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Develop Core Plugins in JavaScript

Introduction

Services and Interceptors can be developed in JavaScript and TypeScript when running RESTHeart with the GraalVM or using RESTHeart native.

Tip
 See example JS plugins
Note
 The default RESTHeart native binaries, can only be extended with JavaScript plugins. With Java plugins, you need to build RESTHeart and the plugins with the native-image tool. See Build RESTHeart with custom plugins as native-image

RESTHeart Concurrency Model

RESTHeart is a multi-threaded application and it handles each request in a dedicated thread. This makes all code running in a request thread safe, and this also applies to JavaScript services and interceptors.

This is different than usual JavaScript concurrency model, where all code is usually executed in a single thread and requires asynchronous programming, with callbacks, promises, observable, etc.

In RESTHeart, you can write simple JavaScript code that also includes blocking calls, without incurring in performance problems.

Service

The JavaScript code that defines a Service must export the object options and the function handle(req, res).

The resulting service will be a special instance of StringService, that delegates the handling logic to the JavaScript code. For this reason, the request and response bodies are treated as strings.

export const options = {
    name: "helloWorldService",
    description: "just another Hello World",
    uri: "/hello"
}

export function handle(req, res) {
    res.setContent(`{ "msg": `Hello ${rc.name || 'World'}` } `);
    res.setContentTypeAsJson();
}

The object options

The options object must contain the following properties:

param description mandatory default value

name

the name of the service

yes

none

description

description of the service

yes

none

uri

the uri of the service

yes

none

secured

true to require successful authentication and authorization to be invoked;

no

false

matchPolicy

PREFIX to match request paths starting with /<uri>,EXACT to only match the request path /<uri>

no

PREFIX

modulesReplacements

experimental support for module replacements. See Node.js core modules mockups on Using JavaScript Modules and Packages in GraalVM JavaScript for modules. Example buffer:my-buffer-implementation

no

"" (empty)

The function handle(req, res)

The handle functions accepts two parameters: the request and the response. These are Java objects of StringRequest and StringResponse respectively.

Interceptor

The JavaScript code that defines an Interceptor export the object options and the functions handle(req, res) and resolve(req).

export const options = {
    name: "helloWorldInterceptor",
    description: "modifies the response of helloWorldService",
    interceptPoint: "RESPONSE"
}

export function handle(request, response) {
    const rc = JSON.parse(response.getContent() || '{}');

    let modifiedBody = {
        msg: rc.msg + ' from Italy with Love';
    }

    response.setContent(JSON.stringify(modifiedBody));
    response.setContentTypeAsJson();
}

export function resolve(request) {
    return request.isHandledBy("helloWorldService");
}

The object options

The options object must contain the following properties:

param description mandatory default value

name

the name of the interceptor

yes

none

description

description of the interceptor

yes

none

interceptPoint

the intercept point: REQUEST_BEFORE_AUTH, REQUEST_AFTER_AUTH, RESPONSE, RESPONSE_ASYNC

no

REQUEST_AFTER_AUTH

pluginClass

the class of the interceptor that must match the service to intercept (e.g. MongoInterceptor can intercept a request handled by the MongoService), StringInterceptor, BsonInterceptor, ByteArrayProxyInterceptor, CsvInterceptor, JsonInterceptor, MongoInterceptor

no

StringInterceptor

modulesReplacements

experimental support for module replacements. See Node.js core modules mockups on Using JavaScript Modules and Packages in GraalVM JavaScript for modules. Example buffer:my-buffer-implementation

no

"" (empty)

The function resolve(req)

The function resolve() accepts one parameter req, a Java object of the concrete subclass of Request defined by the parameter pluginClass, e.g. with pluginClass: "StringInterceptor", the request class is StringRequest.

An interceptor of a given class, can intercept requests handled by all services with matching types, e.g. MongoInterceptor can intercept requests handled by the MongoService.

When resolve() returns true the interceptor will be actually invoked, i.e. this function allows to select the requests to intercept.

The function handle(req, res)

The handle() functions accepts two parameters: the request and the response. These a Java objects of the concrete subclasses of Request and Response respectively. For the default pluginClass: "StringInterceptor", these are StringRequest and StringResponse respectively.

Packaging

The plugins js files must be placed in a folder with a package.json file.

Note
 a single plugin folder can contain multiple Services and Interceptors.

The package.json muse declare the services in the rh:services array and interceptors in the rh:interceptors array.

{
  "name": "restheart-js-foo",
  "version": "1.0.0",
  "description": "test js plugins for RESTHeart",
  "rh:services": [ "foo.js" ],
  "rh:interceptors": [ "foo-interceptor.js" ]
}

Modules

The plugins can use npm modules via require statements. See require-module-service.mjs for an example.

Important
 The imported modules cannot use functionalities that are available in Node.js’ built-in modules (e.g., 'fs' and 'buffer', etc.).

For instance, you cannot use the module http, and there is no pure JS implementation available. In this case, you can rely on Java/Javascript interoperability and use the standard Java libraries and all the libraries that are available in RESTHeart.

See GraalVM Modules for more details.

Deploy

To the JavaScript plugin, just copy the folder containing the scripts and the file package.json into the plugins directory of RESTHeart.

Note
 JS plugins can be added or updated without requiring to restart the server, ie RESTHeart supports JS plugins hot deployment.

If you modify the code, you can force RESTHeart to update it by touching the plugin folder.

$ touch plugins/my-plugin

Configuration parameters

It is possible to pass configuration parameters to a plugin by defining them in the RESTHeart’s configuration file using the plugin’s name:

foo: # <-- name of the plugin
    arg: value

The arguments are available in the pluginArgs object.

const arg = pluginArgs.arg

Java/JavaScript interoperability

GraalVM allows to execute JavaScript code from RESTHeart and allows interoperability with Java code.

This means that all the Java classes shipped with RESTHeart can be used in JavaScript code.

For example, see the http-client.mjs plugins, which uses java.net.http.HttpClient to execute an HTTP request.

MongoDB driver

The MongoDb Java driver, configured by RESTHeart configuration file and already connected to MongoDB, is available in the JavaScript code as mclient.

See mclient-service.mjs for an example of how to use it.

Logging

The RESTHeart Java logger can be used from JavaScript code.

LOGGER.debug("pluginArgs {}", pluginArgs);

Pay attention to logging null values. With:

var foo = null;
LOGGER.debug("this is null {}", foo);

An error will be raised.

org.graalvm.polyglot.PolyglotException: TypeError: invokeMember (debug) on ch.qos.logback.classic.Logger@697713cb failed due to: Multiple applicable overloads found for method name debug...

To avoid it, use the following code:

var foo = null;
LOGGER.debug("this is null {}", foo ? foo : "null");