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Error in Azure Function #496

zidad opened this Issue Sep 19, 2017 · 16 comments


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zidad commented Sep 19, 2017


I'm getting errors running this inside an Azure function on the simplest possible razor views:
"Illegal characters in path during compile"

Is this just not supported yet or is there a known workaround?

Workaround mentioned here with a static ReferenceResolver doesn't seem to help:


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bviale commented Sep 20, 2017


Azure Functions are subject of some file system limitations (described here and here) .
My best guess is that the Engine may use the file system for template caching in a way that does not comply with Azure Functions limitations.
Personally I ended up using another template engine where I can handle template caching by myself.


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zidad commented Sep 20, 2017

@bviale thanks, that's unfortunate.... Can I ask you which templating engine you used instead?


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corsjune commented Oct 10, 2017

Westwind.RazorHosting seems to be promising with Azure Functions...


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AlanParr commented Oct 17, 2017

I've got this issue too, it seems to be related to using pre-compiled Azure functions as I was using the old .csx style with RazorEngine without issue. As soon as I rewrote everything to use the pre-compiled .cs functions, I get this error.


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lehn0058 commented Oct 19, 2017

Running into the same issue with RazorEngine when using pre-compiled Azure functions. Funny thing is this was working until we did our latest deployment. I have had issues with Azure functions finding my templates in the past, but had gotten around them by embedding the template in my assembly.

Does anyone know if there is any way to disable file system caching RazorEngine is doing?


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lehn0058 commented Oct 20, 2017

Got them working again. For anyone else looking for a temporary workaround, this exception was not thrown in earlier versions of Azure Functions. Until there is a fix in this repo, if you set the FUNCTIONS_EXTENSION_VERSION setting in the Application Settings to 1.0.11247 (the last version I found that this was still working for), then things seem to work again. I'm guessing the Azure Functions team is restricting more of what can be written to the running directories, and the caching of RazorEngine is trying to write something to a temporary file/directory. More information about what is in each function version can be found here:

I have been trying to find where I could overwrite RazorEngine's file output, but it doesn't seem to be caused by the main template caching interfaces you can override in the config. Does anyone know of any other places that may be trying to write to a file on disk that we could override?


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chandermani commented Nov 27, 2017

Another fix/workaround is to change the configuration of RazorEngine. As described in fix #466.

Create a new TemplateServiceConfiguration object.

var config = new TemplateServiceConfiguration();

Provide a custom implementation of IReferenceResolver (take one described in #466).

c.ReferenceResolver = new UseCurrentAssembliesReferenceResolver();

And assign it the static instance of RazorEngine.

RazorEngine.Engine.Razor = RazorEngine.Templating.RazorEngineService.Create(c);

The custom resolver implementation catches the exception and continues instead of failing.


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shyamal890 commented Jan 28, 2018

@chandermani I tried the workaround but is not working for me with Net.Sdk.Functions version - 1.0.7

var config = new TemplateServiceConfiguration();
            // You can use the @inherits directive instead (this is the fallback if no @inherits is found).
            config.BaseTemplateType = typeof(ExtendTemplateBase<>);
            config.ReferenceResolver = new UseCurrentAssembliesReferenceResolver();
            using (Engine.Razor = RazorEngineService.Create(config))
                emailHtmlBody = Engine.Razor.RunCompile(text, template, null,model,viewBag);
//By default Razor doesn't support @Html and @Url
public abstract class ExtendTemplateBase<T> : TemplateBase<T>

    public HtmlHelper<object> Html { get; private set; }
    public UrlHelper Url { get; private set; }

    protected ExtendTemplateBase() {

    public void InitHelpers()
        //var httpContext = new HttpContextWrapper(HttpContext.Current);
        //var handler = httpContext.CurrentHandler as MvcHandler;
        //if (handler == null)
        //    throw new InvalidOperationException("Unable to run template outside of ASP.NET MVC");

        Url = new UrlHelper();

    public class UrlHelper
        public string Content(string content)
            return VirtualPathUtility.ToAbsolute(content);

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eigil-rosager commented Mar 1, 2018

I was just about to deploy my Azure Function using RazorEngine, when I bumped into this issue, which was quite worrying!

I just tested my function on a 32 bit Azure App Service - the free tier and it works! My production servcie runs 64 bit on a paid tier. Not tested yet.

These are my RazorEngine settings:

            // Find templates in a web application
            var webPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "bin", templatePath);
            // Find templates from a unit test or console application
            var libraryPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, templatePath);

            var config = new TemplateServiceConfiguration
                TemplateManager = new ResolvePathTemplateManager(new[] { webPath, libraryPath })

            config.DisableTempFileLocking = true;
            config.CachingProvider = new DefaultCachingProvider(t => { });

            _service = RazorEngineService.Create(config);

Using version 3.10.0 of RazorEngine.

Hope this helps other with similar problems.


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zidad commented Mar 1, 2018

@eigil-rosager that's an interesting solution, thanks for sharing. It seems like you're completely disabling caching like this, or am I wrong there? I'd be curious to see the performance impact on that.


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lehn0058 commented Mar 1, 2018

Thanks for the comment @eigil-rosager ! Unfortunately, I still have the same error after trying your suggestion. My setup is slightly different, where I have moved my templates to be embedded in the binary instead of as separate files:

    private static Lazy<IRazorEngineService> _service = new Lazy<IRazorEngineService>(() =>
        var config = new TemplateServiceConfiguration
            TemplateManager = new EmbeddedResourceTemplateManager(typeof(RazorTemplateManager)),
            BaseTemplateType = typeof(HtmlTemplateBase<>)

        config.DisableTempFileLocking = true;
        config.CachingProvider = new DefaultCachingProvider(t => { });
        return RazorEngineService.Create(config);

Perhaps I will have to try restructuring a few things and remove them from being embedded to see if that in combination with your suggestion helps.


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MattyBearBytes commented Mar 12, 2018

Hi there,
I have issues with using a class library that has the template files (inc. layout) as embedded resources in an Azure Function. Just wondering if anyone has had any luck with a successful implementation?

The error I get is "System.NotSupportedException: 'The given path's format is not supported."


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harmandeol commented Mar 27, 2018

fixed it for me.


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billtyler commented Jun 13, 2018

@MattyBearBytes, were you able to resolve the path format not supported issue? I'm facing that one now after converting to a precompiled function from a service.


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csimone86 commented Jul 25, 2018

Hope this can help everyone

RazorEngine throw a NotSupportedException when compiling template in Azure Function

But I am still not satisfied because I would like to run RrazorEngine in another app domain


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lehn0058 commented Aug 1, 2018

@csimone86 worked for me! THANK YOU! (especially since Microsoft stopped supporting the version I had to roll back to in order to get around this TODAY)

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