Unable to load External library "libwkhtmltox.dll" while using DinkToPDF for PDF conversion after publishing as app service in azure

Question

I am using DinkToPDF library to convert a html string to it's equivalent PDF. To use this library we have to import a native library provided which is libwkhtmltox.dll. This works fine when I run my .net core project locally,however when I try to publish my web project as an App Service in Azure, I get the following error,

Unhandled Exception: System.DllNotFoundException: Unable to load shared library '/home/site/wwwroot/libwkhtmltox.dll' or one of its dependencies. In order to help diagnose loading problems, consider setting the LD_DEBUG environment variable: /home/site/wwwroot/libwkhtmltox.dll: cannot open shared object file: No such file or directory

I have referred the library usage in the startup.cs file as below.

    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();
        }
    }
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddSingleton(typeof(IConverter), new SynchronizedConverter(new PdfTools()));
            var context = new CustomAssemblyLoadContext();
            context.LoadUnmanagedLibrary(Path.Combine(Directory.GetCurrentDirectory(), "libwkhtmltox.dll"));
         .
         .
         .
        }

Please help me find out the solution for this error.

Answer 1

you need set the absotule path for the library, and for windows it is not necessary use ".dll", in my case it is placed in [project_root]/wkhtmltox/v0.12.4/[x_64|x_86]

var architectureFolder = (IntPtr.Size == 8) ? "x_64" : "x_86";
var wkHtmlToPdfFileName = "libwkhtmltox";
if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
{
    wkHtmlToPdfFileName += ".so";
}
else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
{
    wkHtmlToPdfFileName += ".dylib";
}

var wkHtmlToPdfPath = Path.Combine(
    new string[] {
        _hostingEnvironment.ContentRootPath,
        "wkhtmltox",
        "v0.12.4",
        architectureFolder,
        wkHtmlToPdfFileName
    });

CustomAssemblyLoadContext context = new CustomAssemblyLoadContext();
context.LoadUnmanagedLibrary(wkHtmlToPdfPath);
services.AddSingleton(typeof(IConverter), new SynchronizedConverter(new PdfTools()));

Answer 2

You have to copy the dll extension to the root of your project

After that you have to create an internal class to load the dll

Add this to your class

using System.Runtime.Loader;
using System.Reflection;

the methods to include:

    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();
        }
    }

Answer 3

In dockerfile insert the following commands to the componente engine html to pdf:

FROM microsoft/dotnet:2.1-aspnetcore-runtime AS base

RUN apt-get update

RUN apt-get install -y apt-utils

RUN apt-get install -y libgdiplus

RUN apt-get install -y libc6-dev
 
RUN ln -s /usr/lib/libgdiplus.so/usr/lib/gdiplus.dll