[Feature] Per file attachement size limits (#3090)

* `SendFilesAsync` check file size per attachment instead of combined

* add `AttachmentSizeLimit` to interaction entites

src/Discord.Net.Core/Entities/Interactions/IDiscordInteraction.cs

@@ -111,6 +111,11 @@ namespace Discord
         /// </summary>
         GuildPermissions Permissions { get; }
 
+        /// <summary>
+        ///     Gets the attachment size limit in bytes.
+        /// </summary>
+        ulong AttachmentSizeLimit { get; }
+
         /// <summary>
         ///     Responds to an Interaction with type <see cref="InteractionResponseType.ChannelMessageWithSource"/>.
         /// </summary>

src/Discord.Net.Rest/API/Common/Interaction.cs

@@ -60,4 +60,7 @@ internal class Interaction
 
     [JsonProperty("app_permissions")]
     public GuildPermission ApplicationPermissions { get; set; }
+
+    [JsonProperty("attachment_size_limit")]
+    public ulong AttachmentSizeLimit { get; set; }
 }

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

@@ -406,16 +406,11 @@ namespace Discord.Rest
             foreach (var attachment in attachments)
             {
                 Preconditions.NotNullOrEmpty(attachment.FileName, nameof(attachment.FileName), "File Name must not be empty or null");
-            }
 
-            if (channel is ITextChannel guildTextChannel)
-            {
-                ulong contentSize = (ulong)attachments.Where(x => x.Stream.CanSeek).Sum(x => x.Stream.Length);
-
-                if (contentSize > guildTextChannel.Guild.MaxUploadLimit)
-                {
-                    throw new ArgumentOutOfRangeException(nameof(attachments), $"Collective file size exceeds the max file size of {guildTextChannel.Guild.MaxUploadLimit} bytes in that guild!");
-                }
+                if (channel is ITextChannel guildTextChannel &&
+                    attachment.Stream.CanSeek &&
+                    (ulong)attachment.Stream.Length > guildTextChannel.Guild.MaxUploadLimit)
+                    throw new ArgumentOutOfRangeException(nameof(attachments), $"File size exceeds the max file size of {guildTextChannel.Guild.MaxUploadLimit} bytes in that guild!");
             }
 
             // check that user flag and user Id list are exclusive, same with role flag and role Id list

src/Discord.Net.Rest/Entities/Interactions/RestInteraction.cs

@@ -102,6 +102,9 @@ namespace Discord.Rest
         /// <inheritdoc/>
         public IReadOnlyDictionary<ApplicationIntegrationType, ulong> IntegrationOwners { get; private set; }
 
+        /// <inheritdoc/>
+        public ulong AttachmentSizeLimit { get; private set; }
+
         internal RestInteraction(BaseDiscordClient discord, ulong id)
             : base(discord, id)
         {
@@ -248,6 +251,8 @@ namespace Discord.Rest
                 : null;
 
             Permissions = new GuildPermissions((ulong)model.ApplicationPermissions);
+
+            AttachmentSizeLimit = model.AttachmentSizeLimit;
         }
 
         internal string SerializePayload(object payload)

src/Discord.Net.WebSocket/Entities/Interaction/SocketInteraction.cs

@@ -90,6 +90,9 @@ namespace Discord.WebSocket
         /// <inheritdoc cref="IDiscordInteraction.Entitlements" />
         public IReadOnlyCollection<RestEntitlement> Entitlements { get; private set; }
 
+        /// <inheritdoc/>
+        public ulong AttachmentSizeLimit { get; private set; }
+
         /// <inheritdoc/>
         public IReadOnlyDictionary<ApplicationIntegrationType, ulong> IntegrationOwners { get; private set; }
 
@@ -194,6 +197,8 @@ namespace Discord.WebSocket
                     _ => null
                 };
             }
+
+            AttachmentSizeLimit = model.AttachmentSizeLimit;
         }
 
         /// <summary>