Make H3StaticTable static class (#21705)

* Update H3StaticTable.cs

* Update QPackEncoder.cs

* Update Http3TestBase.cs

* Update EncoderStreamReader.cs

* Update QPackDecoder.cs

* Update Http3Stream.cs

* Use s_ prefix for static fields

src/Servers/Kestrel/Core/src/Internal/Http3/Http3Stream.cs

@@ -116,13 +116,13 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http3
 
         public void OnStaticIndexedHeader(int index)
         {
-            var knownHeader = H3StaticTable.Instance[index];
+            var knownHeader = H3StaticTable.GetHeaderFieldAt(index);
             OnHeader(knownHeader.Name, knownHeader.Value);
         }
 
         public void OnStaticIndexedHeader(int index, ReadOnlySpan<byte> value)
         {
-            var knownHeader = H3StaticTable.Instance[index];
+            var knownHeader = H3StaticTable.GetHeaderFieldAt(index);
             OnHeader(knownHeader.Name, value);
         }
 

src/Servers/Kestrel/Core/src/Internal/Http3/QPack/EncoderStreamReader.cs

@@ -322,7 +322,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http3.QPack
         {
             try
             {
-                return _s ? H3StaticTable.Instance[index] : _dynamicTable[index];
+                return _s ? H3StaticTable.GetHeaderFieldAt(index) : _dynamicTable[index];
             }
             catch (IndexOutOfRangeException ex)
             {

src/Servers/Kestrel/test/InMemory.FunctionalTests/Http3/Http3TestBase.cs

@@ -355,13 +355,13 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Tests
 
             public void OnStaticIndexedHeader(int index)
             {
-                var knownHeader = H3StaticTable.Instance[index];
+                var knownHeader = H3StaticTable.GetHeaderFieldAt(index);
                 _decodedHeaders[((Span<byte>)knownHeader.Name).GetAsciiStringNonNullCharacters()] = HttpUtilities.GetAsciiOrUTF8StringNonNullCharacters(knownHeader.Value);
             }
 
             public void OnStaticIndexedHeader(int index, ReadOnlySpan<byte> value)
             {
-                _decodedHeaders[((Span<byte>)H3StaticTable.Instance[index].Name).GetAsciiStringNonNullCharacters()] = value.GetAsciiOrUTF8StringNonNullCharacters();
+                _decodedHeaders[((Span<byte>)H3StaticTable.GetHeaderFieldAt(index).Name).GetAsciiStringNonNullCharacters()] = value.GetAsciiOrUTF8StringNonNullCharacters();
             }
 
             internal async Task WaitForStreamErrorAsync(Http3ErrorCode protocolError, string expectedErrorMessage)

src/Shared/runtime/Http3/QPack/H3StaticTable.cs

@@ -7,10 +7,9 @@ using System.Text;
 
 namespace System.Net.Http.QPack
 {
-    // TODO: make class static.
-    internal class H3StaticTable
+    internal static class H3StaticTable
     {
-        private readonly Dictionary<int, int> _statusIndex = new Dictionary<int, int>
+        private static readonly Dictionary<int, int> s_statusIndex = new Dictionary<int, int>
         {
             [103] = 24,
             [200] = 25,
@@ -28,7 +27,7 @@ namespace System.Net.Http.QPack
             [500] = 71,
         };
 
-        private readonly Dictionary<HttpMethod, int> _methodIndex = new Dictionary<HttpMethod, int>
+        private static readonly Dictionary<HttpMethod, int> s_methodIndex = new Dictionary<HttpMethod, int>
         {
             // TODO connect is internal to system.net.http
             [HttpMethod.Delete] = 16,
@@ -39,21 +38,15 @@ namespace System.Net.Http.QPack
             [HttpMethod.Put] = 21,
         };
 
-        private H3StaticTable()
-        {
-        }
-
-        public static H3StaticTable Instance { get; } = new H3StaticTable();
-
-        public int Count => _staticTable.Length;
-
-        public HeaderField this[int index] => _staticTable[index];
+        public static int Count => s_staticTable.Length;
 
         // TODO: just use Dictionary directly to avoid interface dispatch.
-        public IReadOnlyDictionary<int, int> StatusIndex => _statusIndex;
-        public IReadOnlyDictionary<HttpMethod, int> MethodIndex => _methodIndex;
+        public static IReadOnlyDictionary<int, int> StatusIndex => s_statusIndex;
+        public static IReadOnlyDictionary<HttpMethod, int> MethodIndex => s_methodIndex;
 
-        private readonly HeaderField[] _staticTable = new HeaderField[]
+        public static HeaderField GetHeaderFieldAt(int index) => s_staticTable[index];
+
+        private static readonly HeaderField[] s_staticTable = new HeaderField[]
         {
             CreateHeaderField(":authority", ""), // 0
             CreateHeaderField(":path", "/"), // 1

src/Shared/runtime/Http3/QPack/QPackDecoder.cs

@@ -413,7 +413,7 @@ namespace System.Net.Http.QPack
 
             if (_index is int index)
             {
-                Debug.Assert(index >= 0 && index <= H3StaticTable.Instance.Count, $"The index should be a valid static index here. {nameof(QPackDecoder)} should have previously thrown if it read a dynamic index.");
+                Debug.Assert(index >= 0 && index <= H3StaticTable.Count, $"The index should be a valid static index here. {nameof(QPackDecoder)} should have previously thrown if it read a dynamic index.");
                 handler.OnStaticIndexedHeader(index, headerValueSpan);
                 _index = null;
 

src/Shared/runtime/Http3/QPack/QPackEncoder.cs

@@ -416,7 +416,7 @@ namespace System.Net.Http.QPack
                 case 404:
                 case 500:
                     // TODO this isn't safe, some index can be larger than 64. Encoded here!
-                    buffer[0] = (byte)(0xC0 | H3StaticTable.Instance.StatusIndex[statusCode]);
+                    buffer[0] = (byte)(0xC0 | H3StaticTable.StatusIndex[statusCode]);
                     return 1;
                 default:
                     // Send as Literal Header Field Without Indexing - Indexed Name