fix: truncate download filenames to prevent 'filename too long' on Windows

Twitch VOD IDs (and other long platform IDs) can produce file names that,
when combined with the download directory path, exceed Windows MAX_PATH
(260 chars). This causes ffmpeg to fail with ERROR_FILENAME_EXCED_RANGE
("The filename or extension is too long") when writing the output file.

Add TruncateFileName() extension that caps the base-name portion at 200
characters (preserving the extension), and apply it after SanitizeFileName()
when constructing VideoFileName, AudioFileName, and SubtitleFileName.

Fixes #875

Author: stakeswky

Grayjay.ClientServer/Extensions.cs

@@ -196,6 +196,24 @@ public static string SanitizeFileName(this string fileName)
                 fileName = fileName.Replace(invalidChar, '_');
             return fileName;
         }
+
+        // Windows MAX_PATH is 260; reserve some room for the directory prefix.
+        private const int MaxFileNameLength = 200;
+        /// <summary>
+        /// Truncates a file name (after sanitization) so that the base name fits within
+        /// <see cref="MaxFileNameLength"/> characters, preserving the extension.
+        /// </summary>
+        public static string TruncateFileName(this string fileName)
+        {
+            if (fileName.Length <= MaxFileNameLength)
+                return fileName;
+
+            string ext = Path.GetExtension(fileName);   // e.g. ".mp4"
+            string baseName = Path.GetFileNameWithoutExtension(fileName);
+            int allowedBase = MaxFileNameLength - ext.Length;
+            if (allowedBase < 1) allowedBase = 1;
+            return baseName.Substring(0, Math.Min(baseName.Length, allowedBase)) + ext;
+        }
         public static string SanitizeFileNameWithPath(this string path)
         {
             string dirName = Path.GetDirectoryName(path);

Grayjay.ClientServer/Models/Downloads/VideoDownload.cs

@@ -321,7 +321,7 @@ public async Task Download(ManagedHttpClient client, Action<double> onProgress,
                 var representation = videoRepresentations?.FirstOrDefault();
                 var mimeType = representation?.MimeType ?? VideoSource.Container;
 
-                VideoFileName = $"{VideoDetails.ID.Value} [{VideoSource.Width}x{VideoSource.Height}].{VideoHelper.VideoContainerToExtension(mimeType)}".SanitizeFileName();
+                VideoFileName = $"{VideoDetails.ID.Value} [{VideoSource.Width}x{VideoSource.Height}].{VideoHelper.VideoContainerToExtension(mimeType)}".SanitizeFileName().TruncateFileName();
                 VideoFilePath = Path.Combine(downloadDir, VideoFileName);
             }
             string audioDash = (AudioSource is DashManifestRawAudioSource dAudioSource) ? dAudioSource.Generate() : null;
@@ -331,12 +331,12 @@ public async Task Download(ManagedHttpClient client, Action<double> onProgress,
                 var representation = audioRepresentations?.FirstOrDefault();
                 var mimeType = representation?.MimeType ?? AudioSource.Container;
 
-                AudioFileName = $"{VideoDetails.ID.Value} [{AudioSource.Language}-{AudioSource.Bitrate}].{VideoHelper.AudioContainerToExtension(mimeType)}".SanitizeFileName();
+                AudioFileName = $"{VideoDetails.ID.Value} [{AudioSource.Language}-{AudioSource.Bitrate}].{VideoHelper.AudioContainerToExtension(mimeType)}".SanitizeFileName().TruncateFileName();
                 AudioFilePath = Path.Combine(downloadDir , AudioFileName);
             }
             if(SubtitleSourcetoUse != null)
             {
-                SubtitleFileName = $"{VideoDetails.ID.Value} [{SubtitleSourcetoUse.Name}].{VideoHelper.SubtitleContainerToExtension(SubtitleSourcetoUse.Format)}".SanitizeFileName();
+                SubtitleFileName = $"{VideoDetails.ID.Value} [{SubtitleSourcetoUse.Name}].{VideoHelper.SubtitleContainerToExtension(SubtitleSourcetoUse.Format)}".SanitizeFileName().TruncateFileName();
                 SubtitleFilePath = Path.Combine(downloadDir, SubtitleFileName);
             }
             var progressLock = new Object();