Remove .Start from BufferSegment (#6832)

src/Http/Http/src/BufferSegment.cs

@@ -13,13 +13,6 @@ namespace System.IO.Pipelines
         private BufferSegment _next;
         private int _end;
 
-        /// <summary>
-        /// The Start represents the offset into AvailableMemory where the range of "active" bytes begins. At the point when the block is leased
-        /// the Start is guaranteed to be equal to 0. The value of Start may be assigned anywhere between 0 and
-        /// AvailableMemory.Length, and must be equal to or less than End.
-        /// </summary>
-        public int Start { get; private set; }
-
         /// <summary>
         /// The End represents the offset into AvailableMemory where the range of "active" bytes ends. At the point when the block is leased
         /// the End is guaranteed to be equal to Start. The value of Start may be assigned anywhere between 0 and
@@ -30,10 +23,10 @@ namespace System.IO.Pipelines
             get => _end;
             set
             {
-                Debug.Assert(value - Start <= AvailableMemory.Length);
+                Debug.Assert(value <= AvailableMemory.Length);
 
                 _end = value;
-                Memory = AvailableMemory.Slice(Start, _end - Start);
+                Memory = AvailableMemory.Slice(0, _end);
             }
         }
 
@@ -54,19 +47,13 @@ namespace System.IO.Pipelines
         }
 
         public void SetMemory(IMemoryOwner<byte> memoryOwner)
-        {
-            SetMemory(memoryOwner, 0, 0);
-        }
-
-        public void SetMemory(IMemoryOwner<byte> memoryOwner, int start, int end)
         {
             _memoryOwner = memoryOwner;
 
             AvailableMemory = _memoryOwner.Memory;
 
             RunningIndex = 0;
-            Start = start;
+            End = 0;
-            End = end;
             NextSegment = null;
         }
 
@@ -81,7 +68,7 @@ namespace System.IO.Pipelines
 
         public Memory<byte> AvailableMemory { get; private set; }
 
-        public int Length => End - Start;
+        public int Length => End;
 
         /// <summary>
         /// The amount of writable bytes in this segment. It is the amount of bytes between Length and End

src/Http/Http/src/StreamPipeReader.cs

@@ -1,14 +1,10 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System;
 using System.Buffers;
 using System.Diagnostics;
-using System.IO;
-using System.IO.Pipelines;
 using System.Runtime.CompilerServices;
 using System.Runtime.ExceptionServices;
-using System.Runtime.InteropServices;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -136,7 +132,7 @@ namespace System.IO.Pipelines
             {
                 // If we examined everything, we force ReadAsync to actually read from the underlying stream
                 // instead of returning a ReadResult from TryRead.
-                _examinedEverything = examinedIndex == _readTail.End - _readTail.Start;
+                _examinedEverything = examinedIndex == _readTail.End;
             }
 
             // Three cases here:
@@ -321,7 +317,7 @@ namespace System.IO.Pipelines
 
         private ReadOnlySequence<byte> GetCurrentReadOnlySequence()
         {
-            return new ReadOnlySequence<byte>(_readHead, _readIndex, _readTail, _readTail.End - _readTail.Start);
+            return new ReadOnlySequence<byte>(_readHead, _readIndex, _readTail, _readTail.End);
         }
 
         private void AllocateReadTail()