From b7876711adac8e57ab53de647feb843f7bf010dc Mon Sep 17 00:00:00 2001
From: Michael Mayer <michael@lastzero.net>
Date: Fri, 4 Dec 2020 11:37:31 +0100
Subject: [PATCH] Fallback to backup path if storage path is not defined or
 writable

---
 internal/config/filenames.go | 13 +++++++++----
 pkg/fs/fs.go                 | 23 ++++++++++++++++++++++-
 pkg/fs/fs_test.go            |  6 ++++++
 3 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/internal/config/filenames.go b/internal/config/filenames.go
index d38efdd52..ac1af3e90 100644
--- a/internal/config/filenames.go
+++ b/internal/config/filenames.go
@@ -275,17 +275,22 @@ func (c *Config) StoragePath() string {
 		storageDir := fs.Abs(dirName)
 
 		// Find existing directories.
-		if fs.PathExists(originalsDir) && !c.ReadOnly() {
+		if fs.PathWritable(originalsDir) && !c.ReadOnly() {
 			return originalsDir
-		} else if fs.PathExists(storageDir) && c.ReadOnly() {
+		} else if fs.PathWritable(storageDir) && c.ReadOnly() {
 			return storageDir
 		}
 
+		// Fallback to backup storage path.
+		if fs.PathWritable(c.params.BackupPath) {
+			return fs.Abs(filepath.Join(c.params.BackupPath, dirName))
+		}
+
 		// Use .photoprism in home directory?
 		if usr, _ := user.Current(); usr.HomeDir != "" {
 			p := fs.Abs(filepath.Join(usr.HomeDir, fs.HiddenPath, dirName))
 
-			if fs.PathExists(p) || c.ReadOnly() {
+			if fs.PathWritable(p) || c.ReadOnly() {
 				return p
 			}
 		}
@@ -304,7 +309,7 @@ func (c *Config) StoragePath() string {
 
 // BackupPath returns the backup storage path.
 func (c *Config) BackupPath() string {
-	if fs.PathExists(c.params.BackupPath) {
+	if fs.PathWritable(c.params.BackupPath) {
 		return fs.Abs(c.params.BackupPath)
 	}
 
diff --git a/pkg/fs/fs.go b/pkg/fs/fs.go
index 24b0fb451..d455f0163 100644
--- a/pkg/fs/fs.go
+++ b/pkg/fs/fs.go
@@ -40,6 +40,8 @@ import (
 	"os/user"
 	"path/filepath"
 	"strings"
+
+	"github.com/photoprism/photoprism/pkg/rnd"
 )
 
 const IgnoreFile = ".ppignore"
@@ -59,7 +61,7 @@ func FileExists(fileName string) bool {
 	return err == nil && !info.IsDir()
 }
 
-// PathExists returns true if path exists and is a directory or symlink.
+// PathExists tests if a path exists, and is a directory or symlink.
 func PathExists(path string) bool {
 	if path == "" {
 		return false
@@ -76,6 +78,25 @@ func PathExists(path string) bool {
 	return m&os.ModeDir != 0 || m&os.ModeSymlink != 0
 }
 
+// PathWritable tests if a path exists and is writable.
+func PathWritable(path string) bool {
+	if !PathExists(path) {
+		return false
+	}
+
+	tmpName := filepath.Join(path, "."+rnd.Token(8))
+
+	if f, err := os.Create(tmpName); err != nil {
+		return false
+	} else if err := f.Close(); err != nil {
+		return false
+	} else if err := os.Remove(tmpName); err != nil {
+		return false
+	}
+
+	return true
+}
+
 // Overwrite overwrites the file with data. Creates file if not present.
 func Overwrite(fileName string, data []byte) bool {
 	f, err := os.Create(fileName)
diff --git a/pkg/fs/fs_test.go b/pkg/fs/fs_test.go
index 7fca67fbc..6826c249f 100644
--- a/pkg/fs/fs_test.go
+++ b/pkg/fs/fs_test.go
@@ -20,6 +20,12 @@ func TestPathExists(t *testing.T) {
 	assert.False(t, PathExists("./testdata3ggdtgdg"))
 }
 
+func TestPathWritable(t *testing.T) {
+	assert.True(t, PathExists("./testdata"))
+	assert.False(t, PathExists("./testdata/test.jpg"))
+	assert.False(t, PathExists("./testdata3ggdtgdg"))
+}
+
 func TestOverwrite(t *testing.T) {
 	data := make([]byte, 3)
 	data[1] = 3