Update shared code for HTTP/2 and HTTP/3 (#18958)

Author: jkotalik

src/Servers/Kestrel/Core/src/Internal/Http2/Http2Connection.cs

@@ -13,6 +13,7 @@
 using System.Security.Authentication;
 using System.Threading;
 using System.Threading.Tasks;
+using System.Net.Http;
 using Microsoft.AspNetCore.Connections;
 using Microsoft.AspNetCore.Connections.Features;
 using Microsoft.AspNetCore.Hosting.Server;

src/Shared/Http2/IHttpHeadersHandler.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+// Don't ever change this unless we are explicitly trying to remove IHttpHeadersHandler as public API.
 #if KESTREL
 using System;
 

src/Shared/Http2/ReadMe.SharedCode.md

@@ -14,7 +14,7 @@ aspnet/AspNetCore code paths:
 
 ## Building dotnet/runtime code:
 - https://github.com/dotnet/runtime/tree/master/docs/workflow
-- Run libraries.cmd from the root once: `PS D:\github\runtime> .\libraries.cmd`
+- Run *build.cmd* from the root once: `PS D:\github\runtime> .\build.cmd -subsetCategory libraries`
 - Build the individual projects:
 - `PS D:\github\dotnet\src\libraries\Common\tests> dotnet msbuild /t:rebuild`
 - `PS D:\github\dotnet\src\libraries\System.Net.Http\src> dotnet msbuild /t:rebuild`

src/Shared/Http3/QPack/QPackDecoder.cs

@@ -6,7 +6,10 @@
 using System.Diagnostics;
 using System.Net.Http.HPack;
 using System.Numerics;
+
+#if KESTREL
 using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http;
+#endif
 
 namespace System.Net.Http.QPack
 {
@@ -221,9 +224,9 @@ private void OnByte(byte b, IHttpHeadersHandler handler)
                     }
                     break;
                 case State.CompressedHeaders:
-                    switch (BitOperations.LeadingZeroCount(b))
+                    switch (BitOperations.LeadingZeroCount(b) - 24)
                     {
-                        case 24: // Indexed Header Field
+                        case 0: // Indexed Header Field
                             prefixInt = IndexedHeaderFieldPrefixMask & b;
 
                             bool useStaticTable = (b & IndexedHeaderStaticMask) == IndexedHeaderStaticRepresentation;
@@ -242,7 +245,7 @@ private void OnByte(byte b, IHttpHeadersHandler handler)
                                 _state = State.HeaderFieldIndex;
                             }
                             break;
-                        case 25: // Literal Header Field With Name Reference
+                        case 1: // Literal Header Field With Name Reference
                             useStaticTable = (LiteralHeaderFieldStaticMask & b) == LiteralHeaderFieldStaticMask;
 
                             if (!useStaticTable)
@@ -260,7 +263,7 @@ private void OnByte(byte b, IHttpHeadersHandler handler)
                                 _state = State.HeaderNameIndex;
                             }
                             break;
-                        case 26: // Literal Header Field Without Name Reference
+                        case 2: // Literal Header Field Without Name Reference
                             _huffman = (b & LiteralHeaderFieldWithoutNameReferenceHuffmanMask) != 0;
                             prefixInt = b & LiteralHeaderFieldWithoutNameReferencePrefixMask;
 
@@ -273,7 +276,7 @@ private void OnByte(byte b, IHttpHeadersHandler handler)
                                 _state = State.HeaderNameLength;
                             }
                             break;
-                        case 27: // Indexed Header Field With Post-Base Index
+                        case 3: // Indexed Header Field With Post-Base Index
                             prefixInt = ~PostBaseIndexMask & b;
                             if (_integerDecoder.BeginTryDecode((byte)prefixInt, PostBaseIndexPrefix, out intResult))
                             {

src/Shared/Http3/ReadMe.SharedCode.md

@@ -14,7 +14,7 @@ To copy code from aspnet/AspNetCore to dotnet/runtime, set RUNTIME_REPO to the r
 ## Building dotnet/runtime code:
 - https://github.com/dotnet/runtime/blob/master/docs/libraries/building/windows-instructions.md
 - https://github.com/dotnet/runtime/blob/master/docs/libraries/project-docs/developer-guide.md
-- Run libraries.cmd from the root once: `PS D:\github\runtime> .\libraries.cmd`
+- Run *build.cmd* from the root once: `PS D:\github\runtime> .\build.cmd -subsetCategory libraries`
 - Build the individual projects:
 - `PS D:\github\dotnet\src\libraries\Common\tests> dotnet msbuild /t:rebuild`
 - `PS D:\github\dotnet\src\libraries\System.Net.Http\src> dotnet msbuild /t:rebuild`