Bind the folder name an item-by-name entity resolves to

MediaBrowser.Controller/Entities/Audio/MusicArtist.cs

@@ -173,10 +173,7 @@ namespace MediaBrowser.Controller.Entities.Audio
 
         public static string GetPath(string name, bool normalizeName)
         {
-            // Trim the period at the end because windows will have a hard time with that
-            var validName = normalizeName ?
-                FileSystem.GetValidFilename(name).Trim().TrimEnd('.') :
-                name;
+            var validName = normalizeName ? GetItemByNameFolderName(name) : name;
 
             return System.IO.Path.Combine(ConfigurationManager.ApplicationPaths.ArtistsPath, validName);
         }

MediaBrowser.Controller/Entities/Audio/MusicGenre.cs

@@ -80,10 +80,7 @@ namespace MediaBrowser.Controller.Entities.Audio
 
         public static string GetPath(string name, bool normalizeName)
         {
-            // Trim the period at the end because windows will have a hard time with that
-            var validName = normalizeName ?
-                FileSystem.GetValidFilename(name).Trim().TrimEnd('.') :
-                name;
+            var validName = normalizeName ? GetItemByNameFolderName(name) : name;
 
             return System.IO.Path.Combine(ConfigurationManager.ApplicationPaths.MusicGenrePath, validName);
         }

MediaBrowser.Controller/Entities/BaseItem.cs

@@ -48,6 +48,10 @@ namespace MediaBrowser.Controller.Entities
 
         public const string ThemeSongFileName = "theme";
 
+        // Well below the 255 byte limit of the common Linux filesystems and the 255 character limit
+        // of Windows, so the files inside the folder still fit within MAX_PATH.
+        private const int MaxItemByNameFolderNameBytes = 128;
+
         /// <summary>
         /// The supported image extensions.
         /// </summary>
@@ -941,6 +945,43 @@ namespace MediaBrowser.Controller.Entities
             return GetSortName(Name, EnableAlphaNumericSorting, ConfigurationManager.Configuration);
         }
 
+        /// <summary>
+        /// Turns an item-by-name entity's name into a folder name every supported filesystem accepts.
+        /// </summary>
+        /// <param name="name">The entity's name.</param>
+        /// <returns>The folder name.</returns>
+        public static string GetItemByNameFolderName(string name)
+        {
+            // Trim the period at the end because windows will have a hard time with that
+            var validName = FileSystem.GetValidFilename(name).Trim().TrimEnd('.');
+
+            // Most Linux filesystems cap a path component at 255 bytes, so a name past that cannot be
+            // turned into a folder at all - and an entity with no folder can never be created, which
+            // leaves the credit behind it stuck: not refreshable, not deletable, retried on every scan.
+            // Only broken provider data gets this long, but it still has to resolve to something, so
+            // keep a readable prefix and let a hash of the whole name tell two of them apart.
+            if (Encoding.UTF8.GetByteCount(validName) <= MaxItemByNameFolderNameBytes)
+            {
+                return validName;
+            }
+
+            var suffix = "-" + validName.GetMD5().ToString("N", CultureInfo.InvariantCulture);
+            var budget = MaxItemByNameFolderNameBytes - suffix.Length;
+            var length = Math.Min(validName.Length, budget);
+            while (length > 0 && Encoding.UTF8.GetByteCount(validName.AsSpan(0, length)) > budget)
+            {
+                length--;
+            }
+
+            // Never cut a surrogate pair in half, the lone half is not a valid file name character.
+            if (length > 0 && char.IsHighSurrogate(validName[length - 1]))
+            {
+                length--;
+            }
+
+            return string.Concat(validName.AsSpan(0, length).TrimEnd().TrimEnd('.'), suffix);
+        }
+
         /// <summary>
         /// Cleans a raw name into its sortable form by applying the configured sort rules.
         /// </summary>

MediaBrowser.Controller/Entities/Genre.cs

@@ -83,10 +83,7 @@ namespace MediaBrowser.Controller.Entities
 
         public static string GetPath(string name, bool normalizeName)
         {
-            // Trim the period at the end because windows will have a hard time with that
-            var validName = normalizeName ?
-                FileSystem.GetValidFilename(name).Trim().TrimEnd('.') :
-                name;
+            var validName = normalizeName ? GetItemByNameFolderName(name) : name;
 
             return System.IO.Path.Combine(ConfigurationManager.ApplicationPaths.GenrePath, validName);
         }

MediaBrowser.Controller/Entities/Person.cs

@@ -98,10 +98,7 @@ namespace MediaBrowser.Controller.Entities
 
         public static string GetPath(string name, bool normalizeName)
         {
-            // Trim the period at the end because windows will have a hard time with that
-            var validFilename = normalizeName ?
-                FileSystem.GetValidFilename(name).Trim().TrimEnd('.') :
-                name;
+            var validFilename = normalizeName ? GetItemByNameFolderName(name) : name;
 
             string subFolderPrefix = null;
 

MediaBrowser.Controller/Entities/Studio.cs

@@ -78,10 +78,7 @@ namespace MediaBrowser.Controller.Entities
 
         public static string GetPath(string name, bool normalizeName)
         {
-            // Trim the period at the end because windows will have a hard time with that
-            var validName = normalizeName ?
-                FileSystem.GetValidFilename(name).Trim().TrimEnd('.') :
-                name;
+            var validName = normalizeName ? GetItemByNameFolderName(name) : name;
 
             return System.IO.Path.Combine(ConfigurationManager.ApplicationPaths.StudioPath, validName);
         }

MediaBrowser.Controller/Entities/Year.cs

@@ -85,10 +85,7 @@ namespace MediaBrowser.Controller.Entities
 
         public static string GetPath(string name, bool normalizeName)
         {
-            // Trim the period at the end because windows will have a hard time with that
-            var validName = normalizeName ?
-                FileSystem.GetValidFilename(name).Trim().TrimEnd('.') :
-                name;
+            var validName = normalizeName ? GetItemByNameFolderName(name) : name;
 
             return System.IO.Path.Combine(ConfigurationManager.ApplicationPaths.YearPath, validName);
         }

tests/Jellyfin.Controller.Tests/Entities/BaseItemTests.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Reflection;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using Jellyfin.Database.Implementations.Entities;
@@ -27,6 +28,57 @@ namespace Jellyfin.Controller.Tests.Entities;
 
 public class BaseItemTests
 {
+    [Fact]
+    public void GetItemByNameFolderName_ShortName_IsKeptAsIs()
+    {
+        SetupPassThroughFileSystem();
+
+        Assert.Equal("Mairghread Scott", BaseItem.GetItemByNameFolderName("Mairghread Scott."));
+    }
+
+    [Fact]
+    public void GetItemByNameFolderName_OverlongName_FitsInAPathComponent()
+    {
+        SetupPassThroughFileSystem();
+
+        // What a provider result that concatenated a whole credit list into one name looks like.
+        var name = string.Join(", ", Enumerable.Repeat("Jerry Siegel (created by: Superman)", 20));
+
+        var folderName = BaseItem.GetItemByNameFolderName(name);
+
+        Assert.True(Encoding.UTF8.GetByteCount(folderName) <= 128);
+        Assert.StartsWith("Jerry Siegel (created by: Superman)", folderName, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void GetItemByNameFolderName_OverlongNamesSharingAPrefix_StayApart()
+    {
+        SetupPassThroughFileSystem();
+
+        var prefix = new string('a', 200);
+
+        Assert.NotEqual(
+            BaseItem.GetItemByNameFolderName(prefix + "Joe Shuster"),
+            BaseItem.GetItemByNameFolderName(prefix + "Bob Kane"));
+    }
+
+    [Fact]
+    public void GetItemByNameFolderName_OverlongName_IsStable()
+    {
+        SetupPassThroughFileSystem();
+
+        var name = new string('a', 300);
+
+        Assert.Equal(BaseItem.GetItemByNameFolderName(name), BaseItem.GetItemByNameFolderName(name));
+    }
+
+    private static void SetupPassThroughFileSystem()
+    {
+        var fileSystem = new Mock<IFileSystem>();
+        fileSystem.Setup(x => x.GetValidFilename(It.IsAny<string>())).Returns((string name) => name);
+        BaseItem.FileSystem = fileSystem.Object;
+    }
+
     [Theory]
     [InlineData("", "")]
     [InlineData("1", "0000000001")]