proxy

Proxy

Proxy is a structural design pattern that lets you provide a substitute or placeholder for another object. A proxy controls access to the original object, allowing you to perform something either before or after the request gets through to the original object.

Example

We will get information about the users. But the users must have enough permissions. So we will create a proxy, that will check if the user can access to the data.

1. Firstly, we will create the interface Service.

   // db/service.go
   
   type Service interface {
     GetData(user string) ([]string, error)
   }

2. Now we need to create database client to get user data. And it will use the interface `Service.

   // db/db.go
   
   type Database struct{}
   
   func (db *Database) GetData(user string) ([]string, error) {
     return []string{
       "line 1",
       "end line",
     }, nil
   }

3. And now we will create the proxy, that will check if the client has enough rights.

   // db/proxy.go
   
   type ProxyDatabase struct {
     Users map[string]bool
     DB    *Database
   }
   
   var ErrInsufficientAccessRights = errors.New("insufficient access rights")
   
   func (pDB *ProxyDatabase) GetData(user string) ([]string, error) {
     if !pDB.Users[user] {
       return nil, ErrInsufficientAccessRights
     }
   
     return pDB.DB.GetData(user)
   }