Writing delightful middlewares in Go

array_usage_example.go

// Chain or middleware to be invoked in order of their index
middlewareChain := MiddlewareChain{
  NewRequestIdInterceptor(),
  NewElapsedTimeInterceptor(),
}

// Invoke all middlewares ending up with HomeRouter
mux.Path("/home").Handler(middlewareChain.Handler(HomeRouter))

LICENSE

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.

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 middleware

import "net/http"

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

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


// Intercept returns back a continuation that will call install middleware to intercept
// the continuation call.
func (cont MiddlewareHandlerFunc) Intercept(mw MiddlewareInterceptor) MiddlewareHandlerFunc {
	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 MiddlewareChain []MiddlewareInterceptor

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

	return http.HandlerFunc(curr)
}

middleware_example.go

func NewElapsedTimeInterceptor() MiddlewareInterceptor {
    return func(w http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
        startTime := time.Now()
        defer func() {
            endTime := time.Now()
            elapsed := endTime.Sub(startTime)
            // Log the consumed time
        }()

        next(w, r)
    }
}

func NewRequestIdInterceptor() MiddlewareInterceptor {
    return func(w http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
        if r.Headers.Get("X-Request-Id") == "" {
            r.Headers.Set("X-Request-Id", generateRequestId())
        }

        next(w, r)
    }
}

usage_example.go

func HomeRouter(w http.ResponseWriter, r *http.Request) {
		// Handle your request
}

// ...
// Some where when installing Hanlder
chain := MiddlewareHandlerFunc(HomeRouter).
  Intercept(NewElapsedTimeInterceptor()).
  Intercept(NewRequestIdInterceptor())

// Install it like regular HttpHandler
mux.Path("/home").HandlerFunc(http.HandlerFunc(chain))