Create a new Filter

A filter is an object that implements the relax.Filter interface, which consists of a Run() function that returns a relax.HandlerFunc closure.

Put simply:

// your filter object with as many options that your filter needs...
type MyFilter struct {
	SomeOption string
}
func (f *MyFilter) Run(next relax.HandlerFunc) relax.HandlerFunc {
	// initialize your filter
	if f.SomeOption == "" {
		f.SomeOption = "some value"
	}

	// delegate
	return func(ctx *relax.Context) {
		// do stuff before next filter...
		if someError() {
			// error found! stop the request.
			ctx.Error(400, "Aborted!")
			return
		}
		// continue to next filter
		next(ctx) // continue to next filter...

		// do stuff after previous filters...
	}
}

Even simpler:

type LogLevel int
func (level LogLevel) Run(next relax.HandlerFunc) relax.HandlerFunc {
  return func(ctx *relax.Context) {
    if level > LOG_ERROR {
      fmt.Printf("ERROR!")
      return
    }
    next(ctx)
  }
}