[YouTube] Fix extraction of next page url for the last page of playlist

Author: XiangRongLin

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

@@ -225,12 +225,17 @@ private Page getNextPageFrom(final JsonArray contents) {
             return null;
         }
 
-        final String continuation = contents.getObject(contents.size() - 1)
-            .getObject("continuationItemRenderer")
-            .getObject("continuationEndpoint")
-            .getObject("continuationCommand")
-            .getString("token");
-        return new Page("https://www.youtube.com/browse_ajax?continuation=" + continuation);
+        final JsonObject lastElement = contents.getObject(contents.size() - 1);
+        if (lastElement.has("continuationItemRenderer")) {
+            final String continuation = lastElement
+                .getObject("continuationItemRenderer")
+                .getObject("continuationEndpoint")
+                .getObject("continuationCommand")
+                .getString("token");
+            return new Page("https://www.youtube.com/browse_ajax?continuation=" + continuation);
+        } else {
+            return null;
+        }
     }
 
     private void collectStreamsFrom(final StreamInfoItemsCollector collector, final JsonArray videos) {

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

@@ -14,14 +14,17 @@
 import org.schabi.newpipe.extractor.exceptions.ParsingException;
 import org.schabi.newpipe.extractor.playlist.PlaylistExtractor;
 import org.schabi.newpipe.extractor.services.BasePlaylistExtractorTest;
+import org.schabi.newpipe.extractor.services.youtube.YoutubePlaylistExtractorTest.ContinuationsTests;
 import org.schabi.newpipe.extractor.services.youtube.YoutubePlaylistExtractorTest.HugePlaylist;
 import org.schabi.newpipe.extractor.services.youtube.YoutubePlaylistExtractorTest.LearningPlaylist;
 import org.schabi.newpipe.extractor.services.youtube.YoutubePlaylistExtractorTest.NotAvailable;
 import org.schabi.newpipe.extractor.services.youtube.YoutubePlaylistExtractorTest.TimelessPopHits;
 import org.schabi.newpipe.extractor.services.youtube.extractors.YoutubePlaylistExtractor;
 import org.schabi.newpipe.extractor.stream.StreamInfoItem;
 
+import static junit.framework.TestCase.assertFalse;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.schabi.newpipe.extractor.ExtractorAsserts.assertIsSecureUrl;
 import static org.schabi.newpipe.extractor.ServiceList.YouTube;
@@ -31,7 +34,8 @@
  * Test for {@link YoutubePlaylistExtractor}
  */
 @RunWith(Suite.class)
-@SuiteClasses({NotAvailable.class, TimelessPopHits.class, HugePlaylist.class, LearningPlaylist.class})
+@SuiteClasses({NotAvailable.class, TimelessPopHits.class, HugePlaylist.class,
+    LearningPlaylist.class, ContinuationsTests.class})
 public class YoutubePlaylistExtractorTest {
 
     public static class NotAvailable {
@@ -123,7 +127,7 @@ public void testThumbnailUrl() throws Exception {
 
         @Ignore
         @Test
-        public void testBannerUrl() throws Exception {
+        public void testBannerUrl() {
             final String bannerUrl = extractor.getBannerUrl();
             assertIsSecureUrl(bannerUrl);
             assertTrue(bannerUrl, bannerUrl.contains("yt"));
@@ -236,7 +240,7 @@ public void testThumbnailUrl() throws Exception {
 
         @Ignore
         @Test
-        public void testBannerUrl() throws Exception {
+        public void testBannerUrl() {
             final String bannerUrl = extractor.getBannerUrl();
             assertIsSecureUrl(bannerUrl);
             assertTrue(bannerUrl, bannerUrl.contains("yt"));
@@ -333,7 +337,7 @@ public void testThumbnailUrl() throws Exception {
 
         @Ignore
         @Test
-        public void testBannerUrl() throws Exception {
+        public void testBannerUrl() {
             final String bannerUrl = extractor.getBannerUrl();
             assertIsSecureUrl(bannerUrl);
             assertTrue(bannerUrl, bannerUrl.contains("yt"));
@@ -361,4 +365,34 @@ public void testStreamCount() throws Exception {
             assertTrue("Error in the streams count", extractor.getStreamCount() > 40);
         }
     }
+
+    public static class ContinuationsTests {
+
+        @BeforeClass
+        public static void setUp() {
+            NewPipe.init(DownloaderTestImpl.getInstance());
+        }
+
+        @Test
+        public void testNoContinuations() throws Exception {
+            final YoutubePlaylistExtractor extractor = (YoutubePlaylistExtractor) YouTube
+                .getPlaylistExtractor(
+                    "https://www.youtube.com/playlist?list=PLXJg25X-OulsVsnvZ7RVtSDW-id9_RzAO");
+            extractor.fetchPage();
+
+            assertNoMoreItems(extractor);
+        }
+
+        @Test
+        public void testOnlySingleContinuation() throws Exception {
+            final YoutubePlaylistExtractor extractor = (YoutubePlaylistExtractor) YouTube
+                .getPlaylistExtractor(
+                    "https://www.youtube.com/playlist?list=PLjgwFL8urN2DFRuRkFTkmtHjyoNWHHdZX");
+            extractor.fetchPage();
+
+            final ListExtractor.InfoItemsPage<StreamInfoItem> page = defaultTestMoreItems(
+                extractor);
+            assertFalse("More items available when it shouldn't", page.hasNextPage());
+        }
+    }
 }