Use new youtube continuations api for playlists

Requires sending a POST request instead of GET.
clientName and clientVersion, which were required as headers previously now need to be part of the request payload.
continuation id also needs to be part of request body.

quick and dirty solution.

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

@@ -1,6 +1,11 @@
 package org.schabi.newpipe.extractor.services.youtube;
 
-import com.grack.nanojson.*;
+import com.grack.nanojson.JsonArray;
+import com.grack.nanojson.JsonObject;
+import com.grack.nanojson.JsonParser;
+import com.grack.nanojson.JsonParserException;
+import com.grack.nanojson.JsonWriter;
+
 import org.schabi.newpipe.extractor.MetaInfo;
 import org.schabi.newpipe.extractor.Page;
 import org.schabi.newpipe.extractor.downloader.Response;
@@ -33,7 +38,12 @@ import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
 import static org.schabi.newpipe.extractor.NewPipe.getDownloader;
-import static org.schabi.newpipe.extractor.utils.Utils.*;
+import static org.schabi.newpipe.extractor.utils.Utils.EMPTY_STRING;
+import static org.schabi.newpipe.extractor.utils.Utils.HTTP;
+import static org.schabi.newpipe.extractor.utils.Utils.HTTPS;
+import static org.schabi.newpipe.extractor.utils.Utils.UTF_8;
+import static org.schabi.newpipe.extractor.utils.Utils.isNullOrEmpty;
+import static org.schabi.newpipe.extractor.utils.Utils.join;
 
 /*
  * Created by Christian Schabesberger on 02.03.16.
@@ -663,6 +673,14 @@ public class YoutubeParsingHelper {
         }
     }
 
+    public static JsonObject toJsonObject(final String responseBody) throws ParsingException {
+        try {
+            return JsonParser.object().from(responseBody);
+        } catch (JsonParserException e) {
+            throw new ParsingException("Could not parse JSON", e);
+        }
+    }
+
     /**
      * Shared alert detection function, multiple endpoints return the error similarly structured.
      * <p>

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

@@ -2,9 +2,12 @@ package org.schabi.newpipe.extractor.services.youtube.extractors;
 
 import com.grack.nanojson.JsonArray;
 import com.grack.nanojson.JsonObject;
+import com.grack.nanojson.JsonWriter;
+
 import org.schabi.newpipe.extractor.Page;
 import org.schabi.newpipe.extractor.StreamingService;
 import org.schabi.newpipe.extractor.downloader.Downloader;
+import org.schabi.newpipe.extractor.downloader.Response;
 import org.schabi.newpipe.extractor.exceptions.ExtractionException;
 import org.schabi.newpipe.extractor.exceptions.ParsingException;
 import org.schabi.newpipe.extractor.linkhandler.ListLinkHandler;
@@ -19,11 +22,19 @@ import org.schabi.newpipe.extractor.stream.StreamInfoItemsCollector;
 import org.schabi.newpipe.extractor.stream.StreamType;
 import org.schabi.newpipe.extractor.utils.Utils;
 
-import javax.annotation.Nonnull;
-import javax.annotation.Nullable;
 import java.io.IOException;
 
-import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.*;
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.fixThumbnailUrl;
+import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.getClientVersion;
+import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.getJsonResponse;
+import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.getTextFromObject;
+import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.getUrlFromNavigationEndpoint;
+import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.getValidJsonResponseBody;
+import static org.schabi.newpipe.extractor.services.youtube.YoutubeParsingHelper.toJsonObject;
+import static org.schabi.newpipe.extractor.utils.Utils.UTF_8;
 import static org.schabi.newpipe.extractor.utils.Utils.isNullOrEmpty;
 
 @SuppressWarnings("WeakerAccess")
@@ -205,12 +216,27 @@ public class YoutubePlaylistExtractor extends PlaylistExtractor {
             throw new IllegalArgumentException("Page doesn't contain an URL");
         }
 
-        final StreamInfoItemsCollector collector = new StreamInfoItemsCollector(getServiceId());
-        final JsonArray ajaxJson = getJsonResponse(page.getUrl(), getExtractorLocalization());
+        // @formatter:off
+        byte[] json = JsonWriter.string()
+                .object()
+                    .object("context")
+                        .object("client")
+                            .value("clientName", "1")
+                            .value("clientVersion", getClientVersion())
+                        .end()
+                    .end()
+                    .value("continuation", page.getId())
+                .end()
+                .done()
+                .getBytes(UTF_8);
+        // @formatter:on
 
-        final JsonArray continuation = ajaxJson.getObject(1)
-                .getObject("response")
-                .getArray("onResponseReceivedActions")
+        final StreamInfoItemsCollector collector = new StreamInfoItemsCollector(getServiceId());
+        final Response response = getDownloader().post(page.getUrl(), null, json, getExtractorLocalization());
+
+        final JsonObject ajaxJson = toJsonObject(getValidJsonResponseBody(response));
+
+        final JsonArray continuation = ajaxJson.getArray("onResponseReceivedActions")
                 .getObject(0)
                 .getObject("appendContinuationItemsAction")
                 .getArray("continuationItems");
@@ -232,7 +258,9 @@ public class YoutubePlaylistExtractor extends PlaylistExtractor {
                     .getObject("continuationEndpoint")
                     .getObject("continuationCommand")
                     .getString("token");
-            return new Page("https://www.youtube.com/browse_ajax?continuation=" + continuation);
+            return new Page(
+                    "https://www.youtube.com/youtubei/v1/browse?key=AIzaSyAO_FJ2SlqU8Q4STEHLGCilw_Y9_11qcW8",
+                    continuation);
         } else {
             return null;
         }