From b6e75925d4f2e6ab5fc50a74f83e8c8a1f726166 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=A9my=20VIGNELLES?= <jeremy.vignelles@gmail.com>
Date: Sun, 16 Aug 2020 21:20:59 +0200
Subject: [PATCH] Avoid a copy in StreamMediaInput on modern platforms.

This requires unsafe code to use the newer Span APIs
netstandard1.1 is also removed
---
 src/LibVLCSharp/Helpers/MarshalExtensions.cs | 26 ++++++++++++++++++++
 src/LibVLCSharp/LibVLCSharp.csproj           | 10 +++++++-
 src/LibVLCSharp/StreamMediaInput.cs          | 12 ++++-----
 3 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/src/LibVLCSharp/Helpers/MarshalExtensions.cs b/src/LibVLCSharp/Helpers/MarshalExtensions.cs
index 94cc5db..22f0027 100644
--- a/src/LibVLCSharp/Helpers/MarshalExtensions.cs
+++ b/src/LibVLCSharp/Helpers/MarshalExtensions.cs
@@ -166,5 +166,31 @@ namespace LibVLCSharp.Helpers
                 MarshalUtils.LibVLCFree(ref nativeString);
             return Encoding.UTF8.GetString(buffer, 0, buffer.Length);
         }
+
+#if !APPLE && !ANDROID && !NETSTANDARD2_1
+        /// <summary>
+        /// The Span-based APIs on Stream are not available on older targets. Span can be backported on older TFMs through the System.Memory package,
+        /// but System.IO does not provide the same benefit. This code is extracted from dotnet/runtime to allow efficient media callbacks implementation.
+        /// </summary>
+        /// <remarks>https://github.com/dotnet/runtime/blob/c4b9dabec8186a0d61f0cc3ea0b7efea579bf24e/src/libraries/System.Private.CoreLib/src/System/IO/Stream.cs#L720-L734</remarks>
+        /// <param name="stream">the .NET stream</param>
+        /// <param name="buffer">the buffer to read</param>
+        /// <returns>number of bytes read</returns>
+        internal static int Read(this System.IO.Stream stream, Span<byte> buffer)
+        {
+            var sharedBuffer = System.Buffers.ArrayPool<byte>.Shared.Rent(buffer.Length);
+            try
+            {
+                var numRead = stream.Read(sharedBuffer, 0, buffer.Length);
+                if ((uint)numRead > (uint)buffer.Length)
+                {
+                    throw new System.IO.IOException("StreamTooLong");
+                }
+                new Span<byte>(sharedBuffer, 0, numRead).CopyTo(buffer);
+                return numRead;
+            }
+            finally { System.Buffers.ArrayPool<byte>.Shared.Return(sharedBuffer); }
+        }
+#endif
     }
 }
diff --git a/src/LibVLCSharp/LibVLCSharp.csproj b/src/LibVLCSharp/LibVLCSharp.csproj
index a5cfac1..e086715 100644
--- a/src/LibVLCSharp/LibVLCSharp.csproj
+++ b/src/LibVLCSharp/LibVLCSharp.csproj
@@ -28,7 +28,7 @@ This package also contains the views for the following platforms:
 If you need Xamarin.Forms support, see LibVLCSharp.Forms.
 
 LibVLC needs to be installed separately, see VideoLAN.LibVLC.* packages.</Description>
-    <TargetFrameworks>netstandard2.1;netstandard2.0;netstandard1.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.1;netstandard2.0</TargetFrameworks>
     <TargetFrameworks Condition="!$([MSBuild]::IsOsPlatform('Linux'))">$(TargetFrameworks);MonoAndroid81;Xamarin.iOS10;Xamarin.Mac20;Xamarin.TVOS10</TargetFrameworks>
     <TargetFrameworks Condition="$([MSBuild]::IsOsPlatform('Windows'))">$(TargetFrameworks);uap10.0;uap10.0.16299;net45;net471</TargetFrameworks>
     <TargetsForTfmSpecificBuildOutput>$(TargetsForTfmSpecificBuildOutput);IncludeAWindow</TargetsForTfmSpecificBuildOutput>
@@ -49,6 +49,7 @@ LibVLC needs to be installed separately, see VideoLAN.LibVLC.* packages.</Descri
     <PackageIcon>icon.png</PackageIcon>
     <PackageReleaseNotes>https://code.videolan.org/videolan/LibVLCSharp/blob/master/NEWS</PackageReleaseNotes>
     <PackageTags>libvlc;vlc;videolan;native;c/c++;video;audio;player;media;mediaplayer;codec;ffmpeg;xamarin;graphics;ios;android;linux;windows;macos;cross-platform</PackageTags>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
   <PropertyGroup Condition="$(TargetFramework.StartsWith('uap'))">
     <GenerateLibraryLayout>true</GenerateLibraryLayout>
@@ -60,6 +61,7 @@ LibVLC needs to be installed separately, see VideoLAN.LibVLC.* packages.</Descri
       <Pack>True</Pack>
       <PackagePath></PackagePath>
     </None>
+
   </ItemGroup>
   <ItemGroup Condition="$(TargetFramework.StartsWith('MonoAndroid'))">
     <Compile Include="Platforms\Android\**\*.cs" />
@@ -86,7 +88,13 @@ LibVLC needs to be installed separately, see VideoLAN.LibVLC.* packages.</Descri
     </Page>
     <PackageReference Include="System.ValueTuple" Version="4.5.0" />
     <PackageReference Include="SharpDX.Direct3D11" Version="4.2.0" />
+    <PackageReference Include="System.Memory" Version="4.5.4" />
+  </ItemGroup>
+   <ItemGroup Condition="$(TargetFramework.StartsWith('net4')) Or '$(TargetFramework)' == 'netstandard2.0' ">
+    <PackageReference Include="System.Memory" Version="4.5.4" />
+
   </ItemGroup>
+
   <Target Name="IncludeAWindow" Condition="$(TargetFramework.StartsWith('MonoAndroid'))">
     <ItemGroup>
       <BuildOutputInPackage Include="$(OutputPath)LibVLCSharp.Android.AWindow.dll" />
diff --git a/src/LibVLCSharp/StreamMediaInput.cs b/src/LibVLCSharp/StreamMediaInput.cs
index f17552b..6f30b2f 100644
--- a/src/LibVLCSharp/StreamMediaInput.cs
+++ b/src/LibVLCSharp/StreamMediaInput.cs
@@ -1,7 +1,9 @@
 using System;
 using System.IO;
 using System.Runtime.InteropServices;
-
+#if !APPLE && !ANDROID && !NETSTANDARD2_1
+using LibVLCSharp.Helpers;
+#endif
 namespace LibVLCSharp
 {
     /// <summary>
@@ -10,7 +12,6 @@ namespace LibVLCSharp
     public class StreamMediaInput : MediaInput
     {
         private readonly Stream _stream;
-        private readonly byte[] _readBuffer = new byte[0x4000];
 
         /// <summary>
         /// Initializes a new instance of <see cref="StreamMediaInput"/>, which reads from the given .NET stream.
@@ -61,14 +62,11 @@ namespace LibVLCSharp
         /// <param name="buf">The buffer where read data must be written</param>
         /// <param name="len">The buffer length</param>
         /// <returns>The number of bytes actually read, -1 on error</returns>
-        public override int Read(IntPtr buf, uint len)
+        public unsafe override int Read(IntPtr buf, uint len)
         {
             try
             {
-                var read = _stream.Read(_readBuffer, 0, Math.Min((int)len, _readBuffer.Length));
-                Marshal.Copy(_readBuffer, 0, buf, read);
-
-                return read;
+                return _stream.Read(new Span<byte>(buf.ToPointer(), (int)Math.Min(len, int.MaxValue)));
             }
             catch (Exception)
             {
-- 
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