README

x-middleware-composite

Build Status](https://travis-ci.org/x-component/x-middleware-composite)

./composite.js

./composite.js

global_log

global_log

Concate middleware to function and handle errors

Composition

call composite(...) with a list of middlewares(req,res,next){..} or an array to compose them into a single composite middleware.

you cann add labels into the list by using a object with a single property:

  '''
  var pipeline=composite([,,,{ name: middleware },,,]);
  '''

The order is significant.

Nesting

Multiple composite pipelines can be nested: p.e. composite([,,,{ name : composite([...]) },,]), as each composite is just a normal middleware. It is also allowed to use an array directly: composite([,,,{ name : [...] },,,,]),

Injection

One can inject middlewares in an existing pipeline at the position 'name', before or after the current middleware at that position:

  '''
  pipeline.after(name:extra_middleware);
  '''

The modified pipeline then has a { name: [middleware,extra_middleware] } element.

To allow a more felixble namin / injection on can also access nested composites using before by passing as name in before /after a JSON selector:

Example:

  '''
  var pipeline=composite([,,,{ transform: [,,,{ dom: middlewares },,,] },,,,]);

  pipeline.after('.transform .dom':extra_middleware); // inserts it at the nested position
  '''

Design Rationale:

Often pipelines and request handlers can be reused. One can define generic functions seting up a url request handler with a default pipeline. or just returning a default pipeline. The caller then modifiy the returned pipeline by injection. For example to add some extra handling for a specific application/url without creating a complete copy of the generic pipeline.

Alternatives would have been:

offer functions which return just building blocks of pipelines and and some function delivering some predefined ones

 positive: no declerative magic involded. Using code explicitly requests building blocks and composes them.
 negative: lots of array composition logic, lots of functions for each eventual possibility.
 This approach is still usable and usefull.

event hooks

 one could mix middlewares with events, and prove hooks forcertain phases within the pipeline.
 For events how ever the order is conceptionally not defined and it results in a mixing of event concepts and middleware concepts.

Usage no npm install needed!