Module.Load often results in FileNotFoundException

[rouke-broersma]

Hi 👋

In stryker we use Mono.Cecil to load embedded resources from dll's. However loading the dll often fails with a FileNotFoundException even though I can confirm on the filesystem that the dll does exist in that location. We get the output location directly from MSBuild. Can anyone give some hints as to why it might be that Cecil cannot open the dll even though it is there?

Here is the class where we load the Embedded Resources: https://github.com/stryker-mutator/stryker-net/blob/v1.0/src/Stryker.Core/Stryker.Core/Initialisation/EmbeddedResourcesGenerator.cs

[jbevain]

Hello,

This is not something that I ever seen. Cecil doesn't throw FileNotFoundException by itself. It can sometimes throw a AssemblyResolutionException which extends FileNotFoundException.

If an actual FileNotFoundException it's being thrown by .NET as the OS is telling the .NET framework the file asked for the path doesn't exist.

[jbevain]

If the file was locked it would be another kind of exception, no?

Down the line that's the code opening the file stream:

cecil/Mono.Cecil/ModuleDefinition.cs

Line 1098 in 3c4ea3f

var stream = GetFileStream (fileName, FileMode.Open, parameters.ReadWrite ? FileAccess.ReadWrite : FileAccess.Read, FileShare.Read);

It's telling the OS it's ok to Share a read handle.

One thing I'm not sure I understand is that you're saying that:

Use Cecil to load embedded resources from dll into memory

But the stacktrace is clearly trying to open a filestream from the disk, not from memory.

[rouke-broersma]

Sorry I meant to say we load the dll from disk so we can copy the embedded resources from the dll into memory. This so we later can do an in-memory roslyn compilation with embedded resources.

[jbevain]

I really can't help much I'm afraid, .NET doesn't throw FileNotFoundExceptions if the file is there :)

It sounds like an issue related to timing possibly, where at the time you try to get the file MSBuild hasn't copied or fully copied the DLL where you expect it to.

[SimonCropp]

@rouke-broersma i recommend placing a File.Exists check here with a throw if not. ensure that your assumption is correct.

[rouke-broersma]

Yep that's a good idea!