creating-handlers.md

Creating handlers

{% hint style="info" %} If you haven't created a project yet, see Get started first. {% endhint %}

Your project contains a Directive.yaml file that controls your entire application. The Directive is included in the Runnable Bundle used by Atmo to run your application.

The Directive has some metadata such as a unique application identifier and a version number, as well as some handlers.

Each handler tells Atmo how to handle a resource. A resource is an input that Atmo makes available via HTTP endpoints, event handlers, and more. To start, Atmo supports handlers for HTTP requests, particulary designed to help building web APIs. Here is an example Directive:

identifier: com.suborbital.test
appVersion: v0.0.1
atmoVersion: v0.4.2

handlers:
  - type: request
    resource: /hello
    method: POST
    steps:
      - group:
        - fn: modify-url
        - fn: helloworld-rs
          as: hello
      - fn: fetch-test
        with:
          url: modify-url
          logme: hello

This describes the application being constructed. It declares a resource (HTTP POST /hello) and a set of steps to handle that request. The steps are a set of Runnable functions to be composed when handling requests to the /hello endpoint.

There are two types of step. The first step you see above is a group, meaning that all of the functions in that group will be executed concurrently.

The second step shown above is a single fn , which calls a Runnable that uses the Runnable API to make an HTTP request. The API is continually evolving to include more capabilities. In addition to making HTTP requests, it includes logging, database connections, caching, and more.

The output of the final function in a handler is used as the response data for the request, by default. If you wish to use the output from a different function, you can include the response option in your handler, listing the name of the function to use as a response. If the final step is a group, then the response clause must be included.

For example:

steps:
  - group:
    - fn: modify-url
    - fn: helloworld-rs
      as: hello
  - fn: fetch-test
    with:
      url: modify-url
      logme: hello
response: hello

Your application can contain as many handlers as needed, and functions can be re-used among many handlers. Each Runnable in your project can be called by its name. The subo tool will validate your directive to ensure it is not calling any Runnables that don't exist in your project.

The as and with clauses shown above will be discussed next.