nest-open-api-validator.js

import { Injectable, NestMiddleware } from '@nestjs/common';
import { Request, Response, NextFunction } from 'express';
import { OpenAPI } from 'openapi-types';
import axios from 'axios';
import { createValidatorMiddleware } from 'openapi-enforcer-middleware';

@Injectable()
export class OpenApiValidationMiddleware implements NestMiddleware {
  private specifications: OpenAPI.Document[] = [];

  constructor() {
    // Define the HTTP locations of the OpenAPI specifications
    const specLocations = [
      'http://example.com/api1/openapi.json',
      'http://example.com/api2/openapi.json',
      'http://example.com/api3/openapi.json',
    ];

    // Fetch and combine the specification files
    Promise.all(specLocations.map((location) => axios.get(location)))
      .then((responses) => {
        this.specifications = responses.map((response) => response.data);
      })
      .catch((error) => {
        console.error('Failed to fetch the OpenAPI specifications:', error);
      });
  }

  async use(req: Request, res: Response, next: NextFunction) {
    // Wait until the specifications are loaded
    while (this.specifications.length === 0) {
      await new Promise((resolve) => setTimeout(resolve, 100));
    }

    // Combine the specifications into one document
    const document: OpenAPI.Document = {
      openapi: '3.0.0',
      info: {
        title: 'Combined OpenAPI Specification',
        version: '1.0.0',
      },
      paths: {},
    };
    this.specifications.forEach((spec) => {
      if (spec.paths) {
        Object.assign(document.paths, spec.paths);
      }
    });

    // Create the validator middleware using the combined document
    const validatorMiddleware = createValidatorMiddleware(document);

    // Use the validator middleware
    validatorMiddleware(req, res, next);
  }
}