@loopback/health/src/controllers/health.controller.ts

An extension exposes health check related endpoints with LoopBack 4

// Copyright IBM Corp. and LoopBack contributors 2019. All Rights Reserved.
// Node module: @loopback/health
// This file is licensed under the MIT License.
// License text available at https://opensource.org/licenses/MIT

import {HealthChecker, HealthStatus, State} from '@cloudnative/health';
import {BindingScope, Constructor, inject, injectable} from '@loopback/core';
import {
  get,
  OperationObject,
  Response,
  ResponseObject,
  RestBindings,
  SchemaObject,
} from '@loopback/rest';
import {HealthBindings} from '../keys';
import {DEFAULT_HEALTH_OPTIONS, HealthOptions} from '../types';

function getHealthResponseObject() {
  /**
   * OpenAPI definition of health response schema
   */
  const HEALTH_RESPONSE_SCHEMA: SchemaObject = {
    type: 'object',
    properties: {
      status: {type: 'string'},
      checks: {
        type: 'array',
        items: {
          type: 'object',
          properties: {
            name: {type: 'string'},
            state: {type: 'string'},
            data: {
              type: 'object',
              properties: {
                reason: {type: 'string'},
              },
            },
          },
        },
      },
    },
  };

  /**
   * OpenAPI definition of health response
   */
  const HEALTH_RESPONSE: ResponseObject = {
    description: 'Health Response',
    content: {
      'application/json': {
        schema: HEALTH_RESPONSE_SCHEMA,
      },
    },
  };

  return HEALTH_RESPONSE;
}

/**
 * OpenAPI spec for health endpoints
 */
const HEALTH_SPEC: OperationObject = {
  // response object needs to be cloned because the oas-validator throws an
  // error if the same object is referenced twice
  responses: {
    '200': getHealthResponseObject(),
    '500': getHealthResponseObject(),
    '503': getHealthResponseObject(),
  },
};

/**
 * OpenAPI spec to hide endpoints
 */
const HIDDEN_SPEC: OperationObject = {
  responses: {},
  'x-visibility': 'undocumented',
};

/**
 * A factory function to create a controller class for health endpoints. This
 * makes it possible to customize decorations such as `@get` with a dynamic
 * path value not known at compile time.
 *
 * @param options - Options for health endpoints
 */
export function createHealthController(
  options: HealthOptions = DEFAULT_HEALTH_OPTIONS,
): Constructor<unknown> {
  const spec = options.openApiSpec ? HEALTH_SPEC : HIDDEN_SPEC;

  /**
   * Controller for health endpoints
   */
  @injectable({scope: BindingScope.SINGLETON})
  class HealthController {
    constructor(
      @inject(HealthBindings.HEALTH_CHECKER)
      private healthChecker: HealthChecker,
    ) {}

    @get(options.healthPath, spec)
    async health(@inject(RestBindings.Http.RESPONSE) response: Response) {
      const status = await this.healthChecker.getStatus();
      return handleStatus(response, status);
    }

    @get(options.readyPath, spec)
    async ready(@inject(RestBindings.Http.RESPONSE) response: Response) {
      const status = await this.healthChecker.getReadinessStatus();
      return handleStatus(response, status, 503);
    }

    @get(options.livePath, spec)
    async live(@inject(RestBindings.Http.RESPONSE) response: Response) {
      const status = await this.healthChecker.getLivenessStatus();
      return handleStatus(response, status, 500);
    }
  }

  return HealthController;
}

/**
 * Create response for the given status
 * @param response - Http response
 * @param status - Health status
 * @param failingCode - Status code for `DOWN`
 */
function handleStatus(
  response: Response,
  status: HealthStatus,
  failingCode: 500 | 503 = 503,
) {
  let statusCode = 200;
  switch (status.status) {
    case State.STARTING:
      statusCode = 503;
      break;
    case State.UP:
      statusCode = 200;
      break;
    case State.DOWN:
      statusCode = failingCode;
      break;
    case State.STOPPING:
      statusCode = 503;
      break;
    case State.STOPPED:
      statusCode = 503;
      break;
  }
  response.status(statusCode).send(status);
  return response;
}