fix(fail-branch): prevent streaming output in exception branches (#17153)

api/core/workflow/nodes/answer/answer_stream_processor.py

@@ -155,9 +155,28 @@ class AnswerStreamProcessor(StreamProcessor):
         for answer_node_id, route_position in self.route_position.items():
             if answer_node_id not in self.rest_node_ids:
                 continue
-            # exclude current node id
+            # Remove current node id from answer dependencies to support stream output if it is a success branch
             answer_dependencies = self.generate_routes.answer_dependencies
-            if event.node_id in answer_dependencies[answer_node_id]:
+            edge_mapping = self.graph.edge_mapping.get(event.node_id)
+            success_edge = (
+                next(
+                    (
+                        edge
+                        for edge in edge_mapping
+                        if edge.run_condition
+                        and edge.run_condition.type == "branch_identify"
+                        and edge.run_condition.branch_identify == "success-branch"
+                    ),
+                    None,
+                )
+                if edge_mapping
+                else None
+            )
+            if (
+                event.node_id in answer_dependencies[answer_node_id]
+                and success_edge
+                and success_edge.target_node_id == answer_node_id
+            ):
                 answer_dependencies[answer_node_id].remove(event.node_id)
             answer_dependencies_ids = answer_dependencies.get(answer_node_id, [])
             # all depends on answer node id not in rest node ids

api/tests/unit_tests/core/workflow/nodes/test_continue_on_error.py

@@ -1,14 +1,20 @@
+from unittest.mock import patch
+
 from core.app.entities.app_invoke_entities import InvokeFrom
+from core.workflow.entities.node_entities import NodeRunMetadataKey, NodeRunResult
 from core.workflow.enums import SystemVariableKey
 from core.workflow.graph_engine.entities.event import (
     GraphRunPartialSucceededEvent,
     NodeRunExceptionEvent,
+    NodeRunFailedEvent,
     NodeRunStreamChunkEvent,
 )
 from core.workflow.graph_engine.entities.graph import Graph
 from core.workflow.graph_engine.graph_engine import GraphEngine
+from core.workflow.nodes.event.event import RunCompletedEvent, RunStreamChunkEvent
+from core.workflow.nodes.llm.node import LLMNode
 from models.enums import UserFrom
-from models.workflow import WorkflowType
+from models.workflow import WorkflowNodeExecutionStatus, WorkflowType
 
 
 class ContinueOnErrorTestHelper:
@@ -492,10 +498,7 @@ def test_no_node_in_fail_branch_continue_on_error():
         "edges": FAIL_BRANCH_EDGES[:-1],
         "nodes": [
             {"data": {"title": "Start", "type": "start", "variables": []}, "id": "start"},
-            {
+            {"data": {"title": "success", "type": "answer", "answer": "HTTP request successful"}, "id": "success"},
-                "data": {"title": "success", "type": "answer", "answer": "HTTP request successful"},
-                "id": "success",
-            },
             ContinueOnErrorTestHelper.get_http_node(),
         ],
     }
@@ -506,3 +509,47 @@ def test_no_node_in_fail_branch_continue_on_error():
     assert any(isinstance(e, NodeRunExceptionEvent) for e in events)
     assert any(isinstance(e, GraphRunPartialSucceededEvent) and e.outputs == {} for e in events)
     assert sum(1 for e in events if isinstance(e, NodeRunStreamChunkEvent)) == 0
+
+
+def test_stream_output_with_fail_branch_continue_on_error():
+    """Test stream output with fail-branch error strategy"""
+    graph_config = {
+        "edges": FAIL_BRANCH_EDGES,
+        "nodes": [
+            {"data": {"title": "Start", "type": "start", "variables": []}, "id": "start"},
+            {
+                "data": {"title": "success", "type": "answer", "answer": "LLM request successful"},
+                "id": "success",
+            },
+            {
+                "data": {"title": "error", "type": "answer", "answer": "{{#node.text#}}"},
+                "id": "error",
+            },
+            ContinueOnErrorTestHelper.get_llm_node(),
+        ],
+    }
+    graph_engine = ContinueOnErrorTestHelper.create_test_graph_engine(graph_config)
+
+    def llm_generator(self):
+        contents = ["hi", "bye", "good morning"]
+
+        yield RunStreamChunkEvent(chunk_content=contents[0], from_variable_selector=[self.node_id, "text"])
+
+        yield RunCompletedEvent(
+            run_result=NodeRunResult(
+                status=WorkflowNodeExecutionStatus.SUCCEEDED,
+                inputs={},
+                process_data={},
+                outputs={},
+                metadata={
+                    NodeRunMetadataKey.TOTAL_TOKENS: 1,
+                    NodeRunMetadataKey.TOTAL_PRICE: 1,
+                    NodeRunMetadataKey.CURRENCY: "USD",
+                },
+            )
+        )
+
+    with patch.object(LLMNode, "_run", new=llm_generator):
+        events = list(graph_engine.run())
+        assert sum(isinstance(e, NodeRunStreamChunkEvent) for e in events) == 1
+        assert all(not isinstance(e, NodeRunFailedEvent | NodeRunExceptionEvent) for e in events)