[YouTube] Refactor JavaScript player management API

This commit is introducing breaking changes.

For clients, everything is managed in a new class called
YoutubeJavaScriptPlayerManager:
- caching JavaScript base player code and its extracted code (functions and
variables);
- getting player signature timestamp;
- getting deobfuscated signatures of streaming URLs;
- getting streaming URLs with a throttling parameter deobfuscated, if
applicable.

The class delegates the extraction parts to external package-private classes:
- YoutubeJavaScriptExtractor, to extract and download YouTube's JavaScript base
player code: it always already present before and has been edited to mainly
remove the previous caching system and made it package-private;
- YoutubeSignatureUtils, for player signature timestamp and signature
deobfuscation function of streaming URLs, added in a recent commit;
- YoutubeThrottlingParameterUtils, which was originally
YoutubeThrottlingDecrypter, for throttling parameter of streaming URLs
deobfuscation function and checking whether this parameter is in a streaming
URL.

YoutubeJavaScriptPlayerManager caches and then runs the extracted code if it
has been executed successfully. The cache system of throttling parameters
deobfuscated values has been kept, its size can be get using the
getThrottlingParametersCacheSize method and can be cleared independently using
the clearThrottlingParametersCache method.

If an exception occurs during the extraction or the parsing of a function
property which is not related to JavaScript base player code fetching, it is
stored until caches are cleared, making subsequent failing extraction calls of
the requested function or property faster and consuming less resources, as the
result should be the same until the base player code changes.

All caches can be reset using the clearAllCaches method of
YoutubeJavaScriptPlayerManager.

Classes using JavaScript base player code and utilities directly (in the code
and its tests) have been also updated in this commit.

Author: AudricV

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

@@ -10,18 +10,14 @@
 import org.schabi.newpipe.extractor.utils.Parser;
 
 import javax.annotation.Nonnull;
+import java.net.MalformedURLException;
+import java.net.URL;
 import java.util.regex.Pattern;
 
 /**
  * The extractor of YouTube's base JavaScript player file.
  *
  * <p>
- * YouTube restrict streaming their media in multiple ways by requiring their HTML5 clients to use
- * a signature timestamp, and on streaming URLs a signature deobfuscation function for some
- * contents and a throttling parameter deobfuscation one for all contents.
- * </p>
- *
- * <p>
  * This class handles fetching of this base JavaScript player file in order to allow other classes
  * to extract the needed data.
  * </p>
@@ -31,7 +27,7 @@
  * watch page as a fallback.
  * </p>
  */
-public final class YoutubeJavaScriptExtractor {
+final class YoutubeJavaScriptExtractor {
 
     private static final String HTTPS = "https:";
     private static final String BASE_JS_PLAYER_URL_FORMAT =
@@ -40,49 +36,45 @@ public final class YoutubeJavaScriptExtractor {
             "player\\\\/([a-z0-9]{8})\\\\/");
     private static final Pattern EMBEDDED_WATCH_PAGE_JS_BASE_PLAYER_URL_PATTERN = Pattern.compile(
             "\"jsUrl\":\"(/s/player/[A-Za-z0-9]+/player_ias\\.vflset/[A-Za-z_-]+/base\\.js)\"");
-    private static String cachedJavaScriptCode;
 
     private YoutubeJavaScriptExtractor() {
     }
 
     /**
-     * Extracts the JavaScript file.
+     * Extracts the JavaScript base player file.
      *
-     * <p>
-     * The result is cached, so subsequent calls use the result of previous calls.
-     * </p>
-     *
-     * @param videoId a YouTube video ID, which doesn't influence the result, but it may help in
-     *                the chance that YouTube track it
-     * @return the whole JavaScript file as a string
-     * @throws ParsingException if the extraction failed
+     * @param videoId the video ID used to get the JavaScript base player file (an empty one can be
+     *                passed, even it is not recommend in order to spoof better official YouTube
+     *                clients)
+     * @return the whole JavaScript base player file as a string
+     * @throws ParsingException if the extraction of the file failed
      */
     @Nonnull
-    public static String extractJavaScriptCode(@Nonnull final String videoId)
+    static String extractJavaScriptPlayerCode(@Nonnull final String videoId)
             throws ParsingException {
-        if (cachedJavaScriptCode == null) {
-            String url;
-            try {
-                url = YoutubeJavaScriptExtractor.extractJavaScriptUrlWithIframeResource();
-            } catch (final Exception e) {
-                url = YoutubeJavaScriptExtractor.extractJavaScriptUrlWithEmbedWatchPage(videoId);
-            }
+        String url;
+        try {
+            url = YoutubeJavaScriptExtractor.extractJavaScriptUrlWithIframeResource();
             final String playerJsUrl = YoutubeJavaScriptExtractor.cleanJavaScriptUrl(url);
-            cachedJavaScriptCode = YoutubeJavaScriptExtractor.downloadJavaScriptCode(playerJsUrl);
-        }
 
-        return cachedJavaScriptCode;
-    }
+            // Assert that the URL we extracted and built is valid
+            new URL(playerJsUrl);
 
-    /**
-     * Reset the cached JavaScript code.
-     *
-     * <p>
-     * It will be fetched again the next time {@link #extractJavaScriptCode(String)} is called.
-     * </p>
-     */
-    public static void resetJavaScriptCode() {
-        cachedJavaScriptCode = null;
+            return YoutubeJavaScriptExtractor.downloadJavaScriptCode(playerJsUrl);
+        } catch (final Exception e) {
+            url = YoutubeJavaScriptExtractor.extractJavaScriptUrlWithEmbedWatchPage(videoId);
+            final String playerJsUrl = YoutubeJavaScriptExtractor.cleanJavaScriptUrl(url);
+
+            try {
+                // Assert that the URL we extracted and built is valid
+                new URL(playerJsUrl);
+            } catch (final MalformedURLException exception) {
+                throw new ParsingException(
+                        "The extracted and built JavaScript URL is invalid", exception);
+            }
+
+            return YoutubeJavaScriptExtractor.downloadJavaScriptCode(playerJsUrl);
+        }
     }
 
     @Nonnull
@@ -134,7 +126,7 @@ static String extractJavaScriptUrlWithEmbedWatchPage(@Nonnull final String video
             }
         }
 
-        // Use regexes to match the URL in a JavaScript embedded script of the HTML page
+        // Use regexes to match the URL in an embedded script of the HTML page
         try {
             return Parser.matchGroup1(
                     EMBEDDED_WATCH_PAGE_JS_BASE_PLAYER_URL_PATTERN, embedPageContent);
@@ -145,29 +137,28 @@ static String extractJavaScriptUrlWithEmbedWatchPage(@Nonnull final String video
     }
 
     @Nonnull
-    private static String cleanJavaScriptUrl(@Nonnull final String playerJsUrl) {
-        if (playerJsUrl.startsWith("//")) {
+    private static String cleanJavaScriptUrl(@Nonnull final String javaScriptPlayerUrl) {
+        if (javaScriptPlayerUrl.startsWith("//")) {
             // https part has to be added manually if the URL is protocol-relative
-            return HTTPS + playerJsUrl;
-        } else if (playerJsUrl.startsWith("/")) {
+            return HTTPS + javaScriptPlayerUrl;
+        } else if (javaScriptPlayerUrl.startsWith("/")) {
             // https://www.youtube.com part has to be added manually if the URL is relative to
             // YouTube's domain
-            return HTTPS + "//www.youtube.com" + playerJsUrl;
+            return HTTPS + "//www.youtube.com" + javaScriptPlayerUrl;
         } else {
-            return playerJsUrl;
+            return javaScriptPlayerUrl;
         }
     }
 
     @Nonnull
-    private static String downloadJavaScriptCode(@Nonnull final String playerJsUrl)
+    private static String downloadJavaScriptCode(@Nonnull final String javaScriptPlayerUrl)
             throws ParsingException {
         try {
             return NewPipe.getDownloader()
-                    .get(playerJsUrl, Localization.DEFAULT)
+                    .get(javaScriptPlayerUrl, Localization.DEFAULT)
                     .responseBody();
         } catch (final Exception e) {
-            throw new ParsingException(
-                    "Could not get JavaScript base player's code from URL: " + playerJsUrl, e);
+            throw new ParsingException("Could not get JavaScript base player's code", e);
         }
     }
 }