aah Server Extension Point

aah server exposes the App and Request life cycle stages as server events. It is called as Server Extension Point. Function signature is the same as events (aah.EventCallbackFunc).

aah server events are executed synchronously. Reference to Event Emitter/Publisher.

Table of Contents

• Application Extension Points
  • OnInit
  • OnStart
  • OnPreShutdown
  • OnPostShutdown
• HTTP Engine Extension Points
  • OnRequest
  • OnPreAuth
  • OnPostAuth
  • OnPreReply
  • OnHeaderReply
  • OnPostReply
• WebSocket Engine Extension Points

Application Extension Points

Application extension points by default, a given function is executed as an added sequence unless priority is specified.

Event: OnInit

Event OnInit is published once the aah.AppConfig() is loaded. At this stage, only aah.conf config is initialized. App Variables, Routes, i18n, Security, View Engine, Logs and so on will be initialized after this event.

Supports Multiple: Yes

// As an anonymous func
func init() {
  aah.OnInit(func(e *Event) {
		// logic comes here
	})
}

// Or define a func and supply it [recommended approach, name gets logged in log]
func loadUserConfig(e *aah.Event)  {
  // loading user config from /etc/myapp/myapp.conf
  // merge it to aah.AppConfig().Merge(...)
}

func init() {
  aah.OnInit(loadUserConfig)

  // OR
  aah.OnInit(loadUserConfig, 10) // with priority
}

Event: OnStart

Event OnStart is published just before the start of aah Server. The application is completely initialized at this stage. The server is yet to be started.

Supports Multiple: Yes

func connectDatabase(e *aah.Event)  {
  // logic comes here
}

func connectRedis(e *aah.Event) {
  // logic comes here
}

func refreshCache(e *aah.Event) {
  // logic comes here
}

func init() {
  // By default, a given function is executed as an added sequence
  // unless `priority` is specified.
  aah.OnStart(connectDatabase)
  aah.OnStart(refreshCache, 3) // with priority
  aah.OnStart(connectRedis, 2) // with priority
}

Event: OnPreShutdown

Event OnPreShutdown is published when application receives OS Signals SIGINT or SIGTERM and before the triggering graceful shutdown. After this event, aah triggers graceful shutdown with config value of server.timeout.grace_shutdown.

Supports Multiple: Yes

func announceImGonnaShutdown()  {
  // announce it
}

func init()  {
  // By default, a given function is executed as an added sequence
  // unless `priority` is specified.
  aah.OnPreShutdown(announceImGonnaShutdown)
}

Event: OnPostShutdown

Event OnPostShutdown is published just after the successful grace shutdown of aah server and then application does clean exit.

Supports Multiple: Yes

func disconnectDatabase(e *aah.Event)  {
  // logic comes here
}

func disconnectRedis(e *aah.Event) {
  // logic comes here
}

func flushCache(e *aah.Event) {
  // logic comes here
}

func init() {
  // By default, a given function is executed as an added sequence
  // unless `priority` is specified.
  aah.OnPostShutdown(flushCache)
  aah.OnPostShutdown(disconnectDatabase)
  aah.OnPostShutdown(disconnectRedis)
}

HTTP Engine Extension Points

Event: OnRequest

Event OnRequest is published on each incoming request to the aah server.

func init() {
  aah.AppHTTPEngine().OnRequest(func(e *aah.Event)  {
    ctx := e.Data.(*aah.Context)

    // logic comes here
  })
}

Event: OnPreAuth

Since v0.7 Event OnPreAuth is published just before the Authentication and Authorization.

func init() {
  aah.AppHTTPEngine().OnPreAuth(func(e *aah.Event)  {
    ctx := e.Data.(*aah.Context)

    // logic comes here
  })
}

Event: OnPostAuth

Since v0.7 Event OnPostAuth is published once the Authentication and Authorization info gets populated into Subject.

func init() {
  aah.AppHTTPEngine().OnPostAuth(func(e *aah.Event)  {
    ctx := e.Data.(*aah.Context)

    // logic comes here
  })
}

Event: OnPreReply

Event OnPreReply is published just before writing a reply/response on the wire. At this point, the response writer is clean. i.e. Headers, Cookies, Redirects, Status Code and Response Body are not written.

func init() {
  aah.AppHTTPEngine().OnPreReply(func(e *aah.Event)  {
    ctx := e.Data.(*aah.Context)

    // logic comes here
  })
}

Event: OnHeaderReply

Since v0.11.0 Event OnHeaderReply is published before writing HTTP header Status. At this point, all the headers except the header Status get written on the http.ResponseWriter.

func init() {
  aah.AppHTTPEngine().OnHeaderReply(func(e *aah.Event)  {
    hdr := e.Data.(http.Header)

    // Header instance is the direct reference to http.ResponseWritter
  	// Any changes reflect immediately :)
  	//
  	// logic comes here
  })
}

Event: OnPostReply

Event OnPostReply is published right after the response gets written on the wire. We can do nothing about the response, however the context has valuable information such as response bytes size, response status code, etc.

func init() {
  aah.AppHTTPEngine().OnPostReply(func(e *aah.Event)  {
    ctx := e.Data.(*aah.Context)

    // logic comes here
  })
}