Interceptors

An interceptor pattern offers a way to change or augment their usual processing cycle. Key aspects of the pattern are that the change is transparent and used automatically.

aah provides per Controller and per Action level interceptor. To stop the execution flow, use ctx.Abort() within the interceptor.

The order of interceptor execution in the request life cycle -

Interceptor	Description
`Before`	Always called if present
`Before<ActionName>`	Always called if present, except `panic()`, `ctx.Abort()`
	Controller action gets called
`After<ActionName>`	Always called if present, except `panic()`, `ctx.Abort()`
`After`	Always called if present, except `panic()`, `ctx.Abort()`
`Panic<ActionName>`	Always called if present in the event of `panic`
`Panic`	Always called if present in the event of `panic` except when `Panic<ActionName>(r)` does not exist. In that case, it propagates to framework.
`Finally<ActionName>`	Always called if present.
`Finally`	Always called if present.

Note:

Panic interceptors method has a parameter.
If ctx.Abort() was called, subsequent interceptors and targeted controller Action will not be called. Control goes back to the framework flow.

For example:
- Let's say, method ctx.Abort() called in interceptor Before(). Then remaining request lifecycle skipped and control goes back to framework.

Example

// UserController ...
type UserController struct {
  *aah.Context
}

//‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
// Controller Level Interceptors
//___________________________________

// Before interceptor is called for every action in the Controller.
func (u *UserController) Before() {
  u.Log().Info("UserController before interceptor is called")
}

// After interceptor is called for every action in the Controller.
func (u *UserController) After() {
  u.Log().Info("UserController after interceptor is called")
}

// Finally interceptor is called for every action in the Controller
// except when `ctx.Abort()`.
func (u *UserController) Finally() {
  u.Log().Info("UserController finally interceptor is called")
}

// Panic interceptor is called for every action in the Controller
// except when
//
//  - `ctx.Abort()` is called
//
//  - action level Panic interceptor is present
//
// Note: Panic interceptor has a parameter
func (u *UserController) Panic(r interface{}) {
  u.Log().Info("UserController panic interceptor is called")
}

//‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
// Actions
//___________________________________

// Login action to perform login.
func (u *UserController) Login() {
  u.Log().Info("UserController login action is called")
}

// Logout action to perform logout.
func (u *UserController) Logout() {
  u.Log().Info("UserController logout action is called")
}

//‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
// Controller Action Level Interceptors
//_____________________________________

// BeforeLogin is called before `Login` action.
func (u *UserController) BeforeLogin() {
  u.Log().Info("UserController before login action interceptor is called")
}

// AfterLogout is called after `Logout` action.
func (u *UserController) AfterLogout() {
  u.Log().Info("UserController after logout action interceptor is called")
}