HttpRequestMessageExtensions not being found at run-time in Azure Function

Question

I've got an Azure Function app that creates a precompiled DLL (so it uses normal .cs files, not the older .csx method, pre-VS2017). Previously, it was targeting .Net Framework 4.5.2. I updated it to 4.7 so as to use some of the new C# 7 features. I updated my NuGet packages by doing "Update-Package -Reinstall" and verified that they all have the "net47" target set in my packages.config file.

Everything compiles fine. But when I call a function that uses either of 2 HttpRequestMessageExtensions methods, I get an exception. One example of the exception is this:

Method not found: 'System.Net.Http.HttpResponseMessage 
  System.Net.Http.HttpRequestMessageExtensions.CreateResponse(
  System.Net.Http.HttpRequestMessage, System.Net.HttpStatusCode)'.

Here's an example of a tiny test function that will cause the error:

using System.Net;
using System.Net.Http;
public static HttpResponseMessage Run(HttpRequestMessage req)
{
        return req.CreateResponse(HttpStatusCode.Accepted, "");         
}       

Upon calling this function with say Postman, I'll receive the aforementioned exception. I also get a similar method not found exception when I call GetQueryNameValuePairs() on the HttpRequestMessage.

I've tried updating my NuGet packages to the latest, no difference. I've cleaned and rebuilt and restarted a bunch of times, making sure to nuke my bin and obj directories.

I'm not sure what could be the problem. I guess I could downgrade back to .Net 4.5.2 but I'd rather not. For one, I want to use C# 7, and for two, I want to understand what the problem is rather than avoid it.

Update: interesting. The issue seems to be with System.Net.Http. If I lower it to 4.0.0 everything works fine. If I raise it to any higher version I get the issues listed above. I tried selectively lowering each of my packages, one by one, to their previous version number to find this out. I then updated all but this one to the latest version and it fixed the issue.

Answer 1

I also tested it on my side. The issue is related to the latest version of System.Net.Http assembly(4.3.2). If I don't install this package manually or install the earlier versions(4.3.1/4.3.0), the application could work fine.

The CreateResponse method is a extension method which is written in System.Web.Http assembly(version 5.2.3). It seem that it is not compatible with the latest version of System.Net.Http. Please could just skip the error by using the earlier version of System.Net.Http and you can also submit this issue to Microsoft using follow channel.

https://connect.microsoft.com/VisualStudio/Feedback

Interesting. For me, if I got above version 4.0.0 (including 4.1.1 or 4.3.1) I still get the same problem of not finding those extension methods.

The assembly might not be updated during you change the package version. From the bin\Debug\net47 folder, we could check the current assembly version we used.

If the modified date of assembly is 2/9/2017, the package version is 4.3.1. If the modified date of assembly is 4/19/2017, the package version is 4.3.2. If the assembly is not the latest version, it could work fine on my side.

In addition, Microsoft.Asp.Net.WebApi.Client package is installed by default when creating an Azure function. System.Net.Http is one of its dependencies. So we don't need to install the System.Net.Http package manually. When running our application, NuGet will choose a right version of System.Net.Http for our application.

Answer 2

I had the same issue running my Azure Function locally and eventually tracked it down to conflicting System.Net.Http assemblies. I created my Azure function from a blank ASP.NET Web App and initially pulled down the System.Net.Http NuGet package to use within the project. I also pulled down the Microsoft.AspNet.WebApi.Client for use within the project. It did not matter which version of System.Net.Http I tried my project would compile but fail when the request was made.

Eventually, I removed packages I had downloaded, cleaned the build folder and added just the Microsoft.AspNet.WebApi.Client. I noticed that this automatically referenced the System.Net.Http on my machine for my version of the .NET Framework. (C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework.NETFramework). This compiled successfully and I was able to make requests to the function without any exceptions.