file in bytes, or `null` if the file's size is
+     * unknown.
+     * @type {Number|null}
+     */
+    size: size === -1 ? null : size,
+    /**
+     * The percentage of the file transfer that has been completed, or `null`
+     * if the file's size is unknown.
+     */
+    progress: size === -1 ? null : percentComplete,
+    /**
+     * The downloads transfer speed in bytes per second.
+     * @type {Number}
+     */
+    speed: speed,
+    /**
+     * The downloads current state. See [nsIDownloadManager.Constants]
+     * (https://developer.mozilla.org/en/XPCOM_Interface_Reference/nsIDownloadManager#Constants)
+     * @type {Number}
+     */
+    state: state,
+    /**
+     * Targets MIME type, or `null` if unknown.
+     * @type {String|null}
+     */
+    mime: MIMEInfo ? String(MIMEInfo.MIMEType) : null,
+    /**
+     * The referrer URI of the download. This is only valid for HTTP downloads,
+     * and can be null.
+     * @type {String|null}
+     */
+    referrer: referrer ? String(referrer.spec) : null,
+    /**
+     * The source URI of the download.
+     * @type {String}
+     */
+    source: String(source.spec),
+    /**
+     * The target URI of the transfer.
+     * @type {String}
+     */
+    target: String(target.spec),
+    /**
+     * The time at which the transfer was started.
+     * @type {Number}
+     */
+    started: startTime
+  };
+}
+
+function getDownloads() {
+  var activeDownloads = dowloadManager.activeDownloads;
+  var downloads = [];
+  while (activeDownloads.hasMoreElements())
+    downloads.push(Download(activeDownloads.getNext()))
+  return downloads;
+}
+
+exports.stream = function stream(next, stop) {
+  function onSecurityChange(progress, request, state, download) {
+    next({
+      type: 'security',
+      active: dowloadManager.activeDownloadCount,
+      download: Download(download)
+    })
+  }
+
+  function onProgress(progress, request, value, maxP, total, maxT, download) {
+    next({
+      type: 'progress',
+      downloads: getDownloads()
+    })
+  }
+
+  function onStateChange(progress, request, status, state, download) {
+    next({
+      type: 'status',
+      status: status,
+      downloads: dowloadManager.activeDownloadCount,
+      download: Download(download)
+    })
+  }
+
+  function onDownloadStateChange(state, download) {
+    next({
+      type: 'state',
+      previousState: state,
+      downloads: dowloadManager.activeDownloadCount,
+      download: Download(download)
+    })
+  }
+
+  const listener = {
+    onSecurityChange: onSecurityChange,
+    onProgressChange: onProgress,
+    onStateChange: onStateChange,
+    onDownloadStateChange: onDownloadStateChange
+  };
+
+  unload.when(function onUnload() {
+    try {
+      dowloadManager.removeListener(listener);
+      if (stop) stop();
+    } catch (exception) {
+      console.exception(exception);
+    }
+  });
+
+  dowloadManager.addListener(listener);
+}