fix: Files handling in sign_file

Author: tmathern

src/c2pa/c2pa.py

@@ -6,7 +6,7 @@
 import warnings
 from pathlib import Path
 from typing import Optional, Union, Callable, Any, overload
-import time
+import io
 from .lib import dynamically_load_library
 import mimetypes
 
@@ -1955,16 +1955,24 @@ def sign_file(self,
             raise C2paError.NotSupported(
                 f"Could not determine MIME type for file: {source_path}")
 
-        # Open source and destination files
-        with open(source_path, 'rb') as source_file, open(dest_path, 'wb') as dest_file:
+        # Open source file and create BytesIO for destination
+        with open(source_path, 'rb') as source_file:
             # Convert Python streams to Stream objects
             source_stream = Stream(source_file)
-            dest_stream = Stream(dest_file)
+            dest_stream = Stream(io.BytesIO(bytearray()))
 
             # Use the internal stream-base signing logic
-            return self._sign_internal(
+            # Sign the content to the BytesIO stream
+            result = self._sign_internal(
                 signer, mime_type, source_stream, dest_stream)
 
+            # Write the signed content from BytesIO to the destination file
+            dest_stream._file.seek(0)  # Reset to beginning of stream
+            with open(dest_path, 'wb') as dest_file:
+                dest_file.write(dest_stream._file.getvalue())
+
+            return result
+
 
 def format_embeddable(format: str, manifest_bytes: bytes) -> tuple[int, bytes]:
     """Convert a binary C2PA manifest into an embeddable version.

tests/test_unit_tests.py

@@ -812,6 +812,33 @@ def test_builder_set_remote_url_no_embed(self):
         # Return back to default settings
         load_settings(r'{"verify": { "remote_manifest_fetch": true} }')
 
+    def test_sign_single_file(self):
+        """Test signing a file using the sign_file method."""
+        # Create a temporary directory for the test
+        temp_dir = tempfile.mkdtemp()
+        try:
+            # Create a temporary output file path
+            output_path = os.path.join(temp_dir, "signed_output.jpg")
+
+            # Use the sign_file method
+            builder = Builder(self.manifestDefinition)
+            output = io.BytesIO(bytearray())
+
+            with open(self.testPath, "rb") as file:
+              builder.sign(self.signer, "image/jpeg", file, output)
+              output.seek(0)
+
+              # Read the signed file and verify the manifest
+              reader = Reader("image/jpeg", output)
+              json_data = reader.json()
+              self.assertIn("Python Test", json_data)
+              self.assertNotIn("validation_status", json_data)
+              output.close()
+
+        finally:
+            # Clean up the temporary directory
+            shutil.rmtree(temp_dir)
+
     def test_sign_file(self):
         """Test signing a file using the sign_file method."""
         # Create a temporary directory for the test
@@ -823,9 +850,9 @@ def test_sign_file(self):
             # Use the sign_file method
             builder = Builder(self.manifestDefinition)
             manifest_bytes = builder.sign_file(
-                source_path=self.testPath,
-                dest_path=output_path,
-                signer=self.signer
+                self.testPath,
+                output_path,
+                self.signer
             )
 
             # Verify the output file was created