Merge pull request #45 from m-lab/sandbox-roberto-safari-tests

Update uploader() to slow down initial message doubling

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@m-lab/ndt7",
-  "version": "0.0.4",
+  "version": "0.0.5-beta.0",
   "description": "NDT7 client for measuring networks",
   "main": "src/ndt7.js",
   "scripts": {

src/ndt7-upload-worker.js

@@ -57,10 +57,8 @@ const uploadTest = function(sock, postMessage, now) {
    * is used as a speed test, we don't know before the test which strategy we
    * will be using, because we don't know the speed before we test it.
    * Therefore, we use a strategy where we grow the message exponentially over
-   * time and maintain the invariant that the message size is always either 8k
-   * or less than 1/8 of the total number of bytes we have enqueued. In an
-   * effort to be kind to the memory allocator, we always double the message
-   * size instead of growing it by e.g. 1.3x.
+   * time. In an effort to be kind to the memory allocator, we always double
+   * the message size instead of growing it by e.g. 1.3x.
    *
    * @param {*} data
    * @param {*} start
@@ -74,37 +72,28 @@ const uploadTest = function(sock, postMessage, now) {
       // observed this behaviour with pre-Chromium Edge.
       return;
     }
-    let t = now();
+    const t = now();
     if (t >= end) {
       sock.close();
       return;
     }
 
-    const maxMessageSize = 16777216; /* = (1<<24) = 16MB */
+    const maxMessageSize = 8388608; /* = (1<<23) = 8MB */
+    const clientMeasurementInterval = 250; // ms
+
+    // Message size is doubled after the first 16 messages, and subsequently
+    // every 8, up to maxMessageSize.
     const nextSizeIncrement =
         (data.length >= maxMessageSize) ? Infinity : 16 * data.length;
-    if (total >= nextSizeIncrement) {
-      // Optional todo: fill this message with randomness.
+    if ((total - sock.bufferedAmount) >= nextSizeIncrement) {
       data = new Uint8Array(data.length * 2);
     }
 
-    const clientMeasurementInterval = 250; // ms
-    const loopEndTime = Math.min(previous + clientMeasurementInterval, end);
-    const desiredBuffer = 8 * data.length;
-
-    // While we would still like to buffer more messages, and we haven't been
-    // running for too long, and we don't need to resize the message... keep
-    // sending.
-    //
-    // The buffering bound prevents us from wasting local memory, the time bound
-    // prevents us from stalling the UI event loop, and the sizeIncrement bound
-    // allows us to dynamically respond to fast connections.
-    while (sock.bufferedAmount < desiredBuffer &&
-           t < loopEndTime &&
-           total < nextSizeIncrement
-    ) {
+    // We keep 7 messages in the send buffer, so there is always some more
+    // data to send. The maximum buffer size is 8 * 8MB - 1 byte ~= 64M.
+    const desiredBuffer = 7 * data.length;
+    if (sock.bufferedAmount < desiredBuffer) {
       sock.send(data);
-      t = now();
       total += data.length;
     }