user_permissions_by_id.go

package handler

import (
    "fmt"
    "net/http"
    "strings"
)

// Declaring our local needs from the user db instance,
type UserDB interface {
    UserRoleByID(id string) string
}

// ... and our local needs from the in memory permission storage.
type PermissionStorage interface {
    RolePermissions(role string) []string
}

// Lastly, our handler cannot be purely functional,
// since it requires references to non singleton instances.
type UserPermissionsByID struct {
    UserDB             UserDB
    PermissionsStorage PermissionStorage
}

func (u *UserPermissionsByID) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    id := r.URL.Query()["id"][0]
    role := u.UserDB.UserRoleByID(id)
    permissions := u.PermissionsStorage.RolePermissions(role)
    fmt.Fprint(w, strings.Join(permissions, ", "))
}