fix(dash): Fix performance regression (#4064)

See: #4062 (comment)

Author: Álvaro Velad Galván

lib/dash/dash_parser.js

@@ -22,7 +22,6 @@ goog.require('shaka.text.TextEngine');
 goog.require('shaka.util.CmcdManager');
 goog.require('shaka.util.Error');
 goog.require('shaka.util.Functional');
-goog.require('shaka.util.Iterables');
 goog.require('shaka.util.LanguageUtils');
 goog.require('shaka.util.ManifestParserUtils');
 goog.require('shaka.util.MimeUtils');
@@ -104,7 +103,7 @@ shaka.dash.DashParser = class {
 
     /**
      * Period IDs seen in previous manifest.
-     * @private {!Array.<number>}
+     * @private {!Array.<string>}
      */
     this.lastManifestUpdatePeriodIds_ = [];
 
@@ -555,10 +554,9 @@ shaka.dash.DashParser = class {
     const periods = [];
     let prevEnd = 0;
     const periodNodes = XmlUtils.findChildren(mpd, 'Period');
-    // This uses a for-loop rather than a for-of loop because this needs to look
-    // ahead to the next element.
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item: elem, next} of enumerate(periodNodes)) {
+    for (let i = 0; i < periodNodes.length; i++) {
+      const elem = periodNodes[i];
+      const next = periodNodes[i + 1];
       const start = /** @type {number} */ (
         XmlUtils.parseAttr(elem, 'start', XmlUtils.parseDuration, prevEnd));
       const periodId = elem.id;

lib/dash/mpd_utils.js

@@ -12,7 +12,6 @@ goog.require('shaka.net.NetworkingEngine');
 goog.require('shaka.util.AbortableOperation');
 goog.require('shaka.util.Error');
 goog.require('shaka.util.Functional');
-goog.require('shaka.util.Iterables');
 goog.require('shaka.util.ManifestParserUtils');
 goog.require('shaka.util.XmlUtils');
 goog.requireType('shaka.dash.DashParser');
@@ -142,8 +141,9 @@ shaka.dash.MpdUtils = class {
     const timeline = [];
     let lastEndTime = -unscaledPresentationTimeOffset;
 
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {item: timePoint, next} of enumerate(timePoints)) {
+    for (let i = 0; i < timePoints.length; ++i) {
+      const timePoint = timePoints[i];
+      const next = timePoints[i + 1];
       let t = XmlUtils.parseAttr(timePoint, 't', XmlUtils.parseNonNegativeInt);
       const d =
           XmlUtils.parseAttr(timePoint, 'd', XmlUtils.parseNonNegativeInt);
@@ -225,8 +225,7 @@ shaka.dash.MpdUtils = class {
         timeline[timeline.length - 1].end = startTime / timescale;
       }
 
-      for (const _ of shaka.util.Iterables.range(repeat + 1)) {
-        shaka.util.Functional.ignored(_);
+      for (let j = 0; j <= repeat; ++j) {
         const endTime = startTime + d;
         const item = {
           start: startTime / timescale,

lib/dash/segment_template.js

@@ -14,7 +14,6 @@ goog.require('shaka.media.InitSegmentReference');
 goog.require('shaka.media.SegmentIndex');
 goog.require('shaka.media.SegmentReference');
 goog.require('shaka.util.Error');
-goog.require('shaka.util.Iterables');
 goog.require('shaka.util.ManifestParserUtils');
 goog.require('shaka.util.ObjectUtils');
 goog.requireType('shaka.dash.DashParser');
@@ -504,8 +503,9 @@ shaka.dash.SegmentTemplate = class {
 
     /** @type {!Array.<!shaka.media.SegmentReference>} */
     const references = [];
-    const enum_ = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item: {start, unscaledStart, end}} of enum_(info.timeline)) {
+    for (let i = 0; i < info.timeline.length; i++) {
+      const {start, unscaledStart, end} = info.timeline[i];
+
       // Note: i = k - 1, where k indicates the k'th segment listed in the MPD.
       // (See section 5.3.9.5.3 of the DASH spec.)
       const segmentReplacement = i + info.startNumber;

lib/util/string_utils.js

@@ -158,9 +158,8 @@ shaka.util.StringUtils = class {
   static toUTF16(str, littleEndian) {
     const result = new ArrayBuffer(str.length * 2);
     const view = new DataView(result);
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item} of enumerate(str)) {
-      const value = item.charCodeAt(0);
+    for (let i = 0; i < str.length; ++i) {
+      const value = str.charCodeAt(i);
       view.setUint16(/* position= */ i * 2, value, littleEndian);
     }
     return result;

lib/util/uint8array_utils.js

@@ -74,9 +74,8 @@ shaka.util.Uint8ArrayUtils = class {
     // byte.
     const bytes = window.atob(str.replace(/-/g, '+').replace(/_/g, '/'));
     const result = new Uint8Array(bytes.length);
-    const enumerate = (it) => shaka.util.Iterables.enumerate(it);
-    for (const {i, item} of enumerate(bytes)) {
-      result[i] = item.charCodeAt(0);
+    for (let i = 0; i < bytes.length; ++i) {
+      result[i] = bytes.charCodeAt(i);
     }
     return result;
   }

lib/util/xml_utils.js

@@ -57,9 +57,13 @@ shaka.util.XmlUtils = class {
    * @return {!Array.<!Element>} The child XML elements.
    */
   static findChildren(elem, name) {
-    return Array.from(elem.childNodes).filter((child) => {
-      return child instanceof Element && child.tagName == name;
-    });
+    const found = [];
+    for (const child of elem.childNodes) {
+      if (child instanceof Element && child.tagName == name) {
+        found.push(child);
+      }
+    }
+    return found;
   }
 
 
@@ -82,10 +86,14 @@ shaka.util.XmlUtils = class {
    * @return {!Array.<!Element>} The child XML elements.
    */
   static findChildrenNS(elem, ns, name) {
-    return Array.from(elem.childNodes).filter((child) => {
-      return child instanceof Element && child.localName == name &&
-          child.namespaceURI == ns;
-    });
+    const found = [];
+    for (const child of elem.childNodes) {
+      if (child instanceof Element && child.localName == name &&
+          child.namespaceURI == ns) {
+        found.push(child);
+      }
+    }
+    return found;
   }