index.js

const joi = require('joi')

/**
 * Helper function to validate an object against the provided schema,
 * and to throw a custom error if object is not valid.
 *
 * @param {Object} object The object to be validated.
 * @param {String} label The label to use in the error message.
 * @param {JoiSchema} schema The Joi schema to validate the object against.
 */
function validateObject (object = {}, label, schema, options) {
  // Skip validation if no schema is provided
  if (schema) {
    // Validate the object against the provided schema
    const { error, value } = joi.validate(object, schema, options)
    if (error) {
      // Throw error with custom message if validation failed
      throw new Error(`Invalid ${label} - ${error.message}`)
    }
  }
}

/**
 * Generate a Koa middleware function to validate a request using
 * the provided validation objects.
 *
 * @param {Object} validationObj
 * @param {Object} validationObj.headers The request headers schema
 * @param {Object} validationObj.params The request params schema
 * @param {Object} validationObj.query The request query schema
 * @param {Object} validationObj.body The request body schema
 * @returns A validation middleware function.
 */
function validate (validationObj) {
  // Return a Koa middleware function
  return (ctx, next) => {
    try {
      // Validate each request data object in the Koa context object
      validateObject(ctx.headers, 'Headers', validationObj.headers, { allowUnknown: true })
      validateObject(ctx.params, 'URL Parameters', validationObj.params)
      validateObject(ctx.query, 'URL Query', validationObj.query)

      if (ctx.request.body) {
        validateObject(ctx.request.body, 'Request Body', validationObj.body)
      }

      return next()
    } catch (err) {
      // If any of the objects fails validation, send an HTTP 400 response.
      ctx.throw(400, err.message)
    }
  }
}

module.exports = validate