Generate code

Introduction

In this tutorial, you'll learn how to generate code from your AsyncAPI document using the AsyncAPI generator tool.

Background context

The AsyncAPI Generator is a tool that you can use to generate whatever you want based on the AsyncAPI document. You can generate docs and code. It can be used as a library in a Node.js application or through the AsyncAPI CLI.

The generator tool supports a number of templates to generate code for a variety of different languages and protocols as the output. These templates help to specify what exactly must be generated, and in this tutorial, you'll use a Node.js template.

Installation guide

CLI Installation

Follow the AsyncAPI CLI installation instructions below, based on your computer’s operating system.

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# Download latest release. To download specific release, your link should look similar to https://github.com/asyncapi/cli/releases/download/v0.13.0/asyncapi.pkg. All releases are listed in https://github.com/asyncapi/cli/releases
curl -OL https://github.com/asyncapi/cli/releases/latest/download/asyncapi.pkg
# Install AsyncAPI CLI
sudo installer -pkg asyncapi.pkg -target /

Using NPM and Node.js

Alternitavely, you can install the AsyncAPI CLI with Node.js >=v10 and NPM.

npm install -g @asyncapi/cli

npm install -g @asyncapi/cli@{version}

Generate code

To generate code from the AsyncAPI document created in a previous tutorial, follow the steps listed below:

1. Trigger generation of the Node.js code:

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   asyncapi generate fromTemplate asyncapi.yaml @asyncapi/nodejs-template -o output -p server=mosquitto

   Let's break down the previous command:

   • asyncapi generate fromTemplate is how you use AsyncAPI Generator via the AsyncAPI CLI.
   • asyncapi.yaml is how you point to your AsyncAPI document and can be a URL.
   • @asyncapi/nodejs-template is how you specify the Node.js template.
   • -o determines where to output the result.
   • -p defines additional parameters you want to pass to the template. Here, the server parameter specifies the server's name as it is defined in AsyncAPI document.

2. List all files in directory and check that the Node.js application is generated:

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   cd output && ls

   Upon execution of the command above, the following is an example of the expected result:

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   $ ls
   Dockerfile
   asyncapi.yaml
   docs
   src
   README.md
   config
   package.json
   

Start generated application

1. Install dependencies of the newly generated application:

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   npm install

2. Start the application:

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   npm start

Send message to broker

1. In another terminal install the MQTT.js library:

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   npm install mqtt -g

2. Send a message to the MQTT broker that's connected to your generated application. Run the following MQTT client command:

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   mqtt pub -t 'light/measured' -h 'test.mosquitto.org' -m '{"id": 1, "lumens": 3, "sentAt": "2017-06-07T12:34:32.000Z"}'

3. Go back to the previous terminal to check if your application logged the streetlight condition you just sent. You should see something like this displayed in the terminal:

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   light/measured was received:
   { id: 1, lumens: 3, sentAt: '2017-06-07T12:34:32.000Z' }

Summary

In this tutorial, you learned how to generate your code from the Streetlights API specification document created in a previous tutorial using the AsyncAPI generator tool.

Additionally, you've learned how to run your code by installing the generated code's dependencies and sending several test messages to the Streelights application using the MQTT client.

Next steps

Now that you've completed this tutorial, go ahead and learn how to validate your AsyncAPI messages (events) through the message validation techniques supported by AsyncAPI.