go: make sure flags are properly checked

app/settings/helper.go

@@ -0,0 +1,16 @@
+package settings
+
+import "flag"
+
+// as per https://stackoverflow.com/a/54747682.
+func isFlagPassed(name string) bool {
+	found := false
+
+	flag.Visit(func(f *flag.Flag) {
+		if f.Name == name {
+			found = true
+		}
+	})
+
+	return found
+}

app/settings/settings.go

@@ -45,19 +45,25 @@ func (s *Settings) Consolidate(conf *config.Config, host *string, port *int, dev
 
 	overrideMsg := "overriding '%s' based on a flag: %+v"
 
-	if h := *host; h != "unset" && h != conf.Host {
-		log.Debugf(overrideMsg, "host", h)
-		s.SetHost(h)
+	if isFlagPassed("host") {
+		if h := *host; h != "unset" && h != conf.Host {
+			log.Debugf(overrideMsg, "host", h)
+			s.SetHost(h)
+		}
 	}
 
-	if p := *port; p != 0 && p > 0 && p < 65536 && p != conf.Port {
-		log.Debugf(overrideMsg, "port", p)
-		s.SetPort(p)
+	if isFlagPassed("port") {
+		if p := *port; p > 0 && p < 65536 && p != conf.Port {
+			log.Debugf(overrideMsg, "port", p)
+			s.SetPort(p)
+		}
 	}
 
-	if d := *devel; d != conf.DevelMode {
-		log.Debugf(overrideMsg, "develMode", d)
-		s.SetIsDevel(d)
+	if isFlagPassed("devel") {
+		if d := *devel; d != conf.DevelMode {
+			log.Debugf(overrideMsg, "develMode", d)
+			s.SetIsDevel(d)
+		}
 	}
 
 	s.SetVersion(version)

run.go

@@ -52,7 +52,7 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.`
 
 var (
 	host       = flag.String("host", "unset", "host address to listen on")
-	port       = flag.Int("port", 0, "TCP port to listen on")
+	port       = flag.Int("port", -1, "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")