[Feature] Support new parameter - EBNF in xgrammar (#2526)

test/srt/test_openai_server.py

@@ -5,6 +5,7 @@ python3 -m unittest test_openai_server.TestOpenAIServer.test_completion
 """
 
 import json
+import re
 import time
 import unittest
 
@@ -535,5 +536,92 @@ The SmartHome Mini is a compact smart home assistant available in black or white
         )
 
 
+# -------------------------------------------------------------------------
+#    EBNF Test Class: TestOpenAIServerEBNF
+#    Launches the server with xgrammar, has only EBNF tests
+# -------------------------------------------------------------------------
+class TestOpenAIServerEBNF(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.model = DEFAULT_SMALL_MODEL_NAME_FOR_TEST
+        cls.base_url = DEFAULT_URL_FOR_TEST
+        cls.api_key = "sk-123456"
+
+        # passing xgrammar specifically
+        other_args = ["--grammar-backend", "xgrammar"]
+        cls.process = popen_launch_server(
+            cls.model,
+            cls.base_url,
+            timeout=DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
+            api_key=cls.api_key,
+            other_args=other_args,
+        )
+        cls.base_url += "/v1"
+        cls.tokenizer = get_tokenizer(DEFAULT_SMALL_MODEL_NAME_FOR_TEST)
+
+    @classmethod
+    def tearDownClass(cls):
+        kill_process_tree(cls.process.pid)
+
+    def test_ebnf(self):
+        """
+        Ensure we can pass `ebnf` to the local openai server
+        and that it enforces the grammar.
+        """
+        client = openai.Client(api_key=self.api_key, base_url=self.base_url)
+        ebnf_grammar = r"""
+        root ::= "Hello" | "Hi" | "Hey"
+        """
+        pattern = re.compile(r"^(Hello|Hi|Hey)[.!?]*\s*$")
+
+        response = client.chat.completions.create(
+            model=self.model,
+            messages=[
+                {"role": "system", "content": "You are a helpful EBNF test bot."},
+                {"role": "user", "content": "Say a greeting (Hello, Hi, or Hey)."},
+            ],
+            temperature=0,
+            max_tokens=32,
+            extra_body={"ebnf": ebnf_grammar},
+        )
+        text = response.choices[0].message.content.strip()
+        print("EBNF test output:", repr(text))
+        self.assertTrue(len(text) > 0, "Got empty text from EBNF generation")
+        self.assertRegex(text, pattern, f"Text '{text}' doesn't match EBNF choices")
+
+    def test_ebnf_strict_json(self):
+        """
+        A stricter EBNF that produces exactly {"name":"Alice"} format
+        with no trailing punctuation or extra fields.
+        """
+        client = openai.Client(api_key=self.api_key, base_url=self.base_url)
+        ebnf_grammar = r"""
+        root    ::= "{" pair "}"
+        pair    ::= "\"name\"" ":" string
+        string  ::= "\"" [A-Za-z]+ "\""
+        """
+        pattern = re.compile(r'^\{"name":"[A-Za-z]+"\}$')
+
+        response = client.chat.completions.create(
+            model=self.model,
+            messages=[
+                {"role": "system", "content": "EBNF mini-JSON generator."},
+                {
+                    "role": "user",
+                    "content": "Generate single key JSON with only letters.",
+                },
+            ],
+            temperature=0,
+            max_tokens=64,
+            extra_body={"ebnf": ebnf_grammar},
+        )
+        text = response.choices[0].message.content.strip()
+        print("EBNF strict JSON test output:", repr(text))
+        self.assertTrue(len(text) > 0, "Got empty text from EBNF strict JSON test")
+        self.assertRegex(
+            text, pattern, f"Text '{text}' not matching the EBNF strict JSON shape"
+        )
+
+
 if __name__ == "__main__":
     unittest.main()