Gist to accompany my blogpost https://darahayes.com/document-your-hapi-application-swagger

hapi-swagger-example.js

const Hapi = require('hapi')
const Joi = require('joi')
const Boom = require('boom')

const server = new Hapi.Server()
server.connection({ host: 'localhost', port: 8000 })

server.register(
  [
    {
      register: require('inert')
    },
    {
      register: require('vision')
    },
    {
      register: require('hapi-swagger'),
      options: {
        info: { // metadata rendered in the Swagger UI
          title: 'Math API',
          description: 'The Math API lets you perform basic arithmetic operations over HTTP',
          version: '1.0.0'
        }
      }
    }
  ]
)

// Our Math Functions
const operations = {
  'add': (a, b) => {
    return a + b
  },
  'subtract': (a, b) => {
    return a - b
  },
  'multiply': (a, b) => {
    return a * b
  },
  'divide': (a, b) => {
    if (b === 0) return Boom.badRequest('cannot divide by 0')
    return a / b
  }
}

// The /math endpoint's response schema
// This is rendered as an example response in the Swagger UI
const mathResponse = Joi.object({
  values: {
    a: Joi.number(),
    b: Joi.number()
  },
  operation: Joi.string().valid(Object.keys(operations)).required(),
  result: Joi.number()
})

server.route({
  method: 'GET',
  path:'/math', 
  handler: (request, reply) => {
    let {a, b, op} = request.query
    let operation = operations[op]
    return reply({
      values: {
        'a': a,
        'b': b
      },
      operation: op,
      result: operation(a, b)
    })
  },
  config: {
    validate: {
      query: {
        a: Joi.number().required(),
        b: Joi.number().required(),
        op: Joi.string().valid(Object.keys(operations)).required()
      }
    },
    tags: ['api'],
    description: 'Takes in two numbers (a,b) and performs the desired operation on them',
    response: {schema: mathResponse}
  }
})

server.start((err) => {
  if (err) throw err
  console.log('Server running at:', server.info.uri)
})