Make YoutubeJavaScriptExtractor and JavaScript methods static

Also address review and rewrite some comments

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeJavaScriptExtractor.java

@@ -12,47 +12,51 @@ import org.schabi.newpipe.extractor.utils.Parser;
 import javax.annotation.Nonnull;
 
 /**
- * Youtube restricts streaming their media in multiple ways by requiring clients to apply a cipher function
+ * YouTube restricts streaming their media in multiple ways by requiring clients to apply a cipher function
  * on parameters of requests.
  * The cipher function is sent alongside as a JavaScript function.
  * <p>
  * This class handling fetching the JavaScript file in order to allow other classes to extract the needed functions.
  */
-public class YoutubeJavascriptExtractor {
+public class YoutubeJavaScriptExtractor {
 
     private static final String HTTPS = "https:";
-    private static String cachedJavascriptCode;
+    private static String cachedJavaScriptCode;
+
+    private YoutubeJavaScriptExtractor() {
+    }
 
     /**
      * Extracts the JavaScript file. The result is cached, so subsequent calls use the result of previous calls.
      *
-     * @param videoId Does not influence the result, but a valid video id can prevent tracking
+     * @param videoId Does not influence the result, but a valid video id may help in the chance that YouTube tracks it.
      * @return The whole javascript file as a string.
      * @throws ParsingException If the extraction failed.
      */
     @Nonnull
-    public static String extractJavascriptCode(String videoId) throws ParsingException {
+    public static String extractJavaScriptCode(String videoId) throws ParsingException {
-        if (cachedJavascriptCode == null) {
+        if (cachedJavaScriptCode == null) {
-            final YoutubeJavascriptExtractor extractor = new YoutubeJavascriptExtractor();
+            final String playerJsUrl = YoutubeJavaScriptExtractor.cleanJavaScriptUrl(
-            String playerJsUrl = extractor.cleanJavascriptUrl(extractor.extractJavascriptUrl(videoId));
+                    YoutubeJavaScriptExtractor.extractJavaScriptUrl(videoId));
-            cachedJavascriptCode = extractor.downloadJavascriptCode(playerJsUrl);
+            cachedJavaScriptCode = YoutubeJavaScriptExtractor.downloadJavaScriptCode(playerJsUrl);
         }
 
-        return cachedJavascriptCode;
+        return cachedJavaScriptCode;
     }
 
     /**
-     * Same as {@link YoutubeJavascriptExtractor#extractJavascriptCode(String)} but with a constant value for videoId.
+     * Same as {@link YoutubeJavaScriptExtractor#extractJavaScriptCode(String)} but with a constant value for videoId.
      * Possible because the videoId has no influence on the result.
-     *
+     * <p>
-     * For tracking avoidance purposes it may make sense to pass in valid video ids.
+     * In the off chance that YouTube tracks with which video id the request is made, it may make sense to pass in
+     * video ids.
      */
     @Nonnull
-    public static String extractJavascriptCode() throws ParsingException {
+    public static String extractJavaScriptCode() throws ParsingException {
-        return extractJavascriptCode("d4IGg5dqeO8");
+        return extractJavaScriptCode("d4IGg5dqeO8");
     }
 
-    private String extractJavascriptUrl(String videoId) throws ParsingException {
+    private static String extractJavaScriptUrl(String videoId) throws ParsingException {
         try {
             final String embedUrl = "https://www.youtube.com/embed/" + videoId;
             final String embedPageContent = NewPipe.getDownloader()
@@ -80,7 +84,7 @@ public class YoutubeJavascriptExtractor {
         throw new ParsingException("Embedded info did not provide YouTube player js url");
     }
 
-    private String cleanJavascriptUrl(String playerJsUrl) {
+    private static String cleanJavaScriptUrl(String playerJsUrl) {
         if (playerJsUrl.startsWith("//")) {
             return HTTPS + playerJsUrl;
         } else if (playerJsUrl.startsWith("/")) {
@@ -91,7 +95,7 @@ public class YoutubeJavascriptExtractor {
         }
     }
 
-    private String downloadJavascriptCode(String playerJsUrl) throws ParsingException {
+    private static String downloadJavaScriptCode(String playerJsUrl) throws ParsingException {
         try {
             return NewPipe.getDownloader().get(playerJsUrl, Localization.DEFAULT).responseBody();
         } catch (Exception e) {

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeThrottlingDecrypter.java

@@ -1,7 +1,7 @@
 package org.schabi.newpipe.extractor.services.youtube;
 
 import org.schabi.newpipe.extractor.exceptions.ParsingException;
-import org.schabi.newpipe.extractor.utils.Javascript;
+import org.schabi.newpipe.extractor.utils.JavaScript;
 import org.schabi.newpipe.extractor.utils.Parser;
 
 import java.util.regex.Pattern;
@@ -35,14 +35,14 @@ public class YoutubeThrottlingDecrypter {
      * Otherwise use the no-arg constructor which uses a constant value.
      */
     public YoutubeThrottlingDecrypter(String videoId) throws ParsingException {
-        final String playerJsCode = YoutubeJavascriptExtractor.extractJavascriptCode(videoId);
+        final String playerJsCode = YoutubeJavaScriptExtractor.extractJavaScriptCode(videoId);
 
         functionName = parseDecodeFunctionName(playerJsCode);
         function = parseDecodeFunction(playerJsCode, functionName);
     }
 
     public YoutubeThrottlingDecrypter() throws ParsingException {
-        final String playerJsCode = YoutubeJavascriptExtractor.extractJavascriptCode();
+        final String playerJsCode = YoutubeJavaScriptExtractor.extractJavaScriptCode();
 
         functionName = parseDecodeFunctionName(playerJsCode);
         function = parseDecodeFunction(playerJsCode, functionName);
@@ -78,8 +78,7 @@ public class YoutubeThrottlingDecrypter {
     }
 
     private String decryptNParam(String nParam) {
-        Javascript javascript = new Javascript();
+        return JavaScript.run(function, functionName, nParam);
-        return javascript.run(function, functionName, nParam);
     }
 
     private String replaceNParam(String url, String oldValue, String newValue) {

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/extractors/YoutubeStreamExtractor.java

@@ -4,10 +4,6 @@ import com.grack.nanojson.JsonArray;
 import com.grack.nanojson.JsonObject;
 import com.grack.nanojson.JsonParser;
 import com.grack.nanojson.JsonParserException;
-import org.jsoup.Jsoup;
-import org.jsoup.nodes.Document;
-import org.jsoup.nodes.Element;
-import org.jsoup.select.Elements;
 import org.mozilla.javascript.Context;
 import org.mozilla.javascript.Function;
 import org.mozilla.javascript.ScriptableObject;
@@ -24,7 +20,7 @@ import org.schabi.newpipe.extractor.localization.Localization;
 import org.schabi.newpipe.extractor.localization.TimeAgoParser;
 import org.schabi.newpipe.extractor.localization.TimeAgoPatternsManager;
 import org.schabi.newpipe.extractor.services.youtube.ItagItem;
-import org.schabi.newpipe.extractor.services.youtube.YoutubeJavascriptExtractor;
+import org.schabi.newpipe.extractor.services.youtube.YoutubeJavaScriptExtractor;
 import org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper;
 import org.schabi.newpipe.extractor.services.youtube.YoutubeThrottlingDecrypter;
 import org.schabi.newpipe.extractor.services.youtube.linkHandler.YoutubeChannelLinkHandlerFactory;
@@ -524,7 +520,7 @@ public class YoutubeStreamExtractor extends StreamExtractor {
     public List<VideoStream> getVideoStreams() throws ExtractionException {
         assertPageFetched();
         final List<VideoStream> videoStreams = new ArrayList<>();
-        YoutubeThrottlingDecrypter throttlingDecrypter = new YoutubeThrottlingDecrypter(getId());
+        final YoutubeThrottlingDecrypter throttlingDecrypter = new YoutubeThrottlingDecrypter(getId());
 
         try {
             for (final Map.Entry<String, ItagItem> entry : getItags(FORMATS, ItagItem.ItagType.VIDEO).entrySet()) {
@@ -817,7 +813,7 @@ public class YoutubeStreamExtractor extends StreamExtractor {
     private String loadDeobfuscationCode()
             throws DeobfuscateException {
         try {
-            final String playerCode = YoutubeJavascriptExtractor.extractJavascriptCode(getId());
+            final String playerCode = YoutubeJavaScriptExtractor.extractJavaScriptCode(getId());
             final String deobfuscationFunctionName = getDeobfuscationFuncName(playerCode);
 
             final String functionPattern = "("

extractor/src/main/java/org/schabi/newpipe/extractor/utils/JavaScript.java

@@ -4,9 +4,12 @@ import org.mozilla.javascript.Context;
 import org.mozilla.javascript.Function;
 import org.mozilla.javascript.ScriptableObject;
 
-public class Javascript {
+public class JavaScript {
 
-    public String run(String function, String functionName, String... parameters) {
+    private JavaScript() {
+    }
+
+    public static String run(String function, String functionName, String... parameters) {
         try {
             Context context = Context.enter();
             context.setOptimizationLevel(-1);

extractor/src/test/java/org/schabi/newpipe/extractor/services/youtube/YoutubeJavaScriptExtractorTest.java

@@ -12,7 +12,7 @@ import static org.hamcrest.CoreMatchers.allOf;
 import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.MatcherAssert.assertThat;
 
-public class YoutubeJavascriptExtractorTest {
+public class YoutubeJavaScriptExtractorTest {
 
     @Before
     public void setup() throws IOException {
@@ -20,20 +20,20 @@ public class YoutubeJavascriptExtractorTest {
     }
 
     @Test
-    public void testExtractJavascript__success() throws ParsingException {
+    public void testExtractJavaScript__success() throws ParsingException {
-        String playerJsCode = YoutubeJavascriptExtractor.extractJavascriptCode("d4IGg5dqeO8");
+        String playerJsCode = YoutubeJavaScriptExtractor.extractJavaScriptCode("d4IGg5dqeO8");
         assertPlayerJsCode(playerJsCode);
 
-        playerJsCode = YoutubeJavascriptExtractor.extractJavascriptCode();
+        playerJsCode = YoutubeJavaScriptExtractor.extractJavaScriptCode();
         assertPlayerJsCode(playerJsCode);
     }
 
     @Test
-    public void testExtractJavascript__invalidVideoId__success() throws ParsingException {
+    public void testExtractJavaScript__invalidVideoId__success() throws ParsingException {
-        String playerJsCode = YoutubeJavascriptExtractor.extractJavascriptCode("not_a_video_id");
+        String playerJsCode = YoutubeJavaScriptExtractor.extractJavaScriptCode("not_a_video_id");
         assertPlayerJsCode(playerJsCode);
 
-        playerJsCode = YoutubeJavascriptExtractor.extractJavascriptCode("11-chars123");
+        playerJsCode = YoutubeJavaScriptExtractor.extractJavaScriptCode("11-chars123");
         assertPlayerJsCode(playerJsCode);
 
     }