Creating a Middleware

In this section, you will learn how to create and apply a middleware.

Middleware Interface

The middleware interface is declared like this:

export default interface VCLightMiddleware {
    process(request: VCLightRequest, response: VCLightResponse, responseContent: VCLightResponse, app: VCLight): Promise<void>;

    post(request: VCLightRequest, response: VCLightResponse, responseContent: VCLightResponse, app: VCLight): Promise<void>;
}

This means that you need to have two functions in your middleware, process and post.

In process, you should include the request processing, and in post, you should include the processing after the request is processed. Note that the earlier the middleware is applied, the earlier the process function is called, and the later the post function is called.

Creating a Middleware Class

The middleware class needs to meet the VCLightMiddleware interface. VCLightRequest and VCLightResponse are VCLight's request and response classes.

export default interface VCLightMiddleware {
    process(request: VCLightRequest, response: VCLightResponse, responseContent: VCLightResponse, app: VCLightApp): Promise<void>;

    post(request: VCLightRequest, response: VCLightResponse, responseContent: VCLightResponse, app: VCLightApp): Promise<void>;
}

Now you can fill in the code in these two functions.

For example, if you want to display "Hello!" when accessing /hello/, you can do this:

class ExampleMiddleware implements VCLightMiddleware {
    async process(request: VCLightRequest, response: VCLightResponse, responseContent: Response, app: VCLightApp): Promise<void> {
        if(url.parse(<string>request.url).pathname == "/hello/") {
            responseContent.response = "Hello!";
        }
    }

    async post(request: VCLightRequest, response: VCLightResponse, app: VCLightApp): Promise<void> {
        // We don't need to do anything here for now
    }
}

Applying the Middleware

To apply the middleware, you need to create a middleware instance first:

const exampleMiddleware = new ExampleMiddleware();

Then, you can use it like this:

app.use(exampleMiddleware);

Now, the middleware will be applied to the app.