Handling graceful shutdown.

cmd/api/server.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	"context"
+	"errors"
 	"fmt"
 	"log/slog"
 	"net/http"
@@ -21,6 +23,9 @@ func (app *application) serve() error {
 		ErrorLog:     slog.NewLogLogger(app.logger.Handler(), slog.LevelError),
 	}
 
+	// Create a shutdownError channel. We will use this to receive any errors returned by the graceful Shutdown() function
+	shutdownError := make(chan error)
+
 	// Start a background goroutine
 	go func() {
 		// Create a quit channel which carries os.Signal values
@@ -33,14 +38,33 @@ func (app *application) serve() error {
 		s := <-quit
 
 		// Log a message to say that the signal has been caught. Notice that we also call the String() method on the signal to get the signal name and include it in the log entry attributes
-		app.logger.Info("caught signal", "signal", s.String())
+		app.logger.Info("shutting down server", "signal", s.String())
 
-		// Exit the application with a 0 (success) status code.
-		os.Exit(0)
+		// Create a context with a 30-second timeout
+		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+		defer cancel()
+
+		// Call Shutdown() on our server, passing in the context we just made. Shutdown() will return nil if the graceful shutdown was successful, or an error (which may happen because of a problem closing the listeners, or because the shutdown didn't complete before the 30-second context deadline is hit). We relay this return value to the shutdownError channel.
+		shutdownError <- srv.Shutdown(ctx)
 	}()
 
 	// Start the HTTP server.
 	app.logger.Info("starting server", "addr", srv.Addr, "env", app.config.env)
 
-	return srv.ListenAndServe()
+	// Calling Shutdown() on our server will cause ListenAndServe() to immediately return a http.ErrServerClosed error. So if we see this error, it is actually a good thing and an indication that the graceful shutdown has started. So we check specifically for this, only returning the error if it is NOT http.ErrServerClosed.
+	err := srv.ListenAndServe()
+	if !errors.Is(err, http.ErrServerClosed) {
+		return err
+	}
+
+	// Otherwise, we wait to receive the return value from Shutdown() on the shutdownError channel. If return value is an error, we know that there was a problem with the graceful shutdown and we return the error
+	err = <-shutdownError
+	if err != nil {
+		return err
+	}
+
+	// At this point, we know that the graceful shutdown completed successfully, and we log a "stopped server" message
+	app.logger.Info("stopped server", "addr", srv.Addr)
+
+	return nil
 }