fix(bot): only allow proxying in known-supported channel types

This is so that new channel types added by Discord (that may or may not
support the features we need for proxying to work) don't throw piles of
error codes at users when they try to proxy.

Myriad/Types/Channel.cs

@@ -14,7 +14,10 @@ public record Channel
         GuildNewsThread = 10,
         GuildPublicThread = 11,
         GuildPrivateThread = 12,
-        GuildStageVoice = 13
+        GuildStageVoice = 13,
+        GuildDirectory = 14,
+        GuildForum = 15,
+        GuildMedia = 16,
     }
 
     public ulong Id { get; init; }

PluralKit.Bot/Commands/Checks.cs

@@ -248,10 +248,10 @@ public class Checks
         // Run everything through the checks, catch the ProxyCheckFailedException, and reply with the error message.
         try
         {
-            _proxy.ShouldProxy(channel, msg, context);
+            _proxy.ShouldProxy(channel, rootChannel, msg, context);
             _matcher.TryMatch(context, autoproxySettings, members, out var match, msg.Content, msg.Attachments.Length > 0, true, ctx.Config.CaseSensitiveProxyTags);
 
-            var canProxy = await _proxy.CanProxy(channel, msg, context);
+            var canProxy = await _proxy.CanProxy(channel, rootChannel, msg, context);
             if (canProxy != null)
             {
                 await ctx.Reply(canProxy);

PluralKit.Bot/Proxy/ProxyService.cs

@@ -57,7 +57,9 @@ public class ProxyService
     public async Task<bool> HandleIncomingMessage(MessageCreateEvent message, MessageContext ctx,
                                 Guild guild, Channel channel, bool allowAutoproxy, PermissionSet botPermissions)
     {
-        if (!ShouldProxy(channel, message, ctx))
+        var rootChannel = await _cache.GetRootChannel(message.ChannelId);
+
+        if (!ShouldProxy(channel, rootChannel, message, ctx))
             return false;
 
         var autoproxySettings = await _repo.GetAutoproxySettings(ctx.SystemId.Value, guild.Id, null);
@@ -72,8 +74,6 @@ public class ProxyService
             return false;
         }
 
-        var rootChannel = await _cache.GetRootChannel(message.ChannelId);
-
         List<ProxyMember> members;
         // Fetch members and try to match to a specific member
         using (_metrics.Measure.Timer.Time(BotMetrics.ProxyMembersQueryTime))
@@ -82,7 +82,7 @@ public class ProxyService
         if (!_matcher.TryMatch(ctx, autoproxySettings, members, out var match, message.Content, message.Attachments.Length > 0,
                 allowAutoproxy, ctx.CaseSensitiveProxyTags)) return false;
 
-        var canProxy = await CanProxy(channel, message, ctx);
+        var canProxy = await CanProxy(channel, rootChannel, message, ctx);
         if (canProxy != null)
         {
             if (ctx.ProxyErrorMessageEnabled)
@@ -109,8 +109,32 @@ public class ProxyService
         return true;
     }
 
-    public async Task<string> CanProxy(Channel channel, Message msg, MessageContext ctx)
+#pragma warning disable CA1822 // Mark members as static
+    internal bool CanProxyInChannel(Channel ch, bool isRootChannel = false)
+#pragma warning restore CA1822 // Mark members as static
     {
+        // this is explicitly selecting known channel types so that when Discord add new
+        // ones, users don't get flooded with error codes if that new channel type doesn't
+        // support a feature we need for proxying
+        return ch.Type switch
+        {
+            Channel.ChannelType.GuildText => true,
+            Channel.ChannelType.GuildPublicThread => true,
+            Channel.ChannelType.GuildPrivateThread => true,
+            Channel.ChannelType.GuildNews => true,
+            Channel.ChannelType.GuildNewsThread => true,
+            Channel.ChannelType.GuildVoice => true,
+            Channel.ChannelType.GuildStageVoice => true,
+            Channel.ChannelType.GuildForum => isRootChannel,
+            _ => false,
+        };
+    }
+
+    public async Task<string> CanProxy(Channel channel, Channel rootChannel, Message msg, MessageContext ctx)
+    {
+        if (!(CanProxyInChannel(channel) && CanProxyInChannel(rootChannel, true)))
+            return $"PluralKit cannot proxy messages in this type of channel.";
+
         // Check if the message does not go over any Discord Nitro limits
         if (msg.Content != null && msg.Content.Length > 2000)
         {
@@ -132,7 +156,7 @@ public class ProxyService
         return null;
     }
 
-    public bool ShouldProxy(Channel channel, Message msg, MessageContext ctx)
+    public bool ShouldProxy(Channel channel, Channel rootChannel, Message msg, MessageContext ctx)
     {
         // Make sure author has a system
         if (ctx.SystemId == null)

PluralKit.Bot/Services/WebhookCacheService.cs

@@ -105,7 +105,14 @@ public class WebhookCacheService
     {
         try
         {
-            return await _rest.GetChannelWebhooks(channelId);
+            var webhooks = await _rest.GetChannelWebhooks(channelId);
+            if (webhooks != null)
+                return webhooks;
+
+            // Getting a 404 / null response from the above generally means the channel type does
+            // not support webhooks - this is detected elsewhere for proxying purposes, let's just
+            // return an empty array here
+            return new Webhook[0];
         }
         catch (HttpRequestException e)
         {