Always resolve relative paths in Document class

Make the Document class always resolve relative input/output file paths,
which are usually passed as arguments by users.

Previously, resolving relative filepaths was a job left to the
instantiators of the Document class. This was error-prone since this
conversion must happen in all the places where we instantiated the
Document class.

dangerzone/args.py

@@ -12,8 +12,9 @@ def validate_input_filename(
 ) -> Optional[str]:
     if value is None:
         return None
-    Document.validate_input_filename(value)
-    return value
+    filename = Document.normalize_filename(value)
+    Document.validate_input_filename(filename)
+    return filename
 
 
 @errors.handle_document_errors
@@ -22,5 +23,6 @@ def validate_output_filename(
 ) -> Optional[str]:
     if value is None:
         return None
-    Document.validate_output_filename(value)
-    return value
+    filename = Document.normalize_filename(value)
+    Document.validate_output_filename(filename)
+    return filename

dangerzone/cli.py

@@ -36,11 +36,11 @@ def cli_main(
 
     display_banner()
 
-    document = Document(os.path.abspath(filename))
+    document = Document(filename)
 
     # Validate safe PDF output filename
     if output_filename:
-        document.output_filename = os.path.abspath(output_filename)
+        document.output_filename = output_filename
     else:
         document.output_filename = (
             f"{os.path.splitext(document.input_filename)[0]}-safe.pdf"

dangerzone/document.py

@@ -23,6 +23,10 @@ class Document:
         if input_filename:
             self.input_filename = input_filename
 
+    @staticmethod
+    def normalize_filename(filename: str) -> str:
+        return os.path.abspath(filename)
+
     @staticmethod
     def validate_input_filename(filename: str) -> None:
         try:
@@ -41,7 +45,7 @@ class Document:
         if not filename.endswith(".pdf"):
             raise DocumentFilenameException("Safe PDF filename must end in '.pdf'")
         try:
-            with open(os.path.abspath(filename), "wb"):
+            with open(filename, "wb"):
                 pass
         except PermissionError as e:
             raise DocumentFilenameException("Safe PDF filename is not writable") from e
@@ -55,6 +59,7 @@ class Document:
 
     @input_filename.setter
     def input_filename(self, filename: str) -> None:
+        filename = self.normalize_filename(filename)
         self.validate_input_filename(filename)
         self._input_filename = filename
 
@@ -67,5 +72,6 @@ class Document:
 
     @output_filename.setter
     def output_filename(self, filename: str) -> None:
+        filename = self.normalize_filename(filename)
         self.validate_output_filename(filename)
         self._output_filename = filename

dangerzone/gui/__init__.py

@@ -102,9 +102,7 @@ def gui_main(filename: Optional[str]) -> bool:
     if filename is None:
         new_window()
     else:
-        # If filename is passed as an argument, open it
-        input_filename: str = os.path.abspath(os.path.expanduser(filename))
-        new_window(input_filename)
+        new_window(filename)
 
     # Open a new window, if all windows are closed
     def application_activated() -> None: