Migrating .NET Core 2 to .NET Core 3: HttpContent does not contain a definition for "ReadAsAsync"

Question

I am following this guide https://docs.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.0&tabs=visual-studio to migrate to .NET Core 3.

I am getting the compilation error:

Error CS1061 'HttpContent' does not contain a definition for 'ReadAsAsync' and no accessible extension method 'ReadAsAsync' accepting a first argument of type 'HttpContent' could be found (are you missing a using directive or an assembly reference?)

The project is a class library, I have updated its csproj removing a package reference to Microsoft.AspNetCore.App and adding a framework reference instead:

  <ItemGroup>
    <FrameworkReference Include="Microsoft.AspNetCore.App" />
  </ItemGroup>

Any ideas why this is happening?

Answer 1

ReadAsAsync is a .NET Standard extension that's actually shared between ASP.NET Core and ASP.NET Web Api (via a NuGet library). However, it uses JSON.NET to do the deserialization, and as of .NET Core 3.0, ASP.NET Core now uses System.Text.Json instead. As such, this library (and the extension it contains) is not included in the .NET Core 3.0 framework because doing so would require including the JSON.NET library in addition to System.Text.Json.

While you can manually add the Microsoft.AspNet.WebApi.Client (and Newtonsoft.Json along with it), you should just move on without it. It doesn't save you much anyways, as you can accomplish the same via just:

await JsonSerializer.DeserializeAsync<MyType>(await response.Content.ReadAsStreamAsync());

If you like, you can add your own extension to HttpContent to wrap this up in a ReadAsAsync method:

public static class HttpContentExtensions
{
    public static async Task<T> ReadAsAsync<T>(this HttpContent content) =>
        await JsonSerializer.DeserializeAsync<T>(await content.ReadAsStreamAsync());
}