express-blueforest

Description

Simplify the usage of express.js http server, for API and JSON only. With express-validator lib + error management.

https://www.npmjs.com/package/express-blueforest

Start a server

This will start an http server with the desired configuration

import startExpress from "express-blueforest"

const ENV = {
    PORT: process.env.PORT || 80,
    
    //REST_PATH: the folder where controllers are to be found. Relative to app root.
    REST_PATH: process.env.REST_PATH || "rest",
    
    //MORGAN: optional, to override the morgan log format (https://github.com/expressjs/morgan)
    MORGAN: process.env.MORGAN,
}

const errorMapper = null //don't use any errorMapper for now, see bellow

export default startExpress(ENV, errorMapper)

Adding a REST service

With an empty REST_PATH folder, the server will serve nothing.

Let's add rest/postGameRest.js to add some behaviour

import {check} from 'express-validator/check'
import {objectNoEx} from "mongo-registry"
import {run} from "express-blueforest"
const router = Router()

//A controller pipeline. Validations steps followed by one or many "run" calls.
router.post("/api/game",
    check("_id").exists().isMongoId().withMessage("invalid mongo id").customSanitizer(objectNoEx),
    check("fragment").isIn(["impact", "roots", "facet"]),
    check("fragmentName").isLength({min: 1, max: 100}),
    run(onGameCreate)
)

//game is the object issued from the validation steps.
const onGameCreate = game => console.log("I create a game with fragment ", game.fragment)
//const onGameCreate = ({_id, fragment, fragmentName}) => console.log("I create a game with fragment ", fragment)
//const onGameCreate = ({_id, fragment, fragmentName}, req, res) => console.log("create game with request and response", req, res)

module.exports = router

Note: With multiple "run", the output of the previous is the input of the next.

router.get("/api/game",
    run(()=>"hello"),
    run(msg=>`${msg}` mister!),
    run(msg=>{key:msg})// return {key:'hello mister!'}
)

Handling errors

Errors management is in two parts:

business errors you throw in your business code:

You can throw errors with the structure you want:

const throwThe = (name, msg) => {
    const e = new Error(msg)
    e.name = name
    throw e
}
const onGameCreate = game => {
    [...]
    //Magical business error use case
    Math.random() < 1 && throwThe("SpecificError#495", "It seems Math.random never gives 1 or upper.")    
    [...]
}

errorMapper: how you decide to translate business error into http errors.

errorMapper is a function that must return an error object with the format: {status,body}

[...]
//*insert this extract in the first part "start a server"*
const errorMapper = err => {
    if(err.name === 'SpecificError#495'){
        return {status: 409, body:{errorCode: 495, msg:err.msg}}
    }else if(err.code === 15650){
        return {status: 409, body:{errorCode: 496, msg:"You reach code 15650"}}
    }
}
[...]

The http response will have the status and the body as defined by the error.

Note: If status is not provided, 500 is used.

Note: body is optionnal for an error, so the response will have empty body.