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aah Server Extension Point

aah go server exposes the App and Request life cycle stages as server events. It is called as Server Extension Point. Function signature is same as events (aah.EventCallbackFunc). By default given function executed as they are added sequence unless priority is specified.

aah Server events are executed synchronously.

Note:

For OnRequest, OnPreAuth, OnPostAuth, OnPreReply, OnAfterReply you can only register/add one event callback function.

Reference to Event Emitter/Publisher.

List of Server Extension Points

Event: OnInit

OnInit event is published right after the aah.AppConfig() is loaded. Only aah.conf config is initialized at this stage, such as App Variables, Routes, i18n, Security, View Engine, Logs are not yet initialized.

Supports Multiple: Yes

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

// Or define a func and supply it [recommended, 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

OnStart event is published right before the start of aah go Server. At this stage application is completely initialized, just server is not yet started.

Supports Multiple: Yes

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

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

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

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

Event: OnShutdown

On receiving OS Signals SIGINT or SIGTERM, aah server does graceful shutdown based on config value server.timeout.grace_shutdown and then it publishes the OnShutdown event.

Supports Multiple: Yes

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

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

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

func init() {
  // By default given function executed as they are added sequence
  // unless `priority` is specified.
  aah.OnShutdown(flushCache)
  aah.OnShutdown(disconnectDatabase)
  aah.OnShutdown(disconnectRedis)
}

Event: OnRequest

OnRequest event is published for each incoming request to the aah go server.

  • At this point request Route is not yet populated/evaluated.

Note: The aah.Context object passed to the extension functions is decorated with the ctx.SetURL() and ctx.SetMethod() methods. Calls to these methods will have an impact how the request is routed.

Supports Multiple: No

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

    // logic goes here
  })
}

Event: OnPreAuth

Since v0.7 OnPreAuth event is published right before the Authentication by security manager.

Supports Multiple: No

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

    // logic goes here
  })
}

Event: OnPostAuth

Since v0.7 OnPostAuth event is published right after the Authentication and Authorization info gets populated into Subject by security manager.

Supports Multiple: No

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

    // logic goes here
  })
}

Event: OnPreReply

OnPreReply event is published right before writing an reply/response on the wire. At this point response writer is clean nothing is written i.e. Headers, Cookies, Redirects, Status Code and Response Body not written.

Note: OnPreReply is not called when-

  • Reply().Done() was called

Supports Multiple: No

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

    // logic goes here
  })
}

Event: OnAfterReply

OnAfterReply event is published right after the response is written on the wire. Nothing we can do about the response, however context has a valuable information such as response bytes size, response status code, etc.

Note: OnAfterReply is not called when-

  • Reply().Done() was called
  • Reply().Redirect(...) was called

Supports Multiple: No

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

    // logic goes here
  })
}