middleware.go

/*
Copyright (c) 2019 DoorDash

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/
package middlewares

import "net/http"

// Interceptor intercepts an HTTP handler invocation, it is passed both response writer and request
// which after interception can be passed onto the handler function.
type Interceptor func(http.ResponseWriter, *http.Request, http.HandlerFunc)

// HandlerFunc builds on top of http.HandlerFunc, and exposes API to intercept with MiddlewareInterceptor.
// This allows building complex long chains without complicated struct manipulation
type HandlerFunc http.HandlerFunc


// Intercept returns back a continuation that will call install middleware to intercept
// the continuation call.
func (cont HandlerFunc) Intercept(mw Interceptor) HandlerFunc {
	return func(writer http.ResponseWriter, request *http.Request) {
		mw(writer, request, http.HandlerFunc(cont))
	}
}

// MiddlewareChain is a collection of interceptors that will be invoked in there index order
type Chain []Interceptor

// Handler allows hooking multiple middlewares in single call.
func (chain Chain) Handler(handler http.HandlerFunc) http.Handler {
	curr := HandlerFunc(handler)
	for i := len(chain) - 1; i >= 0; i-- {
		mw := chain[i]
		curr = curr.Intercept(mw)
	}
	return http.HandlerFunc(curr)
}