restore: trying out mmap-based file extraction

Fixes: NuGet/Home#9807

src/NuGet.Core/NuGet.Packaging/Core/ExtractPackageFileDelegate.cs

@@ -11,6 +11,7 @@ namespace NuGet.Packaging.Core
     /// <param name="sourceFile">The path of the file in the package.</param>
     /// <param name="targetPath">The path to write to.</param>
     /// <param name="fileStream">The file <see cref="Stream"/>.</param>
+    /// <param name="size">The size of the incoming file.</param>
     /// <returns>The file name if the file was written; otherwise <c>null</c>.</returns>
-    public delegate string ExtractPackageFileDelegate(string sourceFile, string targetPath, Stream fileStream);
+    public delegate string ExtractPackageFileDelegate(string sourceFile, string targetPath, Stream fileStream, long? size);
 }

src/NuGet.Core/NuGet.Packaging/PackageArchiveReader.cs

@@ -192,7 +192,7 @@ public override IEnumerable<string> CopyFiles(
 
                 using (var stream = entry.Open())
                 {
-                    var copiedFile = extractFile(packageFileName, targetFilePath, stream);
+                    var copiedFile = extractFile(packageFileName, targetFilePath, stream, entry.Length);
                     if (copiedFile != null)
                     {
                         entry.UpdateFileTimeFromEntry(copiedFile, logger);

src/NuGet.Core/NuGet.Packaging/PackageExtraction/StreamExtensions.cs

@@ -2,12 +2,19 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.IO;
+using System.IO.MemoryMappedFiles;
 
 namespace NuGet.Packaging
 {
     public static class StreamExtensions
     {
-        public static string CopyToFile(this Stream inputStream, string fileFullPath)
+
+        /**
+        Only files smaller than this value will be mmap'ed
+        */
+        private const long MAX_MMAP_SIZE = 10 * 1024 * 1024;
+        public static string CopyToFile(this Stream inputStream, string fileFullPath) => CopyToFile(inputStream, fileFullPath, null);
+        public static string CopyToFile(this Stream inputStream, string fileFullPath, long? size)
         {
             if (Path.GetFileName(fileFullPath).Length == 0)
             {
@@ -27,12 +34,24 @@ public static string CopyToFile(this Stream inputStream, string fileFullPath)
                 return fileFullPath;
             }
 
+            // For files of a certain size, we can do some Cleverness and mmap them instead
+            // of writing directly to disk. This can increase performance by a LOT, at the
+            // cost of files taking longer to get to disk -- but that's fine!
+            if (size > 0 && size <= MAX_MMAP_SIZE)
+            {
+                using (MemoryMappedFile mmf = MemoryMappedFile.CreateFromFile(fileFullPath, FileMode.Create, null, (long)size))
+                {
+                    MemoryMappedViewStream mmstream = mmf.CreateViewStream();
+                    inputStream.CopyTo(mmstream);
+                    return fileFullPath;
+                }
+            }
+
             using (var outputStream = NuGetExtractionFileIO.CreateFile(fileFullPath))
             {
                 inputStream.CopyTo(outputStream);
+                return fileFullPath;
             }
-
-            return fileFullPath;
         }
     }
 }

src/NuGet.Core/NuGet.Packaging/PackageExtraction/ZipArchiveExtensions.cs

@@ -57,7 +57,7 @@ public static string SaveAsFile(this ZipArchiveEntry entry, string fileFullPath,
         {
             using (var inputStream = entry.Open())
             {
-                inputStream.CopyToFile(fileFullPath);
+                inputStream.CopyToFile(fileFullPath, entry.Length);
             }
 
             entry.UpdateFileTimeFromEntry(fileFullPath, logger);

src/NuGet.Core/NuGet.Packaging/PackageFileExtractor.cs

@@ -89,7 +89,7 @@ private static string GetBinaryForLanguageSpecificXml(string file)
             return null;
         }
 
-        public string ExtractPackageFile(string source, string target, Stream stream)
+        public string ExtractPackageFile(string source, string target, Stream stream, long? size)
         {
             if ((_xmlDocFileSaveMode == XmlDocFileSaveMode.Skip) && _intellisenseXmlFiles.Contains(source))
             {
@@ -125,7 +125,7 @@ public string ExtractPackageFile(string source, string target, Stream stream)
             }
             else
             {
-                stream.CopyToFile(target);
+                stream.CopyToFile(target, size);
             }
 
             return target;

src/NuGet.Core/NuGet.Packaging/PackageFolderReader.cs

@@ -212,7 +212,7 @@ public override IEnumerable<string> CopyFiles(
 
                 using (var fileStream = sourceFile.OpenRead())
                 {
-                    targetPath = extractFile(sourceFile.FullName, targetPath, fileStream);
+                    targetPath = extractFile(sourceFile.FullName, targetPath, fileStream, null);
                     if (targetPath != null)
                     {
                         File.SetLastWriteTimeUtc(targetPath, sourceFile.LastWriteTimeUtc);

test/NuGet.Core.Tests/NuGet.Packaging.Test/PackageArchiveReaderTests.cs

@@ -1966,7 +1966,7 @@ public void CanVerifySignedPackages_ReturnsValueBasedOnOperatingSystemAndFramewo
             }
         }
 
-        private static string ExtractFile(string sourcePath, string targetPath, Stream sourceStream)
+        private static string ExtractFile(string sourcePath, string targetPath, Stream sourceStream, long? size)
         {
             using (var targetStream = File.OpenWrite(targetPath))
             {

test/NuGet.Core.Tests/NuGet.Packaging.Test/PackageFolderReaderTests.cs

@@ -1082,7 +1082,7 @@ await Assert.ThrowsAsync<NotImplementedException>(
             }
         }
 
-        private static string ExtractFile(string sourcePath, string targetPath, Stream sourceStream)
+        private static string ExtractFile(string sourcePath, string targetPath, Stream sourceStream, long? size)
         {
             using (var targetStream = File.OpenWrite(targetPath))
             {

test/NuGet.Core.Tests/NuGet.Protocol.Tests/Plugins/PluginPackageReaderTests.cs

@@ -1316,7 +1316,7 @@ public async Task CopyNupkgAsync_CopiesNupkgOnSuccess()
             }
         }
 
-        private string ExtractPackageFile(string sourceFile, string targetPath, Stream fileStream)
+        private string ExtractPackageFile(string sourceFile, string targetPath, Stream fileStream, long? size)
         {
             throw new NotImplementedException();
         }