Thursday Quickie: When AssemblyBinding redirect doesn't... and how I fixed it

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TLDR: If your csproj file has AutoGenerateBindingRedirects set to true, then you MUST include the xmlns on the assemblyBinding node for any custom binding redirects in app.config.

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So I've been banging my head against the wall trying to get a piece of code delivered over the last few days, and kept hitting an issue where code runs perfectly locally, but when deployed to the target server was failing with the dreaded error

Could not load file or assembly 'System.Net.Http, Version=4.1.1.2, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

I'd used Gertjan van Montfoort's excellent article as a guide, but whatever version of the NuGet package I installed, and whatever version I referenced in my binding redirects in app.config, it just would not fire up.

Looking at the Fusion logs (helped by Scott Hanselman's article) I could see that my app was initially loading System.Net.Http from the GAC for a 4.0.0.0 reference, then successfully loaded 4.1.1.3 from the app directory (the one from the NuGet package I referenced).

But when it was trying to load 4.1.1.2 because of other dependencies Fusion was not honouring the binding redirect, and so the app was failing on startup.

Finally I found a comment on the net that hinted about case sensitivity within the app config, so I went looking for differences between my custom redirects and those generated on build into MyApp.exe.config.

And I found one - the generated redirects all have an xmlns attribute on the assemblyBinding node - and my custom one did not. 

The solution - add one in your app.config

<?xml version="1.0" encoding="utf-8"?>

<configuration>

  <runtime>

    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">

      <dependentAssembly>

        <assemblyIdentity name="System.Net.Http" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />

        <bindingRedirect oldVersion="0.0.0.0-4.2.0.0" newVersion="4.1.1.2" />

      </dependentAssembly>

    </assemblyBinding>

  </runtime>

</configuration>

Now your binding redirects get merged with the generated ones and it all works.

My interpretation is that Fusion appears to honour the redirects in assemblyBinding nodes only if all have xmlns attributes or none have them - but not if mixed. 

Hopefully others will find this useful - now I can get on and do some actual work!