# Cloud Events - Go

A simple web app written in Go that can receive and send Cloud Events that you
can use for testing. It supports running in two modes:

1. The default mode has the app reply to your input events with the output
   event, which is simplest for demonstrating things working in isolation, but
   is also the model for working for the Knative Eventing `Broker` concept.

2. `K_SINK` mode has the app send events to the destination encoded in
   `$K_SINK`, which is useful to demonstrate how folks can synthesize events to
   send to a Service or Broker when not initiated by a Broker invocation (e.g.
   implementing an event source)

The application will use `$K_SINK`-mode whenever the environment variable is
specified.

Do the following steps to create the sample code and then deploy the app to your
cluster. You can also download a working copy of the sample, by running the
following commands:

```bash
git clone https://github.com/knative/docs.git knative-docs
cd knative-docs/code-samples/serving/cloudevents/cloudevents-go
```

## Before you begin

- A Kubernetes cluster with Knative installed and DNS configured. See
  [Install Knative Serving](https://knative.dev/docs/install/serving/install-serving-with-yaml).
- [Docker](https://www.docker.com) installed and running on your local machine,
  and a Docker Hub account configured (we'll use it for a container registry).

## The sample code.

1. If you look in `cloudevents.go`, you will see two key functions for the different modes of operation:

   ```go
   func (recv *Receiver) ReceiveAndSend(ctx context.Context, event cloudevents.Event) cloudevents.Result {
     // This is called whenever an event is received if $K_SINK is set, and sends a new event
     // to the url in $K_SINK.
   }

   func (recv *Receiver) ReceiveAndReply(ctx context.Context, event cloudevents.Event)  (*cloudevents.Event, cloudevents.Result) {
     // This is called whenever an event is received if $K_SINK is NOT set, and it replies with
     // the new event instead.
   }
   ```

2. Choose how you would like to build the application:

 ### Dockerfile

 * If you look in `Dockerfile`, you will see a method for pulling in the dependencies and building a small Go container based on Alpine. You can build and push this to your registry of choice via:
```bash
# Build and push the container on your local machine.
docker buildx build --platform linux/arm64,linux/amd64 -t "<image>" --push .
```

 ### ko

 * You can use [`ko`](https://github.com/google/ko) to build and push just the image with:
```bash
ko publish github.com/knative/docs/code-samples/serving/cloudevents/cloudevents-go
```
 However, if you use `ko` for the next step, this is not necessary.


3. Choose how you would like to deploy the application:

 ### yaml (with Dockerfile)
 * If you look in `service.yaml`, take the `<image>` name you used earlier and insert it into the `image:` field, then run:
```bash
kubectl apply -f service.yaml
```

 ### yaml (with ko)
 * If using `ko` to build and push:
```bash
ko apply -f service.yaml
```

 ### kn (with Dockerfile)
 * If using `kn` to deploy:
```bash
kn service create cloudevents-go --image=<IMAGE>
```

 ### kn (with ko)
 * You can compose `kn` and `ko` to build and deploy with a single step using:
```bash
kn service create cloudevents-go --image=$(ko publish github.com/knative/docs/code-samples/serving/cloudevents/cloudevents-go)
```

## Testing the sample

Get the URL for your Service with:

```bash
$ kubectl get ksvc
NAME             URL                                            LATESTCREATED          LATESTREADY            READY   REASON
cloudevents-go   http://cloudevents-go.default.1.2.3.4.sslip.io   cloudevents-go-ss5pj   cloudevents-go-ss5pj   True
```

Then send a cloud event to it with:

```bash
$ curl -X POST \
    -H "content-type: application/json"  \
    -H "ce-specversion: 1.0"  \
    -H "ce-source: curl-command"  \
    -H "ce-type: curl.demo"  \
    -H "ce-id: 123-abc"  \
    -d '{"name":"Dave"}' \
    http://cloudevents-go.default.1.2.3.4.sslip.io
```

You will get back:

```bash
{"message":"Hello, Dave"}
```

## Removing the sample app deployment

To remove the sample app from your cluster, delete the service record:

```bash
kubectl delete --filename service.yaml
```
