header-constraint-strategy

a find-my-way header constraint

Usage no npm install needed!

<script type="module">
  import headerConstraintStrategy from 'https://cdn.skypack.dev/header-constraint-strategy';
</script>

README

header-constraint-strategy

JavaScript Style Guide Build Status

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 200 - appOption
9 bar 123 ABC 200 - mustBeIn and appOption
10 bar ops ABC 200 - appOption

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. Only the appOption constraint is matched
  9. When there are multiple matches (the route with foo and route with mustBeIn and appOption), the route with more fulfilled constraint wins!
  10. In case of draws (the route with foo and the route with appOption are metching) wins the last route configured! So in this example, if you move the foo route ad the end of the file, the output will change!

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

License

Copyright Manuel Spigolon, Licensed under MIT.