DefaultHandlers - Suvidha

Suvidha provides default handlers that manage the request/response lifecycle. These handlers support Http classes and plain Protocol objects for responses. You can customize the format of the response body using a formatter function.

The `Formatter` Function

The Formatter function is used to structure the final HTTP response body. It takes the status code, body, and metadata as arguments, and returns the formatted response body.

export type Formatter = (status: number, body: unknown, meta?: Meta) => any;

Suvidha provides a default formatter:

export const defaultFormatter: Formatter = (status, body, meta) => {
    const mapToStatus = (statusCode: number) => {
        if (statusCode >= 400 && statusCode < 500) {
            // Client error
            return "fail";
        } else if (statusCode >= 500) {
            // Server error
            return "error";
        } else {
            return "success";
        }
    };

    return {
        status: mapToStatus(status),
        data: body,
        meta,
    } satisfies ResonseFormat;
};

The default formatter creates a { status, data, meta } object that maps HTTP status codes.

HTTP Status Code Range	`status` Field Value	Description
1xx, 2xx, 3xx	`"success"`	Successful requests or informational responses.
4xx	`"fail"`	Client-side errors.
5xx	`"error"`	Server-side errors.

You can specify a custom formatter when creating DefaultHandlers:

const myFormatter: Formatter = (status, body, meta) => {
    const isDev = process.env["NODE_ENV"] === "development";
    // This will be 'body' of the response
    return {
        data: body,
        debug: isDev ? meta : undefined,
    };
};

const handlers = new DefaultHandlers(myFormatter);

`DefaultHandlers` Class

The DefaultHandlers class implements the Handlers interface and provides default implementations for handling errors, schema errors, successful responses, and post-response actions. It sets the Content-Type to application/json by default.

export class DefaultHandlers implements Handlers {
    constructor(private readonly fmt: Formatter = defaultFormatter) {}

    static create(fmt?: Formatter) {
        return new DefaultHandlers(fmt);
    }

    private setHeaders(conn: Conn, headers: Record<string, string>): void {
        headers = {
            "Content-Type": "application/json",
            ...headers,
        };

        for (const [key, value] of Object.entries(headers)) {
            conn.res.setHeader(key, value);
        }
    }

    onErr(err: unknown, conn: Conn): Promise<void> | void {
        if (err instanceof Http.End) {
            const statusCode = err.getStatus();
            this.setHeaders(conn, err.getHeaders());

            return void conn.res
                .status(statusCode)
                .send(this.fmt(statusCode, err.getBody(), err.getMeta()));
        }

        const statusCode = StatusCodes.INTERNAL_SERVER_ERROR;
        conn.res
            .status(statusCode)
            .send(this.fmt(statusCode, "Internal Server Error", {}));
    }

    onSchemaErr(
        _err: ZodError,
        _conn: Conn,
        _next: NextFunction,
    ): Promise<void> | void {
        throw Http.BadRequest.body(
            "Data provided does not meet the required format.",
        );
    }

    onComplete(output: unknown, conn: Conn): Promise<void> | void {
        if (isProtocol(output) && !(output instanceof Http.End)) {
            output = new Http.End(output);
        }

        if (output instanceof Http.End) {
            const statusCode = output.getStatus();
            this.setHeaders(conn, output.getHeaders());

            return void conn.res
                .status(statusCode)
                .send(this.fmt(statusCode, output.getBody(), output.getMeta()));
        }

        switch (typeof output) {
            case "string":
            case "number":
            case "boolean":
            case "undefined":
            case "object": {
                return void conn.res
                    .status(StatusCodes.OK)
                    .send(this.fmt(StatusCodes.OK, output ?? null, {}));
            }
            default: {
                console.error({
                    cause: output,
                    description: `Suvidha: Can't proccess values of type ${typeof output}.`,
                });
                throw new Http.InternalServerError();
            }
        }
    }

    onPostResponse(data: unknown, _: Conn): Promise<void> | void {
        console.warn(
            `Suvidha(onPostResponse): ${util.inspect(data, { depth: 10 })}`,
        );
    }
}

`onErr(err: unknown, conn: Conn)`

Handles errors.

If err is an Http.End instance, it sends the response with the specified status code, headers, and body (formatted by the formatter).
Otherwise, it sends a 500 Internal Server Error response with a default message.

onErr(err: unknown, conn: Conn): Promise<void> | void {
    if (err instanceof Http.End) { // Http Error
        // ... (send formatted response based on err)
    } else { // Generic Error
        // ... (send 500 Internal Server Error)
    }
}

`onSchemaErr(err: ZodError, conn: Conn, next: NextFunction)`

Handles schema validation errors using Zod. It always throws an Http.BadRequest error with a default message.

onSchemaErr(err: ZodError, conn: Conn, next: NextFunction): Promise<void> | void {
    throw Http.BadRequest.body("Data provided does not meet the required format.");
}

`onComplete(output: unknown, conn: Conn)`

Handles successful responses.

If output is a Protocol object (but not an Http.End instance), it’s wrapped in an Http.End object.
If output is an Http.End instance, it sends the response with the specified status code, headers, and body (formatted by the formatter).
If output is a primitive type (string, number, boolean, undefined(converted to null), object, or null), it sends a 200 OK response with the output as the body (formatted by the formatter).
Otherwise, it logs an error and throws a Http.InternalServerError exception.

onComplete(output: unknown, conn: Conn): Promise<void> | void {
    // ... (logic to handle different output types and send the response)
}

`onPostResponse(data: unknown, conn: Conn)`

Called after a response has been sent (headers already sent). It is primarily used for logging or cleanup. The default implementation logs the response data.

onPostResponse(data: unknown, conn: Conn): Promise<void> | void {
    console.warn(`Suvidha(onPostResponse): ${util.inspect(data, { depth: 10 })}`);
}