Create shorter cache file names

Author: ronaldbarendse

src/ImageSharp.Web/Caching/PhysicalFileSystemCache.cs

@@ -57,7 +57,7 @@ public PhysicalFileSystemCache(
             Guard.NotNull(options, nameof(options));
             Guard.NotNullOrWhiteSpace(environment.WebRootPath, nameof(environment.WebRootPath));
 
-            // Allow configuration of the cache without having to register everything.
+            // Allow configuration of the cache without having to register everything
             PhysicalFileSystemCacheOptions cacheOptions = options != null ? options.Value : new PhysicalFileSystemCacheOptions();
             this.cacheRootPath = GetCacheRoot(cacheOptions, environment.WebRootPath, environment.ContentRootPath);
             this.cacheFolderDepth = (int)cacheOptions.CacheFolderDepth;
@@ -146,17 +146,28 @@ private string ToImageFilePath(string path, in ImageCacheMetadata metaData)
         /// </summary>
         /// <param name="key">The cache key.</param>
         /// <param name="cacheFolderDepth">The depth of the nested cache folders structure to store the images.</param>
-        /// <returns>The <see cref="string"/>.</returns>
+        /// <returns>
+        /// The <see cref="string" />.
+        /// </returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal static unsafe string ToFilePath(string key, int cacheFolderDepth)
         {
-            if (cacheFolderDepth > key.Length)
+            int length;
+            int nameStartIndex;
+            if (cacheFolderDepth >= key.Length)
             {
+                // Keep all characters in file name (legacy behavior)
                 cacheFolderDepth = key.Length;
+                length = (cacheFolderDepth * 2) + key.Length;
+                nameStartIndex = 0;
+            }
+            else
+            {
+                // Remove characters used in folders from file name
+                length = cacheFolderDepth + key.Length;
+                nameStartIndex = cacheFolderDepth;
             }
 
-            // Each key substring char + separator + key
-            int length = (cacheFolderDepth * 2) + key.Length;
             fixed (char* keyPtr = key)
             {
                 return string.Create(length, (Ptr: (IntPtr)keyPtr, key.Length), (chars, args) =>
@@ -173,7 +184,7 @@ internal static unsafe string ToFilePath(string key, int cacheFolderDepth)
                         Unsafe.Add(ref charRef, index++) = separator;
                     }
 
-                    for (int i = 0; i < keySpan.Length; i++)
+                    for (int i = nameStartIndex; i < keySpan.Length; i++)
                     {
                         Unsafe.Add(ref charRef, index++) = Unsafe.Add(ref keyRef, i);
                     }

tests/ImageSharp.Web.Benchmarks/Caching/StringJoinBenchmarks.cs

@@ -12,11 +12,13 @@ namespace SixLabors.ImageSharp.Web.Benchmarks.Caching
     public class StringJoinBenchmarks
     {
         private const string Key = "abcdefghijkl";
-        private const int CachedNameLength = 12;
+
+        [Params(0, 8, 12)]
+        public int CacheFolderDepth { get; set; }
 
         [Benchmark(Baseline = true, Description = "String.Join")]
         public string JoinUsingString()
-            => $"{string.Join("/", Key.Substring(0, CachedNameLength).ToCharArray())}/{Key}";
+            => $"{string.Join("/", Key.Substring(0, this.CacheFolderDepth).ToCharArray())}/{Key}";
 
         [Benchmark(Description = "StringBuilder.Append")]
         public string JoinUsingStringBuilder()
@@ -25,8 +27,8 @@ public string JoinUsingStringBuilder()
             const char separator = '/';
 
             // Each key substring char + separator + key
-            var sb = new StringBuilder((CachedNameLength * 2) + Key.Length);
-            ReadOnlySpan<char> paths = keySpan.Slice(0, CachedNameLength);
+            var sb = new StringBuilder((this.CacheFolderDepth * 2) + Key.Length);
+            ReadOnlySpan<char> paths = keySpan.Slice(0, this.CacheFolderDepth);
             for (int i = 0; i < paths.Length; i++)
             {
                 sb.Append(paths[i]);
@@ -39,7 +41,7 @@ public string JoinUsingStringBuilder()
 
         [Benchmark(Description = "String.Create")]
         public string JoinUsingStringCreate()
-            => PhysicalFileSystemCache.ToFilePath(Key, CachedNameLength);
+            => PhysicalFileSystemCache.ToFilePath(Key, this.CacheFolderDepth);
 
         /*
         BenchmarkDotNet=v0.12.0, OS=Windows 10.0.18363

tests/ImageSharp.Web.Tests/Caching/PhysicialFileSystemCacheTests.cs

@@ -8,14 +8,15 @@ namespace SixLabors.ImageSharp.Web.Tests.Caching
 {
     public class PhysicialFileSystemCacheTests
     {
-        [Fact]
-        public void FilePathMatchesReference()
+        [Theory]
+        [InlineData("abcdefghijkl", 0, "abcdefghijkl")]
+        [InlineData("abcdefghijkl", 4, "a/b/c/d/efghijkl")]
+        [InlineData("abcdefghijkl", 8, "a/b/c/d/e/f/g/h/ijkl")]
+        [InlineData("abcdefghijkl", 12, "a/b/c/d/e/f/g/h/i/j/k/l/abcdefghijkl")]
+        [InlineData("abcdefghijkl", 16, "a/b/c/d/e/f/g/h/i/j/k/l/abcdefghijkl")]
+        public void FilePathMatchesReference(string key, int cacheFolderDepth, string expected)
         {
-            const string Key = "abcdefghijkl";
-            const int CachedNameLength = 12;
-
-            string expected = $"{string.Join("/", Key.Substring(0, CachedNameLength).ToCharArray())}/{Key}";
-            string actual = PhysicalFileSystemCache.ToFilePath(Key, CachedNameLength);
+            string actual = PhysicalFileSystemCache.ToFilePath(key, cacheFolderDepth);
 
             Assert.Equal(expected, actual);
         }