Handle invalid CWD when creating file dialogs

Author: nikoskalogridis

.github/ISSUE_DRAFT_savefiledialog-invalid-cwd.md

@@ -0,0 +1,60 @@
+# Bug: SaveFileDialog crashes when current working directory is deleted/unmounted at runtime
+
+## Summary
+On Linux (GTK/Eto), NAPS2 can throw an unhandled `System.IO.FileNotFoundException` when opening **Save Images** if the process current working directory becomes invalid after startup (for example, removable media unmounted or directory removed).
+
+The dialog never opens and users may be unable to save scanned pages.
+
+## Affected area
+- `NAPS2.Lib/EtoForms/EtoDialogHelper.cs`
+- GTK `SaveFileDialog` / `OpenFileDialog` construction path
+
+## Observed stack trace
+```text
+System.IO.FileNotFoundException: Unable to find the specified file.
+   at string Interop+Sys.GetCwd()
+   at string Environment.get_CurrentDirectoryCore()
+   at string Environment.get_CurrentDirectory()
+   at string System.IO.Directory.GetCurrentDirectory()
+   at new Eto.GtkSharp.Forms.SaveFileDialogHandler()
+   at bool NAPS2.EtoForms.EtoDialogHelper.PromptToSaveImage(...)
+   at async Task<bool> NAPS2.ImportExport.ExportController.SaveImages(...)
+```
+
+## Steps to reproduce
+1. Launch NAPS2 from a directory that is later removed or unmounted.
+2. Scan/import pages.
+3. Click **Save Images**.
+
+## Expected behavior
+NAPS2 should recover from an invalid CWD and still open the file dialog, falling back to a safe directory (typically user home).
+
+## Actual behavior
+An unhandled exception is thrown while creating the dialog handler and the save dialog does not open.
+
+## Proposed resolution
+Harden dialog creation in `EtoDialogHelper`:
+
+- Before creating dialogs, verify current directory is accessible.
+- If inaccessible (exception or non-existent path), set `Environment.CurrentDirectory` to:
+  1. `Environment.GetFolderPath(Environment.SpecialFolder.UserProfile)`
+  2. fallback `Path.GetTempPath()` if needed
+- Wrap `SaveFileDialog` construction in a retry path for `FileNotFoundException`.
+- Apply the same CWD guard before `OpenFileDialog` creation.
+
+## Patch status
+Implemented on branch:
+- `fix/savefiledialog-invalid-cwd-crash`
+
+Files changed:
+- `NAPS2.Lib/EtoForms/EtoDialogHelper.cs`
+
+## Validation done
+- File-level diagnostics clean for `EtoDialogHelper.cs`.
+- Full build was not run in this environment (`dotnet` CLI unavailable here).
+
+## Suggested reviewer checklist
+- [ ] Reproduce with invalid CWD on Linux/GTK before patch
+- [ ] Confirm **Save Images** opens after patch
+- [ ] Confirm **Import** dialog also opens with invalid CWD
+- [ ] Confirm no regressions in normal save/import flows

NAPS2.Lib/EtoForms/EtoDialogHelper.cs

@@ -22,10 +22,8 @@ public override bool PromptToSavePdfOrImage(string? defaultPath, out string? sav
         {
             lastExt = "pdf";
         }
-        var sd = new SaveFileDialog
-        {
-            FileName = GetDefaultFileName(defaultPath, lastExt!)
-        };
+        var sd = CreateSaveFileDialog();
+        sd.FileName = GetDefaultFileName(defaultPath, lastExt!);
         _fileFilters.Set(sd, FileFilterGroup.Pdf | FileFilterGroup.Image, lastExt);
         SetDir(sd, defaultPath);
         EtoPlatform.Current.ConfigureFileDialog(sd);
@@ -41,10 +39,8 @@ public override bool PromptToSavePdfOrImage(string? defaultPath, out string? sav
 
     public override bool PromptToSavePdf(string? defaultPath, out string? savePath)
     {
-        var sd = new SaveFileDialog
-        {
-            FileName = GetDefaultFileName(defaultPath, "pdf")
-        };
+        var sd = CreateSaveFileDialog();
+        sd.FileName = GetDefaultFileName(defaultPath, "pdf");
         _fileFilters.Set(sd, FileFilterGroup.Pdf);
         SetDir(sd, defaultPath);
         EtoPlatform.Current.ConfigureFileDialog(sd);
@@ -64,10 +60,8 @@ public override bool PromptToSaveImage(string? defaultPath, out string? savePath
         {
             lastExt = "jpg";
         }
-        var sd = new SaveFileDialog
-        {
-            FileName = GetDefaultFileName(defaultPath, lastExt!)
-        };
+        var sd = CreateSaveFileDialog();
+        sd.FileName = GetDefaultFileName(defaultPath, lastExt!);
         var filterGroups = EtoPlatform.Current.IsGtk
             ? FileFilterGroup.AllImages | FileFilterGroup.Image
             : FileFilterGroup.Image;
@@ -96,6 +90,46 @@ public override bool PromptToSaveImage(string? defaultPath, out string? savePath
             : normPath;
     }
 
+    private static SaveFileDialog CreateSaveFileDialog()
+    {
+        EnsureCurrentDirectoryIsAccessible();
+        try
+        {
+            return new SaveFileDialog();
+        }
+        catch (FileNotFoundException)
+        {
+            SetSafeCurrentDirectory();
+            return new SaveFileDialog();
+        }
+    }
+
+    private static void EnsureCurrentDirectoryIsAccessible()
+    {
+        try
+        {
+            var currentDirectory = Directory.GetCurrentDirectory();
+            if (!Directory.Exists(currentDirectory))
+            {
+                SetSafeCurrentDirectory();
+            }
+        }
+        catch
+        {
+            SetSafeCurrentDirectory();
+        }
+    }
+
+    private static void SetSafeCurrentDirectory()
+    {
+        var fallbackDirectory = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
+        if (string.IsNullOrWhiteSpace(fallbackDirectory) || !Directory.Exists(fallbackDirectory))
+        {
+            fallbackDirectory = Path.GetTempPath();
+        }
+        Environment.CurrentDirectory = fallbackDirectory;
+    }
+
     private void SetDir(SaveFileDialog dialog, string? defaultPath)
     {
         string? path = null;
@@ -128,6 +162,7 @@ private static string NormalizePath(string path)
 
     public override bool PromptToImport(out string[]? filePaths)
     {
+        EnsureCurrentDirectoryIsAccessible();
         var ofd = new OpenFileDialog
         {
             MultiSelect = true,
@@ -149,4 +184,4 @@ public override bool PromptToImport(out string[]? filePaths)
         filePaths = null;
         return false;
     }
-}
+}