Go Get Notified When an HTTP Request Closes
Most web requests by design take only a few dozen milliseconds to process. But sometimes web apps need to leave a connection open for a longer period of time. And sometimes the remote client closes the connection before the server has had time to respond.
On a Go-based webserver, you can receive notifications when the HTTP connection terminates.
Here's how you do it. <!--break-->
Start with an HTTP handler function, and get the channel for close notifications:
func SomeHandler(res http.ResonseWriter, req *http.Request) {
// Normal stuff
//...
notify := res.(CloseNotifier).CloseNotify()
go func() {
<-notify
fmt.Println("HTTP connection just closed.")
}()
}
The trick here is to get the notify channel from the ResponseWriter. A ResponseWriter is also a CloseNotifier, and a CloseNotifier can return a channel (a chan bool, to be precise) that sends a message when the HTTP connection closes.
So all you need to do is get a handle to that channel and listen for messages. In the code above, we do that in a go routine:
go func() {
<-notify
fmt.Println("HTTP connection just closed.")
}()
This function waits until it receives a notification (<-notify) and then it prints out a message.
A more sophisticated program would do something on notification, like send messages on other channels to tell long-running routines to quit and clean up.
Update: Just to clarify, ResponseWriter is an interface, and the underlying implementation in the Go library also implements CloseNotifier. There is no guarantee that all implementations of ResponseWriter also implement CloseNotifier.
