Sharing a gorilla/mux router across packages

Question

I'm having some issues with implementing a slight MVC design with gorilla/mux.

The layout of the modules is as follows:

main.go
-- controllers
---- base.controller.go
---- example.controller.go
-- models
---- base.model.go
---- example.controller.go

All the files in controllers is in the controllers package, same with models and then the main.go is the main package.

Currently I'm just trying to get the Base Controller to be able to be shared with the main package which is working, although it's throwing some errors when trying to implement routes. The build is not throwing any errors, but the routes are not available. If I implement the Walk function in the Gorilla/Mux documentation to print out all the registered routes for the mux.Router then it gives me this error:

&{%!!(MISSING)s(*mux.Router=&{ [0xc4200901b0] map[] true false false false}) %!!(MISSING)s(http.HandlerFunc=0xc8df0) [%!!(MISSING)s(*mux.routeRegexp=&{/ false false true false 0xc420095360 / [] []})] %!!(MISSING)s(*mux.routeRegexpGroup=&{ 0xc420016240 []}) %!!(MISSING)s(bool=true) %!!(MISSING)s(bool=false) %!!(MISSING)s(bool=false) %!!(MISSING)s(bool=false) %!!(MISSING)s(mux.BuildVarsFunc=)}

The reasoning for the global var V1Router *mux.Router is firstly to access it in the main package and also to create subrouters in the other controllers.

I am fairly new to Go, but I'm trying my best to learn the best practices! Any help would be greatly appreciated!

Example code below:

base.controllers.go

package controllers

import (
        "fmt"
        "bytes"
        "net/http"
        "github.com/gorilla/mux"
)

var V1Router *mux.Router

func init () {
    V1Router = mux.NewRouter()
    V1Router.StrictSlash(true)
    V1Router.HandleFunc("/", BaseHandler)    
}

// Base route to access the API Documentation.
func BaseHandler (w http.ResponseWriter, r *http.Request) {
    fmt.Fprint(w, "Hello, Gophers!")
}

main.go

package main

import (
    "net/http"
    "log"
    "github.com/projectrepo/project/models"
    "github.com/projectrepo/project/controllers"
    "github.com/gorilla/mux"
)

func main () {
    http.Handle("/v1", controllers.V1Router)
    if err := http.ListenAndServe(":8000", nil); err != nil {
        log.Fatal("Serving error.")
    }
}

In response to the comments, I tried this solution with the same result:

package main

import (
    "net/http"
    "log"
    "github.com/projectrepo/project/models"
    "github.com/projectrepo/project/controllers"
    "github.com/gorilla/mux"
)

func main () {
    r := mux.NewRouter()
    r.Handle("/v1", controllers.V1Router)
    if err := http.ListenAndServe(":8000", r); err != nil {
        log.Fatal("Serving error.")
    }
}

You can not mix the standard mux (http.DefaultServerMux) and gorilla/mux. You should pass gorilla router as the second argument of http.ListenAndServe if you wan't to replace the standard one. How is your controller's paths will look like? — putu
@putu What I did now was added a default r := mux.NewRouter() in the main package and handled /v1/ as the controllers.V1Router() and I'm getting a nil pointer error. I did add r to replace the nil in ListenAndServe. — Nick Corin
@putu Okay, that was my mistake - I had an error while debugging. Fixing everything the way it was I get the same error. — Nick Corin
My first comment may be not 100% correct. You can mix it, but it only works if you register it through http.Handle("/", controllers.V1Router) or passing it as second argument of http.ListenAndServe. The sub-router for /v1 must be created using Route.Subrouter, e.g. v1 := V1Router.PathPrefix("/v1").Subrouter(), then register base controller to v1. — putu
@putu, the first part of your comment - is that not the same solution as my first attempt? — Nick Corin

putu putu · Accepted Answer · 2017-06-06T13:42:04

Gorilla mux.Router is supposed to be used to create mapping between a set of predefined rules (e.g. host, path, protocol, scheme, etc...) and it's handler (http.Handler or http.HandlerFunc). Gorilla mux can be used to replace standard server mux. If you combine gorilla/mux with built in http server mux as your original question, i.e.

func main () {
    http.Handle("/v1", controllers.V1Router)
    if err := http.ListenAndServe(":8000", nil); err != nil {
        log.Fatal("Serving error.")
    }
}

what actually happen when a client access /v1 is controllers.V1Router will be called with request path /v1 passed to V1Router1. In the controllers.V1Router, you defined that / will be handled by BaseHandler. However, since incoming request path is /v1, it won't match to your routing table. If you want to define sub routing, you can do as follows (this is what I mean in first comment):

func main () {
    r := mux.NewRouter()
    v1 := r.PathPrefix("/v1").Subrouter()
    controllers.RegisterHandlers(v1)

    if err := http.ListenAndServe(":8000", r); err != nil {
        log.Fatal("Serving error.")
    }
}

Then in the controllers (base.controllers.go) define

//Register handlers and it's sub router
func RegisterHandlers(r *mux.Router) {
    //base handler, i.e. /v1
    r.StrictSlash(true)
    r.HandleFunc("/", BaseHandler)

    //example sub-router, i.e. /v1/example
    ex := r.PathPrefix("/example").Subrouter()
    ex.HandleFunc("/", ExampleHandler)

    //other handlers...
}

Sharing a gorilla/mux router across packages

1 Answers