npm package: @hypsibius/faas-js-runtime
Description: A Node.js framework for executing arbitrary functions in response to HTTP or cloud events
Author: Jonathan Rapoport
Latest version: 2.2.12

# Node.js Function Framework

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This module provides a Node.js framework for executing a function that
exists in a user-provided directory path as an `index.js` file. The
directory may also contain an optional `package.json` file which can
be used to declare runtime dependencies for the function. You can also
provide a path to an arbitrary JavaScript file instead of a directory
path, allowing you to execute a single file as a function.

|                 | Project Info  |
| --------------- | ------------- |
| License:        | Apache-2.0  |
| Issue tracker:  | https://github.com/nodeshift/faas-js-runtime/issues  |
| Engines:        | Node.js >= 16 |

The function is loaded and then invoked for incoming HTTP requests
at `localhost:8080`. The incoming request may be a
[Cloud Event](https://github.com/cloudevents/sdk-javascript#readme.) or
just a simple HTTP GET/POST request. The invoked user function can be
`async` but that is not required.

## The Function Interface

The function file that is loaded may export a single function or a `Function`
object. The `Function` object allows developers to add lifecycle hooks for
initialization and shutdown, as well as providing a way to implement custom
health checks.

The `Function` interface is defined as:

```typescript
export interface Function {
  // The initialization function, called before the server is started
  // This function is optional and should be synchronous.
  init?: () => any;

  // The shutdown function, called after the server is stopped
  // This function is optional and should be synchronous.
  shutdown?: () => any;

  // The liveness function, called to check if the server is alive
  // This function is optional and should return 200/OK if the server is alive.
  liveness?: HealthCheck;

  // The readiness function, called to check if the server is ready to accept requests
  // This function is optional and should return 200/OK if the server is ready.
  readiness?: HealthCheck;

  logLevel?: LogLevel;

  // The function to handle HTTP requests
  handle: CloudEventFunction | HTTPFunction;
}
```

## Handle Signature

This module supports two different function signatures: HTTP or CloudEvents. In the type definitions below, we use TypeScript to express interfaces and types, but this module is usable from JavaScript as well.

### HTTP Functions

The HTTP function signature is the simplest. It is invoked for every HTTP request that does not contain a CloudEvent.

```typescript
interface HTTPFunction {
  (context: Context, body?: IncomingBody): HTTPFunctionReturn;
}
```

Where the `IncomingBody` is either a string, a Buffer, a JavaScript object, or undefined, depending on what was supplied in the HTTP POST message body. The `HTTTPFunctionReturn` type is defined as:

```typescript
type HTTPFunctionReturn = Promise<StructuredReturn> | StructuredReturn | ResponseBody | void;
```

Where the `StructuredReturn` is a JavaScript object with the following properties:

```typescript
interface StructuredReturn {
  statusCode?: number;
  headers?: Record<string, string>;
  body?: ResponseBody;
}
```

If the function returns a `StructuredReturn` object, then the `statusCode` and `headers` properties are used to construct the HTTP response. If the `body` property is present, it is used as the response body. If the function returns `void` or `undefined`, then the response body is empty.

The `ResponseBody` is either a string, a JavaScript object, or a Buffer. JavaScript objects will be serialized as JSON. Buffers will be sent as binary data.

### CloudEvent Functions

CloudEvent functions are used in environments where the incoming HTTP request is a CloudEvent. The function signature is:

```typescript
interface CloudEventFunction {
  (context: Context, event: CloudEvent): CloudEventFunctionReturn;
}
```

Where the return type is defined as:

```typescript
type CloudEventFunctionReturn = Promise<CloudEvent> | CloudEvent | HTTPFunctionReturn;
```

The function return type can be anything that a simple HTTP function can return or a CloudEvent. Whatever is returned, it will be sent back to the caller as a response.

### Health Checks

The `Function` interface also allows for the addition of a `liveness` and `readiness` function. These functions are used to implement health checks for the function. The `liveness` function is called to check if the function is alive. The `readiness` function is called to check if the function is ready to accept requests. If either of these functions return a non-200 status code, then the function is considered unhealthy.

A health check function is defined as:

```typescript
/**
 * The HealthCheck interface describes a health check function,
 * including the optional path to which it should be bound.
 */
export interface HealthCheck {
  (request: Http2ServerRequest, reply: Http2ServerResponse): any;
  path?: string;
}
```

By default, the health checks are bound to the `/health/liveness` and `/health/readiness` paths. You can override this by setting the `path` property on the `HealthCheck` object, or by setting the `LIVENESS_URL` and `READINESS_URL` environment variables.

## CLI

The easiest way to get started is to use the CLI. You can call it
with the path to any JavaScript file which has a default export that
is a function, or that exports a `Function` type. For example,

```js
// index.js
function handle(context) {
  const event = context.cloudevent;
  // business logic
  return {
    statusCode: 200,
    statusMessage: 'OK'
  }
}

module.exports = handle;
```

You can expose this function as an HTTP endpoint at `localhost:8080`
with the CLI.

```console
npx faas-js-runtime ./index.js
```

## Debugging Locally

During local development, it is often necessary to set breakpoints in your code for debugging.  Since functions are just javascript files, using any current debugging(VS Code, Chrome Dev Tools) method will work. The linked blog post shows how to setup and use VS Code for development debugging.

https://developers.redhat.com/articles/2021/07/13/nodejs-serverless-functions-red-hat-openshift-part-2-debugging-locally

## Debugging Remotely

It is also possible to debug your function while it is running on a remote cluster.  The linked blog posts shows how to setup and use the Chrome Dev Tools inspector for debugging on a cluster.

https://developers.redhat.com/articles/2021/12/08/nodejs-serverless-functions-red-hat-openshift-part-3-debugging-cluster



### Functions as ES Modules

Functions can be written and imported as ES modules with either the `.mjs` file extension or by adding the `type` property to the functions package.json and setting it to `module`.

```js
// index.mjs
const handle = async function(context) => { ... };

// Export the function
export { handle };
```

If using the `type` property, the package.json might look something like this:
```js
{
  "name": "moduleName",
  "type": "module"
}
```



## Usage as a Module

In the current working directory, there is an `index.js` file like this.

```js
const { start } = require('faas-js-runtime');
const options = {
  // Pino is used as the logger implementation. Supported log levels are
  // documented at this link:
  // https://github.com/pinojs/pino/blob/master/docs/api.md#options
  logLevel: 'info'
}

// The function directory is in ./function-dir
start(require(`${__dirname}/function-dir/`), server => {
  // The server is now listening on localhost:8080
  // and the function defined in `function-dir/index.js`
  // will be invoked for each HTTP
  // request to this endpoint.
  console.log('Server listening');

  // Whenever you want to shutdown the framework
  server.close();
}, options);
```

In `./function-dir`, there is an `index.js` file that looks
like this.

```js
module.exports = async function myFunction(context) {
  const ret = 'This is a test for Node.js functions. Success.';
  return new Promise((resolve, reject) => {
    setTimeout(_ => {
      context.log.info('sending response to client')
      resolve(ret);
    }, 500);
  });
};
```

You can use `curl` to `POST` to the endpoint:
```console
$ curl -X POST -d 'hello=world' \
  -H'Content-type: application/x-www-form-urlencoded' http://localhost:8080
```

You can use `curl` to `POST` JSON data to the endpoint:
```console
$ curl -X POST -d '{"hello": "world"}' \
  -H'Content-type: application/json' \
  http://localhost:8080
```

You can use `curl` to `POST` an event to the endpoint:
```console
$ curl -X POST -d '{"hello": "world"}' \
  -H'Content-type: application/json' \
  -H'Ce-id: 1' \
  -H'Ce-source: cloud-event-example' \
  -H'Ce-type: dev.knative.example' \
  -H'Ce-specversion: 1.0' \
  http://localhost:8080
```

### Sample

You can see this in action by running `node bin/cli.js sample/index.js`.