How to use middlewares when using julienschmidt/httprouter in goLang? - go

Question

What's the best way to chain middlewares while using julienschmidt/httprouter?
As far as I have googled, http.HandlerFunc accepts functions only in the form func (w ResponseWriter, r *Request) whereas httprouter.Handle functions are of the form func (w http.ResponseWriter, r *http.Request, ps httprouter.Params).
How to I chain middlewares without converting the httprouter.Handle function into http.HandlerFunc?
For example:
My routes.go is of the form,
router := httprouter.New()
router.POST("/api/user/create", middlewares.EscapeStringsMiddleware(User.CreateUser))
log.Fatal(http.ListenAndServe(":8000", router))
How do I write middleware functions for the above mentioned route?
Already tried methods:
1.
func EscapeStringsMiddleware(next http.Handler) httprouter.Handle {
return func (response http.ResponseWriter, request *http.Request, ps httprouter.Params) {
err := request.ParseForm()
if err != nil {
panic(err)
}
for key, values := range request.Form {
for i, value := range values {
value = template.HTMLEscapeString(value)
value = template.JSEscapeString(value)
request.Form[key][i] = value
}
}
next.ServeHTTP(response, request)
}
}
Error obtained:
cannot use User.CreateUser (type func(http.ResponseWriter, *http.Request, httprouter.Params)) as type http.Handler in argument to middlewares.EscapeStringsMiddleware:
func(http.ResponseWriter, *http.Request, httprouter.Params) does not implement http.Handler (missing ServeHTTP method)
2.
func EscapeStringsMiddleware(next httprouter.Handle) httprouter.Handle {
return func (response http.ResponseWriter, request *http.Request, ps httprouter.Params) {
err := request.ParseForm()
if err != nil {
panic(err)
}
for key, values := range request.Form {
for i, value := range values {
value = template.HTMLEscapeString(value)
value = template.JSEscapeString(value)
request.Form[key][i] = value
}
}
next.ServeHTTP(response, request)
}
}
Error obtained:
next.ServeHTTP undefined (type httprouter.Handle has no field or method ServeHTTP)
Also how do I chain multiple middleware?
For example,
router.POST("/api/user/create", middlewares.VerifyCSRF(middlewares.EscapeStringsMiddleware(User.CreateUser)))

Answer 1

This issue is not with your middleware handler. You are getting errs because User.CreateUser is not of type http.Handler.
Try this pattern :
The important bit is to return a http.Handler and wrap func(w http.ResponseWriter, r *http.Request) with http.HandlerFunc.
func Handler() http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// do stuff
})
}
go source :
// The HandlerFunc type is an adapter to allow the use of
// ordinary functions as HTTP handlers. If f is a function
// with the appropriate signature, HandlerFunc(f) is a
// Handler that calls f.
type HandlerFunc func(ResponseWriter, *Request)
// ServeHTTP calls f(w, r).
func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
f(w, r)
}
Based on your feedback:
httprouter.Handle does not implement ServeHTTP. It is called directly. For example : next(w, r, ps)
Below you will find examples of middleware handlers.
// Middleware without "github.com/julienschmidt/httprouter"
func StdToStdMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// do stuff
next.ServeHTTP(w, r)
})
}
// Middleware for a standard handler returning a "github.com/julienschmidt/httprouter" Handle
func StdToJulienMiddleware(next http.Handler) httprouter.Handle {
return func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
// do stuff
next.ServeHTTP(w, r)
}
}
// Pure "github.com/julienschmidt/httprouter" middleware
func JulienToJulienMiddleware(next httprouter.Handle) httprouter.Handle {
return func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
// do stuff
next(w, r, ps)
}
}
func JulienHandler() httprouter.Handle {
return func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
// do stuff
}
}
func StdHandler() http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// do stuff
})
}
func main() {
router := httprouter.New()
router.POST("/api/user/create", StdToJulienMiddleware(StdHandler()))
router.GET("/api/user/create", JulienToJulienMiddleware(JulienHandler()))
log.Fatal(http.ListenAndServe(":8000", router))
}

Answer 2

From https://github.com/cnvrtly/adaptr lib where adapters are also added to chain request middleware functions.
func compatibleHandler(h http.Handler, httprParamsCtxKey interface{}) httprouter.Handle {
return toHttpRouterHandle(h, httprParamsCtxKey)
}
func toHttpRouterHandle(h http.Handler, httprParamsCtxKey interface{}) func(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
return func(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
if httprParamsCtxKey != nil {
r = SetCtxValue(r, httprParamsCtxKey, p)
}
h.ServeHTTP(w, r)
}
}
If you are looking for example/idea how to define routes: https://github.com/cnvrtly/golang-appengine-seed