feat: added json serializer that encodes tables and images (#29)

Closes #20 

### Summary of Changes

- added SafeDSEncoder that is used for custom types (tables, images)
- don't crash when unknown types are attempted to be sent, instead send
a "\<Not Displayable\>" placeholder value
- added encoding tests + not displayable to existing message exchange

---------

Co-authored-by: megalinter-bot <129584137+megalinter-bot@users.noreply.github.com>

src/safeds_runner/server/json_encoder.py

@@ -0,0 +1,51 @@
+"""Module containing JSON encoding utilities for Safe-DS types."""
+
+import base64
+import json
+import math
+from typing import Any
+
+from safeds.data.image.containers import Image
+from safeds.data.image.typing import ImageFormat
+from safeds.data.tabular.containers import Table
+
+
+class SafeDsEncoder(json.JSONEncoder):
+    """JSON Encoder for custom Safe-DS types."""
+
+    def default(self, o: Any) -> Any:
+        """
+        Convert specific Safe-DS types to a JSON-serializable representation.
+
+        If values are custom Safe-DS types (such as Table or Image) they are converted to a serializable representation.
+        If a value is not handled here, the default encoding implementation is called.
+        In case of Tables, note that NaN values are converted to JSON null values.
+
+        Parameters
+        ----------
+        o: Any
+            An object that needs to be encoded to JSON.
+
+        Returns
+        -------
+        Any
+            The passed object represented in a way that is serializable to JSON.
+        """
+        if isinstance(o, Table):
+            dict_with_nan_infinity = o.to_dict()
+            # Convert NaN / Infinity to None, as the JSON encoder generates invalid JSON otherwise
+            return {
+                key: [
+                    value if not isinstance(value, float) or math.isfinite(value) else None
+                    for value in dict_with_nan_infinity[key]
+                ]
+                for key in dict_with_nan_infinity
+            }
+        if isinstance(o, Image):
+            # Send images together with their format
+            match o.format:
+                case ImageFormat.JPEG:
+                    return {"format": o.format.value, "bytes": str(base64.encodebytes(o._repr_jpeg_()), "utf-8")}
+                case ImageFormat.PNG:
+                    return {"format": o.format.value, "bytes": str(base64.encodebytes(o._repr_png_()), "utf-8")}
+        return json.JSONEncoder.default(self, o)

src/safeds_runner/server/main.py

@@ -12,6 +12,7 @@
 from flask_sock import Sock
 
 from safeds_runner.server import messages
+from safeds_runner.server.json_encoder import SafeDsEncoder
 from safeds_runner.server.messages import (
     Message,
     create_placeholder_value,
@@ -127,14 +128,25 @@ def ws_main(ws: simple_websocket.Server, pipeline_manager: PipelineManager) -> N
                 )
                 # send back a value message
                 if placeholder_type is not None:
-                    send_websocket_message(
-                        ws,
-                        Message(
-                            message_type_placeholder_value,
-                            received_object.id,
-                            create_placeholder_value(placeholder_query_data, placeholder_type, placeholder_value),
-                        ),
-                    )
+                    try:
+                        send_websocket_message(
+                            ws,
+                            Message(
+                                message_type_placeholder_value,
+                                received_object.id,
+                                create_placeholder_value(placeholder_query_data, placeholder_type, placeholder_value),
+                            ),
+                        )
+                    except TypeError as _encoding_error:
+                        # if the value can't be encoded send back that the value exists but is not displayable
+                        send_websocket_message(
+                            ws,
+                            Message(
+                                message_type_placeholder_value,
+                                received_object.id,
+                                create_placeholder_value(placeholder_query_data, placeholder_type, "<Not displayable>"),
+                            ),
+                        )
                 else:
                     # Send back empty type / value, to communicate that no placeholder exists (yet)
                     # Use name from query to allow linking a response to a request on the peer
@@ -162,7 +174,7 @@ def send_websocket_message(connection: simple_websocket.Server, message: Message
     message : Message
         Object that will be sent.
     """
-    connection.send(json.dumps(message.to_dict()))
+    connection.send(json.dumps(message.to_dict(), cls=SafeDsEncoder))
 
 
 def start_server(port: int) -> None:  # pragma: no cover

tests/safeds_runner/server/test_json_encoder.py

@@ -0,0 +1,65 @@
+import base64
+import json
+import math
+from io import BytesIO
+from typing import Any
+
+import pytest
+from safeds.data.image.containers import Image
+from safeds.data.image.typing import ImageFormat
+from safeds.data.tabular.containers import Table
+from safeds_runner.server.json_encoder import SafeDsEncoder
+
+
+@pytest.mark.parametrize(
+    argnames="data,expected_string",
+    argvalues=[
+        (
+            Table.from_dict({"a": [1, 2], "b": [3.2, 4.0], "c": [math.nan, 5.6], "d": [5, -6]}),
+            '{"a": [1, 2], "b": [3.2, 4.0], "c": [null, 5.6], "d": [5, -6]}',
+        ),
+        (
+            Image(
+                BytesIO(
+                    base64.b64decode(
+                        "iVBORw0KGgoAAAANSUhEUgAAAAQAAAAECAYAAACp8Z5"
+                        "+AAAAD0lEQVQIW2NkQAOMpAsAAADuAAVDMQ2mAAAAAElFTkSuQmCC",
+                    ),
+                ),
+                ImageFormat.PNG,
+            ),
+            (
+                '{"format": "png", "bytes": '
+                '"iVBORw0KGgoAAAANSUhEUgAAAAQAAAAECAYAAACp8Z5+AAAADElEQVR4nGNgoBwAAABEAAHX40j9\\nAAAAAElFTkSuQmCC\\n"}'
+            ),
+        ),
+        (
+            Image(
+                BytesIO(
+                    base64.b64decode(
+                        "/9j/2wBDAAEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQH/wgALCAABAAEBAREA/8QAFAABAAAAAAAAAAAAAAAAAAAAA//aAAgBAQAAAAE//9k=",
+                    ),
+                ),
+                ImageFormat.JPEG,
+            ),
+            (
+                '{"format": "jpeg", "bytes":'
+                ' "/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAgGBgcGBQgHBwcJCQgKDBQNDAsLDBkSEw8UHRofHh0a'
+                "\\nHBwgJC4nICIsIxwcKDcpLDAxNDQ0Hyc5PTgyPC4zNDL/wAALCAABAAEBAREA/8QAHwAAAQUBAQEB\\nAQEAAAAAAAAAAAECAwQFBgcICQoL"
+                "/8QAtRAAAgEDAwIEAwUFBAQAAAF9AQIDAAQRBRIhMUEGE1Fh"
+                "\\nByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RFRkdISUpTVFVWV1hZ"
+                "\\nWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXG\\nx8jJytLT1NXW19jZ2uHi4"
+                '+Tl5ufo6erx8vP09fb3+Pn6/9oACAEBAAA/AEr/2Q==\\n"}'
+            ),
+        ),
+    ],
+    ids=["encode_table", "encode_image_png", "encode_image_jpeg"],
+)
+def test_encoding_custom_types(data: Any, expected_string: str) -> None:
+    assert json.dumps(data, cls=SafeDsEncoder) == expected_string
+
+
+@pytest.mark.parametrize(argnames="data", argvalues=[(object())], ids=["encode_object"])
+def test_encoding_unsupported_types(data: Any) -> None:
+    with pytest.raises(TypeError):
+        json.dumps(data, cls=SafeDsEncoder)

tests/safeds_runner/server/test_websocket_mock.py

@@ -250,7 +250,8 @@ def test_should_execute_pipeline_return_exception(
                                 "gen_test_a": (
                                     "import safeds_runner.server.pipeline_manager\n\ndef pipe():\n\tvalue1 ="
                                     " 1\n\tsafeds_runner.server.pipeline_manager.runner_save_placeholder('value1',"
-                                    " value1)\n"
+                                    " value1)\n\tsafeds_runner.server.pipeline_manager.runner_save_placeholder('obj',"
+                                    " object())\n"
                                 ),
                                 "gen_test_a_pipe": (
                                     "from gen_test_a import pipe\n\nif __name__ == '__main__':\n\tpipe()"
@@ -265,16 +266,25 @@ def test_should_execute_pipeline_return_exception(
             [
                 # Query Placeholder
                 json.dumps({"type": "placeholder_query", "id": "abcdefg", "data": "value1"}),
+                # Query not displayable Placeholder
+                json.dumps({"type": "placeholder_query", "id": "abcdefg", "data": "obj"}),
                 # Query invalid placeholder
                 json.dumps({"type": "placeholder_query", "id": "abcdefg", "data": "value2"}),
             ],
             [
                 # Validate Placeholder Information
                 Message(message_type_placeholder_type, "abcdefg", create_placeholder_description("value1", "Int")),
+                Message(message_type_placeholder_type, "abcdefg", create_placeholder_description("obj", "object")),
                 # Validate Progress Information
                 Message(message_type_runtime_progress, "abcdefg", create_runtime_progress_done()),
                 # Query Result Valid
                 Message(message_type_placeholder_value, "abcdefg", create_placeholder_value("value1", "Int", 1)),
+                # Query Result not displayable
+                Message(
+                    message_type_placeholder_value,
+                    "abcdefg",
+                    create_placeholder_value("obj", "object", "<Not displayable>"),
+                ),
                 # Query Result Invalid
                 Message(message_type_placeholder_value, "abcdefg", create_placeholder_value("value2", "", "")),
             ],