fix: remove use of ImagePromptTemplate in image handling and adds image utils (#4467)

* remove poetry.lock

* fix: update langchain-core dependency version to 0.3.15

* feat: add functions to convert images to base64 and create data URLs

* refactor: simplify image URL handling by replacing ImagePromptTemplate with create_data_url function

* Fix image URL structure in data schema to use nested dictionary format

* Add unit tests for Data schema message conversion with text and images

* test: add unit tests for image utility functions to validate base64 conversion and data URL creation

* Refactor image URL generation to use `create_data_url` utility function instead of `ImagePromptTemplate`

* Add unit tests for message handling and image processing in schema module

- Introduce fixtures for temporary cache directory and sample image creation.
- Add tests for message creation from human and AI text.
- Implement tests for messages with single and multiple images.
- Include tests for invalid image paths and messages without sender.
- Add message serialization and conversion tests.
- Ensure cleanup of cache directory after tests.

* Use platformdirs to determine cache directory paths in test_schema_message.py

src/backend/tests/unit/utils/test_image_utils.py

@@ -0,0 +1,66 @@
+import base64
+
+import pytest
+from langflow.utils.image import convert_image_to_base64, create_data_url
+
+
+@pytest.fixture
+def sample_image(tmp_path):
+    """Create a sample image file for testing."""
+    image_path = tmp_path / "test_image.png"
+    # Create a small black 1x1 pixel PNG file
+    image_content = base64.b64decode(
+        "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAACklEQVR4nGMAAQAABQABDQottAAAAABJRU5ErkJggg=="
+    )
+    image_path.write_bytes(image_content)
+    return image_path
+
+
+class TestImageUtils:
+    def test_convert_image_to_base64_success(self, sample_image):
+        """Test successful conversion of image to base64."""
+        base64_str = convert_image_to_base64(sample_image)
+        assert isinstance(base64_str, str)
+        # Verify it's valid base64
+        assert base64.b64decode(base64_str)
+
+    def test_convert_image_to_base64_empty_path(self):
+        """Test conversion with empty path."""
+        with pytest.raises(ValueError, match="Image path cannot be empty"):
+            convert_image_to_base64("")
+
+    def test_convert_image_to_base64_nonexistent_file(self):
+        """Test conversion with non-existent file."""
+        with pytest.raises(FileNotFoundError, match="Image file not found"):
+            convert_image_to_base64("nonexistent.png")
+
+    def test_convert_image_to_base64_directory(self, tmp_path):
+        """Test conversion with directory path instead of file."""
+        with pytest.raises(ValueError, match="Path is not a file"):
+            convert_image_to_base64(tmp_path)
+
+    def test_create_data_url_success(self, sample_image):
+        """Test successful creation of data URL."""
+        data_url = create_data_url(sample_image)
+        assert data_url.startswith("data:image/png;base64,")
+        # Verify the base64 part is valid
+        base64_part = data_url.split(",")[1]
+        assert base64.b64decode(base64_part)
+
+    def test_create_data_url_with_custom_mime(self, sample_image):
+        """Test creation of data URL with custom MIME type."""
+        custom_mime = "image/custom"
+        data_url = create_data_url(sample_image, mime_type=custom_mime)
+        assert data_url.startswith(f"data:{custom_mime};base64,")
+
+    def test_create_data_url_invalid_file(self):
+        """Test creation of data URL with invalid file."""
+        with pytest.raises(FileNotFoundError):
+            create_data_url("nonexistent.jpg")
+
+    def test_create_data_url_unrecognized_extension(self, tmp_path):
+        """Test creation of data URL with unrecognized file extension."""
+        invalid_file = tmp_path / "test.unknown"
+        invalid_file.touch()
+        with pytest.raises(ValueError, match="Could not determine MIME type"):
+            create_data_url(invalid_file)