This article introduces developers to the capabilities of FaaS for all supported runtimes: .NET, Go, Java, Node.js, and Python. For each runtime, we provide examples of three abstract functions of ascending levels of complexity:
  • A basic function (“Hello world!”)
  • A function with dependencies
  • A function for accessing a data request/response

​
C#

​
Basic C# “hello world” function

using System;
using System.Collections.Generic;
using System.Threading.Tasks;


// main method will be module.handler
public class module
{
    public Task<object> handler(Dictionary<string, object> k8Event, Dictionary<string, string> k8Context)
    {
        return Task.FromResult<object>("hello world");
    }
}

​
C# function with dependencies

This function uses the YamlDotNet dependencies. 
using System;
using System.Collections.Generic;
using YamlDotNet.Serialization;
using System.Threading.Tasks;


public class module
{
    public Task<object> handler(Dictionary<string, object> k8Event, Dictionary<string, string> k8Context)
    {
        var person = new Person()
        {
            Name = "Michael J. Fox",
            Age = 56
        };
       
        var serializer = new SerializerBuilder().Build();
        return Task.FromResult<object>(serializer.Serialize(person)); // yaml
    }
}
public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}
To build this function, specify the dependencies in the .csproj format: 
<Project Sdk="Microsoft.NET.Sdk">
    <PropertyGroup>
        <TargetFramework>net6.0</TargetFramework>
        <AssemblyName>dependency-yaml</AssemblyName>
    </PropertyGroup>
    <ItemGroup>
        <PackageReference Include="YamlDotNet" Version="13.7.1" />
    </ItemGroup>
</Project>

​
C# function accessing the data request

For all runtimes, you can find the request object in the event map field. Each language has a unique type. For C#, it’s HttpRequest from Microsoft.AspNetCore.Http. 
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;


// main method module.handler
public class module
{
    public Task<object> handler(Dictionary<string, object> k8sEvent, Dictionary<string, string> k8Context)
    {  
        var extension = (Dictionary<string, object>)k8sEvent["extension"];
        HttpRequest request = (HttpRequest)extension["request"];
        Console.WriteLine(request);
       
        if (request.Method == "POST") {
            return Task.FromResult<object>(create());
        } else if (request.Method == "GET") {
            return Task.FromResult<object>(get());
        } else {
            return Task.FromResult<object>("Method not allowed");
        }
    }


    public string create() {
        return "Creating something on POST request";
    }


    public string get() {
        return "Getting something on GET request";
    }
}
The dependencies should be structured as follows: 
<Project Sdk="Microsoft.NET.Sdk">


  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <AssemblyName>access-request</AssemblyName>
  </PropertyGroup>


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


</Project>

​
Go

​
Basic Go “hello world” function

package kubeless


// main function: Handler
func Handler(event map[string]interface{}, context map[string]string) (string, error) {
    return "Hello world!", nil
}

​
Go function with dependencies

This function uses the yaml dependencies. 
package kubeless


import (
    "gopkg.in/yaml.v3"
)


type Person struct {
    Name string
    Age int
}


func Handler(event map[string]interface{}, context map[string]string) (string, error) {
    person := Person{Name: "John", Age: 55}
    data, err := yaml.Marshal(&person)
    return string(data), err
}
Dependencies should be defined as follows: 
module function


go 1.20


require (
    gopkg.in/yaml.v3 v3.0.1
)

​
Go function accessing request/response objects

The event extension includes request, response, and context objects. These can be accessed for improved precision in function management: 
package kubeless


import (
    "net/http"
    "context"
    "fmt"
)


type Person struct {
    Name string
    Age int
}


func create() string {
    return "Use POST to create something"
}


func get() string {
    return "Use GET to get something"
}


func Handler(event map[string]interface{}, k8sContext map[string]string) (string, error) {
    extension := event["extension"].(map[string]interface{})
    r := extension["request"].(*http.Request)
    w := extension["response"].(http.ResponseWriter)
    ctx := extension["context"].(context.Context)
   
    fmt.Println(r, w, ctx)
    if r.Method == "GET" {
        return get(), nil
    } else if r.Method == "POST" {
        return create(), nil
    }
   
    return "Method not allowed", nil
}

​
Java

​
Basic Java “hello world” function

package io.kubeless;


import java.util.HashMap;


public class Module {
    public String handler(HashMap<String, Object> event, HashMap<String, String> context) {
        return "Hello world!";
    }
}

​
Java function with dependencies

package io.kubeless;


import java.util.HashMap;


import org.joda.time.LocalTime;


public class Module {
    public String handler(HashMap<String, Object> event, HashMap<String, String> context) {
        LocalTime currentTime = new LocalTime();
        return "Hello world! Current local time is: " + currentTime;
    }
}
Dependencies should be defined as follows: 
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <artifactId>function</artifactId>
  <name>function</name>
  <version>1.0-SNAPSHOT</version>
  <dependencies>
     <dependency>
       <groupId>joda-time</groupId>
       <artifactId>joda-time</artifactId>
       <version>2.9.2</version>
     </dependency>
  </dependencies>
  <parent>
    <groupId>io.kubeless</groupId>
    <artifactId>kubeless</artifactId>
    <version>1.0-SNAPSHOT</version>
  </parent>
</project>

​
Java function accessing the request

package io.kubeless;


import java.util.HashMap;
import com.sun.net.httpserver.HttpExchange;

public class Module {
    public String handler(HashMap<String, Object> event, HashMap<String, String> context) {
        // Access to Request/Response
        HashMap<String, Object> extension = (HashMap) event.get("extension");
        HttpExchange he = (HttpExchange) extension.get("exchange");
        // Request&Resposne can be manipulated through HttpExchange


        String requestMethod = he.getRequestMethod();
        System.out.println("HTTP Method: " + requestMethod);


        if ("GET".equals(requestMethod)) {
            return "Get some objects";
        } else if ("POST".equals(requestMethod)) {
            return "Create some objects";
        }


        return "Method not allowed";
    }
}

​
Node.js

​
Basic Node.js “hello world” function

module.exports = {
  handler: function (event, context) {
    return 'hello world!';
  }
}

​
Node.js function with dependencies

'use strict';


const _ = require('lodash');


module.exports = {
    handler: (event, context) => {
        _.assign(event.data, {date: new Date().toTimeString()})
        return JSON.stringify(event.data);
    },
};
The dependencies should be structured as follows: 
{
  "name": "my-project",
  "version": "1.0.0",
  "description": "A simple project with Lodash dependency",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "lodash": "^4.17.21"
  }
}

​
Node.js function accessing object request/response

'use strict';


module.exports = {
    handler: (event, context) => {
        request = event.extension.request;
        response = event.extension.response;
        // Manipulate request/response as you wish
       
        return "some message"
    },
};

​
Python

​
Basic Python “hello world” function

def handler(event, context):
    return "hello world"

​
Python function with dependencies

import yaml


def handler(event, context):
    person = {
        "name": "John",
        "age": 55
    }
   
    return yaml.dump(person)
The dependencies should be structured as follows: 
PyYAML==6.0.1

​
Python function accessing object request/response

import yaml
from aiohttp import web


def handler(event, context):
    request: web.Request = event["extension"]["request"]
    response: web.Response = event["extension"]["response"]
   
    print(request, response)
    return "Some result"