README.md

HTTP Problem Details Mapper

Based on http-problem-details (repository | npm), this library allows you to map your Node.js errors to HTTP Problem details by convention.

Installation

npm install http-problem-details-mapper

or

yarn add http-problem-details-mapper

Make sure to have the peer dependency http-problem-details installed as well.

Usage

Architecture

http-problem-details-mapper is part of a set of libraries you can use to create HTTP Problem Details documents (by means of http-problem-details (RFC 7807) and map Errors (or literally everything) into an HTTP Problem Document. http-problem-details-mapper can be used to build a mapping middleware or plugin for your HTTP library of choice. There's already a mapping middleware available for express: express-http-problem-details.

http-problem-details-mapper provides several classes you need to use:

• MapperRegistry which holds an arbitrary number of ErrorMapper instances you implement
• MappingStrategy which has a MapperRegistry containing the ErrorMapper instances
• The ErrorMapper itself maps an object (typically one of your Error types) to a ProblemDocument

Example

The typical workflow with http-problem-details-mapper is this:

First, you implement an Error

class NotFoundError extends Error {
  constructor (options) {
    const { type, id } = options
    super()
    Error.captureStackTrace(this, this.constructor)

    this.message = `${type} with id ${id} could not be found.`
  }
}

Next, you implement an ErrorMapper (in TypeScript you can use an IErrorMapper interface to implement a mapper from scratch):

import { ErrorMapper } from 'http-problem-details-mapper'
import { ProblemDocument } from 'http-problem-details'

class NotFoundErrorMapper extends ErrorMapper {
  constructor () {
    super(NotFoundError)
  }

  mapError (error) {
    return new ProblemDocument({
      status: 404,
      title: error.message,
      type: 'http://tempuri.org/NotFoundError'
    })
  }
}

Then, create the IMappingStrategy implementation:

class MyMappingStrategy {
  constructor (registry) {
    this.registry = registry
  }

  map (error) {
    const err = error
    const errorMapper = this.registry.getMapper(error)
    if (errorMapper) {
      return errorMapper.mapError(err)
    }
    
    // alternatively, return a generic problem document
    throw new Error('Could not map error')
  }
}

Finally, create an instance of MyMappingStrategy and map an registered error type.

import { MapperRegistry } from 'http-problem-details-mapper'

const strategy = new MyMappingStrategy(
    new MapperRegistry()
      .registerMapper(new NotFoundErrorMapper()))

const error = new NotFoundError({ type: 'customer', id: '123' })
const problem = strategy.map()

console.log(problem)

The result will be like this:

{
    "status": 404,
    "title": "customer with id 123 could not be found.",
    "type": "http://tempuri.org/NotFoundError"
}

MapperRegistry also by default has a mapper named DefaultErrorMapper which maps generic Error instances to HTTP status code 500 problem documents. MapperRegistry also has an option useDefaultErrorMapper of type boolean which allows you to disable the DefaultErrorMapper so you can register your own IErrorMapper for Error.

There's another mapper named StatusCodeErrorMapper which simply acts as a factory for ProblemDocuments where you only want to provide an HTTP error status code:

import { StatusCodeErrorMapper } from 'http-problem-details-mapper'

const problem = StatusCodeErrorMapper.mapStatusCode(400)

Similar to the DefaultErrorMapper there's also a DefaultMappingStrategy which you can use if you have no specific requirements regarding the mapping behavior.

It can be used like this:

import { MapperRegistry, DefaultMappingStrategy } from 'http-problem-details-mapper'

const strategy = new DefaultMappingStrategy(
    new MapperRegistry()
      .registerMapper(new NotFoundErrorMapper()))

const error = new NotFoundError({ type: 'customer', id: '123' })
const problem = strategy.map()

console.log(problem)

Running the tests

npm test

or

yarn test

Want to help?

This project is just getting off the ground and could use some help with cleaning things up and refactoring.

If you want to contribute - we'd love it! Just open an issue to work against so you get full credit for your fork. You can open the issue first so we can discuss and you can work your fork as we go along.

If you see a bug, please be so kind as to show how it's failing, and we'll do our best to get it fixed quickly.

Before sending a PR, please create an issue to introduce your idea and have a reference for your PR.

We're using conventional commits, so please use it for your commits as well.

Also please add tests and make sure to run npm run lint-ts or yarn lint-ts.

License

MIT License

Copyright (c) 2019 PDMLab

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.