How to load assembly in an application that publishes as a single file?

[alexdi220]

Description

Hi, I have an application that uses Mono.Cecil and AssemblyDefinition. I take the loaded assembly (System.Reflection.Assembly) and create a definition by Assembly.Location. Unfortunately, the PublishSingleFile mode loads references from resources instead of a disk. In this case the Assembly.Location is null and I can't found any other way to create the definition. The Mono's AssemblyDefinition can be created from the stream, but the NetCore\Net5 has no BinnaryFormatter. I've used the internal method Assembly.GetRawBytes and it also removed from the new version of the framework. Could you give me a way how can I get bytes[]/stream/location for loaded assembly?

Configuration

• .NET 5 / .NetCore 3
• Windows 10
• x64, x86

Regression?

Other information

[ghost]

Tagging subscribers to this area: @vitek-karas, @agocke, @CoffeeFlux
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

Hi, I have an application that uses Mono.Cecil and AssemblyDefinition. I take the loaded assembly (System.Reflection.Assembly) and create a definition by Assembly.Location. Unfortunately, the PublishSingleFile mode loads references from resources instead of a disk. In this case the Assembly.Location is null and I can't found any other way to create the definition. The Mono's AssemblyDefinition can be created from the stream, but the NetCore\Net5 has no BinnaryFormatter. I've used the internal method Assembly.GetRawBytes and it also removed from the new version of the framework. Could you give me a way how can I get bytes[]/stream/location for loaded assembly?

Configuration

• .NET 5 / .NetCore 3
• Windows 10
• x64, x86

Regression?

Other information

Author:	alexdi220
Assignees:	-
Labels:	area-AssemblyLoader-coreclr, untriaged
Milestone:	-

[jkotas]

You can try to use AssemblyExtensions.TryGetRawMetadata. This method returns just the metadata blob, not the whole assembly. It works well for System.Reflection.Metadata reader and Roslyn. I am not sure whether it works for Cecil.

[alexdi220]

Hi, @jkotas. Thanks for a super quick answer. It makes my day. But I faced with the BadImageFormatException when I getting MetadaReader. Please take a look code. What I do wrong?

private static unsafe void ReadAssembly()
        {
            var asm = typeof(JsonConvert).Assembly; //from Newtonsoft.Json package
            asm.TryGetRawMetadata(out byte* blob, out int length);
            byte[] buffer = new byte[length];
            Marshal.Copy((IntPtr)blob, buffer, 0, length);
            using var stream = new MemoryStream(buffer);
            var reader = new PEReader(stream);
            var meta = reader.GetMetadataReader(); // throws System.BadImageFormatException: 'Image is too small.'
        }

The StackTrace:
System.Reflection.Metadata.dll!System.Reflection.Throw.ImageTooSmall() Unknown
System.Reflection.Metadata.dll!System.Reflection.PortableExecutable.SectionHeader.SectionHeader(ref System.Reflection.PortableExecutable.PEBinaryReader reader) Unknown
System.Reflection.Metadata.dll!System.Reflection.PortableExecutable.PEHeaders.ReadSectionHeaders(ref System.Reflection.PortableExecutable.PEBinaryReader reader) Unknown
System.Reflection.Metadata.dll!System.Reflection.PortableExecutable.PEHeaders.PEHeaders(System.IO.Stream peStream, int size, bool isLoadedImage) Unknown
System.Reflection.Metadata.dll!System.Reflection.PortableExecutable.PEReader.InitializePEHeaders() Unknown
System.Reflection.Metadata.dll!System.Reflection.PortableExecutable.PEReader.GetMetadataBlock() Unknown
System.Reflection.Metadata.dll!System.Reflection.Metadata.PEReaderExtensions.GetMetadataReader(System.Reflection.PortableExecutable.PEReader peReader, System.Reflection.Metadata.MetadataReaderOptions options, System.Reflection.Metadata.MetadataStringDecoder utf8Decoder) Unknown
System.Reflection.Metadata.dll!System.Reflection.Metadata.PEReaderExtensions.GetMetadataReader(System.Reflection.PortableExecutable.PEReader peReader) Unknown

[jkotas]

Try this:

asm.TryGetRawMetadata(out byte* blob, out int length);
var meta = new MetadataReader(blob, length);

[alexdi220]

It works great. Thank you a lot!

[alexdi220]

Hi, @jkotas the Mono.Cecil's AssemblyDefinition needs the whole assembly instead of metadata only. With DOSHeader, PEFileHeader, and other info. Is there any way to get the whole assembly's bytes? And how the references' assemblies are distributed in the "SingleFile" mode? I mean, I can load assembly myself if it shipped in resources of the application or any other known place.

[jkotas]

Yes, you can add the reference assemblies as resources yourself.

[alexdi220]

Thank you. But I can't do it, could you advise another solution\workaround? We develop a third party that is used by other developers. In the projects of our clients, there are NuGet packages to our components. Some assemblies of these packages will be patched in runtime by our code (I told about it in the first message). The new behavior of .NET 5 when the location of assembly is null - critical breaking change for our feature.

[jkotas]

You can set <IncludeAllContentForSelfExtract>true</IncludeAllContentForSelfExtract> that will extract the assemblies to disk like in .NET Core 3.1.

Also, we are likely to introduce more optimized form factors going forward that may be missing the IL or metadata completely. https://github.com/dotnet/designs/blob/main/accepted/2020/form-factors.md talks about it in more details. If your feature depends on IL and metadata to be present and patched at runtime, it will not be compatible with these form factors.

[alexdi220]

Thank you, Jan. You really help me. Also, we'll research a new approach of form factors to improve our code in the future.