SOMOD WebSocket Extension

The SOMOD Extension Configure WebSocket routes and validate incoming WebSocket Messages in Serverless Functions.

The middlware in this extension works with Functions of type WebSocket Only.

Install

Install as an npm package in somod modules

npm install somod-websocket-extension

Usage

Attach the middleware to the Serverless Function

Resources:
  MyWebSocketMessageHandler:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri:
        SOMOD::Function:
          # ...
          middlewares:
            - module: somod-websocket-extension
              resource: SomodWebSocketMiddleware
      # ...

Refer to SOMOD's Middleware reference for more information

Configure Routes and Schemas

Routes configuration for each serverless function can be provided using a yaml file at serverless/functions/<function_name>.websocket.yaml.

Example:

# serverless/functions/chat.websocket.yaml

$default:
  body:
    parser: json
    schema:
      type: object
      required: [name]
      properties:
        name:
          type: string
          maxLength: 32
        email:
          type: string
          format: email

Access Sanitized Message

The sanitized Message can be accessed using the middleware's context using the somod-websocket-message key.

Example:

// serverless/functions/chat.ts

const ChatHandler = event => {
  const message = event.somodMiddlewareContext.get("somod-websocket-message");
  // use message to read the data from the incoming websocket message
};

export default ChatHandler;

This module also provides a utility library to create Serverless Functions with multiple routes easily. Refer to RouteBuilder for more details

Specification

Structure of Routes configuration file

In general, routes configuration in <function_name>.websocket.yaml file follows the below structure

<routeKey>:
  body:
    parser?: <"text"|"json"|"formdata">. If not provided, automatically choosen based on the Content-Type Header (text is considered if automatic detection fails)
    schema: <json schema>

The complete JSONSchema is available here

Type of the Message object

The message object accessed using event.somodMiddlewareContext.get("somod-websocket-message") has this type.

type Message<T = unknown> = {
  routeKey: string;
  body: T;
};

The Message Type is available from this module to use (import as shown below)

import { Message } from "somod-websocket-extension";

Error Handling

The middleware immediates ends the Lambda execution and returns appropriate message when Validation fails

RouteBuilder

The RouteBuilder is a wrapper javascript utility library to create serverless functions with multiple routes.

Using the RouteBuilder

// serverless/function/user.ts
import { RouteBuilder } from "somod-websocket-extension";

const builder = new RouteBuilder();

builder.add("$default", defaultMessageHandler);

export default builder.getHandler();

RouteBuilder Specification

RouteBuilder has 2 methods

• add

  function add(
    routeKey: string,
    handler: (message: Message, event: RawEvent) => Promise<Response>
  ): void {
    //
  }

  The handler receives the sanitized message object and the raw event from AWS. The handler has to return a promise which resolves to the Response object.

  The Raw Event type and Response type is documented here in the AWS specification.

• getHandler

  function getHandler(): (event: RawEvent) => Promise<Response> {
    //
  }

  handle function returns the function which is a lambda function handler

Issues

The project issues, features, and milestones are maintained in this GitHub repo.

Create issues or feature requests at https://github.com/somod-dev/somod-websocket-extension/issues

Contributions

Please read our CONTRIBUTING guide before contributing to this project.