Refactor

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

DiscordChatExporter.Core/Discord/Data/MessageKind.cs

@@ -13,4 +13,5 @@ public enum MessageKind
     GuildMemberJoin = 7,
     ThreadCreated = 18,
     Reply = 19,
+    ThreadStarterMessage = 21,
 }

DiscordChatExporter.Core/Discord/DiscordClient.cs

@@ -30,9 +30,8 @@ public class DiscordClient(
         string url,
         TokenKind tokenKind,
         CancellationToken cancellationToken = default
-    )
-    {
-        return await Http.ResponseResiliencePipeline.ExecuteAsync(
+    ) =>
+        await Http.ResponseResiliencePipeline.ExecuteAsync(
             async innerCancellationToken =>
             {
                 using var request = new HttpRequestMessage(HttpMethod.Get, new Uri(_baseUri, url));
@@ -91,7 +90,6 @@ public class DiscordClient(
             },
             cancellationToken
         );
-    }
 
     private async ValueTask<TokenKind> ResolveTokenKindAsync(
         CancellationToken cancellationToken = default
@@ -364,6 +362,7 @@ public class DiscordClient(
             $"guilds/{guildId}/members/{memberId}",
             cancellationToken
         );
+
         return response?.Pipe(j => Member.Parse(j, guildId));
     }
 
@@ -412,14 +411,12 @@ public class DiscordClient(
             ?.GetNonWhiteSpaceStringOrNull()
             ?.Pipe(Snowflake.Parse);
 
-        Channel? parent = null;
-        if (parentId is not null)
-        {
-            // It's possible for the parent channel to be inaccessible, despite the
-            // child channel being accessible.
-            // https://github.com/Tyrrrz/DiscordChatExporter/issues/1108
-            parent = await TryGetChannelAsync(parentId.Value, cancellationToken);
-        }
+        // It's possible for the parent channel to be inaccessible, despite the
+        // child channel being accessible.
+        // https://github.com/Tyrrrz/DiscordChatExporter/issues/1108
+        var parent = parentId is not null
+            ? await TryGetChannelAsync(parentId.Value, cancellationToken)
+            : null;
 
         return Channel.Parse(response.Value, parent);
     }
@@ -607,8 +604,12 @@ public class DiscordClient(
             .SetQueryParameter("after", (after ?? Snowflake.Zero).ToString())
             .Build();
 
-        var response = await GetJsonResponseAsync(url, cancellationToken);
-        var message = response.EnumerateArray().Select(Message.Parse).FirstOrDefault();
+        // Can be null on channels that the user cannot access
+        var response = await TryGetJsonResponseAsync(url, cancellationToken);
+        if (response is null)
+            return null;
+
+        var message = response.Value.EnumerateArray().Select(Message.Parse).FirstOrDefault();
 
         return message;
     }
@@ -625,8 +626,39 @@ public class DiscordClient(
             .SetQueryParameter("before", before?.ToString())
             .Build();
 
-        var response = await GetJsonResponseAsync(url, cancellationToken);
-        return response.EnumerateArray().Select(Message.Parse).LastOrDefault();
+        // Can be null on channels that the user cannot access
+        var response = await TryGetJsonResponseAsync(url, cancellationToken);
+        if (response is null)
+            return null;
+
+        return response.Value.EnumerateArray().Select(Message.Parse).LastOrDefault();
+    }
+
+    public async ValueTask<Message?> TryGetMessageAsync(
+        Snowflake channelId,
+        Snowflake messageId,
+        CancellationToken cancellationToken = default
+    )
+    {
+        // Use the regular message listing endpoint with the 'around' parameter instead of the
+        // dedicated single-message endpoint, because the latter is not accessible to user tokens.
+        var url = new UrlBuilder()
+            .SetPath($"channels/{channelId}/messages")
+            .SetQueryParameter("around", messageId.ToString())
+            .SetQueryParameter("limit", "1")
+            .Build();
+
+        // Can be null on channels that the user cannot access
+        var response = await TryGetJsonResponseAsync(url, cancellationToken);
+        if (response is null)
+            return null;
+
+        // The endpoint returns messages around the requested ID, so make sure to only return
+        // the message that exactly matches it (it may be absent if it has been deleted).
+        return response
+            .Value.EnumerateArray()
+            .Select(Message.Parse)
+            .FirstOrDefault(m => m.Id == messageId);
     }
 
     public async IAsyncEnumerable<Message> GetMessagesAsync(
@@ -701,7 +733,21 @@ public class DiscordClient(
                     );
                 }
 
-                yield return message;
+                // Some messages, for example thread starter messages, are returned by the API as content-less references.
+                // Try to resolve them to the actual message so that they appear as they do in the Discord client.
+                var actualMessage =
+                    message.Kind == MessageKind.ThreadStarterMessage
+                    && message.Reference?.ChannelId is { } referencedChannelId
+                    && message.Reference?.MessageId is { } referencedMessageId
+                        ? await TryGetMessageAsync(
+                            referencedChannelId,
+                            referencedMessageId,
+                            cancellationToken
+                        )
+                        : null;
+
+                yield return actualMessage ?? message;
+
                 currentAfter = message.Id;
             }
         }
@@ -769,7 +815,20 @@ public class DiscordClient(
                     );
                 }
 
-                yield return message;
+                // Some messages, for example thread starter messages, are returned by the API as content-less references.
+                // Try to resolve them to the actual message so that they appear as they do in the Discord client.
+                var actualMessage =
+                    message.Kind == MessageKind.ThreadStarterMessage
+                    && message.Reference?.ChannelId is { } referencedChannelId
+                    && message.Reference?.MessageId is { } referencedMessageId
+                        ? await TryGetMessageAsync(
+                            referencedChannelId,
+                            referencedMessageId,
+                            cancellationToken
+                        )
+                        : null;
+
+                yield return actualMessage ?? message;
             }
 
             currentBefore = messages.Last().Id;

DiscordChatExporter.Core/Exporting/ExportAssetDownloader.cs

@@ -38,23 +38,28 @@ internal partial class ExportAssetDownloader(string workingDirPath, bool reuse)
             return _previousPathsByUrl[url] = filePath;
 
         // Check for a file cached by the legacy naming scheme (5-char hash) and rename it
-        // to the new naming scheme to preserve backwards compatibility with existing exports
+        // to the new naming scheme to preserve backwards compatibility with existing exports.
+        // This will catch both the 5-char lowercase hash and the 5-char uppercase hash variants.
         if (reuse)
         {
-            var legacyFilePath = Path.Combine(workingDirPath, GetLegacyFileNameFromUrl(url));
-            if (File.Exists(legacyFilePath))
+            var legacyFileNames = GetLegacyFileNamesFromUrl(url);
+            foreach (var legacyFileName in legacyFileNames)
             {
-                // Overwrite in case the destination file was created concurrently between our
-                // earlier existence check and this move operation
-                try
+                var legacyFilePath = Path.Combine(workingDirPath, legacyFileName);
+                if (File.Exists(legacyFilePath))
                 {
-                    File.Move(legacyFilePath, filePath, overwrite: true);
-                    return _previousPathsByUrl[url] = filePath;
-                }
-                catch (IOException)
-                {
-                    // The legacy file was moved or deleted concurrently or something else happened.
-                    // Upgrading old files is not crucial, so we can just move on.
+                    // Overwrite in case the destination file was created concurrently between our
+                    // earlier existence check and this move operation
+                    try
+                    {
+                        File.Move(legacyFilePath, filePath, true);
+                        return _previousPathsByUrl[url] = filePath;
+                    }
+                    catch (IOException)
+                    {
+                        // The legacy file was moved or deleted concurrently or something else happened.
+                        // Upgrading old files is not crucial, so we can just move on.
+                    }
                 }
             }
         }
@@ -87,10 +92,16 @@ internal partial class ExportAssetDownloader
 {
     private static string NormalizeUrl(string url)
     {
-        // Remove signature parameters from Discord CDN URLs to normalize them
+        // Remove signature parameters from Discord CDN/media URLs to normalize them
         var uri = new Uri(url);
-        if (!string.Equals(uri.Host, "cdn.discordapp.com", StringComparison.OrdinalIgnoreCase))
+
+        if (
+            !string.Equals(uri.Host, "cdn.discordapp.com", StringComparison.OrdinalIgnoreCase)
+            && !string.Equals(uri.Host, "media.discordapp.net", StringComparison.OrdinalIgnoreCase)
+        )
+        {
             return url;
+        }
 
         var query = HttpUtility.ParseQueryString(uri.Query);
         query.Remove("ex");
@@ -137,13 +148,16 @@ internal partial class ExportAssetDownloader
         );
 
     // Legacy naming used a 5-char hash, kept for backwards compatibility with existing exports
-    private static string GetLegacyFileNameFromUrl(string url) =>
-        GetFileNameFromUrl(
-            url,
-            SHA256
-                .HashData(Encoding.UTF8.GetBytes(NormalizeUrl(url)))
-                .Pipe(Convert.ToHexStringLower)
-                // 5 chars = 20 bits, reaches 1% collision probability at ~145 files
-                .Truncate(5)
-        );
+    private static IReadOnlyList<string> GetLegacyFileNamesFromUrl(string url)
+    {
+        var hashData = SHA256.HashData(Encoding.UTF8.GetBytes(NormalizeUrl(url)));
+
+        return
+        [
+            // Lowercase variant (introduced in 2.46.1)
+            GetFileNameFromUrl(url, Convert.ToHexStringLower(hashData).Truncate(5)),
+            // Uppercase variant (original)
+            GetFileNameFromUrl(url, Convert.ToHexString(hashData).Truncate(5)),
+        ];
+    }
 }

DiscordChatExporter.Core/Exporting/ExportRequest.cs

@@ -206,10 +206,15 @@ public partial class ExportRequest
     {
         var actualOutputPath = FormatPath(outputPath, guild, channel, after, before);
 
-        // Output is a directory
+        // Determine whether the output path refers to a directory or a file.
+        // The extension-based heuristic is evaluated on the original, unsubstituted path,
+        // because the value of a template token (e.g. a guild or channel name) may contain
+        // a period that would otherwise be mistaken for a file extension, incorrectly causing
+        // a directory path to be treated as a file.
+        // https://github.com/Tyrrrz/DiscordChatExporter/issues/1502
         if (
             Directory.Exists(actualOutputPath)
-            || string.IsNullOrWhiteSpace(Path.GetExtension(actualOutputPath))
+            || string.IsNullOrWhiteSpace(Path.GetExtension(outputPath))
         )
         {
             var fileName = GetDefaultOutputFileName(guild, channel, format, after, before);