feat(server): Add basic listenAddress getter from flag or env

server/server.go

@@ -0,0 +1,37 @@
+package server
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/asaskevich/govalidator"
+)
+
+// GetListenAddressFromEnvOrFlags will check flag --host and --port to construct the listen address
+// If they doesn't exist it will fallback on HOST and PORT environment variable and finally fallback
+// to the default value localhost:8080.
+func GetListenAddressFromEnvOrFlags() (string, error) {
+	host := os.Getenv("HOST")
+	port := os.Getenv("PORT")
+
+	if host == "" {
+		host = "localhost"
+	}
+	if port == "" {
+		port = "8080"
+	}
+
+	pHost := flag.String("host", host, "Host address to listen to")
+	pPort := flag.String("port", port, "Port to listen to")
+
+	if govalidator.IsHost(*pHost) {
+		return "", fmt.Errorf("provided 'host' is invalid")
+	}
+
+	if govalidator.IsPort(*pPort) {
+		return "", fmt.Errorf("provided 'port' is invalid")
+	}
+
+	return fmt.Sprintf("%s:%s", *pHost, *pPort), nil
+}