Unable to load DLL 'libwkhtmltox': The specified module could not be found. When using Nuget package

[graemehyde]

When using the DinkToPdf Nuget package I get the error message below because it is looking for the libwkhtmltox DLL in the same folder the Nuget package DLL is in. For me using VS 2017 on Windows 10 this is:

%UserProfile%\.nuget\packages\dinktopdf\1.0.8\lib\netstandard1.6

When I either manually copy the correct libwkhtmltox DLL to this folder or include the source of the DinkToPdf project into my solution I no longer get this error. By including the project source into my solution the DinkToPdf DLL is then compiled into my output folder where it then also successfully finds the libwkhtmltox DLL.

Is it possible to resolve this issue without having to use the project source or regsvr32.exe? I see that TuesPechkin has an IDeployment interface to address this issue (see: tuespetre/TuesPechkin#57). Is it possible to do something similar in DinkToPdf?

System.AggregateException: One or more errors occurred. (Unable to load DLL 'libwkhtmltox': The specified module could not be found. (Exception from HRESULT: 0x8007007E)) ---> System.DllNotFoundException: Unable to load DLL 'libwkhtmltox': The specified module could not be found. (Exception from HRESULT: 0x8007007E)
   at DinkToPdf.WkHtmlToXBindings.wkhtmltopdf_init(Int32 useGraphics)
   at DinkToPdf.PdfTools.Load() in C:\Users\admin\Documents\DinkToPdf\src\DinkToPdf\PdfTools.cs:line 27
   at DinkToPdf.BasicConverter.Convert(IDocument document) in C:\Users\admin\Documents\DinkToPdf\src\DinkToPdf\BasicConverter.cs:line 42
   at DinkToPdf.SynchronizedConverter.<>n__0(IDocument document)
   at DinkToPdf.SynchronizedConverter.<>c__DisplayClass5_0.<Convert>b__0() in C:\Users\admin\Documents\DinkToPdf\src\DinkToPdf\SynchronizedConverter.cs:line 27
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
   --- End of inner exception stack trace ---
   at DinkToPdf.SynchronizedConverter.Invoke[TResult](Func`1 delegate) in C:\Users\admin\Documents\DinkToPdf\src\DinkToPdf\SynchronizedConverter.cs:line 51
   at DinkToPdf.SynchronizedConverter.Convert(IDocument document) in C:\Users\admin\Documents\DinkToPdf\src\DinkToPdf\SynchronizedConverter.cs:line 27

[graemehyde]

FYI I tried using this work around to copy the nuget references to the output folder:

<PropertyGroup>
    <TargetFramework>netcoreapp1.1</TargetFramework>
    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
  </PropertyGroup>

Source here: https://stackoverflow.com/questions/43837638/how-to-get-net-core-projects-to-copy-nuget-references-to-build-output.

This copies the referenced nuget binaries to the output folder but the .net core web app still uses the dinktopdf.dll located in:

%UserProfile%\.nuget\packages\dinktopdf\1.0.8\lib\netstandard1.6

So unfortunately this doesn't work

[rdvojmoc]

Can you please add this class into your project just to test it before i put in the library?

This is custom assembly load context which can load library from absolute path.

internal class CustomAssemblyLoadContext : AssemblyLoadContext
{
	public IntPtr LoadUnmanagedLibrary(string absolutePath)
	{
		return LoadUnmanagedDll(absolutePath);
	}
	protected override IntPtr LoadUnmanagedDll(String unmanagedDllName)
	{
		return LoadUnmanagedDllFromPath(unmanagedDllName);
	}

	protected override Assembly Load(AssemblyName assemblyName)
	{
		throw new NotImplementedException();
	}
}

Create and call CustomAssemblyLoadContext before you create your converter:

CustomAssemblyLoadContext context = new CustomAssemblyLoadContext();
context.LoadUnmanagedLibrary(path);

var converter = new SynchronizedConverter(new PdfTools());

Tested on Windows 10 64bit and Ubuntu LTS 16.04 64bit.

Will this work for your use case?

[graemehyde]

Thanks!

And yes this works in my case.

[arjasepp]

I have a a bit similar problem. I mean all works on my machine, but when I load my service to Azure. I try to use the html2pdf functionality and it cant load the dll. I see the dll is there and all, but not working. I tried making it build on x86, not yet with x64 as this might be the issue. Will keep you updated.

The message I get is this: An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)

[rdvojmoc]

Your Azure instance is 64bit or 32bit?
Your dev machine is 64bit?

[graemehyde]

arjasepp Azure by default requires the 32 bit version. Check your Application Settings under the App Service your deploying to. See also https://serverfault.com/questions/567987/32bits-or-64bits-for-windows-azure-web-sites.

Unless you're running Windows XP locally your Dev environment will require the 64 bit version which for me created quite a problem when it came to getting our solution to build correctly for Dev and also for our Azure Test and UAT environments.

Because we are using a build server operating on a 64 bit OS I had to add the following to the csproj using DinkToPdf and therefore also using the WkHtmlToPdf library.

  <ItemGroup Condition=" '$(CONFIGURATION)' == 'Debug' And '$(PROCESSOR_ARCHITECTURE)' == 'x86' And '$(PROCESSOR_ARCHITEW6432)' == '' ">
    <ContentWithTargetPath Include="..\..\lib\wkhtmltox\32 bit\libwkhtmltox.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <TargetPath>libwkhtmltox.dll</TargetPath>
    </ContentWithTargetPath>
  </ItemGroup>

  <ItemGroup Condition=" '$(CONFIGURATION)' == 'Debug' And '$(PROCESSOR_ARCHITECTURE)' == 'AMD64' Or '$(PROCESSOR_ARCHITEW6432)' == 'AMD64' ">
    <ContentWithTargetPath Include="..\..\lib\wkhtmltox\64 bit\libwkhtmltox.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <TargetPath>libwkhtmltox.dll</TargetPath>
    </ContentWithTargetPath>
  </ItemGroup>

  <ItemGroup Condition=" '$(CONFIGURATION)' == 'Release' ">
    <ContentWithTargetPath Include="..\..\lib\wkhtmltox\32 bit\libwkhtmltox.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <TargetPath>libwkhtmltox.dll</TargetPath>
    </ContentWithTargetPath>
  </ItemGroup>

I added the WkHtmlToPdf binaries in a "lib\wkhtmltox" folder at the solution level hence the ".." parent folder traversing at the project level.

[arjasepp]

I got something to work now. Will observe more about this. Thanks @graemehyde

[graemehyde]

arjasepp Just a quick update in case it helps. We've changed tactic with out solution slightly to choose the correct WkHtmlToPdf binary at run time instead of at build time. To do that involves copying all of the WkHtmlToPdf binaries to the output folder (in a sub folder separated by 32 and 64 bit). The correct binary is then determined at run time and then pre-loaded using rdvojmoc's example above with the following additional code:

public static class WkHtmlToPdf
    {
        public static void Preload()
        {
            var wkHtmlToPdfContext = new CustomAssemblyContext();
            var architectureFolder = (IntPtr.Size == 8) ? "64 bit" : "32 bit";
            var wkHtmlToPdfPath = Path.Combine(AppContext.BaseDirectory, $"wkhtmltox\\{architectureFolder}\\libwkhtmltox");

            wkHtmlToPdfContext.LoadUnmanagedLibrary(wkHtmlToPdfPath);
        }
    }

Note no extension (.dll, dylib, or .os) is provided as my understanding is each OS will handle this for you.

My csproj to copy the WkHtmlToPdf binaries to the output folder now looks like this (note no conditions):

  <ItemGroup>
    <ContentWithTargetPath Include="..\..\lib\wkhtmltox\64 bit\libwkhtmltox.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <TargetPath>wkhtmltox\64 bit\libwkhtmltox.dll</TargetPath>
    </ContentWithTargetPath>
	<ContentWithTargetPath Include="..\..\lib\wkhtmltox\64 bit\libwkhtmltox.dylib">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <TargetPath>wkhtmltox\64 bit\libwkhtmltox.dylib</TargetPath>
    </ContentWithTargetPath>
	<ContentWithTargetPath Include="..\..\lib\wkhtmltox\64 bit\libwkhtmltox.so">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <TargetPath>wkhtmltox\64 bit\libwkhtmltox.so</TargetPath>
    </ContentWithTargetPath>
	<ContentWithTargetPath Include="..\..\lib\wkhtmltox\32 bit\libwkhtmltox.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <TargetPath>wkhtmltox\32 bit\libwkhtmltox.dll</TargetPath>
    </ContentWithTargetPath>
	<ContentWithTargetPath Include="..\..\lib\wkhtmltox\32 bit\libwkhtmltox.dylib">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <TargetPath>wkhtmltox\32 bit\libwkhtmltox.dylib</TargetPath>
    </ContentWithTargetPath>
	<ContentWithTargetPath Include="..\..\lib\wkhtmltox\32 bit\libwkhtmltox.so">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <TargetPath>wkhtmltox\32 bit\libwkhtmltox.so</TargetPath>
    </ContentWithTargetPath>
  </ItemGroup>

[Stan92]

Hi,
I tried to follow the @graemehyde post but without success..
I've added a folder named wkhtmltox with 2 subfolders (32 bit & 64 bit) and copied the the respective files.

I get this error System.DllNotFoundException : 'Unable to load DLL 'libwkhtmltox' and a message saying pdftools.cs not found.
Does the component support Core 2.0?
I use Windows 10.

[graemehyde]

Stan92

Things to check:

1. Does your wkhtmltox folder get copied to the output folder along with the binaries in the correct sub folders when you build?
2. Have you debugged your code to make sure the correct wkhtmltox binary is pre-loaded successfully? If unsuccessful are you paths correct?

I haven't tried with .Net Core 2.0 but the error you're getting suggests to me the problem is not with .Net Core but with one of the two options above.

[Stan92]

@graemehyde
Yes I check the 1st point..
About the 2 point, I think this is point I get a Exception from HRESULT: 0x8007000B (I tried with the 64 bit as well as the 64 bit dll).

[JoshLefebvre]

Also having this problem. Just manually copying the dll into my packages folder for the time being. Any plans on this being fixed in an upcoming release?

[rdvojmoc]

@JoshLefebvre Can you be more specific what do you expect to be fixed?

[dragonemp]

anyone knows where should i put libwkhtmltox.dll in docker container? i have the file in my project, set it to copy always, i can confirm the file exist in docker container in /app and various /bin folders, but when i run app, it's giving the op's error : "Unable to load DLL 'libwkhtmltox': The specified module could not be found.
(Exception from HRESULT: 0x8007007E)|| at DinkToPdf.WkHtmlToXBindings.wkhtmltopdf_init(Int32 useGraphics)
at DinkToPdf.PdfTools.Load()", i have no idea where to go from here