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From Michele Sciabarra <>
Subject First Implementation of the self-replacing Go support for OpenWhisk
Date Tue, 13 Feb 2018 22:07:33 GMT
As promised I released a first implementation of Go support using the technique I described

In short, a library implementing the proxy and serving both /run and /init, with the ability
of replace itself with a new version.

Using the library, implementing a function in Go looks like this:

package main

import (


func hello(event json.RawMessage) (json.RawMessage, error) {
	// input and output
	var input struct{ Name string }
	var output struct {
		Greetings string `json:"greetings"`
	// read the input event
	json.Unmarshal(event, &input)
	if input.Name != "" {
		// handle the event
		output.Greetings = "Hello, " + input.Name
		return json.Marshal(output)
	return nil, fmt.Errorf("no name specified")

func main() {

Actually in practice it is better to place the function in a separate package for implementing
some tests, because apparently adding tests in the main package does not work.

Source code of the library is here:

Here is a simple transcription of how it works and how I tested it.

First you build  a couple of executable, and for simplicity you also prepare the json payload
for the init.

$ cd test
$ go build -o hello ../main/hello.go
$ go build -o ciao ../main/ciao.go
$ echo '{"value":{"binary":true,"code":"'$(base64 hello)'"}}' >hello.json
$ echo '{"value":{"binary":true,"code":"'$(base64 ciao)'"}}' >ciao.json

Now you can start the actual server

$ go run ../main/exec.go

Now the magic happens.

Default behaviour (no executable)

$ curl -XPOST http://localhost:8080/run -d '{"value":{"name":"Mike"}}'
{"error":"the action failed to locate a binary"}

Now post the `hello` handler and run it:

$ curl -XPOST http://localhost:8080/init -d @hello.json
$ curl -XPOST http://localhost:8080/run -d '{"value":{"name":"Mike"}}'
{"greetings":"Hello, Mike"}

As you can see, the function changed and now it implements the "hello" handler.

But the replaced server is still able to run init so let's do it again, replacing with the
"ciao" handler.

$ curl -XPOST http://localhost:8080/init -d @ciao.json
$ curl -XPOST http://localhost:8080/run -d '{"value":{"name":"Mike"}}'
{"saluti":"Ciao, Mike"}


I want to say "thank you" to James Thomas, I basically copied his code for implementing the
/run handler since it was ready, then I added my code for the /init. I also had to dig into
the internals of the http Go package more than I expected.

Work is not yet complete, I have to manage the environment variables (stealing more code from
James Thomas implementation), package in Docker, integrate in OpenWhisk. But definitely I
believe looks like a promising start.

  Michele Sciabarra

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