Add /v1/chat/completions/batch endpoint for batched chat completions (#38011)

Signed-off-by: Matej Rojec <64556640+MatejRojec@users.noreply.github.com>

tests/entrypoints/openai/chat_completion/test_batched_chat_completions.py

@@ -0,0 +1,113 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import json
+
+import httpx
+import pytest
+
+from tests.utils import RemoteOpenAIServer
+
+# any model with a chat template defined in tokenizer_config should work here
+MODEL_NAME = "Qwen/Qwen2.5-1.5B-Instruct"
+
+
+@pytest.fixture(scope="module")
+def default_server_args():
+    return [
+        # use half precision for speed and memory savings in CI environment
+        "--max-model-len",
+        "2048",
+        "--max-num-seqs",
+        "128",
+        "--enforce-eager",
+    ]
+
+
+@pytest.fixture(scope="module")
+def server(default_server_args):
+    with RemoteOpenAIServer(MODEL_NAME, default_server_args) as remote_server:
+        yield remote_server
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "model_name",
+    [MODEL_NAME],
+)
+async def test_batched_chat_completions(
+    server: RemoteOpenAIServer, model_name: str
+) -> None:
+    conversations = [
+        [{"role": "user", "content": "Reply with exactly the word: alpha"}],
+        [{"role": "user", "content": "Reply with exactly the word: beta"}],
+    ]
+
+    async with httpx.AsyncClient() as http_client:
+        response = await http_client.post(
+            f"{server.url_for('v1/chat/completions/batch')}",
+            json={
+                "model": model_name,
+                "messages": conversations,
+            },
+            timeout=60,
+        )
+
+    assert response.status_code == 200, response.text
+    data = response.json()
+
+    choices = data["choices"]
+    assert len(choices) == 2
+
+    indices = {choice["index"] for choice in choices}
+    assert indices == {0, 1}
+
+    # Each conversation should produce a non-empty text response.
+    for choice in choices:
+        assert choice["message"]["content"]
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "model_name",
+    [MODEL_NAME],
+)
+async def test_batched_chat_completions_with_json_schema(
+    server: RemoteOpenAIServer, model_name: str
+) -> None:
+    schema = {
+        "type": "object",
+        "properties": {
+            "answer": {"type": "string", "enum": ["yes", "no"]},
+        },
+        "required": ["answer"],
+    }
+    conversations = [
+        [{"role": "user", "content": "Is the sky blue? Answer in JSON."}],
+        [{"role": "user", "content": "Is fire cold? Answer in JSON."}],
+    ]
+
+    async with httpx.AsyncClient() as http_client:
+        response = await http_client.post(
+            f"{server.url_for('v1/chat/completions/batch')}",
+            json={
+                "model": model_name,
+                "messages": conversations,
+                "response_format": {
+                    "type": "json_schema",
+                    "json_schema": {"name": "answer", "schema": schema, "strict": True},
+                },
+            },
+            timeout=60,
+        )
+
+    assert response.status_code == 200, response.text
+    data = response.json()
+
+    choices = data["choices"]
+    assert len(choices) == 2
+
+    for choice in choices:
+        parsed = json.loads(choice["message"]["content"])
+        assert "answer" in parsed
+        assert parsed["answer"] in ("yes", "no")

tests/entrypoints/openai/test_openai_schema.py

@@ -174,6 +174,7 @@ def test_openapi_stateless(case: Case):
     timeout = {
         # requires a longer timeout
         ("POST", "/v1/chat/completions"): LONG_TIMEOUT_SECONDS,
+        ("POST", "/v1/chat/completions/batch"): LONG_TIMEOUT_SECONDS,
         ("POST", "/v1/completions"): LONG_TIMEOUT_SECONDS,
         ("POST", "/v1/messages"): LONG_TIMEOUT_SECONDS,
     }.get(key, DEFAULT_TIMEOUT_SECONDS)