[SRM] Refactor reading from streams.

src/libraries/System.Reflection.Metadata/src/System.Reflection.Metadata.csproj

@@ -26,6 +26,8 @@ The System.Reflection.Metadata library is built-in as part of the shared framewo
     <Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.ReadFile_SafeHandle_IntPtr.cs"
              Link="Common\Interop\Windows\kernel32\Interop.ReadFile_SafeHandle_IntPtr.cs"
              Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'" />
+    <Compile Include="$(CoreLibSharedDir)System\Runtime\CompilerServices\IsExternalInit.cs" Link="System\Runtime\CompilerServices\IsExternalInit.cs" Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'" />
+    <Compile Include="System\Reflection\Internal\Utilities\IBinaryReader.cs" />
     <Compile Include="System\Reflection\Internal\Utilities\PinnedObject.cs" />
     <Compile Include="System\Reflection\Internal\Utilities\CriticalDisposableObject.cs" />
     <Compile Include="System\Reflection\Internal\Utilities\ExceptionUtilities.cs" />
@@ -104,7 +106,6 @@ The System.Reflection.Metadata library is built-in as part of the shared framewo
     <Compile Include="System\Reflection\Internal\MemoryBlocks\MemoryBlockProvider.cs" />
     <Compile Include="System\Reflection\Internal\MemoryBlocks\MemoryMappedFileBlock.cs" />
     <Compile Include="System\Reflection\Internal\MemoryBlocks\NativeHeapMemoryBlock.cs" />
-    <Compile Include="System\Reflection\Internal\MemoryBlocks\StreamConstraints.cs" />
     <Compile Include="System\Reflection\Internal\MemoryBlocks\StreamMemoryBlockProvider.cs" />
     <Compile Include="System\Reflection\Internal\Utilities\BitArithmetic.cs" />
     <Compile Include="System\Reflection\Internal\Utilities\StringUtils.cs" />
@@ -113,7 +114,6 @@ The System.Reflection.Metadata library is built-in as part of the shared framewo
     <Compile Include="System\Reflection\Internal\Utilities\StreamExtensions.netcoreapp.cs" Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'" />
     <Compile Include="System\Reflection\Internal\Utilities\StreamExtensions.netstandard2.0.cs" Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'" />
     <Compile Include="System\Reflection\Internal\Utilities\Hash.cs" />
-    <Compile Include="System\Reflection\Internal\Utilities\ImmutableMemoryStream.cs" />
     <Compile Include="System\Reflection\Internal\Utilities\MemoryBlock.cs" />
     <Compile Include="System\Reflection\Internal\Utilities\PooledStringBuilder.cs" />
     <Compile Include="System\Reflection\Internal\Utilities\ObjectPool`1.cs" />

src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/MemoryBlocks/ByteArrayMemoryProvider.cs

@@ -34,12 +34,6 @@ protected override AbstractMemoryBlock GetMemoryBlockImpl(int start, int size)
             return new ByteArrayMemoryBlock(this, start, size);
         }
 
-        public override Stream GetStream(out StreamConstraints constraints)
-        {
-            constraints = new StreamConstraints(null, 0, Size);
-            return new ImmutableMemoryStream(_array);
-        }
-
         internal unsafe byte* Pointer
         {
             get

src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/MemoryBlocks/ExternalMemoryBlockProvider.cs

@@ -33,12 +33,6 @@ protected override AbstractMemoryBlock GetMemoryBlockImpl(int start, int size)
             return new ExternalMemoryBlock(this, _memory + start, size);
         }
 
-        public override Stream GetStream(out StreamConstraints constraints)
-        {
-            constraints = new StreamConstraints(null, 0, _size);
-            return new ReadOnlyUnmanagedMemoryStream(_memory, _size);
-        }
-
         protected override void Dispose(bool disposing)
         {
             Debug.Assert(disposing);

src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/MemoryBlocks/MemoryBlockProvider.cs

@@ -38,14 +38,6 @@ public AbstractMemoryBlock GetMemoryBlock(int start, int size)
         /// <exception cref="IOException">IO error while reading from the underlying stream.</exception>
         protected abstract AbstractMemoryBlock GetMemoryBlockImpl(int start, int size);
 
-        /// <summary>
-        /// Gets a seekable and readable <see cref="Stream"/> that can be used to read all data.
-        /// The operations on the stream has to be done under a lock of <see cref="StreamConstraints.GuardOpt"/> if non-null.
-        /// The image starts at <see cref="StreamConstraints.ImageStart"/> and has size <see cref="StreamConstraints.ImageSize"/>.
-        /// It is the caller's responsibility not to read outside those bounds.
-        /// </summary>
-        public abstract Stream GetStream(out StreamConstraints constraints);
-
         /// <summary>
         /// The size of the data.
         /// </summary>

src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/MemoryBlocks/StreamMemoryBlockProvider.cs

@@ -73,13 +73,7 @@ internal static unsafe NativeHeapMemoryBlock ReadMemoryBlockNoLock(Stream stream
             try
             {
                 stream.Seek(start, SeekOrigin.Begin);
-
-                int bytesRead = 0;
-
-                if ((bytesRead = stream.Read(block.Pointer, size)) != size)
-                {
-                    stream.CopyTo(block.Pointer + bytesRead, size - bytesRead);
-                }
+                stream.ReadExactly(block.Pointer, size);
 
                 fault = false;
             }
@@ -101,12 +95,7 @@ protected override AbstractMemoryBlock GetMemoryBlockImpl(int start, int size)
 
             if (_useMemoryMap && size > MemoryMapThreshold)
             {
-                if (TryCreateMemoryMappedFileBlock(absoluteStart, size, out MemoryMappedFileBlock? block))
-                {
-                    return block;
-                }
-
-                _useMemoryMap = false;
+                return CreateMemoryMappedFileBlock(absoluteStart, size);
             }
 
             lock (_streamGuard)
@@ -115,26 +104,18 @@ protected override AbstractMemoryBlock GetMemoryBlockImpl(int start, int size)
             }
         }
 
-        public override Stream GetStream(out StreamConstraints constraints)
-        {
-            constraints = new StreamConstraints(_streamGuard, _imageStart, _imageSize);
-            return _stream;
-        }
-
         /// <exception cref="IOException">IO error while mapping memory or not enough memory to create the mapping.</exception>
-        private unsafe bool TryCreateMemoryMappedFileBlock(long start, int size, [NotNullWhen(true)] out MemoryMappedFileBlock? block)
+        private unsafe MemoryMappedFileBlock CreateMemoryMappedFileBlock(long start, int size)
         {
             if (_lazyMemoryMap == null)
             {
-                // leave the underlying stream open. It will be closed by the Dispose method.
-                MemoryMappedFile newMemoryMap;
-
                 // CreateMemoryMap might modify the stream (calls FileStream.Flush)
                 lock (_streamGuard)
                 {
                     try
                     {
-                        newMemoryMap =
+                        // leave the underlying stream open. It will be closed by the Dispose method.
+                        _lazyMemoryMap ??=
                             MemoryMappedFile.CreateFromFile(
                                 fileStream: (FileStream)_stream,
                                 mapName: null,
@@ -148,17 +129,6 @@ private unsafe bool TryCreateMemoryMappedFileBlock(long start, int size, [NotNul
                         throw new IOException(e.Message, e);
                     }
                 }
-
-                if (newMemoryMap == null)
-                {
-                    block = null;
-                    return false;
-                }
-
-                if (Interlocked.CompareExchange(ref _lazyMemoryMap, newMemoryMap, null) != null)
-                {
-                    newMemoryMap.Dispose();
-                }
             }
 
             MemoryMappedViewAccessor accessor;
@@ -168,14 +138,7 @@ private unsafe bool TryCreateMemoryMappedFileBlock(long start, int size, [NotNul
                 accessor = _lazyMemoryMap.CreateViewAccessor(start, size, MemoryMappedFileAccess.Read);
             }
 
-            if (accessor == null)
-            {
-                block = null;
-                return false;
-            }
-
-            block = new MemoryMappedFileBlock(accessor, accessor.SafeMemoryMappedViewHandle, accessor.PointerOffset, size);
-            return true;
+            return new MemoryMappedFileBlock(accessor, accessor.SafeMemoryMappedViewHandle, accessor.PointerOffset, size);
         }
     }
 }

src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/IBinaryReader.cs

@@ -0,0 +1,43 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace System.Reflection
+{
+    /// <summary>
+    /// Provides an abstraction for reading binary data from a stream.
+    /// </summary>
+    /// <seealso cref="Metadata.BlobReader"/>
+    /// <seealso cref="PortableExecutable.PEBinaryReader"/>
+    internal interface IBinaryReader
+    {
+        public int Offset { get; set; }
+
+        public byte ReadByte();
+
+        public short ReadInt16();
+
+        public ushort ReadUInt16();
+
+        public int ReadInt32();
+
+        public uint ReadUInt32();
+
+        public ulong ReadUInt64();
+
+        /// <summary>
+        /// Reads a fixed-length byte block as a null-padded UTF-8 encoded string.
+        /// The padding is not included in the returned string.
+        ///
+        /// Note that it is legal for UTF-8 strings to contain NUL; if NUL occurs
+        /// between non-NUL codepoints, it is not considered to be padding and
+        /// is included in the result.
+        /// </summary>
+        public string ReadNullPaddedUTF8(int byteCount);
+    }
+}

src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/StreamExtensions.cs

@@ -9,36 +9,6 @@ namespace System.Reflection.Internal
 {
     internal static partial class StreamExtensions
     {
-        // From System.IO.Stream.CopyTo:
-        // We pick a value that is the largest multiple of 4096 that is still smaller than the large object heap threshold (85K).
-        // The CopyTo/CopyToAsync buffer is short-lived and is likely to be collected at Gen0, and it offers a significant
-        // improvement in Copy performance.
-        internal const int StreamCopyBufferSize = 81920;
-
-        /// <summary>
-        /// Copies specified amount of data from given stream to a target memory pointer.
-        /// </summary>
-        /// <exception cref="IOException">unexpected stream end.</exception>
-        internal static unsafe void CopyTo(this Stream source, byte* destination, int size)
-        {
-            byte[] buffer = new byte[Math.Min(StreamCopyBufferSize, size)];
-            while (size > 0)
-            {
-                int readSize = Math.Min(size, buffer.Length);
-                int bytesRead = source.Read(buffer, 0, readSize);
-
-                if (bytesRead <= 0 || bytesRead > readSize)
-                {
-                    throw new IOException(SR.UnexpectedStreamEnd);
-                }
-
-                Marshal.Copy(buffer, 0, (IntPtr)destination, bytesRead);
-
-                destination += bytesRead;
-                size -= bytesRead;
-            }
-        }
-
         /// <summary>
         /// Attempts to read all of the requested bytes from the stream into the buffer
         /// </summary>

src/libraries/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/StreamExtensions.netcoreapp.cs

@@ -7,7 +7,7 @@ namespace System.Reflection.Internal
 {
     internal static partial class StreamExtensions
     {
-        internal static unsafe int Read(this Stream stream, byte* buffer, int size)
-            => stream.Read(new Span<byte>(buffer, size));
+        internal static unsafe void ReadExactly(this Stream stream, byte* buffer, int size)
+            => stream.ReadExactly(new Span<byte>(buffer, size));
     }
 }