header-constraint-strategy

A general purpose find-my-way custom constraint strategy.

Tested for Fastify ✅!

This module let you to drive the incoming HTTP request into a route based on the header's strict content. Doing so, if a request has a specific string header, it can reach a route hide behind a constraint. Go to the Usage section to get a complete overview of this feature!

Install

npm install header-constraint-strategy

Usage with Fastify

Here all the constraint types you can define with this module!
This setup shows you all the settings header-constraint-strategy provides to you.

const headerConstraintStrategy = require('header-constraint-strategy')
const Fastify = require('fastify')

// STEP 1: setup the constraints into your fastify instance
const app = Fastify({
  constraints: {
    // basic usage
    foo: headerConstraintStrategy('foo'),
    // strict usage
    mustBeIn: headerConstraintStrategy({ header: 'mustBeIn', mustMatchWhenDerived: true }),
    // custom header usage
    appOption: headerConstraintStrategy({ name: 'appOption', header: 'x-my-app' })
  }
})

// STEP 2: use the constraint where you need them
app.get('/', {
  handler: reply('no constraint')
})

app.get('/', {
  handler: reply('foo'),
  constraints: {
    foo: 'bar'
  }
})

app.get('/', {
  handler: reply('mustBeIn'),
  constraints: {
    mustBeIn: '123'
  }
})

app.get('/', {
  handler: reply('appOption'),
  constraints: {
    appOption: 'ABC'
  }
})

app.get('/', {
  handler: reply('mustBeIn and appOption'),
  constraints: {
    mustBeIn: '123',
    appOption: 'ABC'
  }
})

app.listen(80)

The routes can be reached via an HTTP request with these headers.

#	foo header	mustBeIn header	x-my-app header	response
1	-	-	-	200 - no constraint
2	bar	-	-	200 - foo
3	hello	-	-	200 - no constraint
4	-	123	-	200 - mustBeIn
5	-	456	-	404
6	-	-	ABC	200 - appOption
7	-	123	ABC	200 - mustBeIn and appOption
8	-	ops	ABC	404
9	bar	123	ABC	200 - mustBeIn and appOption
10	bar	ops	ABC	404

Cases explanation

1. When the is not headers that meets the constraint, the route without constraint will be used if set. Otherwise 404
2. The foo constraint is matched
3. The foo constraint is not matched so the route without constraint is used
4. The mustBeIn constraint is matched
5. Like the 4), but this time the route without constraint is no used because of the flag mustMatchWhenDerived: true
6. The appOption constraint is matched
7. Multiple constraint matches
8. Regardless the appOption constraint is matched, the mustBeIn constraint with mustMatchWhenDerived=true forces the handler to be used
9. When there are multiple matches (the route with foo and route with mustBeIn and appOption), the route with more fulfilled constraint wins!
10. As the 8), the mustBeIn constraint is not fulfilled

Options

You can pass the following options during the registration:

Option	Default	Description
name	as the header if not set	The name of the JSON property that you will set in the route's constraints option
header	as the name if not set	The HTTP header where read the input to match the constraint
mustMatchWhenDerived	false	Define if the same route without constraint must be evaluated for the routing. You can translate it as: is this constraint mandatory?

License

Copyright Manuel Spigolon, Licensed under MIT.