graceful-server

main.go

package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/signal"
	"time"
)

func serve(ctx context.Context) (err error) {

	mux := http.NewServeMux()
	mux.Handle("/", http.HandlerFunc(
		func(w http.ResponseWriter, r *http.Request) {
			fmt.Fprintf(w, "okay")
		},
	))

	srv := &http.Server{
		Addr:    ":6969",
		Handler: mux,
	}

	go func() {
		if err = srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			log.Fatalf("listen:%+s\n", err)
		}
	}()

	log.Printf("server started")

	<-ctx.Done()

	log.Printf("server stopped")

	ctxShutDown, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer func() {
		cancel()
	}()

	if err = srv.Shutdown(ctxShutDown); err != nil {
		log.Fatalf("server Shutdown Failed:%+s", err)
	}

	log.Printf("server exited properly")

	if err == http.ErrServerClosed {
		err = nil
	}

	return
}

func main() {

	c := make(chan os.Signal, 1)
	signal.Notify(c, os.Interrupt)

	ctx, cancel := context.WithCancel(context.Background())

	go func() {
		oscall := <-c
		log.Printf("system call:%+v", oscall)
		cancel()
	}()

	if err := serve(ctx); err != nil {
		log.Printf("failed to serve:+%v\n", err)
	}
}

the err variable is shadowed on line 44, making the check on line 50 a no-op

Well, I don't think there are any variable shadowing since the variable err is declared once in the function declaration. Declaration of variables is with :=.

Though, there could be assignment error as both the go function in 27 and the shutdown error check in line 44 are using the err. The go function is listening to server requests and assign errors after a connection event has occurred, while the assignment in line 44 is performed once. There could be an overlap of assignments.