Use a pointer to retrieve the library's error

As the first step to moving away from marshalling data into managed
memory when we can avoid it, we start with a simple one which we only
read from.

Author: carlosmn

LibGit2Sharp/Core/EncodingMarshaler.cs

@@ -93,7 +93,12 @@ public static void Cleanup(IntPtr pNativeData)
 
         public static unsafe string FromNative(Encoding encoding, IntPtr pNativeData)
         {
-            if (pNativeData == IntPtr.Zero)
+            return FromNative(encoding, (byte*)pNativeData);
+        }
+
+        public static unsafe string FromNative(Encoding encoding, byte* pNativeData)
+        {
+            if (pNativeData == null)
             {
                 return null;
             }
@@ -112,7 +117,7 @@ public static unsafe string FromNative(Encoding encoding, IntPtr pNativeData)
                 return String.Empty;
             }
 
-            return new String((sbyte*)pNativeData.ToPointer(), 0, (int)(walk - start), encoding);
+            return new String((sbyte*)pNativeData, 0, (int)(walk - start), encoding);
         }
 
         public static unsafe string FromNative(Encoding encoding, IntPtr pNativeData, int length)

LibGit2Sharp/Core/Ensure.cs

@@ -130,25 +130,19 @@ private static readonly Dictionary<GitErrorCode, Func<string, GitErrorCode, GitE
                     { GitErrorCode.Peel, (m, r, c) => new PeelException(m, r, c)  },
                 };
 
-        private static void HandleError(int result)
+        private static unsafe void HandleError(int result)
         {
             string errorMessage;
-            GitError error = null;
-            var errHandle = NativeMethods.giterr_last();
-
-            if (errHandle != null && !errHandle.IsInvalid)
-            {
-                error = errHandle.MarshalAsGitError();
-            }
+            GitErrorCategory errorCategory = GitErrorCategory.Unknown;
+            GitError* error = NativeMethods.giterr_last();
 
             if (error == null)
             {
-                error = new GitError { Category = GitErrorCategory.Unknown, Message = IntPtr.Zero };
                 errorMessage = "No error message has been provided by the native library";
             }
             else
             {
-                errorMessage = LaxUtf8Marshaler.FromNative(error.Message);
+                errorMessage = LaxUtf8Marshaler.FromNative(error->Message);
             }
 
             Func<string, GitErrorCode, GitErrorCategory, LibGit2SharpException> exceptionBuilder;
@@ -157,7 +151,7 @@ private static void HandleError(int result)
                 exceptionBuilder = (m, r, c) => new LibGit2SharpException(m, r, c);
             }
 
-            throw exceptionBuilder(errorMessage, (GitErrorCode)result, error.Category);
+            throw exceptionBuilder(errorMessage, (GitErrorCode)result, errorCategory);
         }
 
         /// <summary>

LibGit2Sharp/Core/GitError.cs

@@ -4,9 +4,9 @@
 namespace LibGit2Sharp.Core
 {
     [StructLayout(LayoutKind.Sequential)]
-    internal class GitError
+    internal unsafe struct GitError
     {
-        public IntPtr Message;
+        public char* Message;
         public GitErrorCategory Category;
     }
 }

LibGit2Sharp/Core/Handles/GitErrorSafeHandle.cs

@@ -79,7 +79,7 @@ static NativeMethods()
         }
 
         [DllImport(libgit2)]
-        internal static extern GitErrorSafeHandle giterr_last();
+        internal static extern unsafe GitError* giterr_last();
 
         [DllImport(libgit2)]
         internal static extern void giterr_set_str(

LibGit2Sharp/Core/NativeMethods.cs

@@ -112,6 +112,11 @@ public override IntPtr MarshalManagedToNative(object managedObj)
 
         #endregion
 
+        public static unsafe string FromNative(char* pNativeData)
+        {
+            return FromNative(Encoding, (byte*)pNativeData);
+        }
+
         public static string FromNative(IntPtr pNativeData)
         {
             return FromNative(Encoding, pNativeData);

LibGit2Sharp/Core/Utf8Marshaler.cs

@@ -280,7 +280,6 @@
     <Compile Include="Core\GitErrorCategory.cs" />
     <Compile Include="Core\GitOdbBackend.cs" />
     <Compile Include="Core\GitOdbBackendStream.cs" />
-    <Compile Include="Core\Handles\GitErrorSafeHandle.cs" />
     <Compile Include="Core\Handles\NoteSafeHandle.cs" />
     <Compile Include="Core\Handles\ObjectDatabaseSafeHandle.cs" />
     <Compile Include="Core\Handles\DiffSafeHandle.cs" />