go: handle host+port combinations,shutdown better

* add log messages telling the user what went wrong if the app fails to
  start
* improve existing log messages
* cleanup: close channels when exiting
* cleanup: stop listening for signals when exiting

config.dhall

@@ -45,7 +45,8 @@ let _ =
 
 let Config =
     -- | define configuration schema.
-      { Port : Natural
+      { Host : Text
+      , Port : Natural
       , AppName : Text
       , LiveMode : Bool
       , DevelMode : Bool
@@ -58,7 +59,8 @@ let defconf
     -- | TODO: have this reside on the Internet and import it similar to how
     -- | the Dhall Prelude is imported.
     : Config
-    = { Port = 3000
+    = { Host = ""
+      , Port = 3000
       , AppName = "pcmt"
       , LiveMode = False
       , DevelMode = False

config/config.go

@@ -6,6 +6,7 @@ import (
 )
 
 type Config struct {
+	Host                string
 	Port                int
 	AppName             string
 	LiveMode            bool

main.go

@@ -10,8 +10,7 @@ func main() {
 	err := run()
 	if err != nil {
 		l := slog.New(slog.NewJSONHandler(os.Stderr))
-		// log.Fatalln(err)
-		l.Error("error running app:", err)
+		l.Error("unrecoverable failure, stopping the app", "error", err)
 		os.Exit(1)
 	}
 }

run.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
+	"strconv"
 	"syscall"
 	"time"
 
@@ -49,7 +50,8 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.`
 )
 
 var (
-	addr       = flag.String("addr", ":3000", "TCP address:port to listen at")
+	host       = flag.String("host", "unset", "host address to listen on")
+	port       = flag.Int("port", 0, "TCP port to listen on")
 	configFlag = flag.String("config", "config.dhall", "Default path of the config file")
 	devel      = flag.Bool("devel", false, "Run the application in dev mode, connect to a local browser-sync instance for hot-reloading")
 	license    = flag.Bool("license", false, "Print licensing information and exit")
@@ -129,11 +131,52 @@ func run() error {
 	// }
 
 	e := a.E()
-	go func() {
-		if err = e.Start(*addr); err != nil && err != http.ErrServerClosed {
-			log.Info("shutting down the server")
+
+	// channel used to check whether the app had troubles starting up.
+	started := make(chan error, 1)
+
+	defer close(started)
+
+	go func(ok chan error) {
+		p := conf.Port
+		h := conf.Host
+
+		if flagPort := *port; flagPort != 0 && flagPort > 0 && flagPort < 65536 {
+			p = flagPort
 		}
-	}()
+
+		if flagHost := *host; flagHost != "unset" {
+			h = flagHost
+		}
+
+		address := h + ":" + strconv.Itoa(p)
+
+		if err = e.Start(address); err != nil && err != http.ErrServerClosed {
+			log.Error("troubles running the server, bailing", "error", err.Error())
+
+			ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
+
+			defer func() {
+				cancel()
+				started <- err
+			}()
+
+			log.Info("shutting down the server")
+
+			if err := e.Shutdown(ctx); err != nil {
+				log.Info("error shutting down", "error", err)
+				started <- err
+
+				return
+			}
+		}
+		started <- err
+	}(started)
+
+	err = <-started
+	if err != nil {
+		return err
+	}
 
 	quit := make(chan os.Signal, 1)
 
@@ -148,6 +191,11 @@ func run() error {
 	defer func() {
 		log.Infof("Interrupt received, gracefully shutting down the server (timeout %s)", shutdownTimeout)
 		cancel()
+
+		signal.Stop(quit)
+
+		close(quit)
+
 		log.Info("Bye!")
 	}()