net/http: add example to Server.Shutdown

Fixes #19579

Change-Id: Id99ca6de94d8d895dfaed1ed507e9d36c7f60670
Reviewed-on: https://go-review.googlesource.com/48869
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/example_test.go

@@ -5,11 +5,14 @@
 package http_test
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"log"
 	"net/http"
+	"os"
+	"os/signal"
 )
 
 func ExampleHijacker() {
@@ -109,3 +112,28 @@ func ExampleResponseWriter_trailers() {
 		w.Header().Set("AtEnd3", "value 3") // These will appear as trailers.
 	})
 }
+
+func ExampleServer_Shutdown() {
+	var srv http.Server
+
+	idleConnsClosed := make(chan struct{})
+	go func() {
+		sigint := make(chan os.Signal, 1)
+		signal.Notify(sigint, os.Interrupt)
+		<-sigint
+
+		// We received an interrupt signal, shut down.
+		if err := srv.Shutdown(context.Background()); err != nil {
+			// Error from closing listeners, or context timeout:
+			log.Printf("HTTP server Shutdown: %v", err)
+		}
+		close(idleConnsClosed)
+	}()
+
+	if err := srv.ListenAndServe(); err != http.ErrServerClosed {
+		// Error starting or closing listener:
+		log.Printf("HTTP server ListenAndServe: %v", err)
+	}
+
+	<-idleConnsClosed
+}