Return detailed error when directory is missing

Fixes https://github.com/tus/tusd/issues/98

filestore/filestore.go

@@ -17,6 +17,7 @@ package filestore
 
 import (
 	"encoding/json"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"os"
@@ -62,7 +63,10 @@ func (store FileStore) NewUpload(info tusd.FileInfo) (id string, err error) {
 	// Create .bin file with no content
 	file, err := os.OpenFile(store.binPath(id), os.O_CREATE|os.O_WRONLY, defaultFilePerm)
 	if err != nil {
-		return
+		if os.IsNotExist(err) {
+			err = fmt.Errorf("upload directory does not exist: %s", store.Path)
+		}
+		return "", err
 	}
 	defer file.Close()
 

filestore/filestore_test.go

@@ -72,6 +72,17 @@ func TestFilestore(t *testing.T) {
 	a.True(os.IsNotExist(err))
 }
 
+func TestMissingPath(t *testing.T) {
+	a := assert.New(t)
+
+	store := FileStore{"./path-that-does-not-exist"}
+
+	id, err := store.NewUpload(tusd.FileInfo{})
+	a.Error(err)
+	a.Equal(err.Error(), "upload directory does not exist: ./path-that-does-not-exist")
+	a.Equal(id, "")
+}
+
 func TestFileLocker(t *testing.T) {
 	a := assert.New(t)