ForumChannels returns only threads it is parent of

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -595,6 +595,33 @@ namespace Discord.API
             return await SendAsync<ChannelThreads>("GET", () => $"guilds/{guildId}/threads/active", bucket, options: options);
         }
 
+        public async Task<ChannelThreads> GetActiveThreadsInChannelAsync(ulong guildId, ulong parentChannel, RequestOptions options = null)
+        {
+            Preconditions.NotEqual(guildId, 0, nameof(guildId));
+
+            options = RequestOptions.CreateOrClone(options);
+
+            var bucket = new BucketIds(guildId: guildId);
+
+            ChannelThreads allChannelThreads = await SendAsync<ChannelThreads>("GET", () => $"guilds/{guildId}/threads/active", bucket, options: options);
+            ChannelThreads filteredThreads = new ChannelThreads();
+
+            filteredThreads.Threads = allChannelThreads.Threads.Where(x => x.CategoryId == parentChannel).ToArray();
+
+            List<ThreadMember> members = new List<ThreadMember>();
+
+            foreach (ThreadMember m in allChannelThreads.Members)
+            {
+                if (filteredThreads.Threads.Where(x => x.Id == (ulong)m.Id).Count() == 0)
+                    continue;
+                members.Add(m);
+            }
+
+            filteredThreads.Members = members.ToArray();
+
+            return filteredThreads;
+        }
+
         public async Task<ChannelThreads> GetPublicArchivedThreadsAsync(ulong channelId, DateTimeOffset? before = null, int? limit = null, RequestOptions options = null)
         {
             Preconditions.NotEqual(channelId, 0, nameof(channelId));

src/Discord.Net.Rest/Entities/Channels/RestForumChannel.cs

@@ -92,7 +92,7 @@ namespace Discord.Rest
 
         /// <inheritdoc cref="IForumChannel.GetActiveThreadsAsync(RequestOptions)"/>
         public Task<IReadOnlyCollection<RestThreadChannel>> GetActiveThreadsAsync(RequestOptions options = null)
-            => ThreadHelper.GetActiveThreadsAsync(Guild, Discord, options);
+            => ThreadHelper.GetActiveThreadsInChannelAsync(Guild, this, Discord, options);
 
         /// <inheritdoc cref="IForumChannel.GetJoinedPrivateArchivedThreadsAsync(int?, DateTimeOffset?, RequestOptions)"/>
         public Task<IReadOnlyCollection<RestThreadChannel>> GetJoinedPrivateArchivedThreadsAsync(int? limit = null, DateTimeOffset? before = null, RequestOptions options = null)

src/Discord.Net.Rest/Entities/Channels/ThreadHelper.cs

@@ -67,6 +67,11 @@ namespace Discord.Rest
             var result = await client.ApiClient.GetActiveThreadsAsync(guild.Id, options).ConfigureAwait(false);
             return result.Threads.Select(x => RestThreadChannel.Create(client, guild, x)).ToImmutableArray();
         }
+        public static async Task<IReadOnlyCollection<RestThreadChannel>> GetActiveThreadsInChannelAsync(IGuild guild, IGuildChannel parentChannel, BaseDiscordClient client, RequestOptions options)
+        {
+            var result = await client.ApiClient.GetActiveThreadsInChannelAsync(guild.Id, parentChannel.Id, options).ConfigureAwait(false);
+            return result.Threads.Select(x => RestThreadChannel.Create(client, guild, x)).ToImmutableArray();
+        }
 
         public static async Task<IReadOnlyCollection<RestThreadChannel>> GetPublicArchivedThreadsAsync(IGuildChannel channel, BaseDiscordClient client, int? limit = null,
             DateTimeOffset? before = null, RequestOptions options = null)

src/Discord.Net.WebSocket/Entities/Channels/SocketForumChannel.cs

@@ -89,7 +89,7 @@ namespace Discord.WebSocket
 
         /// <inheritdoc cref="IForumChannel.GetActiveThreadsAsync(RequestOptions)"/>
         public Task<IReadOnlyCollection<RestThreadChannel>> GetActiveThreadsAsync(RequestOptions options = null)
-            => ThreadHelper.GetActiveThreadsAsync(Guild, Discord, options);
+            => ThreadHelper.GetActiveThreadsInChannelAsync(Guild, this, Discord, options);
 
         /// <inheritdoc cref="IForumChannel.GetJoinedPrivateArchivedThreadsAsync(int?, DateTimeOffset?, RequestOptions)"/>
         public Task<IReadOnlyCollection<RestThreadChannel>> GetJoinedPrivateArchivedThreadsAsync(int? limit = null, DateTimeOffset? before = null, RequestOptions options = null)
@@ -105,7 +105,7 @@ namespace Discord.WebSocket
 
         #region IForumChannel
         async Task<IReadOnlyCollection<IThreadChannel>> IForumChannel.GetActiveThreadsAsync(RequestOptions options)
-            => await GetActiveThreadsAsync(options).ConfigureAwait(false);
+            => await GetActiveThreadsInChannelAsync(options).ConfigureAwait(false);
         async Task<IReadOnlyCollection<IThreadChannel>> IForumChannel.GetPublicArchivedThreadsAsync(int? limit, DateTimeOffset? before, RequestOptions options)
             => await GetPublicArchivedThreadsAsync(limit, before, options).ConfigureAwait(false);
         async Task<IReadOnlyCollection<IThreadChannel>> IForumChannel.GetPrivateArchivedThreadsAsync(int? limit, DateTimeOffset? before, RequestOptions options)