From edc162175a43ce985c769f942ac063ea26a271ef Mon Sep 17 00:00:00 2001
From: Frederik Carlier <frederik.carlier@quamotion.mobi>
Date: Fri, 23 Jul 2021 16:37:10 +0200
Subject: [PATCH] GitPack: Don't use MemoryMappedFiles in 32-bit processes

---
 .../ManagedGit/GitPackTests.cs                | 20 ++++++++++++--
 .../ManagedGit/GitPack.cs                     | 27 ++++++++++++++-----
 2 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/src/NerdBank.GitVersioning.Tests/ManagedGit/GitPackTests.cs b/src/NerdBank.GitVersioning.Tests/ManagedGit/GitPackTests.cs
index 94905c70..6a55fe77 100644
--- a/src/NerdBank.GitVersioning.Tests/ManagedGit/GitPackTests.cs
+++ b/src/NerdBank.GitVersioning.Tests/ManagedGit/GitPackTests.cs
@@ -63,7 +63,15 @@ public void GetPackedObject()
                 // This commit is not deltafied. It is stored as a .gz-compressed stream in the pack file.
                 var zlibStream = Assert.IsType<ZLibStream>(commitStream);
                 var deflateStream = Assert.IsType<DeflateStream>(zlibStream.BaseStream);
-                var pooledStream = Assert.IsType<MemoryMappedStream>(deflateStream.BaseStream);
+
+                if (IntPtr.Size > 4)
+                {
+                    var pooledStream = Assert.IsType<MemoryMappedStream>(deflateStream.BaseStream);
+                }
+                else
+                {
+                    var pooledStream = Assert.IsType<FileStream>(deflateStream.BaseStream);
+                }
 
                 Assert.Equal(222, commitStream.Length);
                 Assert.Equal("/zgldANj+jvgOwlecnOKylZDVQg=", Convert.ToBase64String(sha.ComputeHash(commitStream)));
@@ -85,7 +93,15 @@ public void GetDeltafiedObject()
                 var deltaStream = Assert.IsType<GitPackDeltafiedStream>(commitStream);
                 var zlibStream = Assert.IsType<ZLibStream>(deltaStream.BaseStream);
                 var deflateStream = Assert.IsType<DeflateStream>(zlibStream.BaseStream);
-                var pooledStream = Assert.IsType<MemoryMappedStream>(deflateStream.BaseStream);
+
+                if (IntPtr.Size > 4)
+                {
+                    var pooledStream = Assert.IsType<MemoryMappedStream>(deflateStream.BaseStream);
+                }
+                else
+                {
+                    var directAccessStream = Assert.IsType<FileStream>(deflateStream.BaseStream);
+                }
 
                 Assert.Equal(137, commitStream.Length);
                 Assert.Equal("lZu/7nGb0n1UuO9SlPluFnSvj4o=", Convert.ToBase64String(sha.ComputeHash(commitStream)));
diff --git a/src/NerdBank.GitVersioning/ManagedGit/GitPack.cs b/src/NerdBank.GitVersioning/ManagedGit/GitPack.cs
index 27c45c69..eff2eaf8 100644
--- a/src/NerdBank.GitVersioning/ManagedGit/GitPack.cs
+++ b/src/NerdBank.GitVersioning/ManagedGit/GitPack.cs
@@ -31,8 +31,8 @@ public class GitPack : IDisposable
         private readonly Func<FileStream> packStream;
         private readonly Lazy<FileStream> indexStream;
         private readonly GitPackCache cache;
-        private MemoryMappedFile packFile;
-        private MemoryMappedViewAccessor accessor;
+        private MemoryMappedFile? packFile = null;
+        private MemoryMappedViewAccessor? accessor = null;
 
         // Maps GitObjectIds to offets in the git pack.
         private readonly Dictionary<GitObjectId, long> offsets = new Dictionary<GitObjectId, long>();
@@ -98,8 +98,11 @@ public GitPack(GetObjectFromRepositoryDelegate getObjectFromRepositoryDelegate,
             this.indexStream = indexStream ?? throw new ArgumentNullException(nameof(indexStream));
             this.cache = cache ?? new GitPackMemoryCache();
 
-            this.packFile = MemoryMappedFile.CreateFromFile(this.packStream(), mapName: null, 0, MemoryMappedFileAccess.Read, HandleInheritability.None, leaveOpen: false);
-            this.accessor = this.packFile.CreateViewAccessor(0, 0, MemoryMappedFileAccess.Read);
+            if (IntPtr.Size > 4)
+            {
+                this.packFile = MemoryMappedFile.CreateFromFile(this.packStream(), mapName: null, 0, MemoryMappedFileAccess.Read, HandleInheritability.None, leaveOpen: false);
+                this.accessor = this.packFile.CreateViewAccessor(0, 0, MemoryMappedFileAccess.Read);
+            }
         }
 
         /// <summary>
@@ -240,8 +243,8 @@ public void Dispose()
                 this.indexReader.Value.Dispose();
             }
 
-            this.accessor.Dispose();
-            this.packFile.Dispose();
+            this.accessor?.Dispose();
+            this.packFile?.Dispose();
             this.cache.Dispose();
         }
 
@@ -265,7 +268,17 @@ public void Dispose()
 
         private Stream GetPackStream()
         {
-            return new MemoryMappedStream(this.accessor);
+            // On 64-bit processes, we can use Memory Mapped Streams (the address space
+            // will be large enough to map the entire packfile). On 32-bit processes,
+            // we directly access the underlying stream.
+            if (IntPtr.Size > 4)
+            {
+                return new MemoryMappedStream(this.accessor);
+            }
+            else
+            {
+                return this.packStream();
+            }
         }
 
         private GitPackIndexReader OpenIndex()