Use one SequenceReader+Rewind rather than 2

Author: benaadams

src/Servers/Kestrel/Core/ref/Microsoft.AspNetCore.Server.Kestrel.Core.netcoreapp3.0.cs

@@ -228,9 +228,8 @@ public partial class HttpParser<TRequestHandler> : Microsoft.AspNetCore.Server.K
     {
         public HttpParser() { }
         public HttpParser(bool showErrorDetails) { }
-        bool Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.IHttpParser<TRequestHandler>.ParseHeaders(TRequestHandler handler, in System.Buffers.ReadOnlySequence<byte> buffer, out System.SequencePosition consumed, out System.SequencePosition examined, out int consumedBytes) { throw null; }
         bool Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.IHttpParser<TRequestHandler>.ParseRequestLine(TRequestHandler handler, in System.Buffers.ReadOnlySequence<byte> buffer, out System.SequencePosition consumed, out System.SequencePosition examined) { throw null; }
-        public bool ParseHeaders(TRequestHandler handler, in System.Buffers.ReadOnlySequence<byte> buffer, out System.SequencePosition consumed, out System.SequencePosition examined, out int consumedBytes) { throw null; }
+        public bool ParseHeaders(TRequestHandler handler, ref System.Buffers.SequenceReader<byte> reader) { throw null; }
         public bool ParseRequestLine(TRequestHandler handler, in System.Buffers.ReadOnlySequence<byte> buffer, out System.SequencePosition consumed, out System.SequencePosition examined) { throw null; }
     }
     public enum HttpScheme
@@ -253,7 +252,7 @@ public partial interface IHttpHeadersHandler
     }
     public partial interface IHttpParser<TRequestHandler> where TRequestHandler : Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.IHttpHeadersHandler, Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.IHttpRequestLineHandler
     {
-        bool ParseHeaders(TRequestHandler handler, in System.Buffers.ReadOnlySequence<byte> buffer, out System.SequencePosition consumed, out System.SequencePosition examined, out int consumedBytes);
+        bool ParseHeaders(TRequestHandler handler, ref System.Buffers.SequenceReader<byte> reader);
         bool ParseRequestLine(TRequestHandler handler, in System.Buffers.ReadOnlySequence<byte> buffer, out System.SequencePosition consumed, out System.SequencePosition examined);
     }
     public partial interface IHttpRequestLineHandler

src/Servers/Kestrel/Core/src/Internal/Http/Http1Connection.cs

@@ -189,32 +189,77 @@ public bool TakeStartLine(ReadOnlySequence<byte> buffer, out SequencePosition co
             return result;
         }
 
-        public bool TakeMessageHeaders(ReadOnlySequence<byte> buffer, bool trailers, out SequencePosition consumed, out SequencePosition examined)
+        public bool TakeMessageHeaders(in ReadOnlySequence<byte> buffer, bool trailers, out SequencePosition consumed, out SequencePosition examined)
         {
             // Make sure the buffer is limited
-            bool overLength = false;
-            if (buffer.Length >= _remainingRequestHeadersBytesAllowed)
+            if (buffer.Length > _remainingRequestHeadersBytesAllowed)
             {
-                buffer = buffer.Slice(buffer.Start, _remainingRequestHeadersBytesAllowed);
-
-                // If we sliced it means the current buffer bigger than what we're
-                // allowed to look at
-                overLength = true;
+                return TrimAndTakeMessageHeaders(buffer, trailers, out consumed, out examined);
             }
 
-            var result = _parser.ParseHeaders(new Http1ParsingHandler(this, trailers), buffer, out consumed, out examined, out var consumedBytes);
-            _remainingRequestHeadersBytesAllowed -= consumedBytes;
-
-            if (!result && overLength)
+            var reader = new SequenceReader<byte>(buffer);
+            var result = false;
+            try
             {
-                BadHttpRequestException.Throw(RequestRejectionReason.HeadersExceedMaxTotalSize);
+                result = _parser.ParseHeaders(new Http1ParsingHandler(this, trailers), ref reader);
+
+                if (result)
+                {
+                    TimeoutControl.CancelTimeout();
+                }
+
+                return result;
             }
-            if (result)
+            finally
             {
-                TimeoutControl.CancelTimeout();
+                consumed = reader.Position;
+                _remainingRequestHeadersBytesAllowed -= (int)reader.Consumed;
+
+                if (result)
+                {
+                    examined = consumed;
+                }
+                else
+                {
+                    examined = buffer.End;
+                }
             }
 
-            return result;
+            bool TrimAndTakeMessageHeaders(in ReadOnlySequence<byte> buffer, bool trailers, out SequencePosition consumed, out SequencePosition examined)
+            {
+                var trimmedBuffer = buffer.Slice(buffer.Start, _remainingRequestHeadersBytesAllowed);
+
+                var reader = new SequenceReader<byte>(trimmedBuffer);
+                var result = false;
+                try
+                {
+                    result = _parser.ParseHeaders(new Http1ParsingHandler(this, trailers), ref reader);
+
+                    if (!result)
+                    {
+                        // We read the maximum allowed but didn't complete the headers.
+                        BadHttpRequestException.Throw(RequestRejectionReason.HeadersExceedMaxTotalSize);
+                    }
+
+                    TimeoutControl.CancelTimeout();
+
+                    return result;
+                }
+                finally
+                {
+                    consumed = reader.Position;
+                    _remainingRequestHeadersBytesAllowed -= (int)reader.Consumed;
+
+                    if (result)
+                    {
+                        examined = consumed;
+                    }
+                    else
+                    {
+                        examined = trimmedBuffer.End;
+                    }
+                }
+            }
         }
 
         public void OnStartLine(HttpMethod method, HttpVersion version, Span<byte> target, Span<byte> path, Span<byte> query, Span<byte> customMethod, bool pathEncoded)