Go Gorilla Mux not routing as expected

I am having issues getting the Gorilla Mux library for Go to work. From the documentation I have read and all the debugging I've done, I cannot seem to figure out what the problem is. Here's what I've got for routing:

Folder structure:

project_root
  |-- main.go
  |-- routes
         |-- routes.go
         |-- user.go

main.go:

package main

import (
	"fmt"
	"net/http"

	"./routes"
)

func main() {
	r := routes.CreateRoutes(http.Dir("./content"))

	http.Handle("/", r)
	err := http.ListenAndServe(fmt.Sprintf("%s:%d", "localhost", 8000), nil)
	if err != nil {
		fmt.Println("Error: ", err)
	}
}

routes/routes.go

package routes

import (
	"net/http"

	"github.com/gorilla/mux"
)

func CreateRoutes(staticDir http.FileSystem) *mux.Router {
	r := mux.NewRouter()

	// Serve static pages (i.e. web app)
	r.PathPrefix("/").Handler(http.FileServer(staticDir))

	// Serve User Pages
	createUserRoutes(r)

	return r
}

routes/user.go

package routes

import (
	"fmt"
	"net/http"

	"github.com/gorilla/mux"
)

func createUserRoutes(r *mux.Router) {
	user := r.PathPrefix("/user/").Subrouter()

	// Create a new user
	user.Path("/new").Methods("PUT").HandlerFunc(newUserHandler)

	// Remove a user
	user.Path("/remove/{username:[a-z][a-z0-9]+}").Methods("DELETE").HandlerFunc(removeUserHandler)

	// Update a user
	user.Path("update/{username:[a-z][a-z0-9]+").Methods("POST").HandlerFunc(updateUserHandler)

	// Get a user (Get user information)
	user.Path("/{username:[a-z][a-z0-9]+").Methods("GET").HandlerFunc(getUserHandler)
}

func newUserHandler(resp http.ResponseWriter, req *http.Request) {
    // Do something that might cause an error        

	if err != nil {
		fmt.Println(err)
		resp.WriteHeader(409)
		resp.Write([]byte(err.Error()))
	} else {
		fmt.Println("Created new user")
		resp.WriteHeader(201)
		resp.Write([]byte("Created new user"))
	}
}

func removeUserHandler(resp http.ResponseWriter, req *http.Request) {
}

func updateUserHandler(resp http.ResponseWriter, req *http.Request) {
}

func getUserHandler(resp http.ResponseWriter, req *http.Request) {
}

Whenever I make a request to root path of the server (i.e. the path that serves the static content), the server responds as intended, with the main page. However, any other calls result in a 404 response (I test requests using cURL). For example, a malformed request to http://localhost:8000/user/new should return a 409, but instead returns a 404. Same if I expect a 201 response.

Everything looks right and I've triple checked it, but I cannot figure out what the issue here is.

Turns out the solution was simple (like it usually is). This line in routes.go

r.PathPrefix("/").Handler(http.FileServer(staticDir))

was causing the unintended routing. When PathPrefix is used, it seems to route all URLs to the first matching prefix (in this case this prefix). This explains why static files were being served, but nothing else works.

The fix is to use the Path function instead. There's a subtle difference as explained in the docs; PathPrefix "matches if the given template is a prefix of the full URL path", whereas Path does not. Hence the line above now looks like this to solve the issue I was having:

r.Path("/").Handler(http.FileServer(staticDir))