I am developing logging middleware, and want to log response body in 500 responses. In middleware im setting a callback for “finish” event on request, that emits after the response was sent, but no response body in Response object is present.

I assume there is no body because nest js with express under the hood sends response by chanks, and does not saves it in Request or Response objects.

But I hope there is a workaround to get response body from Response object in middleware that someone found. The example of middleware class im working on:

@Injectable()
export class LoggerMiddleware implements NestMiddleware {
  use(request: Request, response: Response, next: NextFunction): void {
    const { ip, method, originalUrl } = request;
    const userAgent = request.get("user-agent") || "";

    response.on("finish", () => {
      const { statusCode } = response;
      const contentLength = response.get("content-length");

      const basicRequestMetaInfo = {
        method,
        originalUrl,
        statusCode,
        ... // other data
      };

      if (this.isErroneousStatusCode(statusCode)) {
        const additionalRequestMetaInfo = {
          body: response.body, // The place i want to reach Response body
        };

        this.winstonLoggerErrorLevel.error({
          ...basicRequestMetaInfo,
          ...additionalRequestMetaInfo,
        });
        return;
      }
      this.winstonLoggerInfoLevel.info(basicRequestMetaInfo);
    });
    next();
  }
}