Azure Function - Core Module

This module provides a base set of core tooling support for Azure Functions for the NodeJS runtime.

• Azure Function - Core Module
  • Bindings
  • Models
    • Errors
  • Services
    • Loging Service
    • Axios HTTP Data Service
  • Utilities

Bindings

Several Azure Function Binding definitions and Data Services

• Service Bus
• Storage Queue
• Timer

Models

Errors

The error model definition is build using RFC 7807. Several error class definitions are provided in this module to provide developers with a starting point

When using in conjunction with the azureFunctionWrapper utility function, these error definitions can be used to return HTTP error responses

The following error definitions are included in this module

• 400 Bad Request
• 401 Unauthorized
• 403 Forbidden
• 415 Unsupported Media Type
• 500 Internal Server Error

And a custom DownstreamApiError class for handling and proxying errors returned from downstream api requests

An example usage:

const response = await azureFunctionWrapper(async () => {

  // Validate the semantics of the inbound http request

  if (!req.body || req.body === {}) {
    throw new BadRequestError('Missing request body');
  }

  if (!req.headers || !req.headers['Content-Type'] || req.headers['Content-Type'] !== 'application/json') {
    throw new UnsupportedMediaTypeError();
  }

  // ... Call service layer class to handle request business logic

  return apiResponse;
});

return response;

$ curl -X POST  http://localhost:7075/api/otp/_requestOtp -d'{}'
{
  "status": 400,
  "type": "https://httpstatuses.com/400",
  "title": "BAD REQUEST",
  "detail": "Missing request body"
}

Services

Loging Service

The LoggingService provides an inversion layer between the Azure Functions runtime context.log object, and support for other logging implementations.

A ConsoleLogger model is provided in this library for use with the LoggingService.

The Logging Service allows clients to provide a list of log aggregators (log aggregators must implement the Azure Function Logger interface)

An example usage:

const loggingService = new LoggingService(context.log, ConsoleLogger);

loggingService.verbose('Received HTTP Request Body', req.body);
loggingService.info('HTTP trigger function processed a request.');
loggingService.warn('Function Timer Trigger is running late');
loggingService.error('Fatal Error', err);

Axios HTTP Data Service

Axios is the chosen library for HTTP communications with downstream API services. The AxiosHttpDataService class implements the AbstractHttpDataService (which provides a base set of required functionality for developers to implement to make a compliant HTTP data Service.

See the AF App Insights HTTP Data Service for an App Insights enabled HTTP client

An example usage:

const http = new AxiosHttpDataService(Axios);
const response = await http.makeHttpGetCall('https://www.google.com');

Utilities

The azureFunctionWrapper provides a simple to use wrapper for any HTTP based Azure Function trigger. It safely returns a HTTP Response object model for a controller router and also safely handles exception error handling.

An example usage:

export class VersionController {

  constructor(
    private readonly versionService: IVersionService
  ) { }

  /**
   * GET api for /version
   * Returns the semantically tagged build number of the API
   * @param req The inbound HTTP Request
   */
  async getVersion(req: HttpRequest): Promise<IHttpResponse<IVersionMessage | IHttpErrorResponse>> {

    const response = await azureFunctionWrapper(async () => {
      
      // Code executed inside the azureFunctionWrapper can run safely
      // with error handling in place to catch errors thrown and represent them
      // as a HTTP Error Response

      const version = await this.versionService.getVersion();
      const apiResponse: IApiResponse<IVersionMessage> = {
        body: version,
        status: 200 // Success
      };

      return apiResponse;

    });

    return response;
  }

}