[Feature][V1] Add xgrammar to support minLength, maxLength with test (#16516)

Signed-off-by: Leon Seidel <leon.seidel@fau.de>

tests/v1/entrypoints/llm/test_struct_output_generate.py

@@ -325,6 +325,45 @@ def test_structured_output(
         output_json = json.loads(generated_text)
         jsonschema.validate(instance=output_json, schema=json_schema)
 
+    #
+    # Test 10: Generate structured with minLength and maxLength
+    #
+    min_length = 50
+    max_length = 50
+    json_schema = {
+        "type": "object",
+        "properties": {
+            "description": {
+                "type": "string",
+                "maxLength": max_length,
+                "minLength": min_length
+            }
+        },
+        "required": ["description"]
+    }
+
+    sampling_params = SamplingParams(
+        temperature=1.0,
+        max_tokens=1000,
+        guided_decoding=GuidedDecodingParams(json=json_schema))
+    outputs = llm.generate(
+        prompts="Generate a description of a frog using 50 characters.",
+        sampling_params=sampling_params,
+        use_tqdm=True)
+
+    assert outputs is not None
+
+    for output in outputs:
+        assert output is not None
+        assert isinstance(output, RequestOutput)
+        prompt = output.prompt
+
+        generated_text = output.outputs[0].text
+        assert generated_text is not None
+        print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
+        output_json = json.loads(generated_text)
+        jsonschema.validate(instance=output_json, schema=json_schema)
+
 
 @pytest.mark.skip_global_cleanup
 @pytest.mark.parametrize("model_name, tokenizer_mode",