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Golang long polling example with request cancellation
package main
import (
func longOperation(ctx context.Context, ch chan<- string) {
// Simulate long operation.
// Change it to more than 10 seconds to get server timeout.
select {
case <-time.After(time.Second * 3):
ch <- "Successful result."
case <-ctx.Done():
func handler(w http.ResponseWriter, _ *http.Request) {
notifier, ok := w.(http.CloseNotifier)
if !ok {
panic("Expected http.ResponseWriter to be an http.CloseNotifier")
ctx, cancel := context.WithCancel(context.Background())
ch := make(chan string)
go longOperation(ctx, ch)
select {
case result := <-ch:
fmt.Fprint(w, result)
case <-time.After(time.Second * 10):
fmt.Fprint(w, "Server is busy.")
case <-notifier.CloseNotify():
fmt.Println("Client has disconnected.")
func main() {
http.HandleFunc("/", handler)
http.ListenAndServe("localhost:8080", nil)
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