Creating and invoking .NET Core actions

The following sections guide you through creating and invoking a single .NET Core action.

In order to compile, test and archive .NET Core projects, you must have the .NET Core SDK installed locally and the environment variable DOTNET_HOME set to the location where the dotnet executable can be found.

A .NET Core action is a .NET Core class library with a method called Main that has the exact signature as follows:

public Newtonsoft.Json.Linq.JObject Main(Newtonsoft.Json.Linq.JObject);

For example, create a C# project called Apache.OpenWhisk.Example.Dotnet:

dotnet new classlib -n Apache.OpenWhisk.Example.Dotnet -lang "C#"
cd Apache.OpenWhisk.Example.Dotnet

Install the Newtonsoft.Json NuGet package as follows:

dotnet add package Newtonsoft.Json -v 12.0.1

Now create a file called Hello.cs with the following content:

using System;
using Newtonsoft.Json.Linq;

namespace Apache.OpenWhisk.Example.Dotnet
    public class Hello
        public JObject Main(JObject args)
            string name = "stranger";
            if (args.ContainsKey("name")) {
                name = args["name"].ToString();
            JObject message = new JObject();
            message.Add("greeting", new JValue($"Hello, {name}!"));
            return (message);

Publish the project as follows:

dotnet publish -c Release -o out

Zip the published files as follows:

cd out
zip -r -0 *

Create the .NET Core Action

You need to specify the name of the function handler using --main argument. The value for main needs to be in the following format: {Assembly}::{Class Full Name}::{Method}, e.q., Apache.OpenWhisk.Example.Dotnet::Apache.OpenWhisk.Example.Dotnet.Hello::Main

To use on a deployment of OpenWhisk that contains the runtime as a kind:

wsk action update helloDotNet --main Apache.OpenWhisk.Example.Dotnet::Apache.OpenWhisk.Example.Dotnet.Hello::Main --kind dotnet:2.2

Invoke the .NET Core Action

Action invocation is the same for .NET Core actions as it is for Swift and JavaScript actions:

wsk action invoke --result helloDotNet --param name World
      "greeting": "Hello World!"