skip write for already stored files

.gitignore

@@ -1,2 +1,3 @@
 bit4sat
 db-storage
+file-storage

storage/storage.go

@@ -1,6 +1,8 @@
 package storage
 
 import (
+	"errors"
+	"fmt"
 	"io"
 	"log"
 	"mime/multipart"
@@ -24,7 +26,18 @@ func GetStoreDestination(filename string) string {
 }
 
 func StoreFormFile(src multipart.File, filename string) error {
-	fd, err := os.Create(GetStoreDestination(filename))
+	filePath := GetStoreDestination(filename)
+	// If file exists just return
+	exists, err := CheckFileExists(filePath)
+	if err != nil {
+		return err
+	}
+	if exists {
+		log.Printf("file %s exists, skipping write", filename)
+		return nil
+	}
+
+	fd, err := os.Create(filePath)
 	defer fd.Close()
 	if err != nil {
 		return err
@@ -36,6 +49,24 @@ func StoreFormFile(src multipart.File, filename string) error {
 	return err
 }
 
+func CheckFileExists(file string) (bool, error) {
+	info, err := os.Stat(file)
+	if err == nil {
+		if info.IsDir() {
+			errMsg := fmt.Sprintf("'%s' is a directory", file)
+			return false, errors.New(errMsg)
+		}
+
+		return true, nil
+	}
+
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+
+	return false, err
+}
+
 func init() {
 	path, set := os.LookupEnv(StoragePathEnv)
 	if !set {