Use a buffered stdout substitute

src/arcaflow_plugin_sdk/atp.py

@@ -76,7 +76,7 @@ class ATPServer:
     step_ids: typing.Dict[str, str]  # Run ID to step IDs
     encoder: cbor2.CBOREncoder
     decoder: cbor2.CBORDecoder
-    user_out_buffer: io.StringIO
+    user_out_wrapper: io.TextIOWrapper
     encoder_lock: threading.Lock
     plugin_schema: schema.SchemaType
     running_threads: typing.List[threading.Thread]
@@ -114,9 +114,11 @@ def run_plugin(
         # potentially interfering with the atp pipes.
         original_stdout = sys.stdout
         original_stderr = sys.stderr
-        self.user_out_buffer = io.StringIO()
-        sys.stdout = self.user_out_buffer
-        sys.stderr = self.user_out_buffer
+        self.user_out_wrapper = io.TextIOWrapper(
+            io.BytesIO(), sys.stdout.encoding
+        )
+        sys.stdout = self.user_out_wrapper
+        sys.stderr = self.user_out_wrapper
 
         # Run the read loop. This blocks to wait for the loop to finish.
         self.run_server_read_loop()
@@ -324,6 +326,8 @@ def start_step(self, run_id: str, step_id: str, config: typing.Any):
                 self.plugin_schema.unserialize_step_input(step_id, config),
             )
 
+            self.user_out_wrapper.flush()
+            self.user_out_wrapper.seek(0)  # go to start to read stdout.
             # Send WorkDoneMessage
             self.send_runtime_message(
                 MessageType.WORK_DONE,
@@ -333,7 +337,7 @@ def start_step(self, run_id: str, step_id: str, config: typing.Any):
                     "output_data": self.plugin_schema.serialize_output(
                         step_id, output_id, output_data
                     ),
-                    "debug_logs": self.user_out_buffer.getvalue(),
+                    "debug_logs": self.user_out_wrapper.read(),
                 },
             )
         except Exception as e:

src/arcaflow_plugin_sdk/plugin.py

@@ -459,7 +459,8 @@ def _execute_file(
         data = serialization.load_from_file(filename)
     original_stdout = sys.stdout
     original_stderr = sys.stderr
-    out_buffer = io.StringIO()
+    buffer = io.BytesIO()
+    out_buffer = io.TextIOWrapper(buffer)
     if options.debug:
         # Redirect stdout to stderr for debug logging
         sys.stdout = stderr
@@ -469,10 +470,12 @@ def _execute_file(
         sys.stderr = out_buffer
     try:
         output_id, output_data = s("file_run", step_id, data)
+        out_buffer.flush()
+        out_buffer.seek(0)  # go to start so that we can read stdout.
         output = {
             "output_id": output_id,
             "output_data": output_data,
-            "debug_logs": out_buffer.getvalue(),
+            "debug_logs": out_buffer.read(),
         }
         stdout.write(yaml.dump(output, sort_keys=False))
         return 0

src/arcaflow_plugin_sdk/test_atp.py

@@ -26,7 +26,7 @@ class Output:
     outputs={"success": Output},
 )
 def hello_world(params: Input) -> Tuple[str, Output]:
-    print("Hello world!")
+    print("printed message")
     return "success", Output("Hello, {}!".format(params.name))
 
 
@@ -182,7 +182,7 @@ def test_step_simple(self):
             self.assertEqual(result.run_id, self.id())
             client.send_client_done()
             self.assertEqual(result.output_id, "success")
-            self.assertEqual("Hello world!\n", result.debug_logs)
+            self.assertEqual("printed message\n", result.debug_logs)
         finally:
             self._cleanup(pid, stdin_writer, stdout_reader)