add response_format support for completion API (#9665)

test/srt/openai_server/basic/test_serving_completions.py

@@ -95,6 +95,63 @@ class ServingCompletionTestCase(unittest.TestCase):
         self.sc.tokenizer_manager.tokenizer.decode.return_value = "decoded"
         self.assertEqual(self.sc._prepare_echo_prompts(req), ["decoded"])
 
+    # ---------- response_format handling ----------
+    def test_response_format_json_object(self):
+        """Test that response_format json_object is correctly processed in sampling params."""
+        req = CompletionRequest(
+            model="x",
+            prompt="Generate a JSON object:",
+            max_tokens=100,
+            response_format={"type": "json_object"},
+        )
+        sampling_params = self.sc._build_sampling_params(req)
+        self.assertEqual(sampling_params["json_schema"], '{"type": "object"}')
+
+    def test_response_format_json_schema(self):
+        """Test that response_format json_schema is correctly processed in sampling params."""
+        schema = {
+            "type": "object",
+            "properties": {"name": {"type": "string"}, "age": {"type": "integer"}},
+        }
+        req = CompletionRequest(
+            model="x",
+            prompt="Generate a JSON object:",
+            max_tokens=100,
+            response_format={
+                "type": "json_schema",
+                "json_schema": {"name": "person", "schema": schema},
+            },
+        )
+        sampling_params = self.sc._build_sampling_params(req)
+        # The schema should be converted to string by convert_json_schema_to_str
+        self.assertIn("json_schema", sampling_params)
+        self.assertIsInstance(sampling_params["json_schema"], str)
+
+    def test_response_format_structural_tag(self):
+        """Test that response_format structural_tag is correctly processed in sampling params."""
+        req = CompletionRequest(
+            model="x",
+            prompt="Generate structured output:",
+            max_tokens=100,
+            response_format={
+                "type": "structural_tag",
+                "structures": [{"begin": "<data>", "end": "</data>"}],
+                "triggers": ["<data>"],
+            },
+        )
+        sampling_params = self.sc._build_sampling_params(req)
+        # The structural_tag should be processed
+        self.assertIn("structural_tag", sampling_params)
+        self.assertIsInstance(sampling_params["structural_tag"], str)
+
+    def test_response_format_none(self):
+        """Test that no response_format doesn't add extra constraints."""
+        req = CompletionRequest(model="x", prompt="Generate text:", max_tokens=100)
+        sampling_params = self.sc._build_sampling_params(req)
+        # Should not have json_schema or structural_tag from response_format
+        # (but might have json_schema from the legacy json_schema field)
+        self.assertIsNone(sampling_params.get("structural_tag"))
+
 
 if __name__ == "__main__":
     unittest.main(verbosity=2)